Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security,...
Transcript of Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security,...
![Page 1: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/1.jpg)
Food security, co-management and the
ecosystem approach to fisheries
African Great lakes Conference,
Entebbe 2-5 may
Jeppe Kolding (University of Bergen, Norway)
Paul van Zwieten (Wageningen University, The Netherlands
Michael Plank (University of Canterbury, New Zealand
Richard Law (University of York, UK)
Hans D. Gerritsen (Marine Institute, Ireland)
David Reid (Marine Institute, Ireland)
![Page 2: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/2.jpg)
The big challenge
With a growing
population: How do we
reconcile food and
conservation?
![Page 3: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/3.jpg)
Which fishing pattern gives the highest yield
and least structural impact on the community ?
Johannesburg 2002 Declaration § 31 (a):
«Stocks should be kept at biomass levels that can produce maximum sustainable yields (MSY).»
CBD Malawi principles for Ecosystem Approach:
«A key feature of the ecosystem approach includes conservation of ecosystem structure and functioning»
![Page 4: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/4.jpg)
The aquatic food web is size structured…
..abundance is inversely correlated with size
Primary producers
Primary consumers
Secondary consumers
Tertiary consumers
Top predators
Log B
iom
ass
Size
![Page 5: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/5.jpg)
Log B
iom
ass
Size
Community size spectrum
The distribution of biomass by body size follows regular patterns
phytoplankton
zooplankton
Small fish
Large fish
Under conventional selective fishing slope and
intercept will change
![Page 6: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/6.jpg)
Changes in the North Sea
Log
Bio
mas
s
Size
Unfished
Garcia et al. 2012
1983–1987
1998–2002
![Page 7: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/7.jpg)
Bio
mass
Size
Balanced harvesting… (Garcia et al 2012)
.. is fishing as many sizes and species as possible in
proportion to natural productivity
It will reconcile objectives
by maintaining community
structure while returning
highest yields
![Page 8: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/8.jpg)
Lake Kariba
Zambezi River
![Page 9: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/9.jpg)
Lake Kariba
Regulated and enforced
Yield = 1000 tonnes yr-1
Non regulated and non enforced
Yield = 6000 tonnes yr-1
![Page 10: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/10.jpg)
Lake Kariba
Average mesh size (mm stretched), Zambia
R2 = 0.86
60
80
100
120
140
160
180
1960 1965 1970 1975 1980 1985 1990 1995
Zambia - Catch rates
0
1
2
3
4
5
6
7
8
9
10
1959 1964 1969 1974 1979 1984 1989 1994 1999
CP
UE
Artisanal CPUE (Kg/net) from CAS surveys
Experimental CPUE (Kg/45 m net set)
Artisanal CPUE (Kg/net/night) from Scholtz 1993
Zimbabwe - Catch rates
0
2
4
6
8
10
12
14
1962 1967 1972 1977 1982 1987 1992 1997
CP
UE
Artisanal CPUE (kg/45m net) from CAS surveys
Experimental CPUE (kg/45m)
Linear (Artisanal CPUE (kg/45m net) from CASsurveys)
Controlled effort Open access
Kolding et al. (2003)
![Page 11: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/11.jpg)
0
5
10
15
20
25
30
35
40
45
2" 2.5" 3'' 3.5'' 4'' 4.5'' 5'' 5.5'' 6'' 6.5'' 7'' 7.5"
Rel
ativ
e fr
equ
ency
(%
)
Mesh size (inches)
Zambia
Zimbabwe
Mesh size distributions
Illegal
![Page 12: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/12.jpg)
Mesh size distributions
and catch rates (Zambia)
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
50 63 76 89 102 114 127 140 152 165 178
Rel
ativ
e no
of n
ets
and
CPU
E
Mesh size (mm)
CPUE
Mesh size
R² = 0.9036
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
4.00 6.00 8.00 10.00 12.00 14.00
Relation between CPUE and number of nets in each mesh size (76-178 mm)
![Page 13: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/13.jpg)
Comparison between unfished and heavily fished areas in Lake Kariba
![Page 14: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/14.jpg)
Comparison between unfished and heavily fished areas in Lake Kariba
Kolding et al. 2015
![Page 15: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/15.jpg)
Comparison between unfished and heavily fished areas in Lake Kariba
Number of species has not
changed and slopes are parallel
meaning ecosystem structure is
maintained while yields are 6x
higher than under regulations
Kolding et al. 2015
![Page 16: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/16.jpg)
Bangweulu swamps Northern Zambia
![Page 17: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/17.jpg)
Carl Huchzermeyer
![Page 18: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/18.jpg)
Bangweulu swamps
• Fish are getting smaller
• Rampant use of illegal gears
![Page 19: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/19.jpg)
Bangweulu swamps Northern Zambia
Mesh size Mesh size
(mm) gillnets kusikila seines weir traps cum %
3 3,869 13
4 8,358 41
6 2,322 49
8 387 50
10
25 534 17 53 52
38 6,719 68 178 75
50 4,233 135 49 90
63 1,260 643 97
76 554 74 99
89 136 - 99
102 - -
114 -
127 255 100
140 -
Total: 13,691 937 280 14,936 29,844
% 46 3 1 50 100
% legal 22
Total number of gear by type
Ndang
a
![Page 20: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/20.jpg)
Species and size composition by gear
![Page 21: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/21.jpg)
Fishing pressure versus size
Large fish
in gillnets
SeinesCiclids
Small fish
illegal
legal
Only largest species in legal
gillnets are overexploited
Overfished
![Page 22: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/22.jpg)
two multispecies fisheries
Celtic Sea (EU)
major commercial fishery
100,000 to 150,000 tonnes yr-1
>1000 vessels
quotas, minimum landing sizes
demersal, ~15 spp, trawls
small-scale artisanal fishery
~15,000 tonnes yr-1
~5000 fishers
largely unregulated
>30 spp, gillnets, seines, traps
Bangweulu Swamps (Zambia)
![Page 23: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/23.jpg)
size distributions of yield
biomass yields as a function over body mass
(aggregated over species)
100 102 104
101
weight (g)
103
105
Celtic Sea
yield (tonnes)
101
103
Bangweulu
yield (kg)
Celtic-Sea landings
Celtic-Sea landings+discards
Bangweulu
landed catch
size distributions of yield
Plank et al. 2016
![Page 24: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/24.jpg)
size distributions of catch
smallest fish:
~250 g
~10 g
size limits not operating in Bangweulu
100 102 104
weight (g)
101101
103
103
105
Celtic Sea
(tonnes)
Bangweulu
(kg)
range of body sizes
~20-fold
~1000-fold
largest fish
~5 kg (fish caught when smaller)
~10 kg (upper limits to growth)
both fisheries are sustainable
![Page 25: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/25.jpg)
how is this possible?
