Fisheries Impacts on North Atlantic Ecosystems: Catch, Effort and National/Regional Data Sets
Estimating Discards from Catch Species Compositions
Paul Medley
Sunny View, Main Street, AlneAbstract
This contribution presents a procedure for estimating discards based on the log-normal abundance model using observed catch data. The method is programmed as a Dynamic Link Library (DLL) in Borland Delphi (a version of Pascal). The DLL procedures can be accessed from a variety of programs. Accessing the DLL from VBA in MS Excel is only dealt with here. The method was tested on simulated data drawn from a log-normal probability distribution. The method was also tested on one year’s Canadian observer data. These data consisted of 52 categories of which 21 were landings. The categories were empirically found to be approximately log-normally distributed, a necessary pre-requisite. In general, the approach works as long as the underlying distribution of catches is log-normal, the number of categories (species, genera, etc.) are known and there are an adequate number of observations. However, the accuracy of the method when applied to real data, including its bias, is untested as yet.