Margaret M. Lamont

INCREASED INCIDENCE OF RED IMPORTED FIRE ANT (HYMENOPTERA: FORMICIDAE) PRESENCE IN LOGGERHEAD SEA TURTLE (TESTUDINES: CHELONIIDAE) NESTS AND OBSERVATIONS OF HATCHLING MORTALITY

Red imported fire ants, Solenopsis invicta Buren, were introduced to North America in the 1930s (Buren 1972). Since their introduction, fire ant distribution and abundance has continued to increase dramatically. Fire ants have infested more than one hundred million hectares and expanded their range throughout most of the southeastern United States (Callcott & Collins 1996). Fire ants are an omnivorous and opportunistic species, and are often aggressive predators and competitors of native species. Fire ants have the potential to negatively affect vertebrates (Allen et al. 1994). Oviparous species may be especially vulnerable to fire ant predation, particularly ground nesting birds and reptiles (Allen et al. 1994, Allen et al. 1997, Tuberville et al. 2000, Wojcik et al. 2001). Observations of fire ant predation on amphibian and reptilian eggs and hatchlings have been reported for numerous species (Landers et al. 1980, Mount et al. 1981, Freed & Neitman 1988, Montgomery 1996, Allen et al. 1997, Buhlmann & Coffman 2001). The occurrence of red imported fire ants in green sea turtle, Chelonia mydas, and loggerhead sea turtle, Caretta caretta, nests have been documented (Wilmers et al. 1996, Moulis 1997), however few researchers have been able to document observations of hatchling mortality due to fire ants. Hatching sea turtles may be particularly vulnerable to fire ant predation. Sea turtles are oviparous, subterranean nesting species. Prior to hatchling emergence from the nest, newly hatched turtles remain in the ground for up to seven days (Lohmann et al. 1997), during which they may be susceptible to injury from fire ants. In addition, fire ants primarily feed on high protein resources during brood production in late spring, which coincides with the start of sea turtle nesting season. In this paper, we provide observations of predation by fire ants on loggerhead sea turtle hatchlings on Cape San Blas, Florida. Cape San Blas, a coastal barrier island along the Northern Gulf of Mexico, supports the largest density of nesting loggerhead turtles in northwest Florida (Fig. 1). Encalada et al. (1998) identified this group of nesting loggerhead sea turtles as genetically distinct from other nesting populations in southeastern United States. Surveys for nesting sea turtles have been conducted every year since 1994 along Eglin Air Force Base property on Cape San Blas by foot and on ATV. Two surveyors conducted daily monitoring surveys of the 5-km area from 6:00 am to 10:00 am every morning from May 15 to August 15. From August 15 to October 31, nests were observed daily for signs of hatchling emergence or depredation. Nest inventories were conducted 72 h after first emergence or after 85 days of incubation, and number of hatched, unhatched, and depredated eggs was recorded. Red imported fire ant presence was not recorded in sea turtle nests on Cape San Blas before 1995 (Table 1). In 1995, fire ants were observed on one of 60 loggerhead sea turtle nests; however, fire ant induced hatchling mortality was not documented. In 1996, fire ant presence was not recorded on any of the 25 loggerhead sea turtle nests. Fire ants were observed again in 1997 on 14 of 54 loggerhead nests (25.9%). Hatchling mortality was witnessed at two of the 54 nests (3.7%). Upon excavation of one nest, fire ants were observed consuming one sea turtle hatchling that had cracked (pipped) the egg shell, entering and stinging a live turtle within a second pipped egg, and stinging a third hatchling. In the second nest, fire ants were observed consuming an undetermined number of pipped eggs, and skeletonizing five hatchlings before emergence from the nest. In 1998, fire ants were observed on 10 of 57 nests (17.5%). Fire ant depredation resulted in mortality of 23 hatchlings, combined in three of the 57 nests (5.3%). Hatchling mortality was not recorded in the remaining seven fire ant infested nests. In 1998, surveyors observed one hatchling being consumed by fire ants near the nest surface. Upon excavation of the nest, an additional twenty dead hatchlings and one live hatchling were observed covered with fire ants. Fifteen live hatchlings were removed from the infested nest and released. Injures observed on numerous live hatchlings included blinding due to removal of eyes and wounds on head and flippers due to necrotizing fire ant stings. All fire ant induced hatchling mortalities were observed in nests left to incubate in-situ along the North beach, not in the nests relocated to East beach.

