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The highly migratory and marine nature of species such as green sea turtles (Chelonia mydas) may hinder understanding of basic life history and impact ensuing management and conservation applications across their full range. To elucidate the linkages between juvenile green turtles foraging in coastal waters of Uruguay in the Southwestern Atlantic Ocean to their future nesting or feeding grounds, this study investigated their genetic composition . A total of 201 tissue samples were collected from turtles that had stranded or were intentionally captured for scientific research along the Uruguayan coast (ca. 33°–35°S) during two sampling periods (2003–2005 and 2009–2014). Samples were pooled for analysis. Twelve mitochondrial control region haplotypes and ten subhaplotypes were identified, all of which had been previously detected at Atlantic or Caribbean nesting beaches. Mixed Stock Analysis revealed that most turtles traced to the Ascension Island rookery, representing a substantial connection to the remote mid-Atlantic island thousands of kilometers distant. Other nesting areas, such as Guinea Bissau in Africa and Trindade Island in Brazil, represented less significant sources. There was no significant temporal or spatial genetic structure within Uruguayan waters, suggesting dispersion along this coast. Despite the geographic distance from the nesting beach, the significant connection to the Ascension Island rookery underscores the importance of considering rookery population size and ocean current influences in understanding source contributions. These findings emphasize the need for conservation efforts, including the maintenance of existing protected areas and the creation of new ones, to ensure the long-term conservation of green turtles connected to various nesting colonies and feeding grounds.

Marine turtles exhibit temperature-dependent sex determination (TSD), and there is widespread concern that global warming is raising nest incubation temperatures, resulting in increasingly female-skewed sex ratios in "feminized" populations. We assessed the sex ratio of a mixed-stock aggregation of immature green turtles (Chelonia mydas) at a midocean developmental foraging ground in the Northwest Atlantic from 1975 to 2018. We used plasma testosterone concentrations, measured by radioimmunoassay (RIA) and calibrated by laparoscopy, to determine the sex of 2,724 green turtles captured 3,940 times in Bermuda (32°18′ N, 64°46′ W) waters. A logistic regression model correctly predicted the sex of 99.5% of turtles (189/190) with associated testosterone concentrations whose sex had been verified via laparoscopy. Empirical evaluation of the trend in sex ratio using four related data sets showed a significant increase (2.8–4.0% yr−1) in the percent females, ranging from 62.7 to 68.1% during the most recent years of evaluation. Using growth rates to predict the year of arrival of turtles in Bermuda, we estimated the sex ratio of recruiting cohorts over 4 decades. Mixed-stock analysis of mtDNA sequences of 602 turtles that recruited to Bermuda between 1970 and 2018 suggested that multiple, geographically dispersed rookeries contributed to the Bermuda aggregation making it regionally representative. Changes in rookery contributions and strong population increases at certain rookeries may partly explain the increasing trend in the percent female. But the steady rate of increase over decades and the increasing female percentage of arriving cohorts are consistent with impacts of global warming at source rookeries. [ABSTRACT FROM AUTHOR]

Two groups of humpback whales inhabit the waters off the Pacific coast of Mexico the coastal wintering aggregation in the north (MX), and the southern Mexico/Central America wintering aggregation (S‐MX/CEA) in the south. However, along the coast of the Mexican Central Pacific (MCP), the population affiliation of humpback whales is uncertain. Some studies have concluded that the MCP whales are part of S‐MX/CEA, while others have suggested that the MCP may represent an overlap zone between the two wintering aggregations. In this study, data from 354 biopsy samples were collected over a 12‐year period, to provide insight from genetic information into the affiliation of MCP whales to and the boundaries between the wintering aggregations. Using mitochondrial control region sequences, we found that the majority (73%) of MCP whales are part of MX, but that the boundary between the two wintering aggregations may shift latitudinally depending on environmental conditions. The high haplotypic (h ± SD = 0.859 ± 0.0138) and nucleotide diversity (π ± SD = 0.0145 ± 0.0075) of the MCP whales are also consistent with our sample, including animals from both wintering aggregations. More research is needed to better describe the ranges of the MX and S‐MX/CEA wintering aggregations to ensure their successful conservation and management. [ABSTRACT FROM AUTHOR]

Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) is a large, anadromous fish native to the Atlantic Coast of North America. Although this species once supported important fisheries, centuries of exploitation and habitat degradation have resulted in dramatic declines, presumed extirpation in some rivers, and ultimately listing under the U.S. Endangered Species Act (ESA). Under the ESA, Atlantic sturgeon are listed as five separate Distinct Population Segments (DPSs), which form the basis for federal management. Despite state and federal protections Atlantic sturgeon still face significant threats to their recovery, including fisheries bycatch mortality, marine construction, dredging, dams, and vessel strikes. However, because subadult and adult Atlantic sturgeon migrate extensively across estuarine and marine environments and frequently form mixed-stock aggregations in non-natal habitats, it can be difficult to determine how these threats impact specific populations and DPSs. To better understand ontogenetic shifts in habitat use and stock-specific exposure to anthropogenic threats, we performed a mixed-stock analysis of 1704 Atlantic sturgeon encountered across the U.S. Atlantic Coast. Collections made north of Cape Cod, MA and south of Cape Hatteras, NC were dominated by individuals from regional stocks; however, we found extensive stock mixing in the mid-Atlantic region, particularly in coastal environments where individuals from all five DPSs were commonly observed. Subadults and adults that were encountered in offshore environments had moved, on average, 277 km from their natal source; however, 23% were sampled over 500 km from their natal river suggesting long-distance movements are relatively common in these age classes. Overall, our work highlights that Atlantic sturgeon populations are vulnerable to threats over vast areas and emphasizes the need for continued genetic monitoring to track recovery progress. [ABSTRACT FROM AUTHOR]

The Atlantic green sea turtle Chelonia mydas is a migratory and endangered species with a network of nesting rookeries (NRs) and foraging grounds (FGs) in the Atlantic basin that needs elucidation. FGs are important areas for immature turtle’s feeding and growth after pelagic migrations. Aggregations of sea turtles at these grounds usually come from genetically distinct NRs; therefore, they are called mixed stocks. The northeastern coast of Colombia has extensive seagrass and macroalgae marine ecosystems that constitute FGs, and perhaps long-term developmental habitats for a significant number of immature C. mydas. However, it is unknown which C. mydas NRs may be using these ecosystems for feeding and development. This study estimated the genetic diversity and genetic origin of C. mydas mixed stocks at two FGs in northeastern Colombia (Santa Marta and La Guajira), and inferred their connections to NRs groups in the Atlantic basin using mitochondrial Control Region (mtCR) as a marker. A high genetic diversity, evidenced by the high nucleotide and haplotype diversities, was found in both studied mixed stocks and may be explained by different contributing NRs groups found with mixed stock analyses (MSAs). At least three genetically distinct groups from different sides of the Atlantic Basin contributed juveniles to the mixed stocks in Colombia. Observed demographic connectivity can be explained by the confluence of two major, opposite directions ocean currents by the study area, the Caribbean Current (westward) and the Panama-Colombia Countercurrent (eastward). The high diversity of turtles at Colombia’s FGs suggests that the area is an important link in the network of habitats used by C. mydas to be considered in management and transnational conservation planning for the species recovery.

