i
818
7 F' 7 H ;
)i o o
^ Ü U >
Validating m an a gem en t sim ulation m od els a n d im plications
for com m u n icatin g results to stakeholders
M a r t i n A. P asto o rs, Jan J a a p P oos, S a ra h B. M . Kraak, a n d M a r c e l A. M. M a c h ie ls
P asto o rs, M. A., Poos, J. J., Kraak, S. B. M., a n d M achiels, M. A. M. 2007. V alidating m a n a g e m e n t sim ulation m o d els a n d im plicatio n s for
c o m m u n ic a tin g results to stakeholders. - ICES Journal o f M arin e Science, 64: 8 1 8 - 8 2 4 .
S im u la tio n s o f m a n a g e m e n t p la n s g e n e ra lly a im t o d e m o n s tr a t e t h e r o b u s tn e s s o f t h e p la n s to a s s u m p tio n s a b o u t p o p u la tio n
d y n a m ic s a n d fle e t d y n a m ic s. S u ch m o d e llin g is c h a r a c te r iz e d by sp e c ific a tio n o f a n o p e r a t i n g m o d e l ( O M ) re p re s e n tin g th e u n d e r ­
ly in g t r u t h a n d a m a n a g e m e n t p r o c e d u r e t h a t m im ic s t h e p ro c e ss o f a c q u irin g k n o w le d g e , f o r m u la tin g m a n a g e m e n t d ecisio n s, a n d
im p le m e n tin g t h o s e d ecisions. W e e m p lo y s u c h a m o d e l t o e v a lu a te a m a n a g e m e n t p la n f o r N o r th Sea fla tfish p r o p o s e d by t h e N o rth
S ea R eg io n al A d v iso ry C ouncil in M a y 20 0 5 . F o cu s is o n t h e c o n s tru c tio n a n d c o n d itio n in g o f O M s, k ey r e q u ir e m e n ts fo r s u c h sim u ­
la tio n s . W e d e s c rib e t h e p ro c e ss o f s e ttin g u p a n d v a lid a tin g O M s alo n g w ith its e ffe c ts o n t h e ability t o c o m m u n ic a t e t h e re su lts to
t h e sta k e h o ld e rs . W e c o n c lu d e t h a t th e r e is te n s io n b e tw e e n th e level o f d e ta il r e q u ire d by s ta k e h o ld e r s a n d t h e level o f d e ta il t h a t can
b e p ro v id e d . In c o m m u n ic a tin g t h e re su lts o f s im u la tio n s , it is n ecessa ry t o m a k e v e ry c le a r h o w O M s d e p e n d o n p a s t p e r c e p tio n s o f
s to c k d y n am ics.
K eyw ords: c o m m u n ic a tio n , flatfish, m a n a g e m e n t strateg y evaluation, N orth Sea, o p e ra tin g m o d el, sim u latio n , stakeholders.
Received 30 June 2006; accepted 3 M arch 2007; ad v an ce access publication 21 M ay 2007.
M. A. Pastoors, J. J. Poos, S. B. M. K raak a n d M. A. M. Machiels: Wageningen-IMARES, PO Box 68, 1970 AB IJmuiden, The Netherlands.
C orrespondence to M . A. Pastoors: tel: + 3 7 255S 64646; fax: + 3 7 2555 64640; e-mail: m artin.pastoors@ w ur.nl
In tro d u c tio n
se lectiv ity c h a ra c te ris tic s o f th e g e a rs u s e d to c a tc h th e m can
F ish e rie s m a n a g e m e n t p la n s allo w fo r th e d e v e lo p m e n t o f lo n g e r-
h ave s u b s ta n tia l s id e effe c ts o n t h e effe ctiv e n ess o f th e m easu res
t e r m stra te g ie s a n d a re in c re a sin g ly b e in g u s e d in th e N o r th e a s t
ta k e n in a c h ie v in g t h e in te n d e d m a n a g e m e n t o b jectiv es. F o r
A tla n tic (C E C , 2 0 0 1 , 2006). W h e n fish e rie s m a n a g e rs o r sta k e ­
e x am p le, if th e q u o ta s se t fo r th e tw o sp e cies a re n o t e x h a u s te d
h o l d e r o rg a n iz a tio n s (e.g. R e g io n a l A d v is o ry C o u n c ils ) d isc u ss
i n sy n c h ro n y , o v e r - q u o ta c a tc h e s m a y b e ta k e n ( a n d d isc a rd e d
s u c h p la n s , th e y o f te n re q u ire a n e v a lu a tio n o f th e p o s s ib le c o n s e ­
o r la n d e d illegally) o f t h e sp e cies w ith th e m o s t re s tric tiv e q u o ta ,
q u e n c e s b e fo re th e p la n s are im p le m e n te d .
w h ic h g e n e ra lly is d e p le te d first. M o re o v e r, th e re la tiv e catch
A m a n a g e m e n t p la n can be e v a lu a te d u s in g a s im u la tio n m o d e l
o p p o r tu n itie s f o r th e tw o sp e cies m a y d iffe r b e tw e e n years.
o f t h e fish e ry sy stem . T h e o p e ra tin g m o d e l ( O M ) d e s c rib e s th e key
B ecause th e m ix e d b e a m tra w l f is h e ry fo r flatfish p r e s e n ts a rela­
p ro c e ss e s, b a se d o n sim p lify in g a s s u m p tio n s a b o u t th e in te r ­
tively tra c ta b le e x a m p le , its p r o b le m s h a v e b e e n w ell s tu d ie d in
a c tio n s a m o n g th e
E x a m p le s o f s u c h
th e p a st ( R ijn s d o rp a n d P a s to o rs , 1995; Keli e t a l , 1999, 2003,
m o d e ls (K irk w o o d , 1997; M c A llister e t a l , 19 9 9 ) m a y u se s im p li­
2004; P a sto o rs e t a l , 2 0 0 0 ; Keli a n d B ro m ley , 2004; K ra a k et a l ,
fie d d y n a m ic s o f fish sto c k s a n d fleets, w h ile a tte m p tin g t o in c o r ­
2004).
d iffe re n t c o m p o n e n ts .
p o r a t e s u ffic ie n t a s p e c ts o f th e c o m p le x d y n a m ic s o f real system s
T h e tw o ta rg e t sp e c ie s a r e m a n a g e d b y n a tio n a l sh a re s in th e
( B u tte r w o r th a n d P u n t, 1999; P u n t e t a l , 2 0 0 2 ). A m a n a g e m e n t
to ta l allo w ab le c a tc h (T A C ), d a y s -a t-s e a re s tric tio n s o n th e fleet,
p r o c e d u r e (M P ; B u tte rw o rth , 2 0 0 7 ) c o n s is ts o f d a ta c o lle c tio n ,
a n d te c h n ic a l m e a s u re s . T h e s p a w n in g -s to c k b io m a s s (SSB) o f
s to c k
s ta tu s
e v a lu a tio n ,
h a rv e st
c o n tr o l
ru le s
( H C R s ),
and
plaice d e c lin e d a f te r th e e arly 1990s a n d h a s b e e n ju s t ab o v e th e
im p le m e n ta tio n . F leet b e h a v io u r h a s g e n e ra lly b e e n c a p tu r e d in
lim it b io m a s s re fe re n c e p o i n t (£ iim) sin c e th e m id -1 9 9 0 s (ICES,
sim p lis tic a s s u m p tio n s (K raa k e t a l , 2 0 0 4 ), a n d th e b io lo g ic a l
2 0 0 6 a). T h e so le s to c k h a s f lu c tu a te d m a r k e d ly in re s p o n s e to
d e ta il is o fte n relativ ely p le n tifu l (K eli a n d B ro m le y , 2 0 0 4 ). T h e
th e a p p e a ra n c e o f s tr o n g y e a r classes. T h e tw o m o s t re c e n t y ear
u n c e r ta in ty a b o u t th e real sy stem a n d its d y n a m ic s p lay s a key
classes are t h o u g h t to b e p o o r , w h ic h c o u ld easily r e d u c e sole
r o le in e v a lu a tin g m a n a g e m e n t stra te g ie s. T h is u n c e r ta in ty reflec ts
SSB b e lo w its J3lim in t h e n e a r f u tu r e (IC E S , 2 006c).
a la c k o f k n o w le d g e o f p ro cesses s u c h as t h e s t o c k - r e c r u i tm e n t
I n 2004, th e C o m m is s io n o f th e E u r o p e a n C o m m u n itie s asked
re la tio n s h ip , d e n s ity -d e p e n d e n c e , n a tu r a l v a ria b ility , a n d re sp o n se s
th e N o r th Sea R e g io n a l A d v iso ry C o u n c il (N S R A C ) f o r ad v ice “o n
o f th e fleet to th e m e a s u re s im p o sed .
th e im p le m e n ta tio n o f a re c o v e ry p la n f o r N o r th Sea p la ic e a n d a
N o r t h S ea p la ic e (Pleuronectes p la te ssa ) a n d so le (S olea solea )
lo n g - te rm m a n a g e m e n t p la n f o r s o le ”. N S R A C (2 0 0 5 ) issu e d its
a r e ta k e n m a in ly in a m ix e d b e a m tra w l fish e ry w ith a b y c a tc h
ad v ice in Ju ly 2 0 0 5 , fo c u sin g o n ly o n th e re co v ery o f th e p laice
o f o t h e r d e m e rs a l species. M a n a g e m e n t o f th e s e tw o species
s to c k
faces m a n y c h a lle n g e s b ec a u se th e ir sp a tia l d is tr ib u tio n s a n d th e
su g g e sted b y IC E S (2 0 0 6 c ). T h e a d v ic e d id n o t d e a l w ith lo n g -te rm
to
above
230 0 0 0 1, th e
p r e c a u tio n a r y
© 2 0 0 7 I n te r n a tio n a l C o u n c il fo r th e E x p lo r a tio n o f th e Sea. P u b lis h e d b y O x fo rd J o u rn a ls . All r ig h ts reserv ed .
F o r P e rm is s io n s , p le a se em ail: jo u rn a ls .p e rm is s io n s @ o x fo rd jo u rn a ls .o rg
b io m a s s
(Bpa)
V a lid a tin g m a n a g e m e n t s im u la tio n m odels
819
m a n a g e m e n t o f so le . B e cau se th e N e th e rla n d s is a m a jo r p la y e r in
a p p ly to sole. A n a lte rn a tiv e
th e s e fla tfis h fish eries, th e D u tc h M in is try o f A g r ic u ltu re , N a tu r e
a d d itio n a l m e a s u re s b e in g ta k e n w h e n SSB w o u ld fall b e lo w Blim.
s c e n a r io e v a lu a te d w as w ith o u t
C o n s e r v a tio n a n d F o o d Q u a lity (L N V ) re q u e ste d a n e v a lu a tio n
o f t h e lik e ly effects o f th e N S R A C -p ro p o s e d re c o v e ry p la n o n th e
T he evaluation process
so le s to c k . T h e d e ta ils o f th e s e e v a lu a tio n s (P o o s e t a l , 2 0 0 6 ) are
T h e p a rtie s in v o lv e d in th e e v a lu a tio n p r o c e s s w ere th e D u tc h
n o t th e fo c u s o f th is m a n u s c rip t; in stea d , w e fo c u s o n th e
M in is try
p ro c e ss . T h e m a in q u e s tio n s w e p o se are: (i) h o w h a s t h e te c h n ic a l
(N S R A C ), a n d th e resea rch o r g a n iz a tio n (W ag en in g en -IM A R E S ).
e v a lu a tio n o f th e re c o v e ry p la n b e e n in itia te d a n d c a r r ie d th r o u g h ;
T h e a p p ro a c h w as to develop a FLR (w w w .flr-p ro je c t.o rg ; Keli
(L N V ),
th e
s ta k e h o ld e r
flatfish
W o rk in g
G ro u p
(ii) h o w h a s th e u n c e r ta in ty in v a rio u s p ro cesses b e e n e n c a p s u ­
e t a l , 2007) sim u la tio n m o d e l t h a t w o u ld allo w in c o r p o ra tio n o f
la te d i n t h e O M ; a n d (iii) h o w h av e th e re su lts b e e n c o m m u n i ­
d iffe re n t h y p o th eses o n p o p u l a ti o n d y n a m ic s a n d th e jo in t e x p lo ita ­
c a te d a n d u se d ?
tio n o f th e tw o stocks. T h e th re e p a r tie s in itia lly in te ra c te d to d efin e
th e resea rch q u e s tio n s a n d th e ty p e o f resu lts expected, a n d ag a in at
th e e n d o f th e p ro cess to d isc u ss t h e resu lts in th e re p o rt. B etw een
P ro p o sed NSRAC m a n a g e m e n t plan
T h e s ta te d o b je c tiv e o f th e m a n a g e m e n t p la n h a s b e e n f o rm u la te d
s ta r t a n d finish, in te ra c tio n b e tw e e n resea rch ers a n d sta k e h o ld e rs
w as negligible.
fo r p la ic e o n ly (N S R A C , 2 0 0 5 ):
“a m u l t i - a n n u a l m a n a g e m e n t p la n s h o u ld b e a d o p te d fo r
p la ic e i n th e N o r t h S ea w ith a n in itia l ta r g e t o f re a c h in g
a n SSB a t t h e B pa level w ith in 3 - 5 years w ith a r e -e v a lu a tio n
a f te r 3 y e a rs a n d w ith th e lo n g te r m a im o f e x c e e d in g B pa.
T h e p la n s h o u ld b e im p le m e n te d as o f t h e 1st o f J a n u a ry
2 0 0 6 . T h e m a n a g e m e n t p la n is a im e d at re d u c in g p re ss u re
o n ju v e n ile p la ic e a n d w o u ld c o m p rise s tr u c tu r a l e ffo rt
r e d u c tio n s a c c o m p a n ie d b y s ta b ility in th e T A C f o r p laice.
