Fishing the last major exploitation of wild populations by mankind © 2008 Paul Billiet ODWSODWS

Fishing

the last major exploitation of wild populations by mankind

© 2008 Paul Billiet ODWS

Fish stocks Though fish farming is increasing, fishing

represents the last major exploitation of wild populations by mankind

ACEL

Factory ship


A case study: The Peruvian Anchovy (Engraulis ringens)


Universidad de La Serena

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.


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


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


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


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


Maximum Sustainable Yield (MSY)

K

Numbers

Time

1

23


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 quotas will produce a constant

harvesting rate (i.e. a constant number of individuals fished in a given period of time)


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


What is required? 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)


Documents

Fishing the last major exploitation of wild populations by mankind © 2008 Paul Billiet ODWSODWS