We developed an approach for estimating changes in relative year-class strength of source populations contributing to mixtures by incorporating ages or lengths of mixture individuals in genetic stock identification models. The approach is intended for long-lived fishes with high pre-recruitment and low post-recruitment mortality rates for which consistent temporal changes in recruitment can be assumed. Age- and collection-year specific contributions of sources to the mixture are modeled as linear functions of two source-specific parameters: an intercept representing relative recruitment for the first modeled year class and a slope representing how relative recruitment changes annually. Based on simulations, the estimation approach performed reasonably well under diverse conditions, including varying numbers of sources, levels of genetic divergence among sources, degrees of change in year-class strength, durations and frequencies of sampling from mixtures, age ranges of individuals from mixtures, and sample sizes from mixtures. The estimation approach was also robust to aging error and uncertainty in length-age relationships. We applied the approach to genetic and length data for lake sturgeon Acipenser fulvescens from Green Bay, Lake Michigan, collected from 2002 to 2008, with sources corresponding to five Lake Michigan tributaries. Two of the Lake Michigan sources showed declining recruitment levels, whereas the other three sources showed increasing recruitment levels. We believe our proposed approach for indexing changes in year-class strength shows promise as a tool for identifying sources potentially at risk due to declining recruitment and for relating changes in recruitment to biotic or abiotic factors. [ABSTRACT FROM AUTHOR]

Despite intense interest in conservation of marine turtles, spatial ecology during the oceanic juvenile phase remains relatively unknown. Here, we used mixed stock analysis and examination of oceanic drift to elucidate movements of hawksbill turtles ( Eretmochelys imbricata) and address management implications within the Caribbean. Among samples collected from 92 neritic juvenile hawksbills in the Cayman Islands we detected 11 mtDNA control region haplotypes. To estimate contributions to the aggregation, we performed ‘many-to-many’ mixed stock analysis, incorporating published hawksbill genetic and population data. The Cayman Islands aggregation represents a diverse mixed stock: potentially contributing source rookeries spanned the Caribbean basin, delineating a scale of recruitment of 200–2500 km. As hawksbills undergo an extended phase of oceanic dispersal, ocean currents may drive patterns of genetic diversity observed on foraging aggregations. Therefore, using high-resolution Aviso ocean current data, we modelled movement of particles representing passively drifting oceanic juvenile hawksbills. Putative distribution patterns varied markedly by origin: particles from many rookeries were broadly distributed across the region, while others would appear to become entrained in local gyres. Overall, we detected a significant correlation between genetic profiles of foraging aggregations and patterns of particle distribution produced by a hatchling drift model (Mantel test, r = 0.77, P < 0.001; linear regression, r = 0.83, P < 0.001). Our results indicate that although there is a high degree of mixing across the Caribbean (a ‘turtle soup’), current patterns play a substantial role in determining genetic structure of foraging aggregations (forming turtle groups). Thus, for marine turtles and other widely distributed marine species, integration of genetic and oceanographic data may enhance understanding of population connectivity and management requirements. [ABSTRACT FROM AUTHOR]

Atlantic bluefin tuna (Thunnus thynnus) are currently managed by the member nations of the International Commission for the Conservation of Atlantic Tunas (ICCAT) as distinct western and eastern stocks, separated by the 45°W meridian. Previous studies of Atlantic bluefin tuna caught in the northeast Atlantic south of Norway suggested mixing of putative stocks in the region, based on abrupt shifts in the size and condition of fish during the fishing season. By contrast, more recent studies south of Iceland reported only small differences in size of tuna caught at different times of the season in that area. To better understand the stock structure and composition of Atlantic bluefin tuna in the region, we surveyed genetic variation at eight microsatellite loci for 800 Atlantic bluefin tuna collected in experimental commercial fishing operations south of Iceland during 1999 and 2002. We tested for heterogeneity between years, between seasons within a year, between two fishing areas within the region, and between sexes. Analysis of molecular variation demonstrated slight, but significant, genetic divergence between collections of fish caught early and late in the season over the two years. These results are consistent with prior observations of Atlantic bluefin tuna of different conditions entering the fishery through the season, and suggest that the northeast Atlantic fishery represents a mixed-stock fishery including animals migrating from different areas and recruited from different spawning grounds. [Copyright &y& Elsevier]