T h e m u l t i - a n n u a l p la n s h o u ld b e a c c o m p a n ie d b y a m o n i ­
Setting up the model
T h e in itia l q u e s tio n in m o d e l d e v e lo p m e n t re fe rre d to th e d efi­
n itio n o f th e d im e n s io n s to b e in c lu d e d . T h e d im e n s io n s reflect
t h e ty p e o f p ro c e sse s in c lu d e d , t h e av ailab le in f o rm a tio n , a n d
t h e d o m i n a n t issu es in th e m a n a g e m e n t p la n . I n th is case, th e
p a r tia l s p a tia l o v e rla p b e tw e e n
sp e cies su g g e ste d
a
p la ic e d o m in a tin g n o r th o f 5 6 ° N ) , a n d a d is tin c tio n b e tw e e n
tw o m a in ty p e s o f fleets ( o n e e a c h ta rg e tin g so le a n d p laice).
T h e sim u la tio n m o d e l c o n s is te d o f tw o su b m o d e ls : a n O M
to r in g a n d e v a lu a tio n s c h e m e , w h ic h w o u ld also in c lu d e
d e s c rib in g
th e m o n i t o r i n g o f so c ial a n d e c o n o m ic im p a c t”.
th e tw o
tw o - a re a m o d e l (so le d o m in a tin g a s th e ta r g e t s o u th o f 56°N ,
th e
b io lo g ic a l
and
fle e t
( in c lu d in g
e c o n o m ic s )
d y n a m ic s o f th e u n d e r ly in g s y s te m ; a n d a n M P c o n s istin g o f
T h e b a s ic m a n a g e m e n t m e a s u re p r o p o s e d w as “ a s tr u c tu r a l e ffo rt
d a ta c o lle c tio n , sto c k a s se s sm e n t, a n d a H C R ( fo r a g ra p h ic a l
r e d u c tio n o f 15% o f e n fo rc e d lic e n s e d c a p a c ity lim its in th e i n t e r ­
p r e s e n ta tio n o f a s im ila r ty p e o f s im u la tio n a p p r o a c h , see Keli
et a l , 2 0 0 5 ).
n a tio n a l 8 0 m m flatfish f is h e ry o v e r 2006 a n d e ffo rt t o b e m a in ­
t a i n e d a t t h e n e w level f o r a f u r th e r tw o y e a rs”. T h e re w ere
The
b io lo g ic a l p ro c e ss e s i n
th e
OM
in c lu d e d
a s to c k -
f o r n a tu r a l
m o rta lity ,
d e ta ile d c o m m e n ts in th e p la n o n e x e m p tio n s f o r s o m e fleets,
r e c r u itm e n t
o n th e w a y e ffo rt r e d u c tio n s c o u ld b e e m b e d d e d in n a tio n a l
m a tu r ity - a t- a g e , a n d w e ig h t- a n d le n g th -a t-a g e , a n d fixed v alu es
f ish in g p la n s , a n d o n th e d iffe re n t fo rm s o f e ffo rt r e d u c tio n p o s s ­
fo r th e relativ e p r o p o r tio n o f e a c h age g r o u p in ea c h o f th e tw o
ib le (d a y s-a t-se a re g u la tio n s o r d e c o m m is s io n in g ).
areas. T h e fle e t-d y n a m ic s m o d e l c o n s is te d o f tw o b e a m traw l
re la tio n s h ip ,
fix ed
v a lu e s
D e s p ite th e s e te c h n ic a l d e ta ils , e v a lu a tio n w ith t h e av ailab le
fleets: th e D u tc h fleet ta rg e tin g p r im a r ily so le (80 m m m e s h in
sc ie n tific to o ls w as d iffic u lt. F o r exam p le, th e p la n sta te d : “ I n
t h e c o d e n d ) s o u th o f 5 5 °N , a n d a U K fleet ta rg e tin g p rim a rily
t h e e v e n t o f th e p la ic e s to c k fa llin g b e lo w B iim n e w m e a s u re s
p la ic e (1 0 0 m m m e s h ) n o r t h o f 5 5 °N . T re n d s in fish in g e ffo rt
w o u ld b e a p p lie d ”. H o w e v e r, th e n a tu r e o f th e s e m e a s u re s w as
w e re d e riv e d fro m in f o r m a tio n i n th e D u tc h lo g b o o k d a ta b a s e
n o t d e s c rib e d . F u rth e rm o r e , t h e s ta te o f th e so le s to c k w a s n o t c o n ­
(c o n ta in in g re c o rd s o f D u tc h vessels as w ell as U K vessels
s id e re d , a n d t h e clie n ts w a n te d t o k n o w a b o u t th e effects o f th e
la n d in g th e ir c a tc h e s in th e N e th e r la n d s ) . F u tu r e e ffo rt a llo c a tio n s
p la n o n sole.
S u c h o p e n e n d s a p p e a r t o b e a g e n e ric p r o p e r ty o f th e o u tc o m e
w e re a s s u m e d to r e ta in th e s a m e p r o p o r ti o n s b y are a a n d fleet.
o f p o litic a l n e g o tia tio n : sp e c ific c o n d itio n s are ra is e d , b u t h o w
of
th e y s h o u ld
u n til p r o b le m s a rise.
(R ijn s d o rp e t a l , 2 0 0 6 ). C a tc h e s w e re g e n e ra te d f ro m th e u n d e r ­
H o w e v e r, f o r te c h n ic a l e v a lu a tio n , o p e n e n d s p r e s e n t d iffic u lty
ly in g ( “tr u e ”) p o p u la tio n a n d s p lit in to la n d in g s a n d d isc a rd s
in
a c c o rd in g to
be
in te r p r e tin g
re so lv e d
a
is le ft o p e n
m a n a g e m e n t p la n :
a s im u la tio n
a p p ro ach
re q u ire s t h a t all a c tio n s b e sp e c ifie d u n d e r all c o n d itio n s .
C o n c e p tu a lly , th e c a tc h in g p ro c e ss w a s m o d e lle d as a c o m b in a tio n
ca tc h a b ility ,
selectivity,
a r e te n tio n
e ffo rt,
and
o give d e riv e d
te c h n o lo g ic a l
fro m
creep
o b se rv e r tr ip s
(V a n K eek en e t a l , 2004).
W h e n m a n a g e m e n t p la n s a re d e v e lo p e d in c o n ju n c tio n w ith a n
T h e M P c o n s is te d o f th r e e m a in p ro cesses: s a m p lin g ra w d a ta
e v a lu a tio n a p p r o a c h , t h e p r o b le m s can b e re so lv e d th r o u g h a
fro m t h e u n d e rly in g p o p u la tio n ; s to c k a sse ssm e n t, a n d s h o r t- te r m
sy ste m
fo re c a stin g fo llo w in g s ta n d a r d p ro c e d u re s ; a n d a H C R d e fin in g
o f fe e d b a c k lo o p s b e tw e e n an aly sts a n d sta k e h o ld e rs .
H o w e v e r, w h e n a n e v a lu a tio n o f a specific p la n is re q u e s te d , th e
th e
o p e n e n d s h a v e to b e i n te r p r e te d b y th e an aly sts b y f o r m u la tin g
S a m p lin g fro m th e tr u e p o p u la tio n w as m im ic k e d b y g e n e ra tin g
a p p r o p r ia te
m anagem ent
m e a s u re
a ra n g e o f p o t e n t i a l sc e n a rio s .
e s tim a te s o f la n d in g s -a t-a g e
(so le)
and
g iv en
th e
c a tc h -a t-a g e
forecast.
(p laice;
T h is h a p p e n e d in th is case: w e in te r p re te d t h e cla u se a b o u t “ th e
in c lu d in g d is c a rd s ), s im ila r t o th e a n n u a l a s se s sm e n ts fo r th e
n e w m e a s u re s ” in s u c h a w a y th a t, i f th e p e rc e iv e d SSB w o u ld fall
tw o sto c k s. T h e c a tc h e s w e re g e n e ra te d u s in g th e se lectiv ity c h a ra c ­
b e lo w B Iim, a f u r th e r d e c re a s e o f n o m in a l fish in g e f fo r t b y 15%
te ris tic s o f th e tw o fleets a n d a sim p le lo g n o r m a l e r r o r w ith a
a n n u a lly w o u ld b e im p le m e n te d u n til th e p e rc e iv e d SSB h a d
re la tiv e ly sm a ll c o e ffic ie n t o f v a ria tio n (C V = 0.1).
r e tu r n e d t o a b o v e B]im. F u rth e r, o u r in te r p re ta tio n w a s th a t th e
T h e s im u la tio n c o n ta in e d a “tr u e ” su rv e y th a t s a m p le d fro m
ru le ( a lth o u g h th is h a d n o t b e e n sp e cified ex p licitly ) w o u ld also
th e p o p u la tio n s o f t h e tw o species u s in g c a tc h a b ility a n d se lectiv ity
820
M . A . Pastoors e t al.
p a tte r n s e s tim a te d f r o m h is to ric a l d a ta in c o n ju n c tio n w ith th e ir
a s se s sm e n t ty p e o f d is c o u r s e b y re fe rrin g to SSB a n d b io lo g ic a l
sp a tia l d is tr ib u tio n . “ O b s e rv e d ” su rv e y c a tc h -a t-a g e b y species
re fe re n c e p o in ts . T h e r e f o r e , th e n u m e ric a l v alu es o f th e v a ria b le s
w as g e n e ra te d b y a p p ly in g a lo g n o r m a l e r r o r (a g a in C V = 0 .1),
d e riv e d fro m t h e s i m u l a t io n s w o u ld b e v iew ed c ritic a lly a g a in s t
a n d th e s e se rie s w e re u se d fo r tu n in g in th e s to c k a sse s sm e n t
t h e v alu es p r o d u c e d b y r o u t i n e s to c k a s se s sm e n t (in th is case as
p ro c e ss . T h e s to c k a s se s sm e n t p ro c e ss e n c o m p a s se d sin g le-sp ecies
p r e s e n te d b y IC E S , 2 0 0 6 a ) .
e x te n d e d s u rv iv o rs a n a ly sis (X SA ) f o r p laice a n d so le , b a s e d o n
T h e c o m b in a tio n o f o v e r -p a ra m e te r iz a tio n o f th e O M (u sin g
c a tc h - a n d la n d in g s - a t- a g e d a ta , respectively. X SA se ttin g s a n d
m o r e p a r a m e te r s t h a n t h e r e is in f o r m a tio n t o e s tim a te th e m
s h o r t- te r m fo re c a s ts c o r r e s p o n d e d t o th o s e u se d b y IC E S (2 0 0 6 a ).
f ro m ) a n d th e r e q u ir e m e n t to g e n e ra te re a listic sto c k a n d fleet
T h e H C R i m p le m e n te d in th e m o d e l a tte m p te d to m im ic th e
d y n a m ic s , im p lie d t h a t fix e s h a d to b e s o u g h t to g e n e ra te larg ely
N S R A C m a n a g e m e n t p la n . N o m in a l fish in g e ffo rt w as re d u c e d
c o m p a r a b le re su lts. W e u s e d th e te c h n iq u e o f h in d c a s tin g to s im u ­
b y 15% in 2 0 0 6 c o m p a r e d w ith 2005, a n d th is level w a s m a in ta in e d
la te th e h isto ric a l tr a je c to r ie s o f sto c k s a n d fleets o v e r th e p e r io d
in s u b s e q u e n t y e a rs. I n th e o b je c tiv e s ta te d in t h e p la n , th e re is a n
1 9 9 5 - 2 0 0 4 . T h e s ta r t p o p u l a ti o n s in 1995 a n d levels o f r e c r u it­
i n h e r e n t te n s io n b e tw e e n re d u c in g e ffo rt a n d m a in ta in in g s ta b ility
m e n t w ere ta k e n d ir e c tly f r o m IC E S (2 0 0 6 a), a n d th e tr e n d s in
o f th e TAC. T h is p o s e d a d d itio n a l ch allen g es to im p le m e n ta tio n o f
fis h in g e ffo rt w e re d e r iv e d fro m th e lo g b o o k d a ta b a s e . G iv en
th e m o d e l. L N V r e q u e s te d a n a d d itio n a l m a x im u m a n n u a l c h a n g e
th e s e fixed in p u ts , s im u la tio n s w e re r u n u n d e r d iffe re n t a s s u m p ­
in T A C o f 1 5 % to b e in c lu d e d in th e s im u la tio n s , re p re s e n tin g a n
tio n s o n th e re la tiv e d i s t r i b u t io n o f fish o v e r th e tw o areas, th e
e x te n s io n o f th e s ta te d o b jectiv es. H o w ev er, th e m e a s u re s s ta te d
c a tc h a b ilitie s o f th e tw o fle e ts fo r th e tw o species, a n d th e in c re a se
d id
in te c h n ic a l effic ie n c y o f t h e tw o fleets (R ijn s d o rp e t a l , 2 0 0 6 ).
not
r e fe r to
T A C s, b u t
o n ly to
d e c o m m is s io n in g
and
d a y s -a t-se a lim its . T h e re f o r e , T A C s w o u ld n o t c o n s tr a in th e
S o m e re su lts o f th e e x p lo r a to r y analyses are sh o w n in F ig u re 1;
fish e ry in t h e m o d e l anyw ay: th e fleets sim p ly e x h a u s te d th e
w e c o m p a r e th e p e rc e iv e d v a lu e s (IC E S , 2 0 0 6 a) o f la n d in g s , d is ­
e ffo rt q u o ta a n d r e p o r te d w h a te v e r catch es th e y g e n e ra te d . W e
c a rd s, r e c r u itm e n t, a v e ra g e fish in g m o r ta lity (.Fbar), se le c tio n
d id n o t im p le m e n t a tw o - tie r sy ste m in w h ic h e ith e r th e T A C o r
p a tt e m , a n d SSB, th e a s s u m e d re la tiv e d is tr ib u tio n o f fish o v e r
th e e ffo rt q u o t a c o u ld c o n s tra in t h e fishery, b e c a u s e th e p r o p o s e d
a re a s , a n d th e r e la tio n s h ip b e tw e e n F b a r a n d e ffo rt w ith th e ir
H C R d id n o t sp e c ify h o w th e p r i o r i ty b e tw e e n s u c h d iffe re n t
s im u la te d ( “ tr u e ” ) v a lu e s , a s d e riv e d fro m th e O M . O b v io u sly , if
m e a s u re s w o u ld h a v e b e e n set.
w e w is h to fix th e s im u la te d h is to ric a l d y n a m ic s to m a tc h th e
T h e a n n u a l d e c is io n p ro c e s s o n e ffo rt q u o ta w as b a s e d o n th e
o b s e rv a tio n s , w e a r e fa c e d w ith t h e c h o ic e b e tw e e n m a n y d iffe re n t
s h o r t - t e r m fo re c a s t o f th e SSB r e m a in in g a fte r th e y e a r to w h ic h
o p tio n s : m e a n se le c tio n p a tte r n , e f f o r t - m o r t a l i t y re la tio n s h ip ,
th e s e w o u ld a p p ly . T h is fo re c a st w as c o m p a r e d w ith th e B lim tr ig ­
la n d in g s , e tc ., m a y all b e fix ed , b u t fixing all s im u lta n e o u s ly is
g ers d e fin e d i n t h e p la n . I m p le m e n ta tio n e r r o r w ith re s p e c t to
im p o s s ib le
m is r e p o r tin g o r b la c k la n d in g s w as n o t in c lu d e d .
p a r a m e te r .
