Fisheries Management

• Lecture Outline

– Maximum Sustained Yield

– Density independent and dependent growth models

– Carrying capacity

– Optimum Sustained Yield

• Assignments

– Read pp. 157 - 220 and 303 - 333 in Fisheries Techniques

Fisheries Management (1930 – 1970)

Maximum Sustainable Yield

1) Maximum Sustainable Yield (MSY)– Management of a fish stock that allows the maximum yearly harvest that can be sustained through time.

2) Assumes that abundance is related to growth, recruitment, and immigration and losses via natural mortality, fishing mortality, and emigration (Russell 1942)

Example

1) Peruvian anchovy (Engraulis ringens)

2) Maximum sustained yield estimated at 10 – 11 million tons

Problem

1) Maximum fish yield for walleye occurs at exactly 500 individuals.

2) What would the population growth rate (dN/dt) be if an additional 600 walleye were stocked?

3) Assume r = 0.005 individuals/day

Problems with Maximum Sustained Yield

1) Economic - May not be consistent with maximizing economic yield

2) Sociological - Does not account for aesthetic value of a fishery

3) Ecological - Only considers a single species

Optimum Sustainable Yield (OSY)

1) A unique management goal exists for each fishery

2) Considers a broad range of considerations (Economic, Sociological, and Ecological)