Technical Challenges and Tradeoffs of
Managing Multi-species Fisheries in the
Northeast US
Mission 2011: Can we save our oceans?
Massachusetts Institute of Technology
September 28, 2007
Paul J. Rago
National Marine Fisheries Service
Northeast Fisheries Science Center
Woods Hole, Massachusetts
Why is Fisheries
Management so Difficult?
Putting the cart before the horse
isn’t the only problem to worry
about.
Common Property Resource
No ownership
Shifting Baselines
History is lost
Allocation
Fisheries, States, Ports
Inelastic demand
Pay any price
Increases in Fishing Power
Electronics
Speed, Capacity
Multiple Jurisdictions
Fed,State,Local
Law suits
~100 pending
Multiple Species
Non-selective harvest
Varying Productivity
Technical challenges are pervasive
“An Indian fisherman speaks
on his cellphone to other
fishermen as he moves toward
a large school of fish.
Fishermen are also using
cellphones while at sea to call
traders and check prices for
their catch”.
Andy Mukherjee, National Post,
2/24/05
Photos by Deshakalyan
Chowdhury
A panoramic view of the New Bedford waterfront
Technical Challenges
•
•
•
•
•
•
Can we engineer our way out of the
problem?
Are closed areas effective?
Is there a downside to closing areas
without additional controls?--Jensen
Inequality
How do we deal with environmental change?
How do we deal with tradeoffs among noncommensurate quantities?
Note that closed areas do not correct the
conditions that led to need of closed areas
in the first place—excess effort. Closed
areas can reduce dependency on effort
reductions, and provide “insurance” policy
but response is necessary
“life does not stand still while specialists
put their minds in order”
Michael Graham, 1950. Address to United Nations
Large Scale
Experiments
• Foreign Fleets
• EEZ and Increase in
Domestic Fleet
• Closed Areas
• Effort Reductions
Foreign
Domestic
Large Scale Changes in Species
Assemblages
120
100
14
Groundfish
Other Species
Elasmobranchs
Pelagics
A
12
10
80
8
60
6
40
4
20
2
0
0
1960 1965 1970 1975 1980 1985 1990 1995 2000
Abundance Index Pelagics (kg/tow)
Abundance Index (kg/tow)
140
Surplus Production Models
80
• Limited Population Growth
70
60
Stock Biomass (kt)
Stock Biomass
– Logistic growth: populations
increase proportional to their
biomass, but the rate of increase
slows as the population
approaches its carrying capacity.
– Rate of change (production) is
maximum when the population is at
half of its carrying capacity.
Carrying Capacity
50
40
30
Rate of Growth
20
10
Time (years)
Time
‘all models are wrong, some are useful’. G.E.P. Box
24
22
20
18
16
14
12
10
8
6
4
2
0
0
Graham-Schaefer Model:
Discrete Time Surplus Production (1)
Bt 

Bt 1  Bt  rBt 1 
 Ct

K

Bt = stock biomass in year t
K = unfished stock biomass at carrying capacity
r = intrinsic rate of stock growth.
Now Catch C can be written as the product of fishing mortality
F and stock size B or more generally as a function of stock
biomass, fishing effort E, and a constant, known as the
“catchability coefficient” q
Ct  qEt Bt
Substituting for Ct gives--
Graham-Schaefer Model:
Discrete Time Surplus Production
Bt 

Bt 1  Bt  rBt 1 
 qEt Bt

K

Et = Effort in year t
q = catchability coefficient (fraction of resource
removed per unit of effort.
At equilibrium, biomass B* can be written as a function of
Effort such that
 qE
B  K 1 
r

