Fishing
the last major exploitation of
wild populations by mankind
© 2008 Paul Billiet ODWS
Fish stocks
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Though fish farming is increasing, fishing
represents the last major exploitation of wild
populations by mankind
Factory ship
© 2008 Paul Billiet ODWS
ACEL
A case study: The Peruvian Anchovy
(Engraulis ringens)
Universidad de La Serena
© 2008 Paul Billiet ODWS
The Peruvian Anchovy
This is a small (12-20cm), short-lived
species maturing in 1 year
 Anchovy live in the surface waters in large
shoals off the coast of Peru and northern
Chile
 Here there are cold currents up-welling
from the sea bed bringing nutrients for
phytoplankton
 Plankton is at the base of the food chain.
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© 2008 Paul Billiet ODWS
The Peruvian Anchovy
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The harvest of this fish doubled every year from
1955 to 1961
Experts estimated the maximum harvestable
yield (MSY) at 10 to 11 million tonnes per year
Through the 1960s the harvest was about this
level
The biggest fishing harvest in the world
Some of the anchovy were used for human food
But a lot was ground into fishmeal for animal
feed
© 2008 Paul Billiet ODWS
The collapse of the anchovy fishery
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In 1972 there was an El Niño event that brought warm
tropical water into the area
The up-welling stopped,
the phytoplankton growth decreased
the anchovy numbers fell and concentrated further south
The concentrated shoals of anchovy were easy targets for
fishing boat eager to recuperate their harvest
The political will was not there to impose reduced quotas
Larger catches were made
No young fish were entering the population (no
recruitment)
No reproduction was taking place
The fish stocks collapsed and did not recover
© 2008 Paul Billiet ODWS
What is causing the damage to
fisheries worldwide?
Uncontrolled harvesting – even if quotas
are imposed they need to be policed
 Unrealistic and inflexible quotas
 Insufficient data on fish populations
 Improved technology in the fishing
industry
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© 2008 Paul Billiet ODWS
The result
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Fish populations are reduced below their recovery
level
Other non-commercial species are being taken
and killed at the same time
Other species (e.g. sea birds) are being deprived
of a food resource
Total ban on some species now imposed:
Peruvian anchovy
Pacific salmon
Newfoundland, Grand Banks cod
North Sea Herring
© 2008 Paul Billiet ODWS
Maximum Sustainable Yield (MSY)
K
3
2
Numbers
1
© 2008 Paul Billiet ODWS
Time
Maximum Sustainable Yield (MSY)
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Based upon:
1. the harvest rate
2. the recruitment rate of new (young) fish into
the population
a population can be harvested at the point in
their population growth rate where it is highest
(the exponential phase)
Harvesting (output) balances recruitment (input)
Fixed fishing quotas will produce a constant
harvesting rate (i.e. a constant number of
individuals fished in a given period of time)
© 2008 Paul Billiet ODWS
Problems with MSY
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Age structure: If all the age groups are harvested
recruitment of young fish into the reproductive group will
be reduced
The answer is to use a net with a big enough mesh size
that lets the young fish escape
Limiting factors: If the limiting factors in the environment
change so does the population growth rate
Limiting factors set the carrying capacity (K) of an
environment
Increasing limiting factors will cause K to drop
Fixed quotas cannot cope with this
Data: For MSY to work accurate data in fish populations is
needed (population size, age structure, recruitment rates)
Usually these are not well known
© 2008 Paul Billiet ODWS
What is required?
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Nets with bigger mesh size
Regulated fishing methods
More data on fish populations (e.g. by fish
tagging investigations – mark and recapture)
Constant monitoring to observe changes in
environmental factors (e.g.El Niño events
Policing of fishing industry – respect of quotas
International agreements
Greater exploitation of fish farming
But this is not without its own problems (space,
diseases and pollution are all associated with
intensive fish culture)
© 2008 Paul Billiet ODWS