population dynamics Flashcards
define over fishing
fishing above the maximum sustainable yield
define maximum sustainable yield
the greatest amount of fish which can sustainable be harvested without causing population decline
outline breeding rates of an unexploited population
1) adult fish breed producing eggs
2) eggs hatch to produce young fish
3) if population exceeds carrying capacity then intra-specific competition occurs and the surplus will die due to lack of resources so pop maintains the same
4) young fish which survive are recruited into the adult population
outline the breeding rates of sustainable fished fish populations
1) adult mortality rate increases
2) fewer eggs are produced
3) eggs produce juvenile fish
4) more young fish recruited to adults as less intra specific competition
5) therefore pop maintains
outline breeding rates of over exploited fish populations
1) adult mortality increases
2) fewer eggs produced
3) fewer survival young fish
4) al surviving young recruited to adult pop but not enough to replace adults loss from fishing
5) pop declines
provide some examples of fish which have been exploited above MSY
1) orange roughy = k select species in New Zealand and Australia which live to ge 150 but dont breed till 30
2) Atlantic cod = reach catchable size at 2 years but dont breed until 4
why is it hard to collect data on fish populations
1) populations are often mobile and move long distances
2) distributions of fish populations is uneven
3) collecting enough data to be representative of a large area occupied is impractical
how can data be collected about fish populations
1) catch size
2) catch per unit fishing effort
3) mean fish size
4) mean age
how can catch size be used to determine fish populations
total landed catch each year can be measured to see the total weight of biomass or number of fish exploited from a species
however
as technology increases such as bigger boats and nets more fish can be caught at once so it appears as if populations are remaining the same
how can catch per unit fishing effort be used to analyse fish populations
if it becomes harder to maintain the catch size then it is a good indicator fish populations are being overfished
how can mean fish size be used to analyse fish populations
catch biomass can be maintained by increasing the number of small fish caught however by by analysing if smaller fish caught increases it indicates only juvenile or young fish are out there so over fishing is occurring
outline how mean age of a fish can be used to analyse fish populations
the age of a fish can be determined by looking at growth rings on the scales
if mean age declines then overfishing is occurring