Parameter estimates
c e iv e d as) “tr u e ” a n d s im u la te d v alu es f ro m th e b a s ic r u n fo r f o u r
T h e av erag e d i s t r i b u t io n o f th e sp e cies b y age o v e r t h e tw o a reas
i m p o r t a n t p o p u la tio n d y n a m ic s p a ra m e te rs . I n th e b a se r u n , all
w as e s tim a te d f r o m th e a n n u a l b e a m traw l survey, w h ic h ta k e s a
p a r a m e te r s w e re b a s e d o n in f o r m a tio n fro m s o m e ty p e o f an aly sis
s y n o p tic s a m p le o f th e p la ic e a n d so le p o p u la tio n s i n la te
e x c e p t fo r o v e ra ll c a tc h a b ility o f th e fleets, w h ic h w a s o b ta in e d b y
s u m m e r (IC E S , 2 0 0 6 b ). I n g e n e ra l, so le a re m a in ly in th e s o u th e r n
m in im iz in g th e d iffe re n c e in c a tc h -a t-a g e b e tw e e n th e m o d e l a n d
u n le s s w e ig h ts
c a n b e a ssig n e d t o
ea c h sp ecific
F ig u re 2 (le ft p a n e ls ) s h o w s th e c o m p a r is o n b e tw e e n t h e ( p e r ­
a re a , a n d p la ic e m ig r a te fro m s o u th to n o r t h w ith in c re a s in g age.
a s a c tu a lly o b s e rv e d in s a m p le s fro m th e fleet. C learly , th e s i m u ­
I n f o r m a tio n o n s to c k tr e n d s w a s av ailab le fo r th e p e r io d 1 9 5 7 -
la te d la n d in g s a n d SSB o f p laice a n d so le a r e s u b s ta n tia lly
2 0 0 4 f ro m IC E S (2 0 0 6 a ). R e c r u itm e n t e s tim a te s fo r th e la s t f o u r
s m a lle r t h a n th o s e a c c o r d in g to th e a ssessm en t. A lth o u g h t h e t e m ­
y ears w e re e x c lu d e d b e c a u s e th e y w e re c o n s id e re d u n re lia b le .
p o r a l d y n a m ic s m a y a p p e a r re a s o n a b ly sim ila r, a d is c re p a n c y in
T h e r e m a in in g
e s tim a te s t o c k - r e c r u i tm e n t
t h e o v e ra ll level m a y h a v e s u b s ta n tia l effects o n p r o s p e c tiv e s im u ­
r e la tio n s h ip s o f th e R ic k e r a n d th e B e v e r t o n - H o l t ty p e. I n th e
la tio n s i f th e s a m e a b s o lu te v a lu e s a r e u se d fo r lim it re fe re n c e
f o rw a r d s im u la tio n , r e c r u it m e n t e s tim a te s w ere ta k e n f ro m th e
p o in ts . F o r in sta n c e , th e sim u la te d sto c k s w ill b e b e lo w Biim
s to c k —r e c r u it m e n t r e la tio n s h ip , ta k in g in to a c c o u n t th e v a ria n c e
m o s t o f th e tim e .
se t w as u s e d
to
e s tim a te d e r iv e d f r o m th e h is to ric a l re la tio n sh ip .
F o r p laice, a n a d d itio n a l p r o b le m a ro se w ith t h e s p lit o f c a tc h e s
E s tim a tin g th e p a r a m e te r s o f th e fle e t-d y n a m ic s m o d e l w as less
b e tw e e n la n d in g s a n d d isc a rd s : s im u la te d la n d in g s w e re b e lo w a n d
str a ig h tf o rw a r d . T h e in te r p la y o f s im u la te d sto c k a b u n d a n c e a n d
s im u la te d d is c a rd s a b o v e th e a sse s sm e n t e s tim a te s. M o s t p laice
s to c k d is tr ib u tio n s b y ag e a n d a re a , to g e th e r w ith th e d is tr ib u tio n s
a g e d 1 a n d 2 y e a rs a re in t h e s o u th e r n are a w h e re th e b e a m
o f th e fleets, d e te r m in e s th e c a tc h p ro file s g e n e ra te d b y th e fleets.
tr a w l fish e ry m a in ly o p e ra te s, r e s u ltin g in h ig h s im u la te d d isc a rd s .
T h e e m p ir ic a l o b s e rv a tio n s o n t h e c a tc h p ro file s o f th e re a l fleets
I n p ra c tic e , th e s e s m a lle r fish m a y n o t b e av ailab le t o th e fish e ry
w ere n o t s u f f ic ie n t t o d e te r m in e t h e p a r a m e te r v alu es fo r th e s im u ­
b e c a u s e th e y live in sh a llo w c o a s ta l re g io n s w h e re la rg e r vessels
la tio n m o d e l u n iq u e ly . T h e re fo re , a n y m is m a tc h b e tw e e n th e
a r e n o t p e r m itte d . H o w ev er, in a s im u la tio n e n v ir o n m e n t b a se d
s im u la te d a n d t h e re a l c a tc h p ro file s c o u ld h av e b e e n c a u s e d b y
o n tw o a re a s o n ly , s u c h s u b tle d iffe re n c e s c a n n o t b e a c c o u n te d for.
in c o r r e c t a s s u m p tio n s in th e fle e t-d y n a m ic s o r sto c k -d y n a m ic s
m o d e ls.
T h e re su lts p r e s e n te d in F ig u re 2 (rig h t p a n e ls ) in c o r p o r a te
a n a tte m p t to r e m e d y th is s h o r tc o m in g b y m a n u a lly m o d ify in g
T h e c ritic a l q u e s tio n in i n te r p r e tin g s im u la tio n re su lts is: h o w
t h e re la tiv e s p a tia l d is tr ib u tio n o f p la ic e ag ed 1 a n d 2. B ecau se
clo se d o th e s e h a v e t o b e to r e a lity as c u rre n tly p erceiv ed ? I n o th e r
th e s e ag e g r o u p s a r e n o w lo c a te d m o r e in th e n o r th e r n a re a , th e
w o rd s , is it a p r o b le m i f s im u la te d c a tc h p ro file s o r sto c k tr e n d s
o v e ra ll d is c a rd s d e c re a s e , so t h e s im u la te d la n d in g s a p p r o a c h th e
d iffe r fro m t h e h is to r ic a l o b s e rv a tio n s ? T h e a n s w e r d e p e n d s o n
o b s e rv e d la n d in g s . A lso, th e SSB e s tim a te s are clo ser. H o w e v e r,
th e ty p e o f e v a lu a tio n p ro c e s s in w h ic h th e s im u la tio n m o d e l
t h e s im u la tio n s s h a re a m a jo r d isc re p a n c y b e tw e e n s im u la tio n s
is u se d . T h e m a n a g e m e n t p la n h a s b e e n p h r a s e d in a sto c k
a n d a s se s sm e n t ( F ig u re If): th e lin e a r a n d p o s itiv e r e la tio n s h ip
V a lid a tin g m a n a g e m e n t s im u la tio n m odels
821
Sole
OM
----- WG
10000
i
i
y \
—
1996
1998
2000
2002
2004
1996
1998
2000
2002
2004
o
o
-
<N
O -
0
i
- f \
o
o _
o
1996
1998
2000
2002
2004
1996
Average mortafity-at-age
1998
2000
2002
2004
Average mortality-at-age
1996
1998
2000
2002
2004
1996
1998
2000
2002
2004
o
o
o
o
so
o
o
o
1996
1998
2000
2002
2004
1996
1998
2000
2002
2004
4
6
8
1998
2000
2002
2004
Proportiorvat-age-in s outh
P ro portion-at-agein so u th
2
1996
10
300 0 0
35000
4 0 000
45000
2
4
6
8
10
30000
350 0 0
400 0 0
45000
Figure 1. C o m p ariso n o f h in d c a s t p o p u la tio n dynam ics p a ra m e te rs for plaice (left) a n d sole (right) from sim ulations (black lines, O M ) using
sp ecies d istrib u tio n by are a from surveys a n d n o t ta k in g in to a c c o u n t technological cre e p w ith th e c o rre sp o n d in g e s tim a te s (red lines,
W orking C ro u p ) available fro m ICES (2006a): landings, discards, m ean F (Fbar), m o rtality -at-ag e, re c ru itm e n t, SSB, p ro p o rtio n o f p o p u la tio n
by ag e g ro u p in th e so u th e rn are a (in p u t), a n d th e relatio n sh ip b etw e e n effort a n d F.
b e tw e e n fish in g e ffo rt a n d fish in g m o r ta lity in th e s im u la tio n
p re c is io n o f th e s im u la tio n m o d e ls u se d , b u t a t th e s a m e tim e a
m o d e l is a d ire c t c o n s e q u e n c e o f a n a s s u m p tio n in th e u n d e rly in g
h ig h d e g re e o f sc e p tic ism r e g a rd in g th e ir o u tc o m e s : th e resu lts
m o d e l, w h e re a s th e a v a ila b le a sse s sm e n t d a ta in d ic a te n o s ig n ifi­
w ere e asily c o n s id e re d to b e falsified w h e n c o m p a r e d w ith p o ss ib ly
e q u a lly u n c e r ta in a s se s sm e n t d a ta .
c a n t re la tio n s h ip a t all.
F ig u re 3 c o m p a re s th e re su lts fo r so le a fte r in tr o d u c in g an
in c re a s e i n te c h n ic a l efficien c y fo r th e tw o sp ecies, as e s tim a te d
b y R ijn s d o rp et al. (2 0 0 6 ). A lth o u g h th e slo p e s o f th e e f f o r t -
D iscussion
m o r ta lity
T h e e v a lu a tio n o f th e N S R A C m a n a g e m e n t p la n r e q u ire d th e u se
re la tio n s h ip
have
becom e
m o re
c o m p a ra b le ,
th e
a b s o lu te e s tim a te s o f fish in g m o r ta lity in t h e s im u la tio n a re still
o f a m u ltifle e t, m u ltis to c k sim u la tio n m o d e l, w h ic h is a level o f
s u b s ta n tia lly h ig h e r t h a n th o s e fro m th e a s se s sm e n t.
c o m p le x ity h ig h e r th a n m o s t m o d e ls u se d so fa r to e v a lu a te fish e ­
ries m a n a g e m e n t sy stem s (K eli e t a l., 2005, 2 0 0 6 b ). T h e d iffic u l­
ties e n c o u n te r e d in try in g t o m a tc h th e resu lts o f th is exercise w ith
Communicating results
th e ty p e o f in f o rm a tio n u n d e rly in g th e m a n a g e m e n t ad v ice h av e
B e cau se o u r fo cu s d u r in g th e s im u la tio n s w a s o n th e a s s u m p tio n s
n o t b e e n p re s e n te d to h ig h lig h t th e m o d e llin g d etails, b u t to illu s­
b e h i n d t h e s im u la tio n m o d e l a n d th e w a y th e O M w as p a r a m e te r ­
tr a te th e g e n e ra l p ro b le m s o f such a n e v a lu a tio n p ro cess, o f e n c a p ­
iz e d o r, m o r e g en erally , o n th e u n c e r ta in tie s in v o lv ed , th e fu ll
s u la tin g u n c e rta in ty , a n d o f c o m m u n ic a tin g c o m p le x results.
ra n g e o f re su lts w as p r e s e n te d to th e p a r tie s th a t c o m m is s io n e d
T h e e v a lu a tio n w as c a r r ie d th r o u g h in a n a lm o s t lin e a r c h a in o f
th e s tu d y . H o w ev er, th o s e clie n ts d id n o t re la te to t h e te c h n ic a l
a c tio n s . F irst, t h e p r o b le m w as d e fin e d jo in tly b y th e c lie n ts a n d
c o m p le x itie s o f th e m o d e llin g p ro c e ss . T h e i r m a in f ra m e o f e v a lu ­
sc ie n tis ts. D u r in g th e n e x t p h ase, th e sc ie n tis ts i n te r p r e te d th e
a tio n w as w h e th e r th e h in d c a s tin g p r o c e s s m a d e se n se ( a re th e
p la n , d e v e lo p e d th e m o d e l, ra n th e sc e n a rio s, a n d e v a lu a te d th e
re s u lts s im ila r to w h a t h a s b e e n o b se rv e d ? ) a n d w h e th e r th e y
re su lts, a lm o s t in iso la tio n . Finally, th e re su lts a n d c o n c lu s io n s
c o u ld u n d e r s ta n d th e lo g ic o f f u tu r e d e v e lo p m e n ts (c a n th e
w ere p r e s e n te d to th e clien ts. T h e lack o f in te r a c tio n w ith tire
re s u lts b e
o u tp u ts
clie n ts d u r i n g t h e a c tu a l resea rch p h a s e m a y b e e x p la in e d p a r tly
clo sely : i f w e s im u la te d la n d in g s o f p la ic e o f 70 000 t w h ile th e
b y th e tim in g o f th e r e q u e s t, b e c a u se th e w o r k h a d to b e d o n e
T A C w as j u s t 60 0 0 0 t, t h e y w o u ld q u e s tio n th e v a lid ity o f th e
in D e c e m b e r a n d J a n u a ry w h e n th e c lie n ts w ere h e a v ily in v o lv ed
re su lts . T h is in d ic a te d a la rg e d e g re e o f t r u s t in th e p o te n tia l
in th e a n n u a l d e c is io n -m a k in g p ro c e ss fo r th e fo llo w in g y e a r’s
e x p la in e d ? ). M a n y s ta k e h o ld e rs
re a d th e
822
M . A . Pastoors e t al.
