Grand Bank

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Grand Bank

• Physical Characteristics
• Atlantic Cod (Gadus morhua)
• Capelin (Mallotus villosus)
• Cod fishery collapse

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Hypothetical marine fish

• Hypothetical population with an annual survival
  rate of 50 and initial reproduction at age 3.
  This population produces an average of 166 eggs
  per recruit.
• eggs spawned fish age mature proportion
  average fecundity at that age
• eggs per recruit total eggs spawned /
  initial population size

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Maturity schedule and average fecundity at length
for a hypothetical population
Proportion mature
Fecundity
Fecundity
Proportion maturing
Age (years)
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Hypothetical marine fish species50 survival
per year after recruitment
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• If fishing reduced survival to 25 per year, the
  average would drop to 29 eggs per recruit only
  17.5 of the unexploited populations production.

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Grand Bank ocean temperature As cold as a cods
nose
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Atlantic Cod (Gadus morhua)

• Gadid
• 20 year life span
• offshore and inshore stocks
• Migrate inshore to feed on capelin
• Enter the fishery at age 3-5, depending on
  latitude

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Atlantic Cod

• Distribution and Population Structure
• Distribution Cape Hatteras, N.C. to Baffin
  Island and Greenland in NW Atlantic. Many
  stocks, with distinct feeding and spawning areas.
  Northern cod are viewed as a complex or a
  collection of related stocks.

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Atlantic Cod

• General Migratory pattern
• Winter - offshore near shelf break (200-600 m,
  4-6 C).
• Summer - Inshore, widely dispersed, following
  capelin.
• Inshore/offshore migration avoids lethally cold
  winter temps
• (-1.0 to -1.5 C). However, some cod stay
  inshore all winter, and they secrete antifreeze
  protein in blood.

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Atlantic Cod Winter distribution Post-spawning
feeding migration
540
500
460
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Atlantic Cod

• Reproduction
• Mature about age 6 for females (45-60 cm)
• Males mature younger
• Northern cod spawn late winter/early spring.
  Other populations spawn at other times.
• Spawn mid-water, closer to bottom than surface
• Fecundity
• 2 million for 80 cm cod, 11 million for 130 cm.
• Eggs buoyant, 1-2 mm
• Hatch at 5 mm, larval cod settle to bottom at 4
  cm.

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Atlantic Cod

• Growth and Feeding
• Young eat copepods, amphipods, and crustacean
  zooplankton.
• Juveniles eat shrimp, amphipods, euphausids,
  fish, and shellfish larvae.
• Adults eat mainly fish,
• including about 90 capelin when they come
  onshore in summer.

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Capelin (Mallotus villosus)
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Average annual consumption of capelin
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Spawning migration of capelin stocks
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Onshore migration of capelin
0 600 1200 1800 2400
3000
Weekly capelin landings (MT)
Tidal Amplitude 0 0.5 1.0 1.5 2.0 2.5
5/31 6/28 7/26 8/23
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Onshore winds inhibit cod and facilitate release
of larval capelin
Onshore Wind
Too warm for cod
Offshore Wind
Too warm for cod
Cod prefer 0.5 to 8.5 C wind-driven waves wash
larval capelin off the beaches
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History of Cod Fisheries

• Fisheries Transitions
• Handlines
• Traps
• Beam trawl
• Otter trawl
• Mechanized trawling
• Offshore trawling
• 1970s foreign fleet
• 200 mile limit

• Basques (?)
• John Cabot 1497
• 1550 128 vessels
• Late 1600s 100,000 t/year
• Late 1700s 200,000 t/year
• Late 1800s
• 150-400,000

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Cod Fisheries

• Handlines

Cod Trap 1780
1840
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Cod trap resembling those used in late 1700s.
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Cod Fisheries
Otter Trawl 1905
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Sustainable Catches of Cod
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Foreign and Offshore trawling
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Northern Cod catch at age
Year
Age
2-5
6-10
11-15
16-20
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Elimination of older age classes
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Northern Cod Biomass (x 1000 t)
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Collapse of the cod stocks

• In 1992 a complete moratorium was put in place,
  halting commercial and subsistence fishing for
  cod over much of their northern range. This
  caused tremendous hardship for the fishermen and
  associated communities, and the populations have
  not fully recovered. At present only very
  limited fishing is permitted.

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Speaking for the FishBrian Tobin, Minister of
Fisheries and Oceans, Canada

• Approximately 40,000 fishermen and plant workers
  who depend on Atlantic groundfish stocks for
  their livelihood are left without work, and
  hundreds of coastal communities are devastated
  economically.
• Thousands of Canadians are seeing their way of
  life disappear. Many live in communities in
  houses built within 50 yards of saltwater. There
  are no trees, no minerals, no tourism, no
  manufacturing base, no information or
  knowledge-bases industry. There is ready access
  to a resource, but the resource is gone.
• So when we speak for the fish and we must speak
  loudly in every forum we are also speaking for
  the people of this and future generations.
• Fisheries 20(7)18-19. 1995

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Northern Cod Collapse was it really overfishing?

• Biological Explanations seem unlikely
• Temperature Recruitment
• Decline in prey (capelin) abundance

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Why didnt fisheries managers prevent the
northern cod collapse?

• Size and age structure declined
• Fisheries surveys CPUE Declined
• Catch per unit of effort
• Fisherman reported high catch rates
• Over-capitalized fleet supported by unemployment
  compensation to achieve social goals
• Political pressure to keep fishing

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Marine Resources and NewfoundlandWilfred
Tempelmen 1966

• In the winter and early spring the inshore
  waters of the adjacent Newfoundland Area and
  those of the banks, are so cold that groundfish,
  chiefly cod, must retreat offshore and to deeper
  water. Also at this time they gather in
  prespawning and spawning concentrations.
• These dense schools are thus concentrated in the
  restricted areas of warmer water on the deeper
  slopes of the bank and shelf areas, where they
  are readily caught by trawlers. It is thus
  likely, as apparently occurred with the southern
  Grand Bank haddock, that as these schools decline
  under the effects of heavy fishing the spawning
  groups and the immature of commercial size of a
  particular stock will continue to concentrate.
• This concentration may thus form a school in a
  smaller and smaller area, and the school will be
  vulnerable to heavy fishing when it is found. In
  this case there would be good deep water trawling
  in winter and spring until the stock has been
  greatly reduced.

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Changing community composition and trophic cascade
Relative changes in abundance (not to scale) of
trophic levels in the Newfoundland-Labrador area.
Cod Capelin Zoopl Phytopl
Carscadden et al. 2001 CJFAS 58 73-85
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Mean number of capelin per tow during summer
research vessel surveys.
1000 100 10 1
Number per tow
1970 1975 1980 1985 1990 1995 2000
Year
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Community interactions cod declined but other
species also changed in abundance
harp seals
Halibut population
0 2 4
6
Cod biomass or seal abundance
halibut
100 200 300 400 500 600
cod
1960 1970 1980
1990
Year
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Harp seals, traditionally hunted for fur, are now
very abundant
2003 2005 Canadian sealers were allowed to
take 975,000 seals
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Age Structure of Cod
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Reconstructed population estimates of cod
recruitment (to age 1) with and without the
effects of grey seal predation.
with seal predation
Recruitment (millions)
0 50 100 150 200
Without seal predation
1970 1975 1980 1885 1990 1995
Year
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Vertically integrated temperature (0-176 m)
anomalies.
1 0.5 0 -0.5 -1
Mean and 5-yr running average
Temperature anomaly
1950 1958 1966 1974 1982
1990 1998
Year
Drinkwater et al. 1999