Fisheries science II: the biology and mathematics of fished stocks Flashcards
What is the definition of a stock?
a population of fish, usually confined to an area that is effectively reproductively isolated from other populations (stocks) of the same species
stock=population
What are the three reasons for lessoned surplus production at higher stock densities?
- Near maximum stock density, there is less food per individual, so less is spare for growth
- There are more old fish than in a fished stock, so:
A) larger fish eat larger food, therefore there may be one more trophic step - reduction in trophic efficiency
B) older fish divert more food into gametes and less into new flesh than young fish - somatic growth diverted to gonads
3. Near maximum stock density, reproduction is less efficient, so the number of recruits falls - reproductive inefficiency
What is the logistic curve of population growth?
if a stock equilibrium (at any biomass) is released from fishing it will start growing according to the LCPG
What is the objective of stock-recruitment curves?
To calculate equilibrium yield
a stock-recruitment curve is the relation betweeen mature recruits and the spawners that produced them
The increment or harvestable surplus can be harvested without affecting the reproductive capacity of the stock
What are the limitations of the stock-recruitment curves?
- fish stocks don’t really obey mathematical laws
- assumes the environment is stable
- species interrelations not considered
- needs a large amount of data
- fishing mortality introduces its own systematic biases
