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Fishing. the last major exploitation of wild populations by mankind. © 2008 Paul Billiet ODWS. Factory ship. ACEL. Fish stocks. Though fish farming is increasing, fishing represents the last major exploitation of wild populations by mankind. © 2008 Paul Billiet ODWS.

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fishing

Fishing

the last major exploitation of wild populations by mankind

© 2008 Paul Billiet ODWS

fish stocks

Factory ship

ACEL

Fish stocks
  • Though fish farming is increasing, fishing represents the last major exploitation of wild populations by mankind

© 2008 Paul Billiet ODWS

the peruvian anchovy
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.

© 2008 Paul Billiet ODWS

the peruvian anchovy1
The Peruvian Anchovy
  • 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
The collapse of the anchovy fishery
  • 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
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

© 2008 Paul Billiet ODWS

the result
The result
  • 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 anchovyPacific salmonNewfoundland, Grand Banks codNorth Sea Herring

© 2008 Paul Billiet ODWS

maximum sustainable yield msy

K

3

2

  • Numbers

1

Time

Maximum Sustainable Yield (MSY)

© 2008 Paul Billiet ODWS

maximum sustainable yield msy1
Maximum Sustainable Yield (MSY)
  • 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 quotaswill 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
Problems with MSY
  • Age structure: If all the age groups are harvested recruitment of young fish into the reproductive group will be reducedThe 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
What is required?
  • Nets with bigger mesh size
  • Regulatedfishing 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