------- -
•
.-
---- - ------------::-_.c::-_.--:c
•.-_--,
__...--,
-..•.-_.••-••..- . - I
••
F
This paper not to be citcd without prior referencc to thc author.
International Council for
the Exploration of the Sca
ICES CM 1981/G: 11
Demcrsal Fish Committee
Tagging results of mature dab in the Southern Bight.
R. De Clerck
Fisheries Research Station
Ankerstraat, 1
8400 Oostt:nde/Belgium
ABSTRACT
During 1979 mature dab was tagged in the Belgian coastal waters. The main migration route in a NE- direction started during the second half of thc ycar. Thc
main distance of this migration was about 80 milc>s. A small fracHon also migratcd into thc eastcrn Channel. During the next spring season areturn to the
release ground became apparent.
e
RESUME
Pendant l'annce 1979 des lirnandes matures ont ete marquecs dans ICI3 eaux
cötthrü$ bölSCl:I. Ltl. migrn.tion prindpo.lc d:lns In. dircction NE commcns:n. dans
le sccond 8c:mesh'e de l'anrtce. La distance moyenne couverte 10rs dc 1a migration etait dl en'Viron 80 milles.
Une fraction minime Se retrouvait dans la
Manche orientale. Pendant le printernps suivant, un retour vers le lieu de liberation se manifesta.
INTRODUCTION
In thc North Gea dab are very abundant and along thc coasts they occur in largc
quanHtics. Howevcr dab catchcs usually do not refiect stock abundanccs as vaGt
quantities of dabs are discardcd and on many fishing trips in thc North Sea
100 % of thc dab catchcs are cliscarded (Anon.,1977).
As dab 15 11 groGs fecder, eMing practicnlly any organism that is locally comm:::I~.
its impörtaficc in a mu1tispccics model is not ncgHgiblc. However little is knowr.
of the bchaviour of dab, cspecially of thc migration. So far rcsults on dab
. . tagging experiments have not yet bcen published and some migration patterns were
_ derived from recordings of seasonal dcnsitics.
Dab seems to occur at greater depths in winter time (20-60 meters) whercas
during summer ·dab favours thc shallower regions (Bohl, 1957, Rae ,1970,
Creutzberg and Fonds, 1971). However there secms to bc few limitations
according to the dcpth as dab was obscrved at dcpths varying from 150-200 meters (Dc Vcen, 1954, Sahrhage, 1964).
The wide distribution oi dab can be ascribed to its high rcsistancc to extreme
high or 10VI temperatures or salinities (Bohl 1957, De Veen 1954, Sahrhage, 1967).
Spa\",ming scason is from January to August in the North Sea. In the Southern
North Sea spawning occurs earlier than in thc Northern North Sea (De Veen,
1954).
This study was subsidized by the "Institute for Scicntific Research in Industry
and Ag:riculture", Brussels, Belgium.
•
-.....
• i.
.
,',.
.
;
.
.'
.
MA TERIAL AND METHODS' ".
'- . .....
-- -
2.
.
T,
~
""' . , '
,
A tClgging experiment was' car:ded out off the Belgb,n co~.~t 'o~, board of thc .'
commer·::i::ll vessel 023 "GeoHrey William" (240 hp). The experiinent took'pla'ce
in the p.:!riod 13 to 28 June 1979.'
. ,:' ,
"
From tho 1688 rclcased 1·19 ""re as yct recapturcd"(a' reca~'t~~ri ' rat'~6f',
8 ~,%).
Thc rcl.::!2.se position was 51 °20' N - 2°.15 1 E.
' ,
The lcngth frcqucncy distribution of thc tClgged dab is shov,rn. in figure,: 1; 'The' ,
majority varicd from 19 to 24 (;m in lcneth. On the bCl~is of thesd: data~ it, ca'n
be assumcd that most of the tagged dClb wns mature.
,:, .; ,<; r:: ;;
8.
Thc follo'l/ir,g migration parC1.mcte::rs were c~tlcu1nt;;d (Jones.
