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Assessments of fisheries by‐catch on marine megafauna are important for developing effective management strategies. For sea turtles, impacts may be evident in nesting population trends, but generally only after a lag, as turtles are slow to mature. We examined 850 loggerhead turtle (Caretta caretta) by‐catch samples collected over 14 years throughout the western North Atlantic to identify source nesting populations. We identified proportions of turtles from 19 distinct management units (MUs), using mitochondrial DNA and mixed stock analysis, considering population size. We found a significant split in the distribution of small versus large loggerheads to the north and south of Cape Hatteras, North Carolina (latitude 35°N). North of Cape Hatteras, large turtles came from south‐east Florida (SEFL; 44% ± 15%) and the northern United States (33% ± 16%) MUs, while south of Cape Hatteras, the major contributors were Central East Florida (52% ± 20%) and south‐east Florida (SEFL; 41% ± 20%). Small turtles in the north came from Central East Florida (64% ± 14%), and in the south, south‐east Florida had the highest representation (56% ± 25%). There was little contribution from Mediterranean and Cape Verde populations, indicating low risk from western North Atlantic by‐catch to MUs in the Mediterranean. Understanding where threats may impact source populations is important, particularly for larger size turtles, as these individuals have the highest reproductive value. These findings allow more informed threat assessments to be conducted for loggerhead turtles considering spatial and demographic structure.

Sea turtle bycatch in longline fishing gear is an ongoing threat to the recovery of sea turtle populations. While considerable research has focused on pelagic longline fisheries, very little attention has been paid to captures of sea turtles in bottom longlines. Estimates of sea turtle takes in the shark bottom longline fishery have raised concern that this fishery may be impacting loggerhead sea turtle, Caretta caretta (Linnaeus, 1758), populations. However, there are no current management actions designed to reduce the bycatch of sea turtles in fisheries that target sharks using bottom longline gear because no studies have identified which factors, if any, influence the capture of a loggerhead sea turtle. We used generalized linear models to determine which factors influence the probability of loggerhead sea turtle captures in the shark bottom longline fishery, and which factors are related to at-vessel mortality. While a variety of fishing techniques were considered as factors, no particular fishing method was found to predict a capture of a sea turtle. The most significant factor in predicting the capture of a loggerhead sea turtle in shark bottom longline gear was the area fished. Soak time was found to predict at-vessel hooking mortality with the median time for a mortality to occur was 14–15 hrs. While no definitive fishing factor was identified in the capture or mortality of a loggerhead sea turtle, research is needed using controlled methods for further examining the factors affecting captures of sea turtles in this and other bottom longline fisheries.

Fisheries that operate at large spatial scales and with high intensity have the potential to impact highly migratory species, and it is important to characterize threats to specific breeding populations of these species. We used many‐to‐many mixed‐stock analysis (MSA) (n = 408) and microsatellite assignment testing (n = 397) to determine source populations for leatherback turtles (Dermochelys coriacea) caught as bycatch in the U.S. pelagic longline fishery from 2002 to 2012 in the western North Atlantic. Within the United States, we had bycatch samples from the majority of statistical fishing areas: Gulf of Mexico (GOM), Northeast Distant (NED), Caribbean (CAR), Florida East Coast (FEC), Mid Atlantic Bight (MAB), Northeast Coastal (NEC), South Atlantic Bight (SAB) and Sargasso (SAR). We determined the proportions of turtles from each of nine nesting stocks in the Atlantic in each of the sampled areas. These nesting stocks included Brazil, Costa Rica, Florida, Trinidad, French Guiana, St. Croix, Ghana, Gabon, and South Africa. The MSA revealed that the NED had a lower relative proportion of turtles from Costa Rica than other areas and that the GOM had the highest relative proportion of turtles from Costa Rica. No turtles were assigned to the African rookeries, lending further evidence that turtles from that region forage elsewhere and therefore may not be affected by western North Atlantic fisheries. This work contributes to the ongoing assessment of threats to leatherback turtles in the Regional Management Unit (RMU) of the western North Atlantic, and draws attention to the disproportionate number of turtles from Costa Rica being caught in the Gulf of Mexico; Costa Rica is one of the only populations in the northern Atlantic that is not experiencing significant increases in nest numbers. This approach should be useful in determining population‐specific threats to other highly migratory protected species that may depend on segregated foraging areas either within or among species.

Because incidental capture in pelagic longline fishing gear potentially kills or injures thousands of sea turtles annually, solutions to reduce the frequency and mortality rate of these interactions are critical conservation priorities. Understanding factors that affect post-hooking mortality rates remains an important component to evaluating the population-level impact of these interactions. Post-release mortality may be dependent upon the nature of the interaction (hooking location and/or entanglement) and amount of gear remaining at release. Hooking location can impact the ability of the crew to remove gear, as deeply ingested hooks cannot be removed safely. We examined the effects of hook type (circle vs J-hooks), offset (degrees), and other factors on hooking location in leatherback, Dermochelys coriacea (Vandelli, 1761), and loggerhead, Caretta caretta (linnaeus, 1758), sea turtles incidentally captured from 2000 to 2010 using fishery observer data. Significant differences in hooking location in loggerheads were observed between offset J-hooks and non-offset and 10° offset circle hooks; loggerheads were most often mouth/beak hooked with circle hooks, whereas most had swallowed offset J-hooks. Greater offsets appear to increase the frequency of deeply ingested hooks. Leatherback sea turtles were predominately externally hooked regardless of hook type, but mouth hookings occurred significantly more often on non-offset (0°) circle and J-hooks than on 10° offset circle hooks. When combined with outreach and education on careful release protocols, the use of circle hooks may increase post-interaction survival by modifying hooking location and facilitating maximum gear removal.

Declines in sea turtle populations worldwide have been attributed in part to incidental capture in hook and line fisheries. Methods to reduce turtle bycatch and mortality must strike a bal- ance between bycatch reduction and target species retention if they are to gain acceptance from fish- ers. To investigate potential bycatch reduction measures, we examined the effects of hook size, bait type, baiting technique, and animal size on the frequency of loggerhead sea turtles Caretta caretta ingesting a baited hook during controlled trials. Results indicated that as hook size increased, the likelihood for deep ingestion decreased. Smaller turtles were less likely to swallow larger hooks. Tur- tles were less likely to swallow hooks baited with sardines than with squid and single-baited rather than threaded baits. Results are likely due to differences in bait texture, hook shielding effects, and turtles' behavioral differences. We suggest that fishing with large hooks, using finfish instead of squid, and using single-baited instead of threaded baits might reduce deep ingestion rates of hooks by loggerheads as large as 65 cm in standard straight carapace length (notch to tip).

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 haplo- type frequencies observed in 23 genetically distinct nesting stocks representing the 4 distinct pop- ulation segments (DPSs) that have been identified throughout the Atlantic Ocean and Mediterran- ean 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.