Fishery impact has traditionally been evaluated using yield-perrecruit
(YPR) analysis (Baranov, 1914). YPR is estimated for different
fishing mortality rates and different ages at entry to the fishery
(Thompson and Bell, 1934; Beverton and Holt, 1957; Anon., 2000).
Isopleth plots are developed to provide a visual representation of
the influence of fishing mortality and age at entry on YPR. YPR
analysis, which represents the tradeoff between growth and natural
mortality, can be used to identify whether fish have been
caught before their full growth potential (i.e. while their growth
rate is still higher than natural mortality) such that growth overfishing
is occurring. Management can use the isopleth plots to help
determine the appropriate minimum legal size and fishing effort.