Proportion-at-age in south
Proportion-at-agein south
CO
d
o
d
o
o
d
2
6
4
8
2
10
4
6
8
10
2002
2004
200 2
200 4
2002
2004
Landings
Landings
o
o
CO
O— o
o
■'t
1996
1998
2000
20 0 2
2004
1996
1998
2000
D iscards
Discards
o
o
o
o
/ \
o
o
o
o
o
o
o
1996
1998
2000
200 2
200 4
1996
1998
SSB
2000
SSB
o
o
o
o
CM
°
1996
1998
2000
-
200 2
2004
1996
1998
2000
Figure 2. C o m p ariso n o f hin d cast landings, discards, a n d SSB o f plaice fo r tw o p a tte rn s o f th e p ro p o rtio n -a t-a g e p re se n t in t h e so u th e rn area
( to p panels): left panels, p ro p o rtio n e s tim a te d fro m survey d a ta (as in Figure 1); right panels, p ro p o rtio n o f y o u n g e r ages m an u ally m o d ified to
m in im ize th e d isc rep an c y in th e landings.
T A C . N e v e rth e le ss, s u c h a lack o f in te r a c tio n m a d e th e p r o c e s s less
fleet: “ if sc ie n tific e v id e n c e s u p p o r t s th e c la im t h a t p la ic e are
tr a n s p a r e n t (w h o ta k e s r e s p o n s ib ility fo r th e c h o ic e s m a d e ? ), a n d
n o t d isc a rd e d in sig n ific a n t q u a n titie s in th e ir ta r g e te d 80 m m
n o a d ju s tm e n ts c o u ld b e m a d e to th e m u t u a l e x p e c ta tio n s o f th e
so le fishery”. A s sc ie n tis ts, w e d id n o t see h o w th is e x e m p tio n
ty p e o f re su lts g e n e ra te d fro m th e s im u la tio n m o d e l.
c o u ld b e in te g r a te d a n d e v a lu a te d in th e s im u la tio n s w ith o u t
A g e n e ric p r o p e r ty o f m a n a g e m e n t p la n s is t h a t th e y a re th e
p r o d u c t o f p o litic a l n e g o tia tio n . S u c h p ro c e ss e s o f te n le a d t o a n
h a v in g access to sp e c ific in f o r m a tio n r e g a rd in g d is c a rd s in th a t
fishery.
e n d p r o d u c t t h a t d e s c rib e s th e o v erall i n t e n t i o n c le a rly a n d c o n ­
R e g a rd in g o p e n e n d s in a m a n a g e m e n t p la n ( s u c h as th e s ta te ­
ta in s s o m e a s p e c ts d e s c rib e d i n m e tic u lo u s d e ta il. H o w e v e r,
m e n t t h a t n e w m e a s u re s m ig h t b e a p p lie d u n d e r specific c o n ­
o t h e r a s p e c ts are o n ly d e a lt w ith c u rso rily , s o r e q u ir in g f u r th e r
d itio n s , w ith o u t a c tu a lly s ta tin g w h a t th e s e m e a s u re s m ig h t b e),
in te r p r e ta tio n . A lso , sp ecific issu es m a y n o t b e tra c ta b le in a s im u ­
o n e m u s t a c c e p t t h a t th e n e g o tia tio n p ro c e ss c a n n o t s im p ly b e re ­
la tio n a p p ro a c h . A n e x a m p le is th e a p p a r e n t w illin g n e ss o f th e
o p e n e d . H o w e v e r, to o b ta in a c le a r e r u n d e r s ta n d in g o f th e ty p e
N S R A C to c o n s id e r a n e x c e p tio n cla u se f o r th e G e r m a n s h r im p e r
o f m e a s u re s e n v is io n e d , it w o u ld h a v e b e e n b e n e fic ia l fo r th e
V a lid a tin g m a n a g e m e n t sim u la tio n m odels
823
F bar
Fbar
0 .4 -
0.4 -
o.o-l
0.0 H
1996
1998
2000
2002
1996
2004
E ffo rt-F b a r
1998
2000
2002
2004
E ffo rt-F b a r
0 .8 -
0 .4 -
0.4 -
0.0
0.0
-
30000
35 000
40000
45000
-i
30000
35000
40000
45000
Figure 3. C o m p ariso n o f h in d cast average F (Fbar) a n d th e e f fo r t- m o r ta lity relationship for sole: left p an els, p ro p o rtio n in th e so u th
e s tim a te d by surveys a n d no technological creep a ssu m e d (as in Figure 1); rig h t panels, p ro p o rtio n in t h e s o u th m an u ally m o d ified (as for
Figure 2) a n d tech n o lo g ical cre e p assu m ed as based o n R ijnsdorp e t al. (2006).
e v a lu a tio n p r o c e s s t o h a v e h a d c lo s e r a n d m o r e r e g u la r i n t e r ­
c a n n o t d e liv e r re m a in s a n i m p o r t a n t issu e . T h e e x p e c ta tio n s o f th e
a c tio n s w ith th e N S R A C o n th e class o f n e w m e a s u re s th a t
d iffe re n t p a rtie s s h o u ld b e la id d e a r l y a n d o p e n ly o n th e ta b le , to
m ig h t b e e x p lo re d .
T h e u n c e r ta in tie s in th e O M e x p lo re d in s im u la tio n s a d d re s s e d
m a k e th e p ro cess as e ffic ie n t a s p o ssib le .
j u s t th r e e p ro c e ss e s, b u t th e s e r e p re s e n t a lim ite d s u b s e t o f all th e
u se fu l, b u t it m ig h t h av e b e e n e v e n m o r e u se fu l i f u s e d d u r in g th e
O u r overall c o n c lu s io n is t h a t t h e s im u la tio n a p p r o a c h h a s b e e n
p ro c e ss e s t h a t m ig h t in flu e n c e th e o v erall u n c e r ta in ty (e.g. selec­
d e v e lo p m e n ta l stage o f th e p la n , a n d w i t h m o r e in te r a c tio n w ith
tiv ity o f t h e fleets, d y n a m ic e ffo rt a llo c a tio n s b y a re a , a lte rn a tiv e
th e N S R A C b e fo re th e p la n w as fin ally ag reed .
re la tio n s h ip s b e tw e e n selectivity, c a tc h a b ility , e ffo rt, a n d fish in g
T h e FLR m o d e llin g e n v ir o n m e n t (K eli e t a l , 20 0 7 ) allow s c o n ­
m o r ta lity ) . T h is ty p e o f m u ltid im e n s io n a l m o d e l r e q u ire s a
s tr u c tio n o f flexible s im u la tio n m o d e ls t h a t re u se g e n e ric to o ls a n d
s tr o n g a n a ly tic a l a p p r o a c h to e x p lo re th e m a in f a c to rs a ffe c tin g
c a n b e a ttu n e d to d iffe re n t ty p e s o f m a n a g e m e n t ru le s a n d o u t p u t
u n c e r t a i n t y (K eli e t a l , 2 0 0 6 a). H in d c a s tin g c a n b e a u se fu l to o l
m e a s u re s r e q u ire d . H o w e v e r, b e c a u s e F L R is still in a d e v e lo p m e n ­
f o r e x p lo r in g t h e b e h a v io u r a l d y n a m ic s o f a m o d e l if t h e d y n a m ic s
ta l sta g e, th e b a la n c e in t h e d e v e lo p m e n t o f g e n e ric a n d specific
c a n b e v e r ifie d b y o b se rv a tio n s . A s a cav eat, w e n o te t h a t t h e o b s e r ­
to o ls h a s te n d e d to b e o n th e la tte r sid e . A s a c o n s e q u e n c e , th e
v a tio n s a v a ila b le m a y th e m se lv e s b e flaw ed in te r p r e ta tio n s o f th e
r e s u ltin g c o d e h a s b e c o m e to o c o m p le x to b e tr a n s f e r re d easily
re a lity th e y a t t e m p t to re p re se n t. T h e d isc a rd o b s e rv a tio n s in th e
to o t h e r a p p lic a tio n s. M o re w o rk is n e e d e d to m a k e th e sim u la tio n
N o r th S ea p la ic e a s s e s s m e n t are a g o o d e x a m p le , b e c a u s e th e e s ti­
m o d e ls m o re tr a n s p a r e n t a n d tra n sfe ra b le .
m a te s a re b a s e d o n a m o d e llin g a p p r o a c h th a t g e n e ra te s h u g e flu c ­
tu a tio n s i n d is c a rd s f ro m y e a r to y ear. I f s im u la te d d is c a rd s d e v ia te
fro m a s s e s s m e n t d isc a rd s , th is m a y r e p re s e n t in c o r r e c t a s s u m p ­
ti o n s in e i t h e r m o d e l.
C o m m u n ic a tio n o f r e s u lts w ith th e c lie n ts h a s b e e n a d d re s s e d
A cknow ledgem ents
T h e s tu d y w as c o m m is s io n e d a n d f u n d e d b y th e D u tc h M in is try o f
A g ric u ltu re , N a tu r e C o n s e r v a tio n a n d F o o d Q u a lity (L N V ). T h e
o n ly b rie fly so far. S ta k e h o ld e rs a n d fish eries m a n a g e r s d id n o t
C o m m is s io n o f th e E u ro p e a n C o m m u n itie s D ir e c to ra te G en eral
a p p e a r to r e la te d ire c tly to th e te c h n ic a l c o m p le x itie s o f t h e m o d ­
fo r F ish eries c o n tr ib u te d to th e d e v e lo p m e n t o f t h e s im u la tio n
e llin g p r o c e s s , a lth o u g h th e y w ere c o n c e r n e d w h e th e r t h e h in d c a s t­
m o d e l a n d th e w r itin g o f th e m a n u s c r ip t u n d e r th e c o n tr a c t
in g c o u ld r e p r o d u c e th e o b se rv e d d y n a m ic s in th e a s s e s s m e n t
“ O p e r a tio n a l e v a lu a tio n to o ls fo r fish e rie s m a n a g e m e n t o p tio n s ”
u n d e r ly in g th e T A C ad v ice, a n d w h e th e r th e y c o u ld lo g ic a lly
( “ E F IM A S ”; S S P 8 -C T -2 0 0 3 -5 0 2 5 1 6 ).
e x p la in i n t h e i r o w n w o r d s t h e d e v e lo p m e n ts in s to c k s a n d fish eries
p r e d ic te d b y t h e s im u la tio n s . W e su g g e st th a t th e iss u e o f fo c u s in g
to o m u c h o n a b s o lu te v alu es in th e s im u la tio n o u t p u t m ig h t b e c ir­
c u m v e n te d b y e x p re ss in g th e re su lts re la tiv e to a n a p p r o p ria te ly
c h o s e n re fe re n c e lev el ( f o r in sta n c e , th e fin al y e a r f o r w h ic h i n f o r ­
m a t i o n is a v a ila b le ). T h e re fe re n c e p o in ts u se d in th e m a n a g e m e n t
p ro c e s s w o u l d th e n a lso h a v e t o b e sc a le d o n t h a t b a s is. E v e n u n d e r
s u c h a s c e n a r io , s h a re d u n d e r s ta n d in g o f w h a t t h e m o d e ls c a n a n d
R eferences
B u tterw o rth , D. S. 2007. W h y a m a n a g e m e n t p ro c e d u re approach?
S om e positives a n d negatives. ICES Jo u rn a l o f M a rin e Science,
64: 6 1 3 -6 1 7 .
B u tterw o rth , D. S., a n d P u n t, A. E. 1999. E xperiences in th e evaluatio n
a n d im p lem en tatio n o f m an ag em en t p ro ced u res. ICES Jo u rn a l o f
M a rin e Science, 56: 9 8 5 -9 9 8 .
824
CEC. 2001. P ro p o sal fo r a council reg u latio n establishing m easures for
th e recovery o f c o d a n d h ake stocks. C O M (2001), 724.
CEC. 2006. C o m m u n ic a tio n fro m th e C o m m issio n to th e C o u n c il a n d
th e E u ro p e a n P arlia m e n t. Im p le m e n tin g su stain ab ility in EU fish­
eries th ro u g h m a x im u m sustainable yield. C O M (2 0 0 6 ), 360.
