Methods: Study Site

Beaches in North East Tobago (11°19′13.53″N, −060°33′1.57″E) were surveyed for sea turtle nesting activity (Fig. 1). Beaches are enclosed by steep, vegetation-covered slopes without human development with the exception of a beach facility at Bloody Bay (BLO; see Fig. 1) and a parallel population settlement at Charlotteville Beach (CHA). Beaches were categorized as either index or nonindex (Fig. 1). Beaches Hermitage Bay (HER) and Campbleton Bay (CAM) were selected as index beaches based on high levels of nesting activity reported by locals, a history of patrols in past years, and accessibility that allowed for regular monitoring. Surveys were conducted by a group of international volunteers and members of a local conservation organization trained on site by an experienced sea turtle ecologist.

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Methods: Patrol Protocols

Two patrol protocols were used. On beach checks, beaches were checked by foot for signs of sea turtle nesting activity. Observations were indirect and required interpretation of characteristic nesting crawls (Schroeder and Murphy 1999). For each nesting event date, the time, beach, and Global Positioning System co-ordinates were recorded. Nesting event outcomes were categorized as either 1) a confirmed lay—visually confirmed oviposition, 2) an estimated lay—only a camouflaged nest site observed, 3) a false crawl—a nonnesting emergence, or 4) unknown—where the outcome could not be determined (e.g., a weathered nesting event). Upon discovering carcasses, shells, or evidence that a sea turtle had been removed from the beach, an outcome of poaching was recorded. A carcass or shell was identified from anatomical features (Pritchard and Mortimer 1999; Wyneken 2001). Estimated lay categorization was validated using a subset of nests on beach CAM. For all estimated lays recorded in April and May (n  =  7), the estimated location of the egg chamber was triangulated (± 0.1 cm) and monitored for hatching. Observation of hatchling emergence in 100% of cases confirmed oviposition had occurred and validated the method. After completing an event report, the body-pit was flattened and tracks destroyed to avoid double-recording. Beach checks occurred predominantly in daylight (0600–1800 hrs), although a minority of checks occurred during other hours.

Beach patrols took place between 2100 and 0230 hrs in order to intercept and tag nesting females. Hawksbill nesting is typically nocturnal (Beggs et al. 2007). During the specified hours, patrollers repeatedly surveyed the entire length of each beach on foot at roughly 25-min intervals to ensure females were encountered prior to egg-laying. During turtle encounters, stage of nesting process (Alvarado and Murphy 1999) and departure time were recorded. Once oviposition commenced and approximately 20 eggs had been laid, each turtle was measured and examined for flipper tags, numbers were recorded, or tags applied. Identifying physical features were noted, as were scars from lost tags. All crawl tracks were subsequently destroyed. No identified nesting turtle was left on the beach even when nesting events extended beyond 0230 hrs.

Inconel 1005-681 flipper tags were provided by the Marine Turtle Tagging Centre in Barbados and applied to turtles following a standard method described by Eckert and Beggs (2006). Tags were available for 46 days (d) from 22 