population dynamics and monitoring fish populations Flashcards
what kind of resource are fish?
renewable
they naturally replace themselves by breeding to replace the adults that have died
what do all species have because of evolution?
a natural breeding rate
that exceeds the rate necessary to sustain the population
the natural breeding rate exceeds the necessary to sustain the population. why will a breeding surplus not increase the long term adult population?
surplus individulas will die because the carrying capacity of the environment has been exceeded
what will increase in a population where the carrying capacity of an environment has been exceeded?
density dependent factors which will increase mortality rate
e.g. intraspecific competition for food
how is a fish population maintained?
if adult mortality rate increases, more juvenile fish will survive
more will be recruited to the adult population because food is available & intraspecific competition will be reduced
what may increase the adult fish mortality rate?
fishing
explain how a reduced adult population can result in population decline
if an excessive number are caught, number of adults declines because there isnt enough young to replace them
less adults, less young produced
this further reduces the ability of a population to recover
how does catching fish, not reduce the total population?
as long as the catch doesnt exceed the populations ability to replace the losses
why might overfishing not be obvious?
the total catch weight may be maintained by catching a larger number of smaller fish
why is overfishing dangerous?
the fishing may continue if it is not obvious
this can result in total population collapse because the breeding population is exploited so very few young are produced
what happens if a fish reaches catchable size after it has started breeding?
means there will always be a breeding population
overfishing however may remove all the large fish
what happens if a fish reaches a catchable size before it is large enough to breed?
it is possible to catch all the breeding adults and destroy an entire population
MSY
Maximum sustainable yield
what is the MSY for a fish population?
the greatest biomass that can be removed from the population each year without the population suffering long term decline
what could cause a fish population to exceed the MSY?
overfishing
