Catchability of the Sigsbee Trawl for bivalve molluscs

Background. Bivalve molluscs are an important component of the benthic ecosystems of the Russian shelf seas; however, the assessment of quantitative characteristics of their sublittoral communities presents several challenges. Relevance. The calculated catchability coefficient plays a crucial role in evaluating the biomass and density of the molluscan communities during the stock assessment surveys. The aim of this work is to calculate the catchability coefficient of the Sigsbee trawl for three forms of bivalve molluscs: surface-dwelling, semi-burrowing (inhabiting the upper layers of the substrate), and deeply burrowing organisms. Methods. The calculations have been performed using the data from 291 trawl stations and 331 bottom grab stations (all samples were taken in five replicates), collected during the benthic survey of the Barents Sea in 2003–2008. Results. Based on a comparison of the occurrence of molluscs in the catches from the Van Veen bottom grab (quantitative fishing gear) and the Sigsbee trawl, three trawl catchability coefficients were obtained: 0.97 for surface-dwelling molluscs, 0.84 for semi-burrowing molluscs, and 0.64 for deeply burrowing molluscs. Conclusion. The obtained catchability coefficients can be used to calculate the density and biomass of bivalve communities during surveys conducted with the Sigsbee trawl.