ICES. 2006a. R e p o rt o f th e W o rk in g G ro u p o n th e A ssessm ent o f
D em ersal S tocks in th e N o rth Sea a n d Skagerrak, C o p e n h ag en ,
6 - 1 5 S ep tem b er 2005. ICES D o c u m e n t C M 2006/A C F M : 09.
ICES. 2006b. R e p o rt o f th e W o rk in g G ro u p o n B eam Traw l Surveys,
H a m b u rg , 1 6 - 1 9 M ay 2006. ICES D o c u m e n t C M 2006/L R C : 11.
M . A . Pastoors e t al.
Keli, L. T., S cott, R. D., a n d H u n te r, E. 2004. Im p lica tio n s fo r c u rre n t
m a n a g e m e n t advice fo r N o r th Sea plaice. 1. M ig ratio n betw een the
N o r th Sea a n d E n g lish C hannel. Journal o f Sea Research, 51:
2 8 7 -2 9 9 .
K irkw ood, G. P. 1997. T h e revised m an ag em en t p ro c e d u re o f the
In te rn a tio n a l W haling C o m m issio n . In G lobal T rends: Fisheries
M an ag em en t, pp. 9 1 - 9 9 . Ed. by E. K. P ikitch, D. D H u p p e rt,
a n d M . P. Sissenwine. A m e ric a n Fisheries S ociety S ym p o siu m , 20.
ICES. 2006c. R e p o rt o f th e ICES A dvisory C o m m ittee o n F ishery
M a n ag em en t, A d visory C o m m ittee o n th e M a rin e E n v iro n m en t
a n d A dvisory C o m m itte e on Ecosystem s, 2006. ICES A dvice, 1 - 1 0 .
K raak, S. B. M ., B uism an, F. C ., Dickey-Collas, M ., P oos, J. J., P astoors,
M . A., S m it, J. G. P., D a a n , N . et al. 2004. H o w can w e m anage
m ix ed fisheries? A sim u la tio n stu d y o f th e effect o f m an ag em en t
choices o n th e su s ta in a b ility a n d econom ic p erfo rm an ce o f a
m ix e d fishery. ICES D o c u m e n t C M 2004/F F : 11.
Keli, L. T., a n d B rom ley, P. J. 2004. Im p lica tio n s fo r c u rre n t m a n a g e ­
m e n t advice fo r N o r th Sea plaice (Pleuronectes platessa
L.). 2. In creased b iological realism in re c ru itm e n t, grow th, densityd e p e n d e n t sexual m a tu ra tio n a n d th e im p act o f sexual d im o rp h is m
a n d fishery discards. Jo u rn al o f Sea Research, 51: 3 0 1 -3 1 2 .
M cA llister, M . K., Starr, P. J., R estrepo, V. R., a n d K irkw ood, G. P.
1999. F o rm u latin g q u a n tita tiv e m eth o d s to evaluate fisherym a n a g e m e n t systems: w h a t fishery processes sh o u ld be m o d elled
a n d w h a t trade-offs s h o u ld be m ade? ICES Jo u rn a l o f M a rin e
Science, 56: 9 0 0 -9 1 6 .
Keli, L. T., C o tter, A. J. R., V an Keeken, O ., P astoors, M ., O ’Brien, C . M .,
Piet, G. J., a n d R ackham , B. D. 2003. T he influence o n stock assess­
m e n t advice o f sam pling e rro r in research survey an d in tern atio n al
m a rk e t sam p lin g d a ta for N o rth Sea cod (Gadus m orhua L.) an d
plaice (Pleuronectes platessa L.). ICES D o cu m en t C M 2003/X : 5.
NSRAC. 2005. Im m e d ia te M an ag em en t M easures for N o rth Sea
plaice. A dvice to th e E u ro p e a n C om m ission. h ttp ://w w w .n sra c .
o rg /a d v ic e s/w f2 0 0 5 0 7 12_A dvice_on_plaice_m anagem en t.p d f.
Keli, L. T., M o sq u eira, I., G rosjean, P., F ro m e n tin , J-M ., G arcia, D.,
H illary, R., Ja rd im , E. et al. 2007. FLR: an o p en -so u rce fram ew ork
f o r th e ev alu atio n a n d d ev elo p m en t o f m an ag em en t strategies.
ICES Jo u rn a l o f M a rin e Science, 64: 6 4 0 -6 4 6 .
Keli, L. T., O ’B rien, C. M ., S m ith, M . T., Stokes, T. K., a n d R ackham , B. D.
1999. A n ev alu ation o f m an ag em en t procedures fo r im plem enting
a p re c au tio n ary a p p ro a c h in th e ICES context fo r N o rth Sea plaice
(Pleuronectes platessa L.). ICES Journal o f M arin e Science, 56:
8 3 4 -8 4 5 .
Keli, L. T., P asto o rs, M . A., S cott, R. D., S m ith, M . T., V an Beek, F. A.,
O ’B rien, C. M ., a n d Pilling, G . M . 2005. E valuation o f m u ltip le
m an a g e m e n t objectives fo r N o rth e a st A tlantic flatfish stocks: su s­
tain ab ility vs. sta b ility o f yield. ICES Jo u rn al o f M arin e Science,
62: 1 1 0 4 -1 1 1 7 .
Keli, L. T., P illing, G. M ., K irkw ood, G. P., P astoors, M . A., M esnil, B.,
K orsbrekke, K., A b au n za , P. e t al. 2006b. A n ev alu atio n o f m u lti­
a n n u a l m a n a g e m e n t strategies fo r ICES ro u n d fish stocks. ICES
Jo u rn a l o f M a rin e Science, 63: 1 2 -2 4 .
Keli, L. T., P illing, G. M ., a n d K uikka, S. 2006a. R elative im p o rta n c e o f
value o f in fo rm a tio n a n d value o f c o n tro l fo r m ix ed fisheries.
P o ster p re se n te d a t th e ICES S y m p o siu m on Fisheries
M a n a g e m e n t S trategies, 2 7 - 3 0 Ju n e 2006, Galway, Ireland.
P asto o rs, M . A., R ijnsdorp, A . D., a n d Van Beek, F. A. 2000. Effects o f a
partially closed area in t h e N o rth Sea (“plaice b o x ”) o n stock devel­
o p m e n t o f plaice. ICES J o u rn a l o f M arine Science, 57: 1 0 1 4 -1 0 2 2 .
P oos, J. J., M achiels, M . A. M ., a n d P astoors, M . A. 2006. Investigation
o f so m e M an ag em en t S cen ario s for N o rth Sea Sole a n d Plaice in
2006 a n d bey o n d . W ageningen-IM A R ES: CV O R eport, 06.004.
IJm u id en , th e N eth erlan d s.
P u n t, A. E., S m ith , A. D. M ., a n d C ui, G. 2002. E valuation o f m an ag e­
m e n t to o ls fo r A ustralia’s S outh East Fishery 1. M odellin g the
so u th e a st fishery tak in g a c c o u n t o f technical in te ra c tio n s. M arin e
a n d F reshw ater R esearch, 53: 6 1 5 -6 2 9 .
R ijn sd o rp , A. D., D aan, N ., a n d D ekker, W . 2006. P artial fishing m o r­
ta lity p e r fishing trip: a u se fu l in d icato r o f effective fishing effort in
m ix e d d em ersal fisheries. ICES Journal o f M a rin e Science, 63:
5 5 6 -5 6 6 .
R ijn sd o rp , A. D ., an d P asto o rs, M . A. 1995. M o d e llin g th e spatial
d y n am ics a n d fisheries o f N o rth Sea plaice (Pleuronectes platessa
L.) based o n tagging d a ta . ICES Journal o f M a rin e Science, 52:
9 6 3 -9 8 0 .
V an K eeken, O . A., Q uirijns, F. J., a n d P astoors, M . A. 2004. A nalysis o f
D isc ard in g in th e D u tch B eam Traw l Fleet. R IV O R ep o rt, C 0 3 4 /0 4 .
IJm u id e n , th e N etherlands.
doi: 10.10 9 3 /ic e s jm s /fs m 0 5 1
818
Validating m an a g em en t sim ulation m od els a n d im plications
for co m m u n ica tin g results to stakeholders
M a r ti n A. P a s to o rs , J a n J a a p Poos, S a ra h B. M. Kraak, a n d M a r c e l A. M . M a c h ie ls
Pastoors, M. A., P oos, J. J., Kraak, S. B. M., an d M achiels, M . A. M. 2007. V alidating m a n a g e m e n t sim u la tio n m odels a n d im plicatio n s for
c o m m u n ic a tin g resu lts to stakeholders. - ICES Journal o f M arin e Science, 64: 8 1 8 - 8 2 4 .
S im u la tio n s o f m a n a g e m e n t p la n s g en erally a im to d e m o n s tr a t e t h e r o b u s tn e s s o f t h e p la n s to a s s u m p tio n s a b o u t p o p u la tio n
d y n a m ic s a n d fle e t d y n a m ic s. S u c h m o d e llin g is c h a r a c te r iz e d b y sp e c ific a tio n o f a n o p e r a tin g m o d e l (O M ) r e p re s e n tin g th e u n d e r ­
lying t r u th a n d a m a n a g e m e n t p r o c e d u r e t h a t m im ic s t h e p ro c e s s o f a c q u irin g k n o w le d g e , f o r m u la tin g m a n a g e m e n t d ecisio n s, an d
im p le m e n tin g th o s e d ecisio n s. W e e m p lo y s u c h a m o d e l t o e v a lu a te a m a n a g e m e n t p la n fo r N o r th Sea flatfish p r o p o s e d by t h e N o rth
S ea R egional A d v iso ry C o u n c il in M ay 2005. F ocus is o n t h e c o n s tr u c tio n a n d c o n d itio n in g o f O M s, key r e q u ire m e n ts fo r s u c h sim u ­
la tio n s. W e d e s c rib e t h e p r o c e s s o f s e ttin g u p a n d v a lid a tin g O M s a lo n g w ith its e ffe c ts o n t h e ab ility t o c o m m u n ic a te th e re su lts to
t h e sta k e h o ld e rs . W e c o n c lu d e t h a t th e r e is te n s io n b e tw e e n th e level o f d e ta il r e q u ire d b y s ta k e h o ld e rs a n d th e level o f d e ta il t h a t can
b e p ro v id ed . In c o m m u n ic a tin g t h e re su lts o f s im u la tio n s , it is n e c e s sa ry to m a k e v ery c le a r h o w O M s d e p e n d o n p a s t p e r c e p tio n s of
s to c k d y n a m ic s.
Keywords: co m m u n ic a tio n , flatfish, m a n a g e m e n t strategy evaluation, N o rth Sea, o p e ra tin g m odel, sim u latio n , stakeholders.
Received 30 June 2006; accepted 3 M arch 2007; advance access publication 21 M ay 2007.
M. A. Pastoors, J. J. Poos, S. B. M . Kraak a n d M. A. M. Machiels: Wageningen-IMARES, PO Box 68, 1970 A B IJmuiden, The Netherlands.
Correspondence to M . A. Pastoors: tel: + 3 7 2555 64646; fax: + 3 1 2555 64640; e-mail: m artin.pastoors@ w ur.nl
In tro d u c tio n
se lectiv ity c h a ra c te ris tic s o f th e g e a rs used to c a tc h th e m can
F ish eries m a n a g e m e n t p la n s a llo w fo r th e d e v e lo p m e n t o f lo n g e r-
have s u b s ta n tia l sid e effects o n th e effectiveness o f th e m e a s u re s
te r m strateg ies a n d a re in c re a s in g ly b e in g u se d in th e N o r th e a s t
ta k e n in a c h ie v in g th e in te n d e d m a n a g e m e n t o bjectiv es. F o r
A tla n tic (C E C , 2 0 0 1 , 2 0 0 6 ). W h e n fish eries m a n a g e rs o r sta k e ­
e x a m p le , if th e q u o ta s set fo r th e tw o species a re n o t e x h a u s te d
h o ld e r o rg a n iz a tio n s (e.g. R e g io n a l A d v iso ry C o u n c ils ) d iscu ss
in sy n c h ro n y , o v e r -q u o ta c a tc h e s m a y be ta k e n ( a n d d isc a rd e d
s u c h p la n s, th e y o f te n re q u ire a n e v a lu a tio n o f th e p o ss ib le c o n se ­
o r la n d e d illegally) o f th e sp ecies w ith th e m o s t re stric tiv e q u o ta ,
q u e n c e s b e fo re t h e p la n s a re im p le m e n te d .
w h ic h g e n e ra lly is d e p le te d first. M o re o v e r, th e re lativ e catch
A m a n a g e m e n t p la n can b e e v a lu a te d u sin g a s im u la tio n m o d e l
o f th e fish ery sy s te m . T h e o p e r a tin g m o d e l (O M ) d e s c rib e s th e key
o p p o r tu n itie s fo r th e
tw o sp e cies m a y d iffer b e tw e e n years.
