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St. Kitts (17°9’N 62°45’W) is a small Caribbean island of volcanic origin that is part of the Lesser Antilles chain. As part of a larger marine ecosystem survey project (Stimmelmayr et al. 2009; Sullivan & Stimmelmayr 2009), sightings of sea turtles have been recorded during roving snorkel (day), and dive surveys (night/day) (2006-2008) on 29 study sites (D = dive sites; S=snorkel sites) including: Anchors Away (D), Ballast Bay (S), Banana Bay (S), Brimstone (D), Channel (D), Cockleshell (S), Challenger (D), Coconut Reef (D), Corinthian (D), Dieppe Bay (S), Fisherman’s Wharf (D) Green Point (D), Half Moon Bay (S), Majors Bay (S), Monkey Shoals (S), Nags Head (D), Paradise Reef (D), River Taw (D), Sandbank (S), Shipping Lane (D), Shitten Bay (S), South Friars (S), St. Peter’s Reef (D), Talata (D), The Rocks (D), Timothy Beach (S), Turtle Beach (S), West Farm (D), and Whitehouse Bay (S). Study sites were mostly on the Caribbean side of the island with few sites located on the Atlantic side due to strong surf and dangerous current conditions. Sites were surveyed opportunistically; however, all night dive/snorkel surveys were limited to 6 sites only (Corinthian, Fisherman’s Wharf, Talata, Half Moon Bay, Majors Bay, and Sandbank). Observations of marine turtles in water were made from the surface using standard snorkeling (water depth<6m) and SCUBA equipment (water depth >6m). Data collected included species, estimated straight carapace length (cm), location, time of day (morning, afternoon, night), and behavior. Classification of behavior was used as previously described by Houghton et al. (2003). Upon encountering a turtle, we made an observation of initial behavior (surfacing, swimming, resting, assisted resting, foraging). Briefly, foraging is defined as ingestion of prey while being stationary and or suspended in the water column. Resting is defined as remaining stationary on the seabed/coral reef structure without foraging. Assisted resting is defined as resting with the use of coral reef structures and/or man-made structures under which and/or between which the turtle is wedged. To gain insight into local threats to sea turtles, we also recorded types and causes of injury (when possible) in sea turtles.

We recorded 140 turtle sightings (morning n=71; afternoon n=33; nighttime n=36). Forty-nine percent (n=69) occurred around the bays of the South East Peninsula. The majority (85%) of sea turtles sighted were juvenile with estimated carapace length ranging from 20-60 cm. Only 15% of observed sea turtles were large (80- 130 cm) adult, possibly resident, turtles. Sightings of large turtles were restricted to the Atlantic side (Half-moon Bay; Sandbank) and/or during dive surveys. Hawksbill turtles were the predominate species observed (n=128), with fewer green turtles observed (n=12). No injuries and/or other abnormalities were observed in juvenile hawksbills. Injuries and abnormalities observed in adult turtles included missing rear flipper (n=1; hawksbill), cracked carapace (n=1; hawksbill); discolored shell (n=1; hawksbill), and fibropapillomatosis (n=1; green turtle).

Figure 1. Daily temporal distribution of in-water behavior of observed hawksbill and green sea turtles (n=140) in St. Kitts (2006-2008).

During morning hours turtles were most often seen swimming (61%; n=43), followed by resting (30%; n=21), assisted resting (7%; n=5), surfacing (1%; n=1), and foraging (1%; n=1) (Figure 1). Foraging was rarely observed (1-3 %) during all time periods. During afternoon a similar pattern was observed, with 60% of turtles seen swimming (n= 20), followed by assisted resting (21%; n=7), resting (12%, n=4), surfacing (3%; n=1), and foraging (3%; n=1). During nighttime, 50% of turtles were observed in assisted resting (n=18), followed by swimming (42%; n=15), resting (6%; n=2), and foraging (3%; n=1).

Our results confirm that St. Kitts’ near shore environments are important habitats for immature hawksbills, particularly along the Southeast Peninsula. The total number of injuries observed was few (n=4; 3%) and none of the observed injuries were fishing or boating related injuries, as characterized by Norem (2005). Apart from the observed case of rear flipper amputation, we have only circumstantial evidence that points to shark predation being a potential mortality/injury factor for the local sea turtle populations. In 2007 and 2008, local marine stakeholders observed two adult marine turtle strandings (hawksbill; green turtle) with large bite wounds to the shell and partial and complete amputation of front and rear flippers. Tiger sharks (Galeocerdo cuvieri), who preferentially prey on large cheloniid sea turtles (Witzell 1987) are not uncommon in the marine environment of St. Kitts and Nevis (Captain Ainslyn pers. comm.), and a case of a large tiger shark with ingested remains of a small hawksbill turtle has been reported from Nevis (Young 1992).

