Sea Turtle

The influence of factors that negatively affect nesting activity of sea turtles on Sint Maarten

Abstract
Seven species of turtles are present in a wide range of areas across the earth. The species that use 
the beaches of Sint Maarten as nesting grounds are the Green sea turtle (Chelonia mydas), 
Leatherback sea turtle (Dermochelys coriacea) and Hawksbill sea turtle (Eretmochelys imbricata). 
Even with their protected status, populations are declining rapidly. This has a negative impact since 
sea turtles have significant ecological, economic and social values. To prevent populations from 
declining further, research is needed to create proper conservation strategies. This research focuses 
on different factors that could hinder nesting activity and how they influence sea turtles on Sint 
Maarten. These potential factors were researched in the literature and were determined to be 
artificial lighting, dune scarps, coastal development, slope, distance from high tide line to beach line, 
sargassum and human disturbances. Using a Spearman correlation test in SPSS, the correlation 
between the presence of these factors and the total nesting activity that takes place was tested. The 
test showed a moderate negative relation which was statistically significant 
(rs = -.681, p = .044). This means that the number of factors that are present at each beach influence 
the total nesting activity to some extent, but no strong correlation is present. These results indicate 
that if more factors which could hinder the sea turtle nesting activity are present, less sea turtle 
nesting activities take place on that beach on St. Maarten.

Date
2022
Data type
Research report
Theme
Research and monitoring
Report number
LKZ428VNST2 – Project Internship
Geographic location
St. Maarten
Author

Habitat utilization and migration in juvenile sea turtles.

Sea turtles are basically creatures that spend their entire lives in marine or estuarine habitats.Their only remaining reptilian ties to terrestrial habitats are for nesting and restricted cases of basking. Consequently.physiological. anatomical. and behavioral adaptations have evolved largely in response to selection in the aquatic environment and sea turtles share many common elements with liirger tislics and cetaceans in their habitat utilization and migrations. A generalized habitat model may he con- structed for sea turtles based on ontogenetic stages (Figure 6.1):

I. Early juvenile nursery habitat (usually pelagic and oceanic).
2. Later juvenile developmental habitat (usually demersal and neritic).

3. Adult foraging habitat.
4. Adult inter-nesting andfor breeding habitat. 

All sea turtles move immediately to the sea after hatching, usually after dark, and swim actively offshore. Most then undertake a mostly passive, denatant {sensu Jones)' migration drifting pelagically in oceanic gyre systems. Subsequently, after a period of years, these now larger and older juveniles actively recruit to demersal neritic dcvelopmentai habitats in the tropical and temperate zones. Demersal juve- niles in some temperate zone populations make seasonal migrations to foraging areas at higher latitudes in summer and lower latitudes in winter (see below) while those in tropical areas are more localized in their movements, When approaching maturity, pubescent turtles move into adult foraging habitats. In some populations adult habitats are geographically distinct from juvenile developmental habitats;24in others they may overlap or coin~ide.U~p.~on maturity as the nesting season approaches adults make a contranatant migration toward the nesting beaches. Most mating occurs t poorly defined courtship areas that are clone KÃthe nesting beaches relitlive lo the distant foraging areas. Afler mating the females move to their respcclivc nesting beaches.'-* Courtship areas may be directly HITthe nesting beaches,*or remote from the beaches,'" depending on the population. During the nesting season, females usually become resident in the internesting habitat in the vicinity of the nesting beach." The focus of the present paper is habitat utilization and migration of juvenile sea turtles and nursery and developmental habitats. 

 

Date
1997
Data type
Book
Theme
Research and monitoring

Climate change and temperature-linked hatchling mortality at a globally important sea turtle nesting site

The study of temperature-dependent sex determination (TSD) in vertebrates has attracted major scientific interest. Recently, concerns for species with TSD in a warming world have increased because imbalanced sex ratios could potentially threaten population viability. In contrast, relatively little attention has been given to the direct effects of increased temperatures on successful embryonic development. Using 6603 days of sand temperature data recorded across 6 years at a globally important loggerhead sea turtle rookery—the Cape Verde Islands—we show the effects of warming incubation temperatures on the survival of hatchlings in nests. Incorporating published data (n = 110 data points for three species across 12 sites globally), we show the generality of relationships between hatchling mortality and incubation temperature and hence the broad applicability of our findings to sea turtles in general. We use a mechanistic approach supplemented by empirical data to consider the linked effects of warming temperatures on hatchling output and on sex ratios for these species that exhibit TSD. Our results show that higher temperatures increase the natural growth rate of the population as more females are produced. As a result, we project that numbers of nests at this globally important site will increase by approximately 30% by the year 2100. However, as incubation temperatures near lethal levels, the natural growth rate of the population decreases and the long-term survival of this turtle population is threatened. Our results highlight concerns for species with TSD in a warming world and underline the need for research to extend from a focus on temperature-dependent sex determination to a focus on temperature-linked hatchling mortalities.