B ecause th e m ix e d b e a m traw l fish e ry fo r flatfish p r e s e n ts a rela­
p ro cesses, b a s e d o n sim p lify in g a s s u m p tio n s a b o u t t h e i n t e r ­
tively tra c ta b le e x a m p le , its p r o b le m s h av e b e e n w ell s tu d ie d in
a c tio n s a m o n g th e d iffe re n t c o m p o n e n ts . E x am p le s o f su c h
th e p a st (R ijn s d o r p a n d P a sto o rs, 1995; Keli e t a l , 1999, 2003,
m o d e ls (K irk w o o d , 1997; M c A llis te r e t a l , 1999) m a y u s e s im p li­
2004; P a s to o rs et a l., 2000; Keli a n d B rom ley, 2004; K ra a k e t a l ,
fied d y n a m ic s o f f ish sto c k s a n d fleets, w h ile a tte m p tin g to in c o r ­
2 0 0 4 ).
p o r a te su ffic ie n t a s p e c ts o f th e c o m p le x d y n a m ic s o f re a l system s
T h e tw o ta rg e t sp ecies are m a n a g e d b y n a tio n a l sh a re s in th e
(B u tte rw o rth a n d P u n t, 1999; P u n t et al., 2 0 0 2 ). A m a n a g e m e n t
to ta l a llo w ab le c a tc h (T A C ), d a y s -a t-se a re s tric tio n s o n th e fleet,
p ro c e d u re (M P ; B u tte r w o r th , 2 0 0 7 ) c o n sists o f d a ta c o lle c tio n ,
a n d te c h n ic a l m e a s u re s . T h e sp a w n in g -s to c k b io m a s s (SSB) o f
s to c k
and
p la ic e d e c lin e d a fte r t h e early 1990s a n d h a s b e e n ju s t a b o v e th e
im p le m e n ta tio n . F le e t b e h a v io u r h a s g en erally b e e n c a p tu r e d in
lim it b io m a s s re fe re n c e p o in t ( B hm) sin c e th e m id -1 9 9 0 s (IC ES,
sta tu s
e v a lu a tio n ,
h arv est
c o n tro l
ru le s
(H C R s ),
sim p listic a s s u m p tio n s (K ra a k e t a l , 2 0 0 4 ), a n d th e b io lo g ic a l
2006a). T h e so le s to c k h a s flu c tu a te d m a rk e d ly in re sp o n s e to
d e ta il is o fte n re la tiv e ly p le n tifu l (K eli a n d B rom ley, 2 0 0 4 ). T h e
th e a p p e a ra n c e o f s tr o n g year classes. T h e tw o m o s t re c e n t y ear
u n c e rta in ty a b o u t th e real s y s te m a n d its d y n a m ic s p lay s a key
classes are t h o u g h t to be p o o r, w h ic h c o u ld easily r e d u c e sole
ro le in e v a lu a tin g m a n a g e m e n t stra te g ie s. T h is u n c e r ta in ty reflects
SSB b e lo w its B )im in th e n e a r f u tu r e (IC E S , 2 0 0 6 c).
a la c k o f k n o w le d g e o f p ro c e ss e s s u c h as th e s t o c k - r e c r u itm e n t
In 20 0 4 , t h e C o m m is s io n o f th e E u ro p e a n C o m m u n itie s ask ed
re latio n sh ip , d e n s ity -d e p e n d e n c e , n a tu r a l v ariab ility , a n d resp o n ses
th e N o r th Sea R e g io n a l A d v iso ry C o u n c il (N S R A C ) f o r ad v ice “ on
o f th e fleet to th e m e a s u re s im p o s e d .
th e im p le m e n ta tio n o f a reco v ery p la n fo r N o r th S ea plaice a n d a
N o r th Sea p la ic e (P leuronectes p la tessa ) a n d so le (Solea solea)
lo n g - te rm m a n a g e m e n t p la n fo r so le ”. N S R A C (2 0 0 5 ) iss u e d its
a re ta k e n m a in ly in a m ix e d b e a m traw l fish e ry w ith a b y c a tc h
ad v ice in Ju ly 2 0 0 5 , fo cu sin g o n ly o n th e re c o v e ry o f t h e p laice
o f o th e r d e m e rs a l species. M a n a g e m e n t o f th e s e tw o sp ecies
sto c k
faces m a n y c h a lle n g e s b e c a u s e t h e ir sp a tia l d is tr ib u tio n s a n d th e
su g g e sted b y IC E S (2 0 0 6 c). T he a d v ic e d id n o t d e a l w ith lo n g - te rm
to
above
230 0 0 0 1, t h e
p r e c a u tio n a r y
© 2007 I n te r n a tio n a l C o u n c il f o r th e E x p lo ra tio n o f th e Sea. P u b lis h e d b y O x fo rd J o u rn a ls . Ali rig h ts reserved.
F o r P e rm is sio n s , p le a se em a il: jo u rn a ls .p e rm is s io n s @ o x fo rd jo u rn a ls .o rg
b io m a s s
(B pa)
Validating m anagem ent sim ulation models
m an ag em en t o f sole. Because the N eth erlan d s is a m ajo r p layer in
th ese flatfish fisheries, th e D utch M in istry o f A griculture, N atu re
C on serv atio n an d F ood Q uality (LNV) req u ested an evaluation
o f the likely effects o f th e N S R A C -proposed recovery p lan o n the
sole stock. T he details o f these evaluations (P oos et al., 2006) are
n o t th e focus o f this m an u scrip t; in stea d , w e focus o n the
process. T he m a in questions we p ose are: (i) how h as th e technical
ev alu atio n o f th e recovery plan b een in itia te d an d carried th ro u g h ;
(ii) ho w h as th e u n certain ty in v arious processes been en cap su ­
lated in th e O M ; an d (iii) how have th e results been c o m m u n i­
cated an d used?
Proposed NSRAC m anagem ent plan
T h e stated objective o f th e m an ag em en t p la n has b een form u lated
fo r plaice o n ly (NSRAC, 2005):
“a m u lti-a n n u a l m an ag em en t p la n sh o u ld be a d o p te d fo r
plaice in th e N o rth Sea w ith a n in itial targ et o f reaching
an SSB a t th e B pa level w ithin 3 - 5 years w ith a re-evaluation
after 3 years a n d w ith th e long term a im o f exceeding Bpa.
T he p lan sh o u ld be im p lem en ted as o f the 1st o f January
2006. T he m an ag em en t plan is aim ed a t reducing pressure
o n juvenile plaice an d w ould co m p rise stru c tu ra l effort
red u ctio n s accom panied by stability in th e TAC fo r plaice.
T h e m u lti-a n n u a l p lan sh o u ld be acco m p an ied by a m o n i­
to rin g a n d evaluation schem e, w hich w o u ld also include
th e m o n ito rin g o f social an d eco n o m ic im p act”.
T h e basic m an ag em en t m easure p ro p o se d was “ a stru ctu ral effort
re d u c tio n o f 15% o f enforced licensed capacity lim its in th e in te r ­
n atio n al 80 m m flatfish fishery over 2006 a n d effort to b e m a in ­
ta in e d at th e new level for a fu rth e r tw o years”. T h ere were
d etailed co m m en ts in the p lan o n ex em p tio n s for som e fleets,
o n th e w ay effort red u ctio n s could b e em b ed d ed in n atio n al
fishing p lan s, a n d o n th e different fo rm s o f effort red u ctio n p o ss­
ible (days-at-sea regulations o r decom m issioning).
D espite these technical details, ev alu atio n w ith th e available
scientific tools w as difficult. F or exam ple, th e plan stated: “In
th e event o f th e plaice sto c k falling b elo w Bnm new m easures
w o u ld be ap p lied”. H ow ever, th e n a tu re o f these m easures was
n o t described. F u rth erm o re, th e state o f th e sole stock w as n o t c o n ­
sidered, a n d th e clients w an ted to k now a b o u t th e effects o f th e
p la n o n sole.
Such o p en ends ap p ear to be a generic p ro p e rty o f th e o u tco m e
o f p o litical negotiation: specific c o n d itio n s are raised, b u t how
th ey sho u ld b e resolved is left o p e n u n til p ro b lem s arise.
H ow ever, fo r technical evaluation, o p e n en d s p resen t difficulty
in in terp retin g a m an ag em en t plan: a sim u latio n ap p ro ach
req u ires th a t all actions be specified u n d e r all conditions.
W h en m an ag em en t plans are d eveloped i n c o n ju n ctio n w ith an
ev alu atio n ap p roach, th e p ro b lem s can be resolved th ro u g h a
system o f feedback lo o p s betw een analysts a n d stakeholders.
H ow ever, w hen a n evaluation o f a specific p la n is req u ested , th e
o p en ends have to be in terp reted b y th e analysts b y fo rm u latin g
a range o f p o te n tia l scenarios.
T his h ap p en ed in th is case: w e in te rp re te d the clause a b o u t “ the
new m easures” in such a way th a t, if th e perceived SSB w ould fall
below B]im, a fu rth e r decrease o f n o m in a l fishing effort by 15%
an n u ally w o uld be im p lem en ted u n til th e perceived SSB had
retu rn e d to above B iim. F u rth er, o u r in te rp re ta tio n was th at th e
ru le (alth o u g h th is had n o t been specified explicitly) w o u ld also
819
apply to sole. A n a lte rn a tiv e scenario evaluated w as w ith o u t
ad d itio n al m easures b ein g ta k e n w h en SSB w o u ld fall below B Um.
The evaluation process
The parties involved in th e evaluation process w ere the D u tch
M inistry (LNV), th e stakeholder flatfish W orking G roup
(NSRAC), a n d th e research organization (W ageningen-IM ARES).
T he approach was to develop a FLR (w w w .flr-project.org; Keli
et al., 2007) sim ulation m o d e l th at w ould allow in co rp o ratio n o f
different hypotheses o n p o p u la tio n dynam ics an d th e jo in t exploita­
tio n o f th e tw o stocks. T he th re e parties initially interacted to define
th e research questions a n d t h e type o f results expected, a n d again at
th e end o f th e process to discuss th e results in th e rep o rt. Between
start an d finish, interaction betw een researchers an d stakeholders
was negligible.
S e t tin g u p t h e m o d e l
T he initial q u estio n in m o d e l developm ent referred to th e defi­
n itio n o f the d im en sio n s to be in clu d ed . T h e d im en sio n s reflect
th e type o f processes in c lu d e d , th e available in fo rm a tio n , and
the d o m in a n t issues in th e m an ag em en t plan. In th is case, the
partial spatial overlap betw een th e tw o species suggested a
tw o-area m o d el (sole d o m in a tin g as th e targ et s o u th o f 56°N,
plaice d o m in atin g n o rth o f 56°N ), an d a d istin ctio n betw een
tw o m ain types o f fleets (o n e each targ etin g sole an d plaice).
T he sim u latio n m odel consisted o f tw o subm odels: an O M
describing th e biological an d fleet (in clu d in g econom ics)
dynam ics o f th e und erly in g system ; an d a n M P consistin g o f
d a ta collection, stock assessm ent, a n d a H C R (fo r a graphical
p resen tatio n o f a sim ilar ty p e o f sim u latio n ap p ro ach , see Keli
et a l , 2005).
T he biological processes in th e O M in clu d ed a s to c k recru itm en t relatio n sh ip , fixed values for n a tu ra l m ortality ,
m aturity-at-age, an d w eight- an d length-at-age, an d fixed values
for th e relative p ro p o rtio n o f each age g ro u p in each o f th e two
areas. T h e fleet-dynam ics m o d e l consisted o f tw o b eam trawl
fleets: th e D u tc h fleet targeting p rim a rily sole (80 m m m esh in
the co d en d ) s o u th o f 55°N , a n d a UK fleet targ etin g prim arily
plaice (100 m m m esh) n o r th o f 55°N . T rends in fishing effort
were derived fro m in fo rm a tio n in th e D u tc h lo g b o o k database
(co n tain in g records o f D u tc h vessels as well as U K vessels
landing th e ir catches in th e N etherlands). F u tu re effort allocations
w ere assum ed to retain the sam e p ro p o rtio n s b y area an d fleet.
C onceptually, th e catching process was m odelled as a c o m b in atio n
o f catchability, selectivity, effort, a n d technological creep
(R ijnsdorp et a l , 2006). C atches w ere generated fro m th e u n d e r­
lying ( “tru e ”) p o p u la tio n an d split in to landings a n d discards
according to a re te n tio n ogive derived fro m observer trips
(Van Keeken et a l , 2004).
T he M P consisted o f th ree m a in processes: sam p lin g raw data
from th e underlying p o p u latio n ; stock assessm ent, a n d sh o rt-te rm
forecasting follow ing sta n d ard procedures; an d a H C R defining
th e a p p ro p riate m an ag em en t m easure given th e forecast.
S am pling fro m th e tr u e p o p u latio n was m im icked by generating
estim ates o f landings-at-age (sole) an d catch-at-age (plaice;
in clu d in g discards), sim ilar to th e an n u a l assessm ents fo r the
tw o stocks. T he catches w ere generated using th e selectivity charac­
teristics o f th e tw o fleets and a sim ple lo g n o rm al e rro r w ith a
relatively sm all coefficient o f v ariatio n (CV = 0.1).
T he sim u latio n contained a “tr u e ” survey th a t sam pled from
th e p o p u latio n s o f th e tw o species u sin g catchability a n d selectivity
820
p a tte rn s estim ated from historical data in c o n ju n ctio n w ith their
spatial d istrib u tio n . “O bserved” survey catch-at-ag e by species
w as g enerated by applying a lo g n o rm al e rro r (again C V = 0.1),
a n d these series were u sed for tu n in g in th e stock assessm ent
process. T he sto c k assessm ent process encom passed single-species
ex ten d ed survivors analysis (XSA) for plaice a n d sole, based o n
catch- a n d landings-at-age data, respectively. XSA settings a n d
sh o rt-te rm forecasts co rresp o n d ed to th o se used b y ICES (2006a).
T he H C R im p lem en ted in th e m o d el attem p ted to m im ic the
NSRAC m an ag em en t plan. N o m in al fishing effort was reduced
by 15% in 2006 com pared w ith 2005, a n d th is level was m ain tain ed
in su b seq u en t years. In th e objective stated in th e p lan , th ere is an
in h e re n t ten sio n betw een reducing effort a n d m a in ta in in g stability
o f th e TAC. T h is posed ad d itio n al challenges to im p le m e n ta tio n o f
th e m odel. LNV requested an ad d itio n al m a x im u m a n n u a l change
in TAC o f 15% to be in clu d ed in th e sim ulations, rep re sen tin g an
ex ten sio n o f th e stated objectives. H ow ever, th e m easures stated
d id n o t refer to TACs, b u t only to deco m m issio n in g and
days-at-sea lim its. T herefore, TACs w o u ld n o t co n stra in th e
fishery in th e m odel anyway: th e fleets sim ply exhausted th e
effo rt q u o ta an d rep o rted w hatever catches they generated. W e
d id n o t im p le m e n t a tw o -tie r system in w hich e ith e r th e TAC o r
th e effo rt q u o ta could co n strain th e fishery, because th e p ro p o se d
H C R d id n o t specify h o w th e p rio rity betw een such different
m easu res w o u ld have b een set.
