Comparing Different Information Sources in a Multispecies Context

Comparing Different Information Sources in a Multispecies Context

G. Stefánsson

Comparing Different Information Sources in a Multispecies ContextThis is part of Fishery Stock Assessment Models
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Different data sources tend to give apparently incompatible information on the state of an ecosystem. Various likelihood functions can be used to incorporate many data sources in a stock estimate. Such likelihoods should be viewed as components in an overall likelihood function. This paper compares the estimates of stock trends and values of likelihood components as a function of what data source is used as the primary criterion in a stock estimation procedure. A multispecies model, Bormicon, is used as the vehicle for these comparisons, based on indications on stock size, growth, migration, and consumption from a variety of different data sources. The model accommodates data from acoustic surveys, groundfish surveys, mean length at age in catches and surveys, and stomach content data. This is an area based, multispecies, multifleet model which includes growth, consumption, and migration in addition to the effects of fishing. It is seen that different data sources may give considerably different views of the world in this complex modeling scenario, but in fact this is also the case even in the simplest of fisheries models. Most of the differences are seen to stem from model errors, where common fisheries models exclude certain important factors which are needed when considering many data sources.

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