Effect of Fishery Closure on Discard Composition of Rapa Whelk, Rapana venosa (Valenciennes 1846) Beam Trawl Fisheries in Black Sea

Abstract

Rapa whelk has become significant commercially, as there is a market that makes it export-oriented species. It has also gained special importance because of catching this species in all riparian countries in the Black Sea basin. The various exploitation methods of this species include beam trawl and diving. Here, the experimental beam trawl survey for Rapa whelk fishing was designed monthly in one year. Catch composition was examined spatially and temporally. Differences in estimated biomass of Rapa whelk and abundance of discard species were used to evaluate the effectiveness of seasonal fishing closure. Our results indicated that, discard composition of Rapa whelk fishery strongly reflected seasonal changes. Total estimated abundance and biomass values showed significant regional, seasonal and depth-related differences, also number of species and diversity index changes regionally and seasonally. Discard ratio was found very low in biomass. At the same time, seasonal fishery closure period was benefited for discard species in spring and summer period. The lowest distribution of Rapa whelk and discard species except blood cockle were found in winter season during fishing period. It becomes apparent that seasonal fishery closure is an important management measure both for stock sustainability, species diversity, and ecosystem health. Therefore, all Black Sea countries should consider similar management.