T he an n u a l decision process o n effort q u o ta was based o n th e
sh o rt-te rm forecast o f th e SSB rem aining after th e y ear to w hich
these w o uld apply. T his forecast was co m p ared w ith th e B)im trig ­
gers defined in th e plan. Im p le m e n ta tio n e rro r w ith respect to
m isrep o rtin g o r black landings w as n o t included.
Parameter estimates
T h e average d istrib u tio n o f th e species by age over th e tw o areas
w as estim ated fro m th e an n u a l b eam traw l survey, w hich takes a
sy n o p tic sam ple o f th e plaice an d sole p o p u la tio n s in late
su m m er (ICES, 2006b). I n general, sole a re m ainly in the so u th e rn
area, a n d plaice m igrate fro m so u th to n o rth w ith increasing age.
In fo rm a tio n o n stock tre n d s was available fo r th e p e rio d 1 9 5 7 2004 fro m ICES (2006a). R ecruitm ent estim ates for th e last four
years w ere excluded because th ey w ere considered unreliable.
T h e rem ain in g set w as u sed to estim ate sto c k -re c ru itm e n t
relatio n sh ip s o f th e Ricker a n d th e B e v e rto n -H o lt type. I n the
forw ard sim u latio n , re c ru itm e n t estim ates were ta k e n from th e
sto c k -re c ru itm e n t relationship, taking in to a c c o u n t th e variance
estim ate derived from th e h istorical relationship.
E stim ating th e param eters o f th e fleet-dynam ics m o d el was less
straig h tfo rw ard. T h e in terp la y o f sim u lated stock ab u n d a n c e and
stock d istrib u tio n s by age a n d area, to g eth er w ith th e d istrib u tio n s
o f th e fleets, d eterm in es th e catch profiles generated b y th e fleets.
T h e em p irical observations o n th e catch profiles o f th e real fleets
w ere n o t sufficient to d ete rm in e th e p a ra m e te r values fo r th e s im u ­
latio n m o d el uniquely. T herefore, an y m ism atch betw een th e
sim u lated an d th e real catch profiles co u ld have b een cau sed by
in co rrec t assu m p tio n s in th e fleet-dynam ics o r stock-dynam ics
m odels.
T he critical q u estio n in in te rp re tin g sim u latio n results is: how
close d o these have to be to reality as cu rren tly perceived? In o th e r
w ords, is it a p ro b lem if sim ulated catch profiles o r stock tren d s
differ fro m th e historical observations? T h e answ er d ep en d s on
th e ty p e o f ev aluation process in w hich the sim u latio n m odel
is used. T h e m an a g e m e n t p lan has b een p h rased in a stock
M . A. Pastoors et al.
assessm ent type o f d isc o u rs e by referring to SSB an d biological
reference p oints. T h erefo re, th e n u m erical values o f th e variables
derived from th e s im u la tio n s w ould b e viewed critically against
th e values p ro d u ced b y r o u tin e sto c k assessm ent (in th is case as
presented by ICES, 2006a).
T he co m b in atio n o f o v e r-p a ra m e te riz a tio n o f th e O M (using
m o re p aram eters th an t h e r e is in fo rm a tio n to estim ate them
from ) and th e re q u ire m e n t to g enerate realistic stock a n d fleet
dynam ics, im plied th a t fixes h ad to be so u g h t to generate largely
com parable results. W e u s e d th e tech n iq u e o f h indcasting to s im u ­
late th e historical tra je c to rie s o f stocks a n d fleets over th e p erio d
1 995-2004. T he sta rt p o p u la tio n s in 1995 an d levels o f recru it­
m e n t were tak en directly fro m ICES (2006a), a n d th e tren d s in
fishing effort were d eriv e d from th e log b o o k database. Given
these fixed in p u ts, s im u la tio n s were r u n u n d e r different assu m p ­
tio n s o n th e relative d istrib u tio n o f fish over th e tw o areas, the
catchabilities o f th e tw o fleets for th e tw o species, an d the increase
in technical efficiency o f t h e tw o fleets (R ijnsdorp e t a l , 2006).
Som e results o f th e ex p lo rato ry analyses are show n in Figure 1;
we com pare th e perceived values (ICES, 2006a) o f landing s, dis­
cards, recru itm en t, average fishing m o rta lity (Fbar), selection
pattern , a n d SSB, th e a ssu m e d relative d istrib u tio n o f fish over
areas, an d th e relatio n sh ip betw een F bar an d effort w ith th eir
sim ulated (“tru e ” ) values, a s derived fro m th e O M . O bviously, if
we w ish to fix th e sim u la te d historical dynam ics to m atch the
observations, we are faced w ith th e choice betw een m an y different
options: m ean selection p a tte rn , e f fo r t- m o r ta lity relationship,
landings, etc., m ay all b e fixed, b u t fixing all sim ultaneo u sly is
im possible unless w eights can b e assigned to each specific
param eter.
F igure 2 (left panels) sh o w s th e co m p ariso n betw een th e (p e r­
ceived as) “tr u e ” an d sim u la te d v alues fro m th e basic r u n fo r four
im p o rta n t p o p u la tio n dy n am ics param eters. In th e base rim , all
param eters were based o n in fo rm a tio n fro m som e type o f analysis
except for overall catch ab ility o f th e fleets, w hich was o b ta in e d by
m inim izing th e difference in catch-at-age betw een th e m o d e l and
as actually observed in sa m p les fro m th e fleet. Clearly, th e sim u ­
lated landings an d SSB o f plaice an d sole are substantially
sm aller th a n th o se according t o th e assessm ent. A lth o u g h th e tem ­
poral dynam ics m ay ap p ear reaso n ab ly sim ilar, a discrepan cy in
th e overall level m ay have su b stan tial effects o n prospective sim u ­
lations if th e sam e absolute values are u sed fo r lim it reference
points. F or instance, th e sim u lated stocks will be below BVim
m o st o f th e tim e.
F o r plaice, an ad d itio n al p ro b lem arose w ith th e split o f catches
betw een landings a n d discards: sim u lated landings were below and
sim ulated discards above th e assessm ent estim ates. M ost plaice
aged 1 and 2 years are in th e so u th e rn area w here th e beam
traw l fishery m ainly operates, resulting in h ig h sim ulated discards.
In practice, these sm aller fish m ay n o t be available to th e fishery
because they live in shallow coastal regions w here larg er vessels
are n o t p erm itted . How ever, in a sim u la tio n e n v iro n m en t based
o n tw o areas only, such subtle differences c an n o t b e acco u n ted for.
T he results presen ted in Figure 2 (rig h t panels) in co rp o rate
a n attem p t to rem ed y this sh o rtc o m in g b y m anually m odifying
th e relative spatial d istrib u tio n o f plaice aged 1 an d 2. Because
these age g ro u p s are now located m o re in th e n o rth e rn area, the
overall discards decrease, so th e sim u lated landings a p p ro ach th e
observed landings. Also, the SSB estim ates are closer. However,
th e sim ulations share a m a jo r discrepancy betw een sim ulatio n s
a n d assessm ent (Figure If): th e lin ear a n d positive relatio n sh ip
Validating m a n agem ent sim ulation models
821
o
o "
o
------ w o
\
\
8 .
/
\
■
o 1996
1998
2000
2002
2004
/
V/
\v
\
...... '-°
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...... WG
....................
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o 1996
1998
2000
2002
2004
1996
1998
2000
2002
2004
1996
Average moctality-at-age
1998
2000
2004
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2002
0. 4
1
" • - • x
^ _
1
/'
\
o
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l i l i
1996
2002
d
j
/
/
2000
Avefage mortality-al-ags
/
d “
\
1998
2004
1996
1998
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2002
/
............ ................ ..............
"■
2004
R ecn ilm en t
8
8
“
o
---------A A A - A
o
2000
2002
2004
1996
2000
2002
2004
E ffort-Fbar
0.8
i
0.8
2000
2002
2004
1996
1998
2000
2002
2004
§ -
i
N
q _
T
0.4
0
1
1998
Proportion-at-ags-in south
d
i
i
s
0.4
0.8
o
1
0.4
1
\
o -
1996
i
Proportion-al-agein soulh
1998
1_ _ _ L
1998
.....................................
__
1996
o _
/ v
—
4
6
8
10
0'0
O’O
1
00
2
30000
35000
40000
45000
p
2
4
6
8
10
_
30000
35000
40000
45000
Figure 1. Com parison o f hindcast population dynamics param eters for plaice (left) an d sole (right) from simulations (black lines, OM ) using
species distribution by area from surveys an d n o t taking into account technological creep with th e corresponding estim ates (red lines,
Working C roup) available from ICES (2006a): landings, discards, mean F (Fbar), m ortal ity-at-age, recruitm ent, SSB, proportion o f population
by age group in th e so u th ern area (input), an d the relationship betw een effort an d F.
betw een fishing effort a n d fishing m o rta lity in th e sim ulation
m odel is a d irect con seq u en ce o f an a ssu m p tio n in th e underlying
m o d el, w hereas th e available assessm ent d a ta indicate no signifi­
can t relatio n sh ip a t all.
Figure 3 co m p ares th e results for sole after in tro d u c in g an
increase in tech nical efficiency for th e tw o species, as estim ated
by R ijn sd o rp et al. (2006). A lth o u g h th e slopes o f th e effort m o rta lity relatio n sh ip have becom e m o re com parable, th e
absolute estim ates o f fishing m o rta lity in th e sim ulation are still
su b stantially h ig h er th a n th o se fro m th e assessm ent.
C o m m u n ic a t in g r e s u lts
Because o u r focus d u rin g th e sim ulations w as o n th e assum ptions
b eh in d th e sim u la tio n m o d e l a n d th e w ay th e O M was p aram eter­
ized or, m o re generally, o n th e un certain ties involved, the full
range o f results w as p re se n te d to th e p arties th at com m issioned
th e study. H ow ever, th o se clients d id n o t relate to th e technical
com plexities o f th e m o d ellin g process. T h eir m a in fram e o f evalu­
atio n was w h eth er th e h in d castin g process m ad e sense (are th e
results sim ilar to w h at h a s b een observed?) an d w h eth er they
could u n d e rsta n d th e logic o f fu tu re developm ents (can the
results b e explained?). M a n y stakeholders read th e o u tp u ts
closely: i f we sim u lated landings o f plaice o f 70 000 t w hile the
TAC was ju st 60 0 0 0 1, th ey w o u ld q u estio n th e validity o f th e
results. T h is in d ic a te d a large degree o f tru s t in th e po ten tial
p recisio n o f th e sim u latio n m o d els used, b u t a t th e sam e tim e a
h ig h degree o f scepticism reg ard in g th e ir outcom es: th e results
w ere easily considered to b e falsified w hen co m p ared w ith possibly
equally u n c e rta in assessm ent data.
Discussion
T h e ev alu atio n o f th e N SRA C m an ag em en t p la n req u ired th e use
o f a m ultifleet, m u ltisto ck sim u latio n m odel, w hich is a level o f
com plexity h ig h er th a n m o st m o d els used so far t o evaluate fishe­
ries m an a g e m e n t system s (Keli et al., 2005, 2006b). T h e difficul­
ties e n co u n tered in trying to m atch the results o f this exercise w ith
th e type o f in fo rm atio n underlying th e m anagem ent advice have
n o t b een presented to highlight th e m odelling details, b u t to illus­
trate the general p roblem s o f such an evaluation process, o f encap­
sulating u ncertainty, an d o f com m unicating com plex results.
T h e ev alu atio n was carried th ro u g h in a n a lm o st linear ch ain o f
actions. First, th e p ro b lem was defined jo in tly by th e clients an d
scientists. D u rin g th e next p hase, th e scientists in te rp re te d the
p lan , developed th e m odel, ra n th e scenarios, a n d evaluated th e
results, alm o st in isolation. Finally, the results an d conclusions
w ere p resen ted to th e clients. T h e lack o f in te ra c tio n w ith th e
clients d u rin g th e actual research phase m ay be explained p artly
b y th e tim in g o f th e request, because th e w o rk h ad to b e d one
i n D ecem b er a n d Jan u ary when th e clients were heavily involved
in th e an n u a l decision-m aking process for th e follow ing y ear’s
822
M . A . Pastoors et al.
Proportion-at-agein south
Proportion-at-agein south
d
co
co
d
d
o
o
d
o
d
2
4
6
8
2
4
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6
Landings
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o
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o
o
o
o
o
co
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o
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o
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■'?
■'T
1996
1998
2000
2002
2004
1996
1998
Discards
o
o
o
o
2000
2002
2004
2002
2004
Discards
o
o
o
o
/ \
o
o
o
o
o
o
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o
o
o
'i
■'*
1996
1998
2000
2002
2004
1996
1998
SSB
2000
SSB
-
°\
0
...
O o
o
o-.
o
cv
o
1996
1998
2000
2002
2004
.......7 ^
O
x
?
-—
-
1996
1998
2000
2002
2004
Figure 2. C om parison o f hindcast landings, discards, an d SSB o f plaice for tw o patterns o f th e proportion-at-age present in th e southern area
(to p panels): left panels, proportion estim ated from survey d a ta (as in Figure 1); right panels, proportion of younger ages manually modified to
m inimize th e discrepancy in th e landings.
