Development of Trap Designs for Rapa Whelk
Project no. 1137 · Status: Kapanmış · 2016
Summary
The sea snail Rapana venosa (Valenciennes 1846) is an Asian oriented gastropod. By 1940’s, its spread to the Black Sea resulted in this predator’s habitat invasion. Excluding extraordinary samples, the species can reach up to 16 cm in length where the commercial size can be down to 3 cm in Turkey. Rapana thomasiana is another species to be encountered in the same habitats. Rapana fishing is mainly done by beam trawls. This method is a conflict of interest for sustainable fishing. The aim of this thesis is to determine alternative rapana trap designs and their criteria, which will have much less effect on the marine ecosystem. In land based studies, trap design and model development processes are covered. In marine, field studies on testing the developed trap models are practiced through free diving and scuba diving, with the help of underwater cameras. Throughout the development of traps for rapana, Closed Tunnel, Rapana Setnet, Transition model to Rapana Catcher and Gap Looped Rapana Catcher (RapCatch) models are developed and prototypes are produced. The models are numerically evaluated within 14 criterias which are categorized in three main groups: ecology, ergonomy and economy. The ratings are 35/56 for Closed Tunnel, 37/56 for Rapana Setnet, 36/56 for Transition model, and 51/56 for RapCatch. During the observational and test studies, having produced a total of about 1500 rapana species samples, RapCatch ended up to be the most innovative and successful design solution. Without any guidance, used by the fishermen, RapCatch trapped 18 rapana, weighting 782 gr per trap, in 48 hour, where 350 gr chicken meat used as bait. Throughout 24 hour long test studies in field, a maximum of 32 rapana were caught in traps. The developed trap solution is 5 times lighter and 2-3 times less costly than the trap designs proposed in literature for rapana fishing purposes. Its high space efficiency enables 50-100 unit traps to be used in traditional small-scale fisherman boats. Comparison of sector results indicated that traps produce less yield per the same fishing time beside the capacity of producing the same total income per year. Compared to dredge fishing investment and operating costs, RapCatch offers an investment ratio of 1/10 and a process cost ratio of 1.56/2.25. Within the evaluations of independent academic sources, considering ecologic, ergonomic and economic capacities of RapCatch, this design proposal may have the potential to meet the definitions of General Fisheries Commission for the Mediterranean (GFCM) regarding alternative fishing techniques for rapana whelk species. Serving for ecologic based management of rapa whelk, the proposed trap design can be used to sustain a regular and efficient fishing income from trap fishing. Keywords:Rapana, Rapana venosa, Rapana thomasiana, rapa whelk trap, RapKap, beam trawl.