Determining origin in a migratory marine vertebrate: a novel method to integrate stable isotopes and satellite tracking

Stable isotope analysis is a useful tool to track animal movements in both terrestrial and marine environments. These intrinsic markers are assimilated through the diet and may exhibit spatial gradients as a result of biogeochemical processes at the base of the food web. In the marine environment, maps to predict the spatial distribution of stable isotopes are limited, and thus determining geographic origin has been reliant upon integrating satellite telemetry and stable isotope data. Migratory sea turtles regularly move between foraging and reproductive areas. Whereas most nesting populations can be easily accessed and regularly monitored, little is known about the demographic trends in foraging populations. The purpose of the present study was to examine migration patterns of loggerhead nesting aggregations in the Gulf of Mexico (GoM), where sea turtles have been historically understudied. Two methods of geographic assignment using stable isotope values in known-origin samples from satellite telemetry were compared: (1) a nominal approach through discriminant analysis and (2) a novel continuous-surface approach using bivariate carbon and nitrogen isoscapes (isotopic landscapes) developed for this study. Tissue samples for stable isotope analysis were obtained from 60 satellite-tracked individuals at five nesting beaches within the GoM. Both methodological approaches for assignment resulted in high accuracy of foraging area determination, though each has advantages and disadvantages. The nominal approach is more appropriate when defined boundaries are necessary, but up to 42% of the individuals could not be considered in this approach. All individuals can be included in the continuous-surface approach, and individual results can be aggregated to identify geographic hotspots of foraging area use, though the accuracy rate was lower than nominal assignment. The methodological validation provides a foundation for future sea turtle studies in the region to inexpensively determine geographic origin for large numbers of untracked individuals. Regular monitoring of sea turtle nesting aggregations with stable isotope sampling can be used to fill critical data gaps regarding habitat use and migration patterns. Probabilistic assignment to origin with isoscapes has not been previously used in the marine environment, but the methods presented here could also be applied to other migratory marine species.

Movements and Habitat-Use of Loggerhead Sea Turtles in the Northern Gulf of Mexico during the Reproductive Period

Nesting strategies and use of important in-water habitats for far-ranging marine turtles can be determined using satellite telemetry. Because of a lack of information on habitat-use by marine turtles in the northern Gulf of Mexico, we used satellite transmitters in 2010 through 2012 to track movements of 39 adult female breeding loggerhead turtles (Caretta caretta) tagged on nesting beaches at three sites in Florida and Alabama. During the nesting season, recaptured turtles emerged to nest 1 to 5 times, with mean distance between emergences of 27.5 km; however, several turtles nested on beaches separated by ∼250 km within a single season. Mean total distances traveled throughout inter-nesting periods for all turtles was 1422.0±930.8 km. In-water inter-nesting sites, delineated using 50% kernel density estimation (KDE), were located a mean distance of 33.0 km from land, in water with mean depth of −31.6 m; other in-water inter-nesting sites, delineated using minimum convex polygon (MCP) approach, were located a mean 13.8 km from land and in water with a mean depth of −15.8 m. Mean size of in-water inter-nesting habitats were 61.9 km2 (50% KDEs, n = 10) and 741.4 km2 (MCPs, n = 30); these areas overlapped significantly with trawling and oil and gas extraction activities. Abundance estimates for this nesting subpopulation may be inaccurate in light of how much spread there is between nests of the same individual. Further, our results also have consequences for critical habitat designations for northern Gulf loggerheads, as protection of one nesting beach would not encompass the entire range used by turtles during breeding seasons.