*



Production Models
MSY=rK/4
4.0
• Graham’s Theory of
Sustainable Fishing
(1935):
3.0
Maximum
Sustainable
Yield = MSY
Sustainable Yield (kt)
Sustainable Yield
– If removals can be
replaced by stock
production each year, the
fishery is sustainable.
– If stock size is
maintained at half its
carrying capacity, the
population growth rate is
fastest, and sustainable
yield is greatest
(Maximum Sustainable
Yield).
3.5
2.5
2.0
1.5
Biomass at
MSY
1.0
0.5
0.0
0
0
10
20
K/2
30
40
50
Stock Biomass (kt)
Stock Biomass
60
70
K
80
Managing at the Margins
Overfished
4.0
3.5
3.0
Maximum
Sustainable
Yield = MSY
Sustainable Yield (kt)
Sustainable Yield
• Balancing a population
at BMSY can be
precarious
• Changes in stock size
can occur due to many
factors—many of which
cannot be controlled.
• Targeting for a
population size greater
than BMSY creates a
“reserve” that reduces
yield slightly and
protects against
changes in stock status
Not Overfished
2.5
2.0
1.5
Biomass at
MSY
1.0
K/2
0.5
0.0
0
0
10
20
30
40
Stock Biomass (kt)
50
Stock Biomass
60
70
K
80
Managing at the Margins
Not Overfishing
4.0
3.5
3.0
Maximum
Sustainable
Yield = MSY
Sustainable Yield (kt)
Sustainable Yield
• Balancing a population
at FMSY can be
precarious also
• Changes in fishing
mortality can arise form
several sources
• Targeting for a fishing
mortality rate LESS
than FMSY leads to
higher biomass, a slight
reduction in yield and
reduces the need for
future reductions in
effort.
Overfishing
2.5
2.0
Fishing
Mortality Rate
at MSY
1.5
1.0
r/2
0.5
0.0
0
0
10
20
30
40
50
60
Stock Biomass (kt)
Fishing Mortality Rate
70
80
r
Current Year Stock Status - Status Determination
2.0
1/2 B-MSY
F / F-MSY
1.5
overfishing
not overfished
overfishing
overfished
1.0
F-MSY
0.5
0.0
0.00
no overfishing
overfished
0.25
no overfishing
not overfished
0.50
0.75
Biomass / B-MSY
1.00
Status determination
is based on a
comparison of
current estimates of
fishing mortality and
spawning stock
biomass with their
respective biological
reference points.
The comparison is
based on the ratio of
the current value to
the reference value.
There are 4 possible
categories based on
overfishing and
overfished status.
Where do you want to manage the resource?
Current Year Stock Status - Status Determination
2.0
1/2 B-MSY
F / F-MSY
1.5
overfishing
not overfished
overfishing
overfished
1.0
F-MSY
0.5
0.0
0.00
no overfishing
overfished
0.25
no overfishing
not overfished
0.50
0.75
Biomass / B-MSY
1.00
Managing at the
margin makes
changes in
stock status
very likely given
the expected
variation in
assessments.
In this instance,
75% of the
outcomes are
bad.
Where do you want to manage the resource?
Current Year Stock Status - Status Determination
2.0
1/2 B-MSY
F / F-MSY
1.5
overfishing
not overfished
overfishing
overfished
1.0
F-MSY
0.5
0.0
0.00
no overfishing
overfished
0.25
no overfishing
not overfished
0.50
0.75
Biomass / B-MSY
1.00
Managing
AWAY from the
margin makes
changes in
stock status
less likely and
increases
planning time
for
management
and business
Graham-Schaefer Model:
Extension to multiple species
 Bs ,t 
Bs ,t 1  Bs ,t  rs Bs ,t 1 
 qs Et Bs ,t

Ks 

Bs,t = stock biomass of species s in year t
Ks = unfished stock biomass at carrying capacity
rs = intrinsic rate of stock growth.
Et = Effort in year t
At equilibrium, biomass Bs* can be written as a function of Effort
such that
 qs E
Bs  K s 1 
rs

*



Extension to multiple species.
Which species will be overfished?
A stock is overfished when B<1/2 K. Using the equilibrium
formulation, then the effort sufficient to create an over fished
status is
 qs E
1
K s  K s 1 
2
rs

E



rs
2q s
Overfishing will occur whenever
F  FMSY 
qs E 
E
rs
2
rs
2q s
rs
2
Cod: The Misery of
Decline
Haddock:
The Agony of
Recovery
Species Key
Results of 2005 Groundfish Assessment Review Meeting:
Comparisons with Reference Points
Groundfish Stock Status - 2004
1/2 B-MSY
8.0
7.0
6.5
overfishing
overfished
6.0
F2004 / F-MSY
Stock/Species
GBYT1
Georges Bank
Yellowtail Fl.
“Base Model”
GBYT2
Georges Bank
Yellowtail Fl.
“Major Change
Model”
CCYT
Cape Cod/Gulf of
Maine Yellowtail Fl.
SNEYT
S. New England/Mid
Atlantic Yellowtail Fl
GM Cod
Gulf of Maine Cod
W Hake
White Hake
GG Cod
Georges Bank Cod
SNE Winter
S. New England
Winter
GM Had
Gulf of Maine
Haddock
GB Had
Georges Bank
Haddock
Plaice
American Plaice
S Window
Southern
Windowpane Fl.
Pout
Ocean Pout
GB Wint
Georges Bank
Winter Flounder
Witch
Witch Flounder
Pollock
Pollock
GM Winter
Gulf of Maine Winter
Flounder
Redfish
Acadian Redfish
N Window
Northern
Windowpane Fl.
GB YT2
7.5
5.5
5.0
overfishing
not overfished
GB YT1
4.5
4.0
Abbreviation
CC YT
SNE YT
3.5
3.0
GM Cod
2.5
W Hake
2.0
1.5
1.0
GB Cod
SNE Winter
GB Had
GM Had
0.5 no overfishing
Plaice
overfished S Window Pout
0.0
0.00
GB Wint
0.25
0.50
Witch
Pollock
Redfish
no overfishing
GM Winter
not overfished
N Window
0.75
Biomass 2004 / B-MSY
1.00
F-MSY
1.25
Is the single species surplus production paradigm
applicable to multispecies management?
• Well, only if intrinsic rates of population increase r,
carrying capacity K and catchability q are the same.
• Otherwise, stocks will respond differently to a common
level of effort E.
• If it is undesirable to create an overfished condition
then total effort must be lower than
 rs 
 s
E  min 
 2q s 
•
THEREFORE—Weakest Link Management
•
Manipulations of qs via gear modifications etc may be possible
but such changes will affect other species.