Loggerhead turtle by-catch depends on distance to the coast, independent of fishing effort: implications for conservation and fisheries management

Abstract

Drifting longline is considered one of the most dangerous fishing gears for marine turtles and is their principal threat in the western Mediterranean Sea. During the summers of 2000 to 2003, 179 fishing operations were observed onboard a traditional Spanish drifting longline boat in the Balearic Sea (western Mediterranean) to analyse the effects of fishing effort and ecogeographical factors on the by-catch of loggerhead turtles Caretta caretta. We observed 4074 swordfish captured and 675 loggerhead turtles by-caught. The probability of catching at least 1 loggerhead was related to the distance of the fishing-ground to the coast and, to a lesser extent, depth, both independent of fishing effort. The average number of loggerheads captured was spatially structured only according to mean distance to the coast. However, the number of swordfish captured was correlated with fishing effort but was not correlated with distance to the coast or depth. Distance to the coast was correlated with gear retrieval time, sea surface temperature and velocity, and phytoplankton concentration. As the number of loggerheads captured was independent of the number of hooks, the number of fishing operations was a better unit than the number of hooks to assess loggerhead by-catch. Limiting drifting longline fishing activity to within 35 international nautical miles from the coast could reduce loggerhead by-catch substantially without affecting swordfish captures and with little resistance from fishermen.KEY WORDS: By-catch · Drifting longline · Sea turtle · Loggerhead · Caretta caretta · South-western Mediterranean · Swordfish fishery Resale or republication not permitted without written consent of the publisher

Marine mammal bycatch in Spanish Mediterranean large pelagic longline fisheries, with a focus on Risso’s dolphin (Grampus griseus)

“…A total of 2587 longline sets were observed from January to December, between 2000 and 2009. The Spanish longline fishery and the data collection performed by this onboard observer program have been previously described by Camiñas et al (2006), Báez et al (2007b), García-Barcelona et al (2010a,b), Báez et al (2010Báez et al ( , 2011 and Macías et al (2012).…”

Seabird bycatch in Spanish Mediterranean large pelagic longline fisheries, 2000-2008

“…Vessel length ranged from 12 to 27 m and fishing trips were often of short duration (1 to 6 days). (Valeiras and Camiñas 2003;Camiñas et al 2006;Báez et al 2007). A total of 2278 fishing operations were observed onboard from January to December, during years 2000 to 2008, which represented 4 786 466 hooks observed directly.…”

Assessing the influence of the atmospheric oscillations on pelagic and highly migratory sharks bycatches from Spanish Mediterranean Sea, a meta-analytic approach

“…Many studies indicate that the Spanish longline fleet is concentrated mainly around the Balearic Islands (Camiñas et al 2006, Báez et al 2007a, 2007b, García-Barcelona et al 2010, Báez et al 2013b. Thus, Alboran Sea was used by approximately 5% of the operative fleet; while Balearic Sea was used by approximately 80% of the operative fleet.…”