model of an unregulated fishery:
fishers share an aquatic ecosystem (commons)
each fisher decides what size of fish to catch
what happens to the fish stock and catch?
how does fishing mortality F(x), aggregated over fishers, get distributed over over fish body size x?
bac Kwww awbw
bookkeeping of biomass
Dynamic size-spectrum model a different ecological model:
+
stochastic event
![Page 26: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/26.jpg)
Model overview (Law et al. 2015)
dwwUwGwE1
MUGUw
Et
U
1. The fish population
![Page 27: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/27.jpg)
2. The fishers
• know nothing about ecology or size-spectrum dynamics
• do know their own catch, and the catch obtained by their neighbours – and their gears
From time to time he will evaluate his own catch (and gears) compared to those of his neighbours. If he catches less, he will tend to shift gear
![Page 28: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/28.jpg)
rule for each individual fisher
fishing effort is area under curve
each fisher i chooses a net mesh centred on an arbitrary fish size
body weight x (log scaled)
Fi(x
) b
y fi
sher
update net mesh from time to time
more likely to move if his yield (cpue) is small compared to others: 1 – Yi/max(Yj).
new net mesh size chosen uniformly at random on range of body sizes
body weight x (log scaled)
Fi(x
)b
y fi
sher
random shift
Fi(x
)b
y fi
sher
aggregate fishing mortality F(x)
sums over all fishers (simple SEES model)
body weight x (log scaled)
![Page 29: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/29.jpg)
few fishers (100)
110-2 102
weight (g)
1
10-2
10-4
bio
mas
s (g
m-3
)
unfished
fished
110-2 102
weight (g)
pro
du
ctiv
ity
(g m
-3 y
r-1)
0
0.2
0.4
0.4
productivityfishing mortality
0.6
0.2
fish
ing
mo
rtal
ity
rate
(yr
-1)
emergent
F(x) aggregated close to biomass peak
many fishers (8000)
110-2 102
weight (g)
110-2 102
weight (g)
4
8
0
0.2
0.4
fish
ing
mo
rtal
ity
rate
(yr
-1)
fishers remove biomass peak: flat ‘Sheldon’ biomass spectrum
(constant biomass on log-scaled intervals of body mass)
F(x) spreads out over body size x on RHS of productivity peak
F(x) ~proportional to productivity
110-2 102
weight (g)
bio
mas
s (g
m-3
)
10-4
1
10-2
biomass spectrum (unfished)
F(x)aggregated
![Page 30: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/30.jpg)
Result = emergence of balanced harvesting
F(x) proportional to productivity balanced harvesting
a fisher cannot increase yield by a change in gear
constant biomass all fishers get equal biomass yield
Nash equilibrium: No fisher has an incentive to change fishing strategy, given the strategies of all other fishers
![Page 31: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/31.jpg)
aggregate biomass yield
total fishing effort must still be controlled
caveats:
biomass yield and profit are very different things
balanced harvesting
without min. landing
weight regulation‘Bangweulu-like’
= collapse of stock and fishery
BH gives
much greater
biomass yield100 g min. landing
weight regulation‘Celtic-Sea-like’
![Page 32: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/32.jpg)
Conclusions
Mesh size regulations in small-scale fisheries are
impeding maximum yield and healthy resilient
ecosystems
When food security (biomass) is more important
than commercial value, then catch-rates (CPUE)
will regulate the fishing pattern towards a
Balanced harvest regime.
For co-management to work the State will have to
abandon size and gear regulations.
![Page 33: Food security, co-management and the ecosystem approach to … · 2017-05-12 · Food security, co-management and the ecosystem approach to fisheries African Great lakes Conference,](https://reader034.fdocuments.us/reader034/viewer/2022050503/5f9586122c74a93df57dcdf2/html5/thumbnails/33.jpg)
Conclusions:
A trait-based size spectrum model is able to quite
accurately simulate the Kariba fishery
The model confirms that starting fishing on
smaller individuals and fishing ‘balanced’
according to size will:
Increase total yields
Minimize impact on fish community
By fishing ‘illegally’ the Zambian fishers are able
to catch 6x more without causing deep structural
changes to the fish community
Thank you for your attention