Improved interspecific selectivity of nylon shrimp (Heterocarpus reedi) trawling in Chile

Abstract

ABSTRACT. In order to improve the inter-specific selectivity of a new bottom trawl design for demersal crustaceans, an experimental attempt was carried out to compare the shrinkage effect in length of net structure accessories, particularly shorter bridles and sweeps, based on previous studies on escape behavior of gadiform fishes. For this purposes, an experimental fishing for nylon shrimp (Heterocarpus reedi) was carried out on board of two trawler vessels. The results showed no significant differences in catch per unit of fishing effort (CPUE) for the target species between gears and significant reductions (p < 0.05) for the most important bycatch species (Merluccius gayi) with the modified gear. In fact, the average CPUE for M. gayi decreased 5.6 kg h -1 (19.2%) and 35.7 kg h -1 (47.5%) for each vessel.Keywords: by-catch, interspecific selectivity, trawl, nylon shrimp, Heterocarpus reedi, Chile.Mejoramiento de la selectividad interespecífica en arrastre de camarón nailon (Heterocarpus reedi) en Chile RESUMEN. Con la finalidad de mejorar la selectividad interespecífica de un nuevo diseño de red de arrastre de fondo de crustáceos demersales, se efectuó una experiencia destinada a probar el efecto del acortamiento de la longitud de las estructuras anexas de la red, específicamente estándares y malletas, basado en investigaciones similares respecto del comportamiento de escape de peces gadiformes. Para ello, se realizó una pesca experimental de camarón nailon (Heterocarpus reedi) con dos embarcaciones arrastreras. Los resultados mostraron que el arte de arrastre modificado, respecto del tradicional, presentó rendimientos de pesca (CPUE) sin diferencias significativas para el recurso objetivo y disminuciones significativas (valor p < 0,05) en la principal especie de fauna acompañante, Merluccius gayi, cuyos rendimientos de pesca promedio disminuyeron 5,6 kg h -1 (19,2%) y 35,7 kg h -1 (47,5%) en cada nave.Palabras clave: fauna acompañante, selectividad interespecífica, arrastre, camarón nailon, Heterocarpus reedi, Chile. ________________________Corresponding author: Dante Queirolo (dante.queirolo@ucv.cl)

Behaviour of fish by‐catch in the mouth of a crustacean trawl

“…In order to reduce the by‐catch of M. g. gayi , Queirolo et al (2009) reduced the path of the trawl by using shorter sweeps and bridles which reduces the spread of the doors, and therefore the herding capacity. This modification also reduces the distance between the net mouth and the doors, allowing for some fishes to escape by the area preceding the doors (Wardle, 1993), especially at low trawl speeds like in these fisheries.…”

Species composition and bycatches of a new crustacean trawl in Chile

“…Diverse alternatives to reduce bycatch can be tested. In the front section of the trawl, the reduction of the catch of M. gayi was possible by shortening the bridles and sweeps, whereas others species no evidence differences (Queirolo et al, 2009b). Then, alternatives in the rear section of the trawl should be tested, such as square mesh codends and reduction devices (i.e., square mesh panels and sorting grids).…”

Alternative codends to reduce bycatch in Chilean crustacean trawl fisheries

“…Different mesh sizes, shapes and escape devices for the codend were selected, taking the target species into account. Three commercial trawl vessels were involved (300-320 kW), each using 1-m sweeps and 5-m bridles, according to the results obtained by Queirolo et al (2009). The hauls were made between 06:30 and 20:00 at depths between 110 and 430 m, with a towing duration of between 15 and 70 min, depending on the experiment and the target species (Table 1).…”

“…Construction deficiencies, such as thick twines, heavy materials and small meshes (50 mm knot-centre to knot-centre), result in the poor functional and selective performance of traditional trawl nets (Melo et al, 2008). For these reasons, a new design, mandated by the fisheries authorities, is under evaluation (Queirolo et al, 2009).…”

“…It is possible to identify three groups of technological improvements that contribute towards reducing the bycatch of crustacean trawl fisheries: (i) modifying structures and components of the trawl nets, such as bridles and footropes, among others (Hannah and Jones, 2000;Queirolo et al, 2009), (ii) changing the size and shape of meshes (Campos et al, 2003;Guijarro and Massutí, 2006;Krag et al, 2008;Sala and Lucchetti, 2010), and (iii) 0165-7836/$ -see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fishres.2011.03.005 Table 1 Summary of experiments carried out according to target species.…”