Assessing the effects of a trawling ban on diet and trophic level of hake, <i>Merluccius merluccius</i>, in the southern Tyrrhenian Sea

Abstract

SUMMARY: This study assesses the effects of a trawling ban on the diet and trophodynamics of the hake Merluccius merluccius by comparing stomach contents and stable isotopes (δ 15 N and δ 13 C) in two trawled gulfs and one untrawled gulf in northern Sicily (western Mediterranean). Comparisons were made for three size classes of hake encompassing 60 to 410 mm total length. Fish were collected from 50 to 200 m depth on muddy bottoms. The diets of hake of small and medium size were similar overall but more selective in the untrawled gulf. Greater differences were detected between the diets of larger specimens from trawled and untrawled areas. In the untrawled gulf large hake mainly preyed on clupeoid fish, while in the trawled gulfs other fish prey were found in the stomach contents. δ 15 N values of hake did not vary significantly between trawled and untrawled areas, while there was a clear effect of size, with larger individuals being significantly more enriched than juveniles. Conversely, δ 13 C values were generally more depleted for individuals collected in the untrawled area, suggesting a more pelagic source of carbon. The results from the mixing model agree fairly well with the known feeding habits found for each size class in each area.Keywords: diet, fishing impact, Merluccius merluccius, stable isotopes, trophodynamics, Mediterranean. RESUMEN: Efectos de un área de veda a la pesca de arrastre sobre la dieta y el nivel trófico de la merluza, Merluccius Merluccius, en el sur del Mar Tirreno. -Este estudio evaluó los efectos de la pesca de arrastre comercial en la dieta y la trofodinámica de la merluza mediterránea, Merluccius merluccius, mediante la comparación de sus contenidos estomacales y de la composición isotópica (δ 15 N y δ 13 C) en dos golfos donde está permitida la pesca de arrastre y en uno donde está prohibida, en el norte de Sicilia (Mediterráneo Occidental). Las comparaciones se hicieron para tres clases de talla que abarca la merluza entre 60 y 410 mm de longitud total. Los peces fueron recolectados en los fondos fangosos de la plataforma continental de 50 a 200 m de profundidad. Los hábitos alimenticios de las merluzas pequeñas y medianas eran similares, pero más selectivo en el golfo donde la pesca está prohibida. Las mayores diferencias se produjeron en la dieta de los especímenes más grandes comparando los golfos arrastrados con el golfo protegido. En el área protegida las merluzas grandes cazaban sobre todo en clupeidos y engráulidos, mientras que otros peces se encuentran en el contenido estomacal de M. merluccius de las áreas de pesca. Los valores de δ 15 N de la merluza no variaron significativamente entre las áreas protegidas y no protegidas, mientras que hubo un efecto claro de la talla: valores más alto, se han observado en los animales más grandes. Por el contrario los valores de δ 13 C fueron en general más empobrecidos (más negativos) en los ejemplares recolectados en el área protegida, esto indica una fuente más planctónica de carbono. Los resultados de los mixing models concue...

A multitracer approach to assess the spatial contamination pattern of hake (Merluccius merluccius) in the French Mediterranean

“…Considering isotopic ratios, juveniles exhibited lower values than adults. This change could be explained by the ontogenetic change of diet (Ferraton et al, 2007;Harmelin-Vivien et al, 2012a,b;Sinopoli et al, 2012). The correlation between δ 15 N and length observed here is consistent with observations from other studies in the Mediterranean Sea or the Atlantic Ocean (Harmelin-Vivien et al, 2012a;Chouvelon et al, 2014).…”

“…Since their growth rate is slower (de Pontual et al, 2006;Mellon-Duval et al, 2010), males stay longer on the shelf, and are predominantly harvested, which explains the imbalanced sex-ratio and the predominance of female hake in the Gulf of Lions. The high trophic position of hake and its predominance in Mediterranean fisheries (Aldebert et al, 1993;Harmelin-Vivien et al, 2012a;Sinopoli et al, 2012;Bănaru et al, 2013) have made necessary extensive assessment of the contamination patterns. Recent studies in the Gulf of Lions identify sex, growth rate, reproduction and diet as key factors to explain the contamination patterns (Bodiguel et al, 2009a(Bodiguel et al, , 2009bMellon-Duval et al, 2010;Cossa et al, 2012;Harmelin-Vivien et al, 2012a).…”

Meta-analysis review of fish trophic level at marine protected areas based on stable isotopes data

“…Sci., 17/2, 2016, 496-507 503 Our overall results indicate that the trophic level does not increase with the presence of the protection itself. This conclusion is in line with previous studies indicating that trophic level does not necessarily increase with protection and in some cases it can even decrease (Deudero et al, 2004;Vizzini & Mazzola, 2009;Sinopoli et al, 2012).…”

Spatial Management of Fisheries in the Mediterranean Sea

“…The ecosystem effects of the trawl ban assessed through investigation of the trophodynamics of two commercial fish species in the Gulf of Castellammare and in the two controls did not yield clear and homogeneous results (Fanelli et al, 2010;Sinopoli et al, 2012). Badalamenti et al (2008) found only limited effects of trawling on the trophodynamics of three .…”