Addressing catch mechanisms in gillnets improves modeling of selectivity and assessment of an endangered stock of Arctic charr
(English)Manuscript (preprint) (Other academic)
Estimation of fish stock size distributions from survey data requires knowledge about gear selectivity. However, selectivity models rest on assumptions that seldom are analysed. Departures from these can lead to misinterpretations and biased management recommendations. Here, we use data on great Arctic charr (Salvelinus umbla) to analyse how these assumptions affect estimated selectivity curves, estimate the size frequency distribution of the stock, and estimate mortality in different years.
Initial selectivity curves, using the entire data, were wide and asymmetric, with poor model fits. Removing data for non-meshed fish and taking non-isometric growth into account, resulted in narrower and less asymmetric selection curves, with good model fits. Estimated relative abundance of charr across all sizes increased from 2006 to 2010 while estimated mortality rates indicate a decrease in mortality for medium-aged, but not for older fish. Likely causes for these changes are stronger fishery regulations implemented in 2007. Our study demonstrates an approach that increases the accuracy of estimates of fish size-distributions from survey data and leads to a better understanding of the dynamics of an endangered fish stock.
IdentifiersURN: urn:nbn:se:liu:diva-77679OAI: oai:DiVA.org:liu-77679DiVA: diva2:528411