Kemp's Ridley Sea Turtle

THOUSANDS OF SINGLE NUCLEOTIDE POLYMORPHISMS IN THE CRITICALLY EN- DANGERED KEMP’S RIDLEY SEA TURTLE (LEPIDOCHELYS KEMPII) REVEALED BY DOU- BLE-DIGEST RESTRICTION-ASSOCIATED DNA SEQUENCING: OPPORTUNITIES FOR PREVIOUSLY ELUSIVE CONSERVATION GE- NETICS RESEARCH.—Among sea turtles, the Kemp’s ridley is the most endangered and geographically restricted, with its distribution mostly confined to the Gulf of Mexico (NMFS and USFWS, 2015). After experiencing a severe and sustained bottleneck that put this species on the verge of extinction, it appeared to be rebounding successfully, as evidenced by an exponential growth in the number of nests observed per nesting season, following decades of Mexico–United States bi-national efforts aimed at its recovery (Heppell et al., 2007). Unfortunately, nesting was severely reduced by ~35% during 2010 (the year of the BP Deepwa- ter Horizon oil spill in the Gulf of Mexico), as compared to nesting rates in 2009 (NMFS and USFWS, 2015). Although nesting rebounded during 2011 and 2012 to levels similar to that of 2009, nesting declined drastically again during 2013 and experienced a further drop during 2014 (NMFS and USFWS, 2015; Shaver et al., 2016). The number of nests in 2014 represents a 46% decrease from 2012, which was the year with the highest recorded number of nests since 1965 (Sarti, 2014). Should nesting continue to de- cline, long-term species recovery efforts will be compromised. Therefore, there is deep concern about the future of the Kemp’s ridley, and data to inform and assess bi-national management and conservation measures are urgently needed (Plotkin and Bernardo, 2014). Population ge- netics information crucial to the long-term conservation of the Kemp’s ridley, including baseline data required for monitoring its future status, is lacking. This includes estimations of genomic diversity, effective population size, and number of breeders; assessment of levels of population differentiation; and detection of genomic signatures of bottlenecks. 

LONG-TERM MOVEMENTS OF AN ADULT MALE KEMP’S RIDLEY SEA TURTLE (LEPI- DOCHELYS KEMPII) IN THE NORTHWEST- ERN GULF OF MEXICO—Despite recent insights into the spatial ecology of juvenile (Morreale and Standora, 2005; Renaud and Williams, 2005; Mansfield, 2006; McClellan, 2009; Seney and Landry, 2011; Lyn et al., 2012) and postnesting female Kemp’s ridleys (Lepi- dochelys kempii) (Seney and Landry, 2008, 2011; Shaver and Rubio, 2008; Shaver et al., 2013, 2016), the breeding, migratory, and foraging behaviors of adult male Kemp’s ridleys remain largely unknown (Shaver et al., 2005).

The current paradigm suggests that adult male Kemp’s ridleys primarily reside in neritic forag- ing habitats near nesting beaches year round and engage in courtship and mating activities in March, immediately before the April–July nest- ing season (Owens, 1980; Rostal et al., 1998; Rostal, 1991, 2005; Shaver et al., 2005). Field observations of mounted pairs near known nesting beaches have occurred between October and May in Mexico (Rancho Nuevo) and in early June in Texas [Padre Island National Seashore (PAIS)], although confirmation of copulation is lacking (Pritchard and Ma ́rquez, 1973; Shaver et al., 2005). This tendency for male Kemp’s ridleys to establish year-round residency near nesting beaches is behaviorally disparate from seasonal migratory movements displayed by adult female conspecifics (Seney and Landry, 2008, 2011; Shaver and Rubio, 2008; Shaver et al., 2016; Hughes and Landry, unpubl. data) and males of other species (Lepidochelys olivacea: Beavers and Cassano, 1996; Plotkin et al., 1996; Caretta caretta: Arendt et al., 2012; Casale et al., 2013; Chelonia mydas: Limpus, 1993; Hays et al., 2001; Der- mochelys coriacea: James et al., 2005).

Identification of spatially and temporally defined areas frequented by adult male Kemp’s ridleys for breeding, migrating, or foraging is necessary to accomplish a Priority 1 Recovery Task in the Kemp’s Ridley Recovery Plan mandating protection and management of im- portant marine habitats (National Marine Fish- eries Service, 2011). Implementation of marine protected areas and other conservation measures to facilitate protection of adult males utilizing

critical habitats will require a comprehensive effort to better delineate habitat boundaries, assess localized sources of mortality, and, in foraging areas, to quantify and qualify prey resources and physical site characteristics. Infor- mation on adult male Kemp’s ridley migratory behavior is currently limited to a single source describing the movements of 11 individuals incidentally captured from waters near Rancho Nuevo (Shaver et al., 2005). Our analysis herein of a single adult male Kemp’s ridley’s long-term movements in northwestern Gulf of Mexico (GOM) waters, which recently have been identi- fied as critical foraging (Shaver et al., 2013) and migratory (Shaver et al., 2016) habitat for adult female conspecifics, is the longest time series of information to date for a male sea turtle. This study provides valuable insight into the behavior of an individual male Kemp’s ridley and has implications for the management and conserva- tion of the species. 

Coincident with the 2010 Deepwater Horizon oil spill, unprecedented numbers of Kemp’s ridley sea turtles (Lepidochelys kempii) stranded on northern Gulf of Mexico beaches and the number of nests recorded on the primary nesting beaches plummeted far below expected levels. High levels of strandings have continued since 2010 and the number of nests recovered to approximately 2009 levels in 2011, and improved slightly in 2012. A stock assessment conducted in 2012 indicated that a mortality event occurred in 2010, and that the number of nests should once more exhibit an increasing trend from 2013 and beyond. This has not happened; rather, the number of nests declined sharply in 2013. We conducted a new stock assessment to evaluate additional scenarios, including 1) three stock-recruitment options; 2) the potential that a new source of ongoing mortality is present; and 3) the potential that the number of nests- per-adult-female is dependent on the size of the age-2þ benthic population. The latter model provided the best fit to the data. Further, the preliminary estimate of actual nesting in 2014 is consistent with model projections. The reduction in reproductive output could be due to the combination of a large population and reduced prey levels. Together these may have increased the remigration interval or reduced the number of nests per female. However, research is needed to evaluate this and other plausible hypotheses. Nesting may be highly variable in the future depending on feeding conditions on the foraging grounds. 

Long-term monitoring of in-water life history stages of the critically endangered Kemp’s ridley sea turtle (Lepidochelys kempii) is essential for management because it generates information on the species’ at-sea abundance, size composition, distribution, and habitat requirements. We documented trends in Kemp’s ridley size, relative abundance, and distribution using entanglement netting surveys at three study areas adjacent to tidal passes in the northwestern Gulf of Mexico (NWGOM) during intermittent sampling periods from 1991 to 2013. A total of 656 Kemp’s ridley sea turtles were captured ranging in size from 19.5 to 66.3 cm straight carapace length (SCL) (mean 1⁄4 35.0 cm SCL). The dominance of juveniles (25–40 cm SCL) captured during sampling suggests the nearshore waters of the NWGOM are an important developmental foraging ground for Kemp’s ridley. Characterization of Kemp’s ridley long-term relative abundance reveals a generally stable trend in catch- per-unit-effort (CPUE) across all study areas combined. Based on the increasing trend in the number of hatchlings released from the species’ primary nesting beach, Rancho Nuevo, Mexico, since the early 1990s, the lack of a corresponding overall increase in juvenile abundance at nearshore sampling locations is puzzling. This disparity is most likely an artifact of the present study’s sampling design, but could also indicate shifts in Kemp’s ridley recruitment away from the NWGOM. While conservation efforts have contributed to this species’ overall growth since the 1980s, as measured by the increasing number of nests, recent declines in this rate of increase are a concern and call for a more comprehensive approach to managing Kemp’s ridley recovery efforts. 

Kemp’s ridley (Lepidochelys kempii) is the world’s most endangered sea turtle species, and nests primarily on the Gulf of Mexico coast in Mexico. In 1978, a binational project was initiated to form a secondary nesting colony of this species in south Texas at Padre Island National Seashore (PAIS), as a safeguard against extinction. During 1978–2014, we documented 1,667 Kemp’s ridley nests in Texas, with 56% found at PAIS. Most nests (89%) found in south Texas were from wild-stock turtles; south Texas is the northern extent of the documented historic nesting range for the species. We documented nesting in north Texas starting in 2002, and most nests (53%) found there were from turtles that had been head-started (reared in captivity for 9–11 mo), and released off the Texas coast as yearlings. Kemp’s ridley nesting increased in Texas during the mid-1990s through 2009, before annual nest numbers dropped in 2010, rebounded and plateaued in 2011 and 2012, and then decreased again in 2013 and 2014. Annual numbers of nests found in Texas and Mexico followed similar trends and were correlated (R2 1⁄4 0.95). We examined nesting turtles for presence of tags at 55% of the nests located in Texas. Of the Kemp’s ridleys we examined during 2000–14, the annual percentage of apparent neophytes decreased and the annual percentage of remigrants increased over time. Mean annual remigration intervals of Kemp’s ridleys increased steadily from 1.9 yr in 2008 to 3.3 yr in 2014. These changes in demographic parameters are critical to understanding the recent fluctuation in the number of nesting Kemps ridleys and will be used in population models to investigate possible causes of the recent and sudden decline of nesting Kemp’s ridleys in Texas and Mexico. 

We developed a Kemp’s ridley (Lepidochelys kempii) stock assessment model to evaluate the relative contributions of conservation efforts and other factors toward this critically endangered species’ recovery. The Kemp’s ridley demographic model developed by the Turtle Expert Working Group (TEWG) in 1998 and 2000 and updated for the binational recovery plan in 2011 was modified for use as our base model. The TEWG model uses indices of the annual reproductive population (number of nests) and hatchling recruitment to predict future annual numbers of nests on the basis of a series of assumptions regarding age and maturity, remigration interval, sex ratios, nests per female, juvenile mortality, and a putative ‘‘turtle excluder device effect’’ multiplier starting in 1990. This multiplier was necessary to fit the number of nests observed in 1990 and later. We added the effects of shrimping effort directly, modified by habitat weightings, as a proxy for all sources of anthropogenic mortality. Additional data included in our model were incremental growth of Kemp’s ridleys marked and recaptured in the Gulf of Mexico, and the length frequency of stranded Kemp’s ridleys. We also added a 2010 mortality factor that was necessary to fit the number of nests for 2010 and later (2011 and 2012). Last, we used an empirical basis for estimating natural mortality, on the basis of a Lorenzen mortality curve and growth estimates. Although our model generated reasonable estimates of annual total turtle deaths attributable to shrimp trawling, as well as additional deaths due to undetermined anthropogenic causes in 2010, we were unable to provide a clear explanation for the observed increase in the number of stranded Kemp’s ridleys in recent years, and subsequent disruption of the species’ exponential growth since the 2009 nesting season. Our consensus is that expanded data collection at the nesting beaches is needed and of high priority, and that 2015 be targeted for the next stock assessment to evaluate the 2010 event using more recent nesting and in-water data.