TAC. N evertheless, such a lack o f in teractio n m ad e th e process less
tra n sp a re n t (w ho takes responsibility for th e choices m ade?), an d
n o ad ju stm en ts co u ld be m a d e to th e m utual expectations o f th e
ty p e o f resu lts generated fro m th e sim u latio n m odel.
A generic p ro p e rty o f m an ag em en t plans is th a t th ey are th e
p ro d u c t o f p o litical n eg o tiatio n . S uch processes o ften lead to an
en d p r o d u c t th a t describes th e overall in ten tio n clearly a n d c o n ­
tain s so m e aspects described in m eticulous detail. H ow ever,
o th e r aspects are o n ly d ealt w ith cursorily, so req u irin g fu rth er
in te rp re ta tio n . A lso, specific issues m ay n o t be tractab le in a s im u ­
latio n ap p ro ach . A n exam ple is th e ap p aren t w illingness o f th e
NSRAC to co n sid er an exception clause fo r the G erm an sh rim p er
fleet: “if scientific evidence su p p o rts th e claim th a t plaice are
n o t discarded in significant quan tities in th eir targ eted 80 m m
sole fishery”. As scientists, we d id n o t see how th is exem p tio n
could be integrated and evaluated in th e sim u latio n s w ith o u t
hav in g access to specific in fo rm atio n regarding discards in th at
fishery.
R egarding o p en en d s in a m an ag em en t p lan (su c h as th e state­
m e n t th a t new m easures m ig h t be applied u n d e r specific c o n ­
d itio n s, w ith o u t actually stating w hat these m easures m ig h t be),
o n e m u st accept th a t th e n egotiation process can n o t sim p ly b e re­
o p en ed . H ow ever, to o b tain a clearer u n d e rsta n d in g o f th e type
o f m easures envisioned, it w o u ld have b een beneficial fo r the
Validating m anagem ent sim ulation models
823
Fbar
Fbar
0.8 -
(
1
o
/
0
1
0
/
0
1/
0 c
1 \
0
/ /
0 .8 -
Î \
o
o
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............. .
s
0 .4-
\
00-
°"°
0.4 -
~
\
o.o 1996
1998
2000
2002
2004
1996
E f fo rt- F b a r
0.4 -
0. 0-1
0.0
35000
40000
2000
2002
2004
E f fo rt- F b a r
0 .4 -
30000
1998
45000
30000
35000
40000
45000
Figure 3. Com parison of hindcast average F (Fbar) and the effort - m ortality relationship for sole: left panels, proportion in th e south
estim ated by surveys an d no technological creep assum ed (as in Figure 1); right panels, proportion in th e so u th m anually modified (as for
Figure 2) an d technological creep assum ed as based on Rijnsdorp et al. (2006).
ev aluation process to have h a d closer a n d m o re regular in te r­
actions w ith th e NSRAC o n th e class o f new m easures th at
m ig h t b e explored.
T he u n certain ties in th e O M explored in sim u latio n s addressed
ju st th re e processes, b u t these rep re sen t a lim ite d subset o f all th e
p rocesses th a t m ig h t influence the overall u n certain ty (e.g. selec­
tivity o f th e fleets, dy n am ic effort allocations by area, alternative
relationships betw een selectivity, catchability, effort, an d fishing
m o rtality ). T his ty p e o f m u ltid im e n sio n al m o d el requires a
stro n g analytical a p p ro ach to explore th e m a in factors affecting
u n certain ty (Keli e t a l , 2006a). H in d castin g can be a useful tool
for exploring th e b eh av io u ral dynam ics o f a m o d e l if th e dynam ics
can b e verified b y observations. As a caveat, w e n o te th a t the o b ser­
vatio n s available m ay them selves be flaw ed in terp retatio n s o f th e
reality th ey a tte m p t to represent. T h e discard observations in th e
N o rth Sea plaice assessm ent are a goo d exam ple, because the esti­
m ates are b ased o n a m o d ellin g a p p ro ach th a t generates huge fluc­
tu atio n s in d iscards fro m y ear to year. I f sim u lated discards deviate
from assessm ent discards, th is m ay rep re se n t incorrect assum p­
tio n s in eith er m odel.
C o m m u n icatio n o f results w ith th e clients has b een addressed
o nly briefly so far. S takeholders a n d fisheries m anagers d id n o t
ap p ear t o relate directly to th e technical com plexities o f th e m o d ­
elling process, a lth o u g h they w ere co n cern ed w h eth er th e h in d cast­
in g co u ld rep ro d u c e th e observed dy n am ics in th e assessm ent
un d erly in g th e TAC advice, a n d w h e th e r th ey could logically
explain in th eir ow n w ords th e developm ents in stocks a n d fisheries
predicted by th e sim ulations. W e suggest th a t th e issue o f focusing
to o m u ch o n ab solute values in th e sim u la tio n o u tp u t m ig h t be cir­
cu m v en ted by expressing th e results relative to a n ap propriately
chosen reference level (for in stan ce, th e final y ear for w hich in fo r­
m atio n is available). T h e reference p o in ts u se d in th e m an ag em en t
process w ou ld th e n also have to be scaled o n th a t basis. Even u n d e r
such a scenario, sh a red u n d e rsta n d in g o f w h a t th e m odels can an d
ca n n o t d eliver rem ain s a n im p o rta n t issue. T h e expectations o f th e
different p a rtie s sh o u ld be la id clearly a n d openly o n th e table, to
m ake th e process as efficient as possible.
O u r overall con clu sio n is th a t th e sim u latio n app ro ach has been
useful, b u t it m ig h t have b een even m o re useful if used d u rin g th e
d evelopm ental stage o f th e p la n , a n d w ith m o re in teractio n w ith
th e NSRAC befo re th e p lan w as finally agreed.
T he FLR m o d ellin g e n v iro n m en t (Keli e t a í , 2007) allows co n ­
s tru c tio n o f flexible sim u latio n m o d els th a t reuse generic tools an d
can be a ttu n e d to different types o f m an ag em en t rules an d o u tp u t
m easures req u ired . H ow ever, b ecause FLR is still in a developm en­
ta l stage, th e balance in th e d ev elo p m en t o f generic a n d specific
tools has te n d e d to be o n th e latter side. As a consequence, the
resulting co d e has becom e to o com plex to be tran sferred easily
to o th e r ap p licatio n s. M ore w o rk is n eeded to m ak e th e sim ulatio n
m odels m o re tra n sp a re n t a n d transferable.
Acknowledgements
T he stu d y w as com m issioned a n d fu n d ed b y th e D u tc h M inistry o f
A griculture, N a tu re C onservation a n d F ood Q uality (LNV). The
C om m ission o f th e E uropean C o m m u n ities D irecto rate General
fo r Fisheries c o n trib u te d to th e d evelopm ent o f th e sim ulatio n
m o d el a n d th e w ritin g o f th e m a n u sc rip t u n d e r th e contract
“O p eratio n al evaluation tools fo r fisheries m an ag em en t o p tio n s”
(“EFIM AS”; SSP8-C T-2003-502516).
References
Butterworth, D. S. 2007. W hy a m anagem ent procedure approach?
Some positives and negatives. ICES Journal o f M arine Science,
64: 613-617.
Butterworth, D. S., and P unt, A E. 1999. Experiences in the evaluation
and im plem entation o f m anagem ent procedures. ICES Journal of
M arine Science, 56: 985-998.
824
CEC. 2001. Proposal for a council regulation establishing m easures for
the recovery o f cod and hake stocks. COM (2001), 724.
CEC. 2006. C om m unication from the C om m ission to the Council and
the European P arliam ent Im plem enting sustainability in EU fish­
eries through m axim um sustainable yield. COM (2006), 360.
ICES. 2006a. Report o f the W orking G roup o n th e Assessment of
Demersal Stocks in the N o rth Sea and Skagerrak, Copenhagen,
6 -1 5 September 2005. ICES D ocum ent CM 2006/ACFM : 09.
ICES. 2006b. Report o f the W orking G roup on Beam Trawl Surveys,
H am burg, 16 -1 9 May 2006. ICES D ocum ent C M 2006/LRC: 11.
ICES. 2006c. Report o f the ICES Advisory C om m ittee o n Fishery
M anagem ent, Advisory C om m ittee o n th e M arine Environm ent
an d Advisory Com m ittee on Ecosystems, 2006. ICES Advice, 1-1 0 .
Keli, L. T., and Bromley, P. J. 2004. Im plications for current m anage­
m ent advice for N orth Sea plaice (Pleuronectes platessa
L.). 2. Increased biological realism in recruitm ent, growth, densitydependent sexual m aturation and the im pact o f sexual dim orphism
and fishery discards. Journal o f Sea Research, 51: 301-312.
Keli, L. T., Cotter, A. J. R., Van Keeken, O., Pastoors, M., O ’Brien, C. M.,
Piet, G. J., and Rackham, B. D. 2003. The influence o n stock assess­
m ent advice o f sampling error in research survey and international
m arket sampling data for N orth Sea cod (Gadus morhua L.) and
plaice (Pleuronectes platessa L.). ICES D ocum ent CM 2003/X; 5.
Keli, L. T., Mosqueira, I., Grosjean, P., From entin, J-M., Garcia, D.,
Hillary, R., Jardim, E. et al. 2007. FLR: an open-source fram ework
for the evaluation and developm ent o f m anagem ent strategies.
ICES Journal of M arine Science, 64: 640-646.
Keli, L. T., O ’Brien, C. M., Smith, M . T., Stokes, T. K., and Rackham, B. D.
1999. An evaluation o f managem ent procedures for implementing
a precautionary approach in the ICES context for N orth Sea plaice
(Pleuronectes platessa L.). ICES Journal o f M arine Science, 56:
834-845.
Keli, L. T., Pastoors, M. A., Scott, R. D., Sm ith, M . T., Van Beek, F. A.,
O ’Brien, C. M., and Pilling, G. M . 2005. Evaluation o f multiple
m anagem ent objectives for N ortheast Atlantic flatfish stocks: sus­
tainability vs. stability o f yield. ICES Journal o f M arine Science,
62: 1104-1117.
Keli, L. T., Pilling, G. M., Kirkwood, G. P., Pastoors, M . A., Mesnil, B.,
Korsbrekke, K., Abaunza, P. et al. 2006b. A n evaluation o f m ulti­
annual m anagem ent strategies for ICES roundfish stocks. ICES
Journal o f M arine Science, 63: 12-24.
Keli, L. T., Pilling, G. M., and Kuikka, S. 2006a. Relative im portance o f
value o f inform ation and value o f control for m ixed fisheries.
Poster presented at the ICES Sym posium on Fisheries
M anagem ent Strategies, 2 7 -3 0 June 2006, Galway, Ireland.
M . A . Pastoors et a l
Keli, L. T., Scott, R. D., a n d H unter, E. 2004. Im plications for current
m anagem ent advice f o r N o rth Sea plaice. 1. M igration between the
N o rth Sea and E nglish ChanneL Journal o f Sea Research, 51:
287-299.
Kirkwood, G. P. 1997. T h e revised m anagem ent procedure o f the
International W haling Com m ission. In Global Trends: Fisheries
M anagement, pp. 9 1 - 9 9 . Ed. by E. K. Pikitch, D. D H uppert,
and M . P. Sissenwine. A m erican Fisheries Society Sym posium , 20.
Kraak, S. B. M., B uism an, F. C., Dickey-Collas, M ., Poos, J. J., Pastoors,
M. A., Smit, J. G. P., D aan, N. et al. 2004. H ow can we manage
m ixed fisheries? A sim ulation study o f the effect o f managem ent
choices on the sustainability and econom ic perform ance o f a
m ixed fishery. ICES D o cu m en t CM 2004/FF: 11.
McAllister, M . K., Starr, P. J., Restrepo, V. R., and Kirkwood, G. P.
1999. Form ulating quantitative m ethods to evaluate fisherym anagem ent systems: w h a t fishery processes should be m odelled
and w hat trade-offs sh o u ld be made? ICES Journal o f Marine
Science, 56: 900-916.
NSRAC. 2005. Im m ediate M anagem ent M easures for N o rth Sea
plaice. A drice to th e E uropean Com m ission. http://w w w .nsrac.
org/adrices/w f20050712_Adrice_on_plaice_m anagem ent.pdf.
Pastoors, M. A , Rijnsdorp, A. D., and Van Beek, F. A. 2000. Effects o f a
partially dosed area in th e N o rth Sea (“plaice box” ) on stock devel­
opm ent o f plaice. ICES Journal o f M arine Sdence, 57: 1014-1022.
Poos, J. J., Machiels, M . A. M ., and Pastoors, M . A. 2006. Investigation
o f som e M anagem ent Scenarios for N orth Sea Sole and Plaice in
2006 and beyond. W ageningen-IMARES: CVO Report, 06.004.
IJm uiden, th e N etherlands.
P unt, A. E., Smitii, A D. M ., an d Cui, G. 2002. Evaluation o f m anage­
m ent tools for A ustralia’s South East Fishery 1. M odelling the
southeast fishery taking account o f technical interactions. M arine
and Freshwater Research, 53: 615-629.
Rijnsdorp, A. D., Daan, N., an d Dekker, W. 2006. Partial fishing m or­
tality per fishing trip: a useful indicator o f effective fishing effort in
mixed demersal fisheries. ICES Journal o f M arine Science, 63:
556-566.
Rijnsdorp, A D., and Pastoors, M. A. 1995. Modelling the spatial
dynamics an d fisheries o f N o rth Sea plaice (Pleuronectes platessa
L.) based o n tagging data. ICES Journal o f M arine Science, 52:
963-980.
Van Keeken, O. A., Q uirijns, F. J., and Pastoors, M. A. 2004. Analysis of
Discarding in the D utch Beam Trawl Fleet. RIVO Report, C034/04.
IJm uiden, the Netherlands.
doi: 10.1093/icesjm s/fsm 051