Lepidochelys kempii

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 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. 

Abstract:

Ingestion of marine debris can have lethal and sublethal effects on sea turtles and other wildlife. Although researchers have reported on ingestion of anthropogenic debris by marine turtles and implied inci- dences of debris ingestion have increased over time, there has not been a global synthesis of the phenomenon since 1985. Thus, we analyzed 37 studies published from 1985 to 2012 that report on data collected from before 1900 through 2011. Specifically, we investigated whether ingestion prevalence has changed over time, what types of debris are most commonly ingested, the geographic distribution of debris ingestion by marine turtles relative to global debris distribution, and which species and life-history stages are most likely to ingest debris. The probability of green (Chelonia mydas) and leatherback turtles (Dermochelys coriacea) ingesting debris increased significantly over time, and plastic was the most commonly ingested debris. Turtles in nearly all regions studied ingest debris, but the probability of ingestion was not related to modeled debris densities. Furthermore, smaller, oceanic-stage turtles were more likely to ingest debris than coastal foragers, whereas carnivorous species were less likely to ingest debris than herbivores or gelatinovores. Our results indicate oceanic leatherback turtles and green turtles are at the greatest risk of both lethal and sublethal effects from ingested marine debris. To reduce this risk, anthropogenic debris must be managed at a global level.