Our observation of a severe case of cutaneous fibropapillomatosis in an adult resident green turtle confirms previous sightings by local marine knowledge holders (Kenneth Samuels pers. comm.). Marine turtle fibropapillomatosis has a circumtropical distribution including the Caribbean region (Aguirre & Lutz 2004; Williams et al. 1994). This virus-induced disease is characterized by a protracted external (flippers, head) and internal (esophagus; liver) tumor growth. Depending on location, tumors may impede foraging efficiency and can ultimately be fatal.

Assisted resting showed a distinct temporal pattern as it was most commonly observed at night (50%), followed by afternoon (21%), and morning (7%). Diel diving patterns in hawksbill turtles (juvenile and adults) with flat bottomed resting dive profiles have been reported to take up 50-80% of the time during night (van Dam & Diez 1996; Starbird et al. 1999). However, these studies used electronic dive recorders that cannot discriminate between resting and assisted resting. We observed 12% of the turtles displaying assisted resting (12/104). Similarly, Houghton et al. (2003) reported that juvenile hawksbills in the Seychelles displayed assisted resting 12% of the time. Blumenthal et al. (2009) reported that assisted resting occurred during nighttime in the Cayman Islands; however, comparative nighttime data on percentage of assisted resting are not available.

Assisted resting may be a useful strategy for improving buoyancy control at greater depths by turtles, thus, maximizing dive duration (Houghton et al. 2003). Blumenthal et al. (2009) hypothesized that assisted resting may allow sea turtles to improve large pelagic predator avoidance by shelter seeking during nighttime.

Additionally, microhabitats such as assisted resting sites come with their own microclimate that could confer a thermoregulatory advantage to turtle energetics while resting. The ability for thermal selection has been recently demonstrated in free-ranging adult loggerhead turtles (Schofield et al. 2009). In addition, ledges and large crevices used as assisted resting sites are also suitable habitats for cleaner shrimp. Hawksbill turtles in Brazil have been shown to actively visit cleaning stations by Barber pole shrimp (Stenopus hispidus) (Sazima et al. 2004). Interestingly, a hawksbill’s visit to the cleaner station during daytime looked very much like an assisted resting turtle, with the turtle’s body being partly wedged under rocky ledges where the cleaner stations were located. Barber pole shrimp do not venture from their station and attend to clients from within the crevice/ledges. We did not explore ledges where turtles were resting, thus we do not know whether cleaner shrimp were present.

From a bioenergetics point of view, assisted resting is a behavioral strategy that most likely translates into an ecological and energetic benefit, whether it represents shelter-seeking behavior motivated by buoyancy control issues, predator avoidance, visitation to a cleaner station and removal of ectoparasites, or a search for a suitable microclimate. Because our study turtles during nighttime were more often engaged in assisted resting (50%) than resting (6%), we suggest that the overall energetic benefit of assisted resting is likely greater than resting.

Our study confirms that the St. Kitts near shore marine environment provides important habitats for juvenile hawksbill. Assisted resting in turtles was the predominant type of resting observed during nighttime. Further in situ studies of in-water behavior are needed to confirm our findings on the distinct temporal pattern of assisted resting and to identify and characterize the underlying ecological and physiological factors that are important in shaping the observed timing difference in assisted resting vs. resting.

Acknowledgements: We especially thank Kate Orchard (St. Christopher Heritage Society), Captain Ainslyn (Department of Fisheries, Nevis), Ralph Wilkins (Department of Fisheries, St. Kitts), Lionel Pemberton (Department of Fisheries, Nevis), and Kenneth Samuels (Kenneth Dive Center, St. Kitts) for sharing local ecological knowledge on nesting and in water sea turtle threats with us, as well as knowledge on local turtle harvest techniques and human consumption patterns. Special thanks to Dr. J. Maier and two anonymous reviewers for critical comments on the manuscript. For contributing additional sighting information we thank in alphabetical order: T. Beths, L. Betance, J. Browning, J. Carloni, J. DeGroves, S. Fitzharris, F. Heidema, G.Touzot-Jourdes, S. Mottram, D. Mottram, and the Ross University Scuba and Swim Club.

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