Migration, foraging, and residency patterns for Northern Gulf loggerheads: implications of local threats and international movements.

Northern Gulf of Mexico (NGoM) loggerheads (Caretta caretta) make up one of the smallest subpopulations of this threatened species and have declining nest numbers. We used satellite telemetry and a switching state-space model to identify distinct foraging areas used by 59 NGoM loggerheads tagged during 2010–2013. We tagged turtles after nesting at three sites, 1 in Alabama (Gulf Shores; n = 37) and 2 in Florida (St. Joseph Peninsula; n = 20 and Eglin Air Force Base; n = 2). Peak migration time was 22 July to 9 August during which >40% of turtles were in migration mode; the mean post-nesting migration period was 23.0 d (±13.8 d SD). After displacement from nesting beaches, 44 turtles traveled to foraging sites where they remained resident throughout tracking durations. Selected foraging locations were variable distances from tagging sites, and in 5 geographic regions; no turtles selected foraging sites outside the Gulf of Mexico (GoM). Foraging sites delineated using 50% kernel density estimation were located a mean distance of 47.6 km from land and in water with mean depth of −32.5 m; other foraging sites, delineated using minimum convex polygons, were located a mean distance of 43.0 km from land and in water with a mean depth of −24.9 m. Foraging sites overlapped with known trawling activities, oil and gas extraction activities, and the footprint of surface oiling during the 2010 Deepwater Horizon oil spill (n = 10). Our results highlight the year-round use of habitats in the GoM by loggerheads that nest in the NGoM. Our findings indicate that protection of females in this subpopulation requires both international collaborations and management of threats that spatially overlap with distinct foraging habitats.

Declining Reproductive Parameters Highlight Conservation Needs of Loggerhead Turtles (Caretta caretta) in the Northern Gulf of Mexico

Abstract Marine turtles in the Gulf of Mexico are at risk due to many anthropogenic threats including habitat degradation, commercial fishing, and petroleum activities. The severity of this risk was made apparent in 2010 with the occurrence of the Deepwater Horizon oil spill. The objectives of this study were to assess long-term trends in abundance and reproductive parameters for this genetically distinct nesting group. From 1994 to 2010, morning surveys were conducted along 3 beaches on the St Joseph Peninsula, Florida, including within our primary study site on Cape San Blas. Nest abundance on all 3 beaches declined by at least 47% (p < 0.01). Mean nesting success on Cape San Blas was 40% and also declined (p  =  0.002). Mean clutch size was 108 and mean emergence success was 58%. Throughout the study there were no changes in clutch size and emergence success. We found that nesting characteristics for the northern Gulf of Mexico subpopulation appear similar to those from other loggerhead turtle nesting groups in the southeastern United States in some ways, such as emergence success, timing of peak nesting, and incubation duration and different in other ways such as nesting success. Variation in some of the parameters may indicate turtles among the different nesting groups experience different environmental conditions. The severity of declines in nest abundance and the low nesting success reported for this small subpopulation suggest potentially serious consequences for this nesting group.

Response of Nesting Sea Turtles to Barrier Island Dynamics

ABSTRACT Although barrier island beaches provide important nesting habitat for sea turtles, they are constantly changing. To determine how nesting sea turtles have responded to this dynamic environment, we assessed: 1) wind, current, and tidal patterns and changes in beach profiles, 2) sea turtle nesting patterns, and 3) success of turtle nests deposited along 5 km of beach on Cape San Blas, Florida, an extremely dynamic barrier beach in northwest Florida. From 1998 to 2000, nesting turtles were tagged, nests were monitored, and hatching success was determined. Throughout this study, West beach lost ∼ 5 m of sand while East beach gained ∼ 4 m; however 61% of nests were deposited on West beach and 39% on East beach. Hatchling emergence success did not differ between beaches. Wind direction influenced current direction and sand movement and affected the number of nests deposited along East beach but not on West beach. Nearly all nests (98%) oviposited on both beaches were deposited during a rising tide. Although West beach is narrow and eroding, the steep slope may enable nesting turtles to expend less energy to reach higher nesting sites while still providing successful nests. Nesting on a rising tide and using offshore currents during the internesting period may assist this effort.

