This document discusses several key issues regarding fisheries sustainability: 1) It defines what constitutes a fishery and examines the global status of fisheries, finding that 25-30% have collapsed. 2) It explores what sustainability means ecologically, in terms of maintaining surplus production and compensatory improvements in fish populations. 3) It outlines some of the challenges involved in managing fisheries to balance harvesting multiple interconnected stocks while protecting biodiversity.

1. Issues in fisheries sustainability
• What is a “fishery”?
• The global status of fisheries: will we soon
be eating only jellyfish?
• What does “sustainability” mean, and what
is the ecological basis for it?
• What does it mean to “manage” a fishery?

2. What is a “fishery”
• A linked dynamic relationship between a
set of valued fish and a set of fishermen
who pursue those fish
Fish stock(s) Fishing “fleet”
Catch
Mortality

3. The global status of fisheries

4. The global
status of
fisheries,
revisited
From Branch et al. 2010.
The trophic fingerprint of
marine fisheries. Nature,
doi:10.1038/nature09528

5. Many (25-30%)
of the world’s
fisheries have
“collapsed”
to catches less
than 10% of
historical peak
Plateau
0
0.5
1
0246810
Years before collapse
Relativecatch
20
Smooth
0
0.5
1
0246810
Years before collapse
Relativecatch
31 12 16 38
Erratic
0
0.5
1
0246810
Years before collapse
Relativecatch
5 17 8 16From Mullon et al. 2005.
The dynamics of collapse
in world fisheries. Fish
and Fisheries 6: 111-120.
(an examination of 1500
catch time series)

6. Where are fisheries collapsing?
Newfoundland
North sea
California current
India
China
Indonesia
Australia
Benguela

7. What does “sustainability” mean?
• Lack of collapse?
• Capable of recovery after collapse,
especially for collapses not caused by
fishing?
• Harvested at near maximum sustainable
yield?
• Harvested at near maximum sustainable
harvest rate?

8. Sustainable fisheries depend on
creation of “surplus production”
• Surplus production
is biological
production (growth)
that can be
translated either into
catch or into
population growth.
• On average, surplus
production is zero in
unharvested natural
populations
• High fishing mortality
rate can result in
sustainability, but at
low biomass and
catch
0
5000
10000
15000
20000
25000
30000
0 0.2 0.4 0.6 0.8 1
Fishing mortality rate F
Biomass
Biomass
Production
Catch x 10
Food consumption

9. What causes surplus production to occur
when fishing reduces stock size?
• “Compensatory” improvement in juvenile
survival rates and/or growth rates
• These compensatory improvements result
from
– Reduction in predator abundances (uncommon)
– Increase in food abundance (more common)
– Increase in available food abundance leading to
better growth and/or reduced predation risk (very
common)
– Reduction in juvenile mortality due to
cannibalism (common)

10. What does it mean to “manage” a
fishery?
• Protect the ecological basis for production
(biophysical habitat, forage base)
• Control the quality (size, age) of fish harvested
• Regulate the fishing mortality rate F
– Input control: control fishing activity, area swept by
fishing
– Output control: control the catch, given estimate of
biomass (since F=catch/biomass)
• Seek balance in situations where fishing impacts
multiple stocks so as to create tradeoffs

11. Most fisheries impact multiple stocks,
create tradeoffs where not all stocks
can be harvested at best rates
• Fishing may “target” particular
stocks/species, but fishing activity typically
causes catch of other species
• Discarding non-target stocks is typically
wasteful
• “collateral damage” reduces biological
diversity and threatens ecological basis for
sustainability

12. Fraser sockeye salmon have returned
to near historical peak levels, but there
has been a worrisome decline
Total Fraser River sockeye run size, Pacific Salmon Commission estimates
0
10,000,000
20,000,000
30,000,000
40,000,000
50,000,000
1890 1910 1930 1950 1970 1990 2010
Totalrunsize
Total Run
Spawners

13. Productive fisheries often depend on diverse
mixtures of individual spawning stocks, most
obvious with Pacific salmon
0
2,000,000
4,000,000
6,000,000
8,000,000
10,000,000
12,000,000
1952
1956
1960
1964
1968
1972
1976
1980
1984
1988
1992
1996
2000
2004
2008
latemisc
harrison
cultus
portage
weaver
early shuswap
adams
birkenhead
stellako
late stuart
quesnel
chilko
upi
gates
nadina
estuart
seymour
scotch
raft
fennell
bowron
Hilborn showed a similar
pattern of shifting
contributions for major
Bristol Bay stocks
Fraser sockeye abundance by stock

14. There is a severe tradeoff between
harvesting and maintenance of
stock structure (biodiversity)
0
5000000
10000000
15000000
20000000
25000000
0 0.2 0.4 0.6 0.8 1
Overall exploitation rate
Catch,Escapement
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Proportionofstocksoverfishedorextinct
Total Harvest
Total Escapement
Pextinct
Poverfished
Tradeoff between catch and stock "health"
Fraser River sockeye
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2000000 4000000 6000000 8000000 10000000 12000000 14000000 16000000
Average long term catch
Proportionofstocksnotoverfished
At the harvest rate expected to
produce maximum average yield,
about 50% of the (mostly small)
stocks would be overharvested, and
about 10% would be threatened with
extinction. The tradeoff will be even
worse if diverge in productivity
continues
Is it wise or just for people who
will not pay the bill to demand
that fishers give up 50% of their
income as an insurance policy
for biodiversity?