Genetic stock composition of loggerhead turtles Caretta caretta bycaught in the pelagic waters of the North Atlantic

Abstract

Sea turtle populations disperse widely across oceans and migrate between terrestrial nesting habitat and distant feeding and developmental habitats. Understanding population stock structure is important for accurately assessing threats such as mortality from fishery bycatch and for defining specific demographic units of conservation concern. We compared 775 bp mtDNA control region haplotypes from 389 juvenile loggerhead turtles sampled as bycatch in the US pelagic longline fishery in the western North Atlantic Northeast Distant (NED) region to haplotype frequencies observed in 23 genetically distinct nesting stocks representing the 4 distinct population segments (DPSs) that have been identified throughout the Atlantic Ocean and Mediterranean Sea. We used Bayesian mixed-stock analysis to produce stock composition estimates for juvenile loggerhead turtles that use pelagic habitat in the central North Atlantic. We found that nearly all of the loggerheads caught in NED waters belonged to the Northwest Atlantic DPS (mean = 99.2%), with the majority coming from the large eastern Florida rookeries (mean = 84.0%). We also detected contributions from the western Florida rookeries (mean = 11.7%) and Mexico (mean = 3.5%) but found little evidence of contributions from the rookeries of the South Atlantic, Northeast Atlantic, or Mediterranean DPSs. These results will help improve specific threat assessments and are relevant to ongoing development of conservation plans that are aligned to the recent DPS listings for loggerheads.

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

“…The recent use of more variable genetic markers and extended coverage of nesting areas has increased the resolution of mitochondrial DNA (mtDNA) studies, aiding the identification of further sub-populations (Shamblin et al 2014). This improved baseline can contribute to increased resolution in mixed stock analyses (MSAs) of foraging aggregations, which are used to highlight likely turtle origin and movements and possible conservation requirements (Roberts et al 2005; Carreras et al 2006; Reece et al 2006; Monzón-Argüello et al 2012; Garofalo et al 2013; LaCasella et al 2013). …”

Nesting population origins of leatherback turtles caught as bycatch in the U.S. pelagic longline fishery

“…In addition to furthering knowledge about marine species' life history, population structure and threats, results from genetic analyses of these samples may be used to investigate proportional impacts of fisheries bycatch by population and region (e.g., LaCasella et al. ), and to identify fisheries that may impact highly vulnerable or declining turtle populations. The U.S. pelagic longline data are reported by statistical area: Caribbean (CAR), Gulf of Mexico (GOM), Florida East Coast (FEC), South Atlantic Bight (SAB), Mid Atlantic Bight (MAB), North East Coastal (NEC), Northeast Distant (NED), Sargasso (SAR), North Atlantic Central (NCA), Tuna North (TUN), and Tuna South (TUS; Fig.…”

New findings about the spatial and temporal use of the Eastern Atlantic Ocean by large juvenile loggerhead turtles

“…While two turtles made apparently directed migrations westwards across the Atlantic, a third took a much more meandering route across the Atlantic heading towards the northern USA and Newfoundland, where the presence of loggerhead turtles as incidental captures by fisheries has been reported (Witzell, 1999;LaCasella et al, 2013). From the present study, it is unclear whether their movements were influenced by prevailing currents, or whether they were directed migrations or indirect trips in which turtles forage en route.…”

“…From the present study, it is unclear whether their movements were influenced by prevailing currents, or whether they were directed migrations or indirect trips in which turtles forage en route. While two turtles made apparently directed migrations westwards across the Atlantic, a third took a much more meandering route across the Atlantic heading towards the northern USA and Newfoundland, where the presence of loggerhead turtles as incidental captures by fisheries has been reported (Witzell, 1999;LaCasella et al, 2013). Unfortunately, it is not possible to determine from the present dataset whether these individuals would have settled to neritic habitat in the western Atlantic.…”

“…These juveniles are thought to belong to different nesting populations from the west and east North Atlantic, presumably migrating between the two sides of the Atlantic (Bolten et al, 1998;Monz on-Arg€ uello et al, 2009). The North Atlantic has a high level of fisheries activity, and incidental captures of sea turtles are well described (Bolten, 2003;Watson et al, 2005;Service, 2008;LaCasella et al, 2013). While significant progress has been made to reduce by-catch in some fisheries in the north-west Atlantic, the eastern Atlantic lags behind (Conant et al, 2009) and in the case of the Canary Islands, there is a lack of information regarding incidental captures.…”