- 0,2
"
•• ,
:.
••
.
mean square,'~lispersion coefficient,.
V
,;-::' "I;,"
i.: ",:' _~ ..
mcan velocity in this direcÜ'on (nautical. rniles/day). '" ,:.
tn. V
mean distance (n
a,
'
•
•
~ numb~r
I
•
, . l .
•
.-~
of recapttnes).' " ' : , ".,.'
VJ hen" clear d111crcnces in the dircction were nott:d a, separation was mad,e, in,' ,'.
thc 'calcübtions :
.,':,
" , "
;,',
,
" ::;. . "
',' .....
A": rCc;lptur..:s u'round the r~lcasepoint:(20 'n'a~ticCl1'~ilcs)' : . '
'.:.>:
B ' migration' in NE':' direction
,':
I '.'
"
" ,
.' . : ; :
C
migration in SW - direction (English. Channel)
! .
D
migr;ltion' in NW - direction'
)1.
,•• ,.~
:':-!
I.
. .... ,
')'
,
,- ,. I
the recaptures werc also
1
'2
'" ·.. ·3·
: <1 :
i1'
mean direction of dis1ocation.;.;"/~~(r'
.
..
}
1965)
[;roup~d
into 4: r0capture periods . :
':
i
;","';,'
.
~.
•
!
,
• .' ". , •.," " \ ". 4"":..
Janu;lry- March
April-June.
Ju~y -September
October-D~ce,mber
e
.1
",
.....
The rcsulting parameters' ,,-re given in tablel. The position of the recaptures
'as \vell. ·a.B the 'mean direction and the mean .:listance arc' illtishated in ,
,",
figurcs 2;-~-2h,
.
' .. :
-.
.:
'!
RESULTS'
Several ::;.tudi~s ,h;lV~ be~n publi'shcd concerning the densiti<,;s Of<diffe;cnt"length.
c1asses cf dClb ~n·the Be1cian coast,"c1 \vaters (De Clerck. l,975a. "1976). Although
densitics' can differ fr'om one yeaT ta another gencrilly high concentrations of
'dab were found. A p~:rinancnt miture d;l0 stock (dab '''ofmoie 'than 15 cm in ;
length) was rccordcd buf thc' dC!1üity. 'scemcd thc' l~west"'~uring thc summer.
,
Thc Bdgian coastal waters :arc also. an important nurs:::ry aroLl. for dab. Small
dab of ~.;.S' cm occurrcd in ,experimental cD,tches du'ring August. The maximum
bnr,th during thc first year, vari~d' durine thc p~riod 1970-1931 betwecn 6 and
7 cm (De Clcrck. 1976. :19783.. J 979. "1980). A"gi-owth stagnation was' observed
during thc winter poriod (Novcmbcr-March).i Growth' acceleration took place fro~-fl
April onwards and the maximum length during the sccond year showed a r.1ean
.' ','Valuc of 15 :ern. Highest weights of food in the stornach wcreindeed, foun'd, in
the period June-Octcibcr (Gilis', 1966)'"
1\""
'~,.,,'
, " " , ' '" ::. ',;,'
u
'
.
'.
..':"
,,'
1,
3.
Fo'rmC1 atudies also indicated ri. sex.-rn.tio of.80/20 for the . females (Gilis,':19,66).
More or 'less the same ratio was fbund in thc resovci:-ies 'Irom" this'~xperimerit.,
The r~sultso.r:'~äturity' studie,Ei: (GÜ.is, 1966) demon'strated '~that:'~a~~'~ity',~iag~s VI
to VIII ,werc:.,lim~ted to ovary sampies 'from theperiod March-:April. ' On., the '
basis, of these" r:Csults thc Belgiä~ coastal wat'crs':'could ,'be considered' ,as' ~ , ,
spawning area for dab. :Eggs and'l:irvaeof dab were, howeverseid'om,detccted
during ~t:udies w~th.. a G~lf III :sa"mrl,~r (D~ Clcrck 'and Van: De V~ld'e, ':1977).