Winter Diets of Immature Green Turtles ( Chelonia mydas ) on a Northern Feeding Ground: Integrating Stomach Contents and Stable Isotope Analyses

The foraging ecology and diet of the green turtle, Chelonia mydas, remain understudied, particularly in peripheral areas of its distribution. We assessed the diet of an aggregation of juvenile green turtles at the northern edge of its range during winter months using two approaches. Stomach content analyses provide a single time sample, and stable isotope analyses integrate diet over a several-month period. We evaluated diet consistency in prey choice over time by comparing the results of these two approaches. We examined stomach contents from 43 juvenile green turtles that died during cold stunning events in St. Joseph Bay, Florida, in 2008 and 2011. Stomach contents were evaluated for volume, dry mass, percent frequency of occurrence, and index of relative importance of individual diet items. Juvenile green turtles were omnivorous, feeding primarily on seagrasses and tunicates. Diet characterizations from stomach contents differed from those based on stable isotope analyses, indicating the turtles are not feeding consistently during winter months. Evaluation of diets during warm months is needed.

Effects of Ocean Temperature on Nesting Phenology and Fecundity of the Loggerhead Sea Turtle (Caretta caretta)

Abstract Ocean temperature is a key determinant of the distribution and phenology of marine life, particularly poikilotherms. We examined effects of ocean temperature on nesting phenology and fecundity for Loggerhead Sea Turtles (Caretta caretta) in the northern Gulf of Mexico using long-term nesting survey data from northwest Florida. The first clutch of the year was deposited earlier when sea surface temperature in months prior to the nesting season was warmer and this resulted in a longer nesting season. Nest abundance and clutch size were associated with the monthly mean temperature just prior to the nesting season, with higher fecundity occurring in warmer years. Higher nest success was associated with higher February temperature and lower May temperature. Median nest date was not associated with monthly temperature prior to the nesting season. Our results provide further details about the impacts of the thermal environment on Loggerhead Sea Turtle life history and suggest that altered ocean temperatures may affect phenology and fecundity of marine poikilotherms.

Characterization of the juvenile green turtle ( Chelonia mydas ) microbiome throughout an ontogenetic shift from pelagic to neritic habitats

The gut microbiome of herbivorous animals consists of organisms that efficiently digest the structural carbohydrates of ingested plant material. Green turtles (Chelonia mydas) provide an interesting model of change in these microbial communities because they undergo a pronounced shift from a surface-pelagic distribution and omnivorous diet to a neritic distribution and herbivorous diet. As an alternative to direct sampling of the gut, we investigated the cloacal microbiomes of juvenile green turtles before and after recruitment to neritic waters to observe any changes in their microbial community structure. Cloacal swabs were taken from individual turtles for analysis of the 16S rRNA gene sequences using Illumina sequencing. One fecal sample was also obtained, allowing for a preliminary comparison with the bacterial community of the cloaca. We found significant variation in the juvenile green turtle bacterial communities between pelagic and neritic habitats, suggesting that environmental and dietary factors support different bacterial communities in green turtles from these habitats. This is the first study to characterize the cloacal microbiome of green turtles in the context of their ontogenetic shifts, which could provide valuable insight into the origins of their gut bacteria and how the microbial community supports their shift to herbivory.

Head-Started Kemp's Ridley Turtle (Lepidochelys kempii) Nest Recorded in Florida: Possible Implications

Abstract A head-started Kemps ridley sea turtle (Lepidochelys kempii) was documented nesting on South Walton Beach, Florida on 25 May 2015. This record supports the possibility that exposure to Florida waters after being held in captivity through 1–3 yrs of age during the head-starting process may have influenced future nest site selection of this and perhaps other Kemps ridley turtles. Such findings could have important ramifications for marine water experimentation and release site selection for turtles that have been reared in captivity.