Abstract
This study aimed to test the effectiveness of a “guarding net”, a device placed at the bottom of a trammel net, for reducing unwanted catches in the caramote prawn trammel net fishery of the Ligurian Sea. This specialized and profitable fishery is affected by unwanted catches that generate high discard rates and damage to the nets, with environmental impacts and costs for fishermen. The experimental study consisted in comparing the catches of a standard trammel net (STN) with those of two “experimental” trammel nets, e.g. STNs provided with a guarding net of 19 cm (TGN20) and 24 cm height (TGN25), respectively. The guarding net, a strip of gillnet placed at the bottom of the net, can be considered a by-catch reducer device (BRD). Some fishermen of the investigated fishery have been using this device for several years. The results of the 15 experimental fishing trials performed from June to July 2016 indicate that the guarding nets significantly reduce discards (e.g. crabs and other invertebrates); the biomass of the unwanted species caught was 75% lower than that produced by the STN. The catch rates of the target species obtained with TGN20 and TGN25 were also significantly lower than those of the STN, though of a lesser amount. Nonetheless, this economic loss can be compensated by the decrease in sorting time and material and labour costs that can be achieved using the guarding net.
Highlights
Discarding is a consequence of fishing activities that consists in bringing marine fauna on board fishing vessels and subsequently returning it to the sea; it may constitute a large amount of the total catch (Alverson et al 1994, Hall 1999, Kelleher 2005)
20 small-scale vessels of Viareggio were involved in the caramote prawn fishery
The usual fishing period ranges from April to July, fishermen stated that the beginning and the end of the fishing season can vary every year according to the availability of the target species
Summary
Discarding is a consequence of fishing activities that consists in bringing marine fauna on board fishing vessels and subsequently returning it to the sea; it may constitute a large amount of the total catch (Alverson et al 1994, Hall 1999, Kelleher 2005). The reasons for discarding are numerous and involve legal aspects (e.g. catches under the minimum landing size or exceeding quotas), economic (low market value, high grading), technical aspects (e.g. type of gear, vessel capacity), and environmental aspects (e.g. weather conditions affecting sorting practices) (Stratoudakis et al 1998, Vassilopoulou et al 2012, Bellido et al 2014). The otter trawl is undoubtedly the gear responsible for most discards (Kelleher 2005). In the Mediterranean, the available studies report a discarded fraction for trawling ranging from 20% to 40% of the total biomass caught (Machias et al 2001, Sánchez et al 2004, Tsagarakis et al 2008, among others)
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