Lectures 13-14 Fisheries Flashcards
what are the Core principles of fisheries science
A stock of known size
Recruitment is density-dependent, competition is strong
Allee effects are weak
What do you need to asses in a fishery
size of the stock, its natural mortality and density
dependence
What are the steps in the best case for fisheries management?
- Assess the size of the stock, its natural mortality and density dependence
- Determine the sustainable yield
- Set the total allowable catch
- Monitor the catch
What does the Biological reference point B mean?
B = Sustainable Biomass
What does B < B threshold mean?
The stock is overfished
What does F < F threshold mean
Overfishing is not occuring
What does the Biological reference point F mean?
F = Fishing mortality
What does Fmsy mean?
fishing mortality rate at the level that would produce maximum sustainable yield from a stock that has a size of Bmsy
What does Bmsy mean?
stock size that can produce maximum sustainable yield when it is finished at a level equal to Fmsy
What does B threshold mean?
stock size threhold, the threhold below which a stock is overfished
What does F threshold mean?
fishing mortality threhold, the fishing mortality rate that causes a stock to fall below its stock size threshold
What does F max mean?
Fishing mortality rate that achieves maximum yield per recuit
What does F% mean?
Fishing mortality rate that reduces the spawning stock per recuit to a given percentage of the maximum spawning potential in the absence of fishing
What is Steepness?
an estimate of density dependence
What does a Steepness = 1 mean?
if there is some fraction of the stock left, recruitment is 100% equivalent to a virgin stock
What does a steepness value >0.3 <1?
Density dependence but imperfect compensation. 0.3 would imply no density dependence
What can you calculate if you know?
- Stock spawner biomass
- Growth • Natural mortality
- Fishing mortality
- Fishing selectivity
- Steepness
- Stock recruitment relationship
YOU CAN CALCULATE MAXIMUM SUSTAINABLE YIELD
What can you calculate if you know?
- Growth
- Natural mortality
- Fishing mortality
YOU CAN CALCULATE YIELD PER RECRUIT
What can you calculate if you know?
- Stock spawner biomass
- Growth
- Natural mortality
- Fishing mortality
- Fishing selectivity
YOU CAN CALCULATE SPAWNING POTENTIAL RATIO
What are the different Biological reference points?
Maximum sustainable yield (MSY)
Spawning potential ratio (SPR)
Yield per recruit (YPR)
Reasons for fishery decline?
- Excess landings
- Illegal fishing
- Bycatch and Discards
- Political overreach
- Incorrect models???
