Change in Elasmobranchs and Other Incidental Species in the Spanish Deepwater Black Hake Trawl Fishery off Mauritania (1992-2001)

Abstract

From 1992 to 2001, by-catch that was landed from the Spanish deepwater trawl fishery for black hake off Mauritania was closely monitored. This is a highly specialised fishery, with two species of black hake (Merluccius senegalensis and Merluccius polli) constituting between 77-99% of total landings, which have annually averaged 9 300 tons over the past two decades. Landings of Sparidae were highest among by-catch species of commercial value, with the large-eye dentex, Dentex macrophthalmus being the most important until 1996, after which the family Lophiidae and others predominated. Next were the Elasmobranchii, including large demersal squalids and several species of rays, although their annual landings fell from 182 tons in 1992 to only 4 tons in 1999, rising to 37 tons in 2001. The present paper analyses these changes using by-catches retained in the black hake fishery. We believe that the decline could be due to a set of different factors: a change in depths fished, economic reasons and probable over-exploitation of both targeted species and by-catch. Elasmobranchs constituted only 0.1% of total landings in 1999, compared to 1.9% in 1992, although their contribution to total commercial by-catch was constant. Seasonality was clearly evident, with an absolute and proportional rise in elasmobranch by-catch during warm periods, reaching 75% of by-catch landings in some months, coinciding with a drop in total by-catch. These seasonal variations could be related to the migratory habits of the fishery's target species, black hake.

Elasmobranch bycatch in a trammel net fishery in the Portuguese west coast

“…As for studies on bycatch and discards of elasmobranchs there are some worldwide (e.g. Carbonell et al, 2003;Fernandez et al, 2005;McKinnell and Seki, 1998;Revill et al, 2005;Shepherd and Myers, 2005), but in Portugal few works have been conducted (Coelho et al, 2005;Coelho and Erzini, 2008). In the past few years elasmobranch catches have been decreasing in Portugal, which might indicate that these species are being over-exploited (Coelho et al, 2005).…”

Does otolith macrostructure record environmental or biological events? The case of black hake (Merluccius polli and Merluccius senegalensis)

“…Currently, black hake fisheries from the Sahara to Senegal are exclusively prosecuted by the Spanish fleet, which concentrates mainly in waters off Mauritania and fishing around 6700 t in 2008 (FAO, in press). The most recent detailed information from these fisheries is available elsewhere (Diop et al, 2004;Fernández et al, 2004;Ramos and Fernández, 1995).…”

Reproductive biology of black hakes (Merluccius polli and M. senegalensis) off Mauritania

“…Yields of trawlers operating off Mauritania have exceeded 3000 kg per day of hake, and from 20 to 40 t are landed in Cádiz (southern Spain) per trip, the duration of which has been reduced in recent years to about seven days of fishing. More detailed and recent descriptions of these fisheries can be found in Ramos and Fernández (1992, 1994, Ramos et al (1998), Diop et al (2004), andFernández et al (2004).…”

“…Los rendimientos de los arrastreros en aguas de Mauritania han superado los 3000 kg diarios de merluza, descargando en Cádiz (sur de España), entre 20 y 40 t por marea, cuya duración se ha reducido en los últimos años a unos siete días de pesca. Se pueden encontrar descripciones más detalladas y recientes de estas pesquerías en los trabajos de Ramos y Fernández (1992, 1994, Ramos et al (1998), Diop et al (2004), y Fernández et al (2004).…”