Perhaps thc resultl?g tlda.l strcams 'cause' thc driftingin NE- 'directions as
already ObFlcrved wlth p!::l.lce egge ':l.nn larvac (De Clerck" 1978b).,'"
The migration pattern of the tagged dab can bc' describcd as follows
•
.".
~.
I.
: .
•
Period 0/2 -, J~c' 1979 (figure '2a)
________ ....
... _
..
•
"..
'I
: , .
"
....
"
~
..
During thc· month'of reIöase :some r~captures were alreaCiy made> Mdst of"
thein were still present around the release, point. H~wcv~r on~ recovery in,dicated ä migrcltion in' a NE direction " (28 mHes! in 7' daYI?).'
'
~~!~~~_2L~_:_~~~t:~~~~e~~~:_~~?2, (fieure 2b)
During the first summer period i1: bec'amc apparent that ,an overall migration
in aNE -directi.on took plaee,' Indeed some,42 out of '16 recaptures werc' taken
NE of the rClease position. ' ,Most of them were found in thc' East Dcep ,Water
and the BroWn Bank Grounds. 'The dispersion coefficicnt of this' group \vas the
higl1.e~t,.of the who1e e~pcriment, viz'32. ,Themean.dist,ance was in thc order
of . 70 mHes. The 'furthest distance 'was, a' recovery in, the Oyster' Grounds:
Afemale dcib cf about' 25' cm had migrated 'some 150 mHes ,in aperiod of
86 dclys.
.
'
'.
'
" . '
Despitc this general migration direction one dab was recaptured' in tnc 'Thames
Estuary, ,viza clear1y western· migration. ,This migration of 53 miles was undertaken oy h' fe'mate dab. of 'about '26 em in length in aperiod of"68 ·days. ' ,
During this period thre~ recoverie~'(7 ~, of th~' ~otal) ';~re "'stIll 'ob~,~'~v~~"in
thc release area. However two of them Wel'c already at a distance of about
16 mHes and also ina NE direction from thc release point.,
"'
A "more or le~s 'identicaLpieturc was obs~rved:fro~.'thc 'distribution, of the:
'recoverics during the last quarter of 'the first ycar of release. Indeed witq.
a :-high ,dispersion coefficient of about 14 the main distributionarea was again
in
NE i'di~ection .trom thc' ~elease point '(80 % ,of the rccoveries)." The most
importan"t a'reas we~c the "East Dcep ,Water, and the Zeeland Grounds. Again
"t';"ö taggeddabs were fished in the Oyster Grounds at distanccs from' the'" ~
relca'se point of 14~ :.and 167 m i l e s . '
:
a,
. '
.
.
.
','.
.
.
'.,
'..
l
'. Thc perceIitagc' of dab retur~ing to ~r remaining at the release point incre,ased
to 17 % 'of the total recaptures.
A~'2"of ,thcse 5 recoveries were'·fished inid
Deccmber it could be more an indication o! 'a 'return 'to the release point. i
,This
is ,also
supported
by.
the.
'findings
and 1/2..
.
. .
. .
. in the . periods,1/1.
. .:
'.'
In' coritradiction with a11 the former res'ults duringperiod 0/4 one recovery
was' öbserved near Calais indicating a SW - migration. '
.
.(
'·1'"",
'
~
L,
..~
4.
p.~ri~·~ 1 /i ~
january-:-March 1980 (figure 2d)
:.
"l
---------~-------------------------------..
Although the number of, rec~ptu:".es ·amou.nted ~nly to 11 "all the cÜ.fferent'·'inigradon routes. qbserved 'dildng the first 'year became again apparent ::. pne
dab yvas .·:ound elose to...the release ,point,' "three tagged dab, were fished .at a
distance uf about 70' rriiles ,NE of :thc'release' point, thrcc recoveries .indicated
a NW - migration (t~v<? of them "elose to 'Harwich) ,and iinally four recaptures
were observed in tho English Channel.' ;
,
The latter observation indicated a migratiön of a 'mean distance of about 90 mHes
from the release poin't.
