AN EXTENDED COHORT ANALYSIS - INCORPORATING THE EFFECT OF SEASONAL CATCHES

A virtual population analysis relates changes in numbers at age of fis h to commercial catch, fishing mortality, and natural mortality. We re formulate the standard virtual population analysis and corresponding c atch equation in a manner that incorporates any seasonal pattern of ca tches, which may represent continuous fisheries or pulse fisheries. An advantage of this treatment is that it leads to a virtual population analysis formulated as cohort analysis, with e(M/2) replaced with a fa ctor representing (and easily calculable from) the particular seasonal pattern of catches. The method presented here circumvents the standar d assumption (leading to the Baranov catch equation) that fishing mort ality is constant throughout the year.