Linking loggerhead locations: using multiple methods to determine the origin of sea turtles in feeding grounds

Abstract

Many marine megavertebrate taxa, including sea turtles, disperse widely from their hatching or birthing locations but display natal homing as adults. We used flipper tagging, satellite tracking and genetics to identify the origin of loggerhead turtles living in Amvrakikos Gulf, Greece. This location has been identified as hosting regionally important numbers of large-juvenile to adult sized turtles that display long-term residency and/or association to the area, and also presents a male biased sex ratio for adults. A total of 20 individuals were linked to nesting areas in Greece through flipper tagging and satellite telemetry, with the majority (16) associated with Zakynthos Island. One additional female was tracked from Amvrakikos Gulf to Turkey where she likely nested. Mitochondrial DNA mixed stock analyses of turtles captured in Amvrakikos Gulf (n = 95) indicated 82% of individuals originated from Greek nesting stocks, mainly from Zakynthos Island (63%), with lesser contributions from central Turkey, Cyprus and Libya. These results suggest that the male-biased sex ratio found in Amvrakikos Gulf may be driven by the fact that males breed twice as frequently on Zakynthos, resulting in their using foraging grounds of greater proximity to the breeding site. Conservation measures in localised foraging habitats for the protection of marine vertebrates, such as sea turtles, may have positive impacts on several disparate breeding stocks and the use of multiple methods to determine source populations can indicate the relative effectiveness of these measures.Electronic supplementary materialThe online version of this article (doi:10.1007/s00227-016-3055-z) contains supplementary material, which is available to authorized users.

Mitochondrial DNA reveals the natal origin of Caretta caretta (Testudines: Cheloniidae) stranded or bycaught along the Southwestern Adriatic coasts

“…Therefore, the interpretation of the MSA in these circumstances should be made with great caution (e.g. Rees et al 2017). Similarly, a wide confidence limit characterised also the unexpected source contribution from the South African rookery (NAT, 5.51%; Figure 2).…”

Mediterranean sea turtles: current knowledge and priorities for conservation and research

“…Cases of more vagile behaviour have also been observed (Bentivegna 2002, Cardona et al 2005, Eckert et al 2008. A stronger fidelity to neritic areas has been observed through tag returns (Casale et al 2007a, Revelles et al 2008 Patel et al 2015a,b, Stokes et al 2015, Rees et al 2017 tracking (Cardona et al 2009, Casale et al 2012c. Site fidelity is even stronger in adults, as they appear to return to the same foraging ground after the reproductive migration (Godley et al 2003, Lazar et al 2004b, Broderick et al 2007, Zbinden et al 2008,b, Casale et al 2013a, although they may also use up to 5 different foraging grounds over a period of 1 or more years (Schofield et al 2013a).…”

“…4). Flipper tagging (Margaritoulis 1988b, Casale et al 2007a, Margaritoulis & Panagopoulou 2010, satellite tracking (Zbinden et al 2011, Scho field et al 2013a, Luschi & Casale 2014, Patel et al 2015a,b, Snape et al 2016, Rees et al 2017) and strandings (Casale et al 2010a, Türkozan et al 2013) also support the relative importance of these neritic areas as well as of other areas such as the Aegean Sea, northern Africa, the eastern Mediterranean coast of Turkey and western Greece (Fig. 4).…”

“…The long-term monitoring of bycatch data relating to specific fishing gear (e.g. Albania) (Haxhiu 2010) may provide trend indices, and a few in-water monitoring programmes have been set up, for instance in Amvrakikos Gulf, Greece (Rees et al 2013(Rees et al , 2017. However, to our knowledge, the only information about in-water trends at present is repre-sented by 3 studies of loggerhead turtle bycatch rates.…”

Mitochondrial DNA short tandem repeats unveil hidden population structuring and migration routes of an endangered marine turtle

“…Mixed-stock analysis (MSA) was first developed to assess the stock origin of mixed aggregations of fishes (Grant, Milner, Krasnowski, & Utter, 1980;Pella & Masuda, 2001;Pella & Milner, 1987), before being applied to other highly migratory marine organisms like marine turtles (Bass, Epperly, & Braun-McNeill, 2004). It has been used to assess migratory routes (Carreras et al, 2006), foraging grounds (Jensen, Pilcher, & FitzSimmons, 2016;Rees et al, 2017), and the impact of threats in common foraging grounds on source populations (Clusa et al, 2016). Accurate MSA relies on the power of the genetic markers used to detect structuring among the nesting populations, however, and for this reason no attempt has been made, to date, to evaluate the composition of the known foraging aggregations of Mediterranean green turtles.…”