Bycatch of loggerhead sea turtles: insights from 14 years of stranding data

Abstract

We present a detailed analysis of sea turtle strandings (n = 619) over a 14 yr period (1993 to 2006) from the Valencian Community (eastern Spain). Loggerhead turtles Caretta caretta accounted for 98.1% of recorded strandings. Although we detected an increasing trend in the annual number of strandings over the study period, we expect that this was driven primarily by the increase in detection effort. Loggerhead turtles were mainly juveniles (mean ± SD curved carapace length from notch to tip [CCL] = 53.6 ± 12.6; range: 16 to 80.2 cm, n = 312) and strandings were far more frequent in summer months (69.6% June to September). We believe that interaction with longline fisheries was by far the main cause of observed stranding (> 28% of all cases, 43.5% of 393 turtles with likely mortality cause identified). Turtles showing signs of interaction with longlines were, on average, larger (CCL = 57.5 ± 10.4; range: 29.8 to 80.2 cm, n = 116) than turtles stranded due to other causes (CCL = 51.4 ± 13.3; range: 16 to 79 cm, n = 196; t-test: t = -4.49, p < 0.001) and were more frequent in summer months, when longline fishing effort off the coast was highest. Recent reductions in longline effort may have led to a decrease in recent years in the proportion of stranded turtles with evidence of longline interaction. Although inferences from stranding data must be subject to a number of caveats, when considered over wide spatio-temporal extents and in conjunction with other data sources, they can offer useful insights into the geographic ranges, seasonal distribution and life history of marine species of conservation concern.

An interview-based approach to assess sea turtle bycatch in Italian waters

“…breeding and feeding migrations), loggerhead turtles interact with 45 several types of fishing gears (e.g. demersal and pelagic towed gears, set nets, longlines; Wallace 46 et al, 2008; Lucchetti & Sala, 2010 47 three main fishing methods adopted in the region (Lucchetti & Sala, 2010; Casale, 2011): 48 drifting longlines (Guglielmi, Di Natale & Pelusi, 2000;Piovano et al, 2004; Deflorio et al, 49 2005; Jribi et al, 2008;Tomás et al, 2008;Piovano, Swimmer & Giacoma, 2009; Clusa et al, 50 2016), trawling (Casale, Laurent & De Metrio, 2004; Jribi, Bradai & Bouain, 2007; Sala, 51 Lucchetti & Affronte, 2011; Domènech et al, 2015; Lucchetti et al, 2016), and set nets (Lazar, 52 Ziza & Tvrtkovic, 2006; Echwikhi et al, 2010).…”

“…breeding and feeding migrations), loggerhead turtles interact with 45 several types of fishing gears (e.g. demersal and pelagic towed gears, set nets, longlines; Wallace 46 et al, 2008; Lucchetti & Sala, 2010 47 three main fishing methods adopted in the region (Lucchetti & Sala, 2010; Casale, 2011): 48 drifting longlines (Guglielmi, Di Natale & Pelusi, 2000;Piovano et al, 2004; Deflorio et al, 49 2005; Jribi et al, 2008;Tomás et al, 2008;Piovano, Swimmer & Giacoma, 2009; Clusa et al, 50 2016), trawling (Casale, Laurent & De Metrio, 2004; Jribi, Bradai & Bouain, 2007; Sala, 51 Lucchetti & Affronte, 2011; Domènech et al, 2015; Lucchetti et al, 2016), and set nets (Lazar, 52 Ziza & Tvrtkovic, 2006; Echwikhi et al, 2010).53 Longline bycatch occurs in open waters during the pelagic stage of the loggerhead turtle life, 54 with high rate areas in Spanish (Báez et al, 2007; Clusa et al, 2016), North African (Jribi et al, 55 2008 Benhardouze, Aksissou & Tiwari, 2012), Greek (Snape et al, 2013), and southern Italian 56 waters (Piovano et al, 2012). Bycatch events involve attraction by bait, hooking, and attempts to 57 escape.…”

An interview-based approach to assess sea turtle bycatch in Italian waters

“…demersal and pelagic towed gears, set nets, longlines; Wallace 46 et al, 2008; Lucchetti & Sala, 2010). In the Mediterranean turtle bycatch is mainly related to the 47 three main fishing methods adopted in the region (Lucchetti & Sala, 2010; Casale, 2011): 48 drifting longlines (Guglielmi, Di Natale & Pelusi, 2000;Piovano et al, 2004; Deflorio et al, 49 2005; Jribi et al, 2008;Tomás et al, 2008;Piovano, Swimmer & Giacoma, 2009; Clusa et al, 50 2016), trawling (Casale, Laurent & De Metrio, 2004; Jribi, Bradai & Bouain, 2007; Sala, 51 Lucchetti & Affronte, 2011; Domènech et al, 2015; Lucchetti et al, 2016), and set nets (Lazar, 52 Ziza & Tvrtkovic, 2006; Echwikhi et al, 2010).…”

“…demersal and pelagic towed gears, set nets, longlines; Wallace 46 et al, 2008; Lucchetti & Sala, 2010). In the Mediterranean turtle bycatch is mainly related to the 47 three main fishing methods adopted in the region (Lucchetti & Sala, 2010; Casale, 2011): 48 drifting longlines (Guglielmi, Di Natale & Pelusi, 2000;Piovano et al, 2004; Deflorio et al, 49 2005; Jribi et al, 2008;Tomás et al, 2008;Piovano, Swimmer & Giacoma, 2009; Clusa et al, 50 2016), trawling (Casale, Laurent & De Metrio, 2004; Jribi, Bradai & Bouain, 2007; Sala, 51 Lucchetti & Affronte, 2011; Domènech et al, 2015; Lucchetti et al, 2016), and set nets (Lazar, 52 Ziza & Tvrtkovic, 2006; Echwikhi et al, 2010).53 Longline bycatch occurs in open waters during the pelagic stage of the loggerhead turtle life, 54 with high rate areas in Spanish (Báez et al, 2007; Clusa et al, 2016), North African (Jribi et al, 55 2008 Benhardouze, Aksissou & Tiwari, 2012), Greek (Snape et al, 2013), and southern Italian 56 waters (Piovano et al, 2012). Bycatch events involve attraction by bait, hooking, and attempts to 57 escape.…”

A critical review of the Mediterranean sea turtle rescue network: a web looking for a weaver

“…Fisheries bycatch, boat strikes, intentional killing, and entanglement in marine debris including ghost gear have been identified as the main threats at sea (Tomás et al 2008, Casale and Margaritoulis 2010, Casale 2011). On land, degradation and reduction of nesting habitat caused by touristic and recreational activities, light pollution, noise, construction, sand extraction, and traffic (Camiñas 2004) are taking their toll.…”