,;'
.....
,
!'~!~~~_~i~':~_~P!!~__-!~~<:~l_~~O_
(figure 2e)
Only 6 recoveries were made during this period... Half of them wcre found',
very;c1ose to the 'place where the tagging w!1s carricd ou't on'e year' earli'er.
'.Two' recapturcs werereP'?~ted in the Brown Ban~Grounds 'ci.t',a· distan:c~ of
37 mHes NE,of the" release point.
"
! '.
'," .:' ; "
Again the migration into the English Channel' 'V;'~S shov.:~ 'by,a:"r:ecapturEi on: .the,
,.yer.goyer Bank elose to Boulogne.
',:,.~" ..,;,
e
------ - --,.. - _.- - - - - - - - - - - -,- - - - - - --
,PeT.lod 1/.3' - July-September 1980 (figure 2f)
, All' the"recoveries came: from th~ sa~e area, V1Z'~, thc' Brown ',Bank Grounds
with a,'mean :distance ,of 75 miles and a l'oVi 'dispe'rsion coefficicnt.
p'eri6ci 1/4 '-. Octcber'-Decembcr 19,80
---------_.----------_._------------
(figure
2~j
Thc 'main conclusio~ ~f the recoveries du~ing this' per'iod was thc.' fact· that
tagged dab was again rccovered frOln the Brown Bank G'rounds and' the English
Channel. No recaptures Were found in.
the '
release
area.
.
,
Pel'iod
2/2 und 2/3 ;- 'April-September 1981 (figure 2h),
---:------------------------.-------------,
"
'
Only tVJo recoveries Were reported both North of the release position., The
respectivc di13tances
were 17' and 132 mHes.
. '
.
DISCUSSION ' .
From this expc:::-iment some major conclusions can );>e, drawn.
first, of all t'he main direction of movement of dab"in !1~~ 'Southern Big'ht,'i~nto
Northeastern areas. The Brown Bank Grounds sho~ed ln nearly all recovery
pe'-riods, the highest c:6ncentrations of tagged dab.
"
."
.. '
".s~co~d1Y o~
severnl occani'ons th?r~ were reports frpm thc,"English ~hamiel,
indicating
that
apart of
the population took'
'.
'.
. . this direction to move.' ""
Apart from these two main migration rout'es' some znigrations' ,with lnllch' .1ower
'numbers Were observed in ,the direction, of thc UK Southcast coast.
,', ,: ,
'Generally large distances were covered. In somc caSüH a migrati~ri. ~p t6 159
nautical ~i1es was covered within aperiod of 86, days. I , '
'
I
'.
,
Those .two ma~n dire~tio'n, viz. NE (Dtitch coäst) and' sw:' (English. Chamiel) had
already been observed, in tagging experiments on plaicc .,(De ,Clc:;:Gk, ,1975b) nd
on sole (Anon. 1984) •. ,
,
" ,
'.,
\
On both occasions these flatfish populations showed two ?pposite migration
I
directions when leaving the Bclgian coastal waters. This migratory behaviout
certainly prevents the identification of the stocks. For stock management pur,poses it 5eems that seaGonal intcrmixing betwecn the Southern Bight and the ~
Eastern English Channel occuro. This serious 1l interferes in the manageme~t
strategy.. ,
'
1
\
..
5.
Another conclusion from thio etudy is the indication that the. migration period
startcd some few wecks, ,after tagging. ' Indeedfrorn 'July onwardsthe majority
of· the, rccoveries were .fou."1P far: awayfr'om ~he ,r~lease point.
Taking into
account that the spawning period can be situated bctwcen January and June thc
observed migration 'could. be attributed to ci. feeding migration. Moreover by
this migrc:Üon the dab movcd into much deeper water of up . to 40 'meters while
at tho release point depths from 15-20 meters occur. This is not in line with
earlier statements (Bohl, 195,(). that dab shoul,d return to shallow waters during
,summerwhile, in ,winter, the population is heading towards 'the, open s ea.
