The catch equation used in virtual population analysis (VPA), and most annual age-structured methods, assumes a constant fishing mortality rate (F) throughout the year even though many, if not most, fisheries are seasonal. Breaking this assumption of a constant F creates a bias in the resulting population-size estimates when the observed catch is used as input in VPA. The bias can be reduced by changing the time step in the analysis to quarters or months, as has been suggested in the past, but this change is not always easy or practical. This paper presents an alternative method for reducing the bias: correction of the catch values to meet the assumption of a constant fishing mortality rate. A simple algorithm is presented that gives the number of fish that would have been caught from a given population if the observed fishing mortality rate had been spread evenly throughout the year. An iterative process improves the required guess for the population size such that the bias is eliminated.
|Original language||English (US)|
|Number of pages||13|
|State||Published - Apr 1997|
ASJC Scopus subject areas
- Aquatic Science