Effects of Turtle Excluder Devices on bycatch and discard reduction in the demersal fisheries of Mediterranean Sea

Abstract

-The Central Mediterranean provides important neritic habitats for loggerhead turtles (Caretta caretta), but Mediterranean bottom trawlers catch an estimated 30 000 turtles a year, with 25% mortality. Mortality by trawling is mainly due to enforced apnoea during towing activity. In order to reduce the submergence time and consequent turtle mortality, a specific technical modification was developed in the early 1980s: the Turtle Excluder Device (TED). In this paper, we field-tested a typical Supershooter TED and three new types of low-cost TED, built with different designs and materials, incorporating aspects of US and Australian TEDs, as well as design features to improve handling and catch rates. The performance of the TEDs was investigated under commercial fishing conditions in diverse trawling grounds in the Adriatic Sea (Mediterranean). All TEDs were easy to operate and did not require changes to normal fishing operations. Due to lack of entry of turtles it was not possible to evaluate the ability of the different TEDs to release turtles, but one large loggerhead turtle (C. caretta) was captured during the experimental tows and was successfully excluded by the Supershooter. The TEDs reduced anthropogenic debris and, consequently, sorting operations on board. Among the four TEDs tested, both the semi-rigid TED and the Supershooter performed in accordance with the design objectives: total discards were reduced but total commercial catches were not significantly reduced. With the Supershooter, all European hake (Merluccius merluccius) individuals equal to or above 16 cm were found in the codend and 10-15% of those between 5.0 and 15.5 cm were released. In general, the total discard rate of the TED-equipped nets was reduced to around 20-60%. Since the Council Regulation (EC) No. 1967/2006 called for a discard reduction policy in waters under the jurisdiction of the European Union, TEDs may have some broader value in this context.

Bottom trawl catch comparison in the Mediterranean Sea: Flexible Turtle Excluder Device (TED)vstraditional gear

“…Nevertheless, [18] were skeptical about the TED efficency in the Mediterranean waters because they would exclude the larger commercial individuals too. On the other hand, recent experiments held in the Mediterranean sea [21,22] did not show any loss in term of the commercial catch. During those scientific trawl surveys they obtained as a result that the main commercial species did not show any decrease in terms of weight and number of individuals respect to a net without the grid.…”

Towards the Introduction of Sustainable Fishery Products: The Bid of a Major Italian Retailer

“…In this multi-species fishery, even though all target species are subject to the same fishing effort, the less abundant and more vulnerable species may take a long time to recover from intense trawling activity. In addition, it has recently been documented that multi-species bottom trawl fisheries are characterized by high discard rates of undersized commercial species (i.e., juveniles, [39][40][41]) and accidental catches of non-target species with low or no market value, such as sharks, sea turtles, and marine mammals [42]. Thus, marine organisms at risk of decline may be caught together with species whose populations can withstand their fishing effort.…”

Fisheries Bycatch of Chondrichthyes

“…Threatened species like chondrichthyes would significantly benefit from conservation and management measures implemented synergistically at international and national levels [66,67]. Historically, international efforts devoted to the conservation and management of sharks have been poorly pursued [60,68].…”

“…Historically, international efforts devoted to the conservation and management of sharks have been poorly pursued [60,68]. During the last decades, several attempts have been made at national or local levels in response to specific conservation objectives for certain species and habitats [66][67][68]. However, the co-operation among national authorities to encourage regional and global measures has been generally inadequate and/or inefficient.…”

“…It is difficult to expect that there is going to be any further increase in mesh size in Mediterranean in near future, which is why some authors advocate using various excluder grid devices, e.g. Turtle Excluder Device (TED) [60,66,67,126,127]. So far, only one study examined the effect of inserting an excluder grid device in front of the size selective codend with the aim to reduce shark bycatch in the Western Mediterranean bottom trawl fishery [60].…”