.Although the' observations during, th~ Jollo~ing 'year were rather scarce the recoveries in the first half o[the yearc could 'support, the hypothesis some return to
the release. point. In that case ,it could be,the spa'\vning ground too.
Asa matter of fact a11 tagged da,!:? '\vere n1a'ture ~md no differences ·where noted
in length sizes between the migrating population and thc popuhi.tion remaining
at the release poinL ,-- .
" ,"
•. !' .~.
:
*
*
•
*
REFERENCES.,
1. ANON.,' 1977 :' Review of some fish resoti~"ces within the NEAFC Conventio~
area.
C. M. 1977/F : 5 - Appendix.
2. ANON.. 1984 : Report of the O-group Flatfish Working Group.
IJmuiden
21-25 Nov. 1983 (in preparation).
3. BOHL, H. 1957 : Die Biologie der Kliesche (Limanda limande.. L. ) in der
Nordsee.
Ber. Dtsch. Wisse Komm. Meeresforsch. XV /1:1-57.,
4. CREUTZBERG. F. and FONDS, M., 1971 : The sensonal variation in the
distribution of some demersal fish species in the Dutch
Wadden Sca.
Thalassia Jugosl. 7(1), 13-26.
5. DE CLERCK, R. 1974-1981 : DensitieG and growth of flatfishes. off the
Belgian coast.
Annl. bio!. Copenh. volumes 29,30,31,32,33,34,35 and 36.
Part III : F1atfishes.
6., DE CLERCK, R., 1975a : Densities of flatfishes off thc Belgian coast during
1970-1973.
Annls. bio!. Copenh., 30:191 -193.
7. DE CLERCK, R. - 1975b : Tagging experiments on juvenile plaicc off the
Belgian coast.
C. M. 1975/F:25.
8. DE CLERCK, R.. 1976 : Densities of flatfishes off the Be1gian coast during
1974.
Annls. bio!. Copenh., 31:170-172.
, . . - - - - - - - - - - - - -------
-- - - -
6.
9.; D,E CLERCK, R., 1976, 1978a, ,1979, 1980 : Growth of juvenile sole, plaice
and dab off ,thc" Belgian coast.
", ,
'
An~ls.' bi61.'Copenh., 33:161-163 '; 35:225-229 ; 36:175-176 ;
37:205-206.
10. DE .CLERCK, R. and VAN DE VELDE, J., 1977 : Embryonale, en 'larvale
(,'
.;
.fas e.
"
Projekt Z ee, Vol. 7/Nationaal Onderzoekings- 'en Ontwikke' ,_
lingsprogramma-leefmilieu / water.
DE CLERCK, R., HECQ, J. H. , . MOM:rv1AER TS, J. P., PICARD, P. and
VAN KEY:MEULEN,'Y~" '1978b : Be1gian contribution to the experiment of
,
plaice egg and larvae diffusion.
"
~. M. 1978/C:55" Hydrography Committee~
DE VEEN, J.,' i 954 : Onze meest belangrijke vissoorten schar.
Visserij 7.(2), 24-27.
_. "
GILIS, Ch., 1966 : La Limande (Limanda limanda' .L.) de la Cote BeIge.
C. M. 1966/C:l, Comite des Mers' Nordiques -Procbes.
JONES, R., 1965 : FAO/UN seminar on sardine tagging, Split, Yugos1ae,
2-14 November 1964, Report and Lecture, FAO Fish
EPTA Rep.
15. RAE, B. B., 1970 : The distribution of flatfishes in Scottish and adjacent
waters.
Mar. Res. 2.
16. SAHRHAGE, D., 1964 : Uber die Verbreitung der Fischarten in der Nord.ee.
Ber. Dt. Wisse Comm. Meeresforsch. XVII(3) : 165-278.
17. SAHRHAGE, D., 1967 : Uber die Verbreitung der Fis.charten in der Nordsee:
Teil H.
Ber. Dt. Wisse _Komm. Meeresforsch. ,XIX (2)
66-179.
.
....'-
,e
:":
Ta ble 1. - Migration parameters.
Season of recapture
V
n. m/day
a
-5
y:)
2
I;
,
n
n.m.
..
numbers of'
mean square
mean directior mean
year jq}larte directiod' mean velocity dispersion coef. of dislocation distance recapures '.
;
0
2
A
B
0
3
0
II
4
e
1
1
I
I
II
II
II
1
2
3
1
4
1
..
.265
4.
10
1.5
O.
53
28.
1
9.
3
A
.527
4.179
20
B
1. 110
32.303
20
D
.78
A
.039
B
.601
c
.169
A
o.
42
70
279
53.
1
.507
329
6.
5
14.208
29
81.
24
o.
224
23.
1
.072
O.
342
17.
1
B
• 281
3.058
37
68•
3
c
.. 432
3.184
236
90.
4
D
.227
2.669
309
49.
3
A
• 016
.017
197
6•
3
B
• 281
3.058
37
37•
Z
C
.279
O.
224
86.
1
O.
0
O.
1
24
75 •
4
24
51.
4
225
60•
2
-
-
-
342
17
1
2
132
1
A
O.
.542
B
• 189
B
.102
C
• 116
.048
-
-
tt
1
2
2
A
.025
2
3
B
.164
i
63
13.258
-
2.6
O.
O.
I
•
".'_.'-'
-
,
I,
I
!
,
1.'
,
J ',~
.,,"
.
. ;'
....
'.'
,"~-,
... --" ....,"
"." ~"
,
'f.
\""
.
'.
,
.... '.,. .
:20 .
..
18
'-
~.
~
\~" ...
....~
"I.
.. ,
......
16
.....
t.
e
'.
"
.\:
14
'•.i
.':
12
...
10
8
'.~
.- .'
6
.....
.;
"
4
:;.
"
:.i
'.
.
2
15
20
.t-
Figure . t
2S
30
35
-
LengthCc:m) ,
;.
The lt~n9th trequency distribution of the tagged dab popu la tion.
2·
I"
O·
,.
2"
J"
4·
5"
e
6"
7-
:l'
0"
54"
o·
I"
2"
J"
4"
5"
(j"
\-
53" -
S3"
!51"
-
I" -
Figura 2a
..
51"
Figura 2b
Beason 0/3
season 0/2
5::- -
54"
53" -
I
52" _
I
'"
:
,.
Figura 20
Figura 2d
soasoh 0/4
. Baason 1/1
"
Figureo 2a-2d.- Pooition of the rooaptures during the different soasons"
• : release point
.'
7"
0'\
1·
O·
,.
2·
3·
'".
7"
.)
2·
O·
51" -
O·
,.
2·
5·
4"
6·
6·
7"
ft4° -
-
",
: 53°
52·
,
51"
Figura 2e
j
Figure 2f
51·
season 1/3
senson 1/2
I
54·
.-..
(2/3)
"
:5:)"
J
!:,
"
-~ ~
I
I
i;
52·
-j'
,:
~
~
!i
~~'-'
---f---+--e--.~
Figure 2g
oouoon
1/4 "
'--_.--J'--_---'_ _-"'-.e..-.J-_ _-"-_ _-'-_ _""-_ _J - . . _ - - - ' ' - _ - ' ' - - - '
15'·
G_O_n_S-. J2L-/_2_a_nJ-d_2_/-:-3~, ~'l"!
~iguro 2h
,--t--+---j_"
r-o:::"._-"_ _.1-_..L--_o_O_D.•.
2c-2h.- Position Of4ltlO rccapturoo durine the diffcrGnt4lt3D.SOnS (continucd) •
• : roI0J,::o point
1 •
-( ,