By-catch in the commercial beam trawl fishery for Rapa Whelk in the Black Sea

Abstract

In this work, the by-catch was investigated in commercial beam trawls used in the rapa whelk (Rapana venosa) fishery, in trials at sea between September 1, 2015 and April 30, 2016. Four commercial boats using beam trawls were chartered and catch data was collected from a total of 87 hauls. Hauls were performed between 7.1–28.3 meters deep for a duration of 20–77 minutes and haul speed varied between 1.4 – 2.7 knots. A total of 28 by-catch species were identified, which amount in average to 11.4% of the total number of specimens in the by-catch. Two different groups were identified in the by-catch (G1: 7-18 m, G2: 19-26 m) according to depth. Although there is a reduction in the amount of by-catch for G2 group, no significant difference was found between groups (p>0.05). According to Generalized Additive Models (GAM) results, the variables affecting the by-catch amount were identified as fishing area, depth, haul duration, and amount of captured rapa whelk (p<0.01). In addition, a large proportion of immature individuals of striped venus clams (Chamelea gallina), blood cockles (Anadara kagoshimensis), Mediterranean mussels (Mytilus galloprovincialis) and wedge clams (Donax trunculus) were caught as by-catch during the study. Finally, the impact of commercial beam trawls on the demersal macrofauna is discussed.