Date
2017
Data type
Scientific article
Theme
Research and monitoring

Temporal, spatial, and body size effects on growth rates of loggerhead sea turtles (Caretta caretta) in the Northwest Atlantic

Abstract In response to a call from the US National Research Council for research programs to combine their data to improve sea turtle population assessments, we analyzed somatic growth data for Northwest Atlantic (NWA) loggerhead sea turtles (Caretta caretta) from 10 research programs. We assessed growth dynamics over wide ranges of geography (9–33°N latitude), time (1978–2012), and body size (35.4–103.3 cm carapace length). Generalized additive models revealed significant spatial and temporal variation in growth rates and a sig- nificant decline in growth rates with increasing body size. Growth was more rapid in waters south of the USA (\24°N) than in USA waters. Growth dynamics in southern waters in the NWA need more study because sample size was small. Within USA waters, the significant spatial effect in growth rates of immature loggerheads did not exhibit a consistent latitudinal trend. Growth rates declined signifi- cantly from 1997 through 2007 and then leveled off or increased. During this same interval, annual nest counts in Florida declined by 43 % (Witherington et al. in Ecol Appl 19:30–54, 2009) before rebounding. Whether these simul- taneous declines reflect responses in productivity to a common environmental change should be explored to determine whether somatic growth rates can help interpret population trends based on annual counts of nests or nesting females. Because of the significant spatial and temporal variation in growth rates, population models of NWA loggerheads should avoid employing growth data from restricted spatial or temporal coverage to calculate demographic metrics such as age at sexual maturity. 

Date
2013
Data type
Scientific article
Theme
Research and monitoring
Journal

Conservation Efforts Continued: New Vegetation on Te Amo Beach

In the beginning of January, as part of the Ecological Restoration of Lac and the South of Bonaire, 50 green buttonwood trees (a native species of mangrove) were planted along the inside of the fence on Te Amo Beach. Over time, the green buttonwood will form a natural barrier that will replace the existing fence.

 The fence, which is covered in palm leaves, has been effective at reducing light pollution from the airport, thereby reducing the disorientation of nesting turtles and hatchlings at Te Amo Beach. As the vegetation alongside the fence grows, it will further reduce light from the airport and the road.

The new vegetation will help nesting turtles, such as the critically endangered hawksbill that likes to nest underneath shore plants. The roots of the trees will also bind the sand, which in its turn prevents the sand from blowing away, maintaining one of Bonaire’s precious beaches. The new vegetation is therefore a win-win; preserving the beach for sea turtles and for humans too!

The conservation efforts at Te Amo Beach, for which Sea Turtle Conservation Bonaire partnered with WILDCONSCIENCE BV, are part of the Ecological Restoration of Lac and the South of Bonaire: a project that is coordinated by the openbaar lichaam Bonaire and funded with ‘natuurgelden’ made available by the Dutch government. In addition, Green Label Landscaping N.V. has sponsored part of the tree planting and also the watering of the plants during their first month to ensure that the buttonwood grows successfully.

Date
2017
Data type
Media
Theme
Education and outreach
Research and monitoring
Geographic location
Bonaire
Author

Thousands of single nucleotide polymorphisms in the critically endangered Kemp's Ridley sea turtle (Lepidochelys kempii) revealed by double-digest restriction-associated DNA sequencing: opportunities for previously elusive conservation genetics research

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. 

Date
2016
Data type
Scientific article
Theme
Research and monitoring

Long-term movements of an adult male Kemp's Ridley sea turtle (Lepidochelys kempii) in the northwestern Gulf of Mexico

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. 

Date
2016
Data type
Scientific article
Theme
Research and monitoring

Evaluation of the Status of the Kemp’s Ridley Sea Turtle After the 2010 Deepwater Horizon Oil Spill

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. 

Date
2016
Data type
Scientific article
Theme
Research and monitoring

Development of a Kemp’s Ridley Sea Turtle Stock Assessment Model

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. 

Date
2016
Data type
Scientific article
Theme
Research and monitoring