FISHERIES

Question 1

What is the equation for change in biomass of fish populations?

Answer 1

Population next year = population this year + (births +growth-deaths) in fishing this is split into natural deaths and fishing deaths.

Question 2

what are the parameters that effect the biomass of a population?

Answer 2

1) Recruitment and reproduction.
- age at first maturity
2) growth
3) mortality

Question 3

What is the stock-recruitment relationship?

Answer 3

the relationship between parental stock size and the following recruitment.

Question 4

Explain recruitment?

Answer 4

survival requires 1:1 replacement in the long term so there is a relationship between population size and recruitment. However, spawning population structure and survival vary.

Question 5

what are different models for sustainable fisheries?

Answer 5

• estimating fishery yields (surplus production)
• delay-difference models (can account for recruitment, growth and natural mortality.)
• age-structured analysis
• yield per recruit models

Question 6

What is Graham’s theory of sustainable fishing?

Answer 6

The fishery is sustainable if removals can be replaced by stock production each year. Population growth is maintained when the stock size is half its carrying capacity. The maximum sustainable yield is at the point of the ‘golden middle’. A high stock size is limited by carrying capacity, a low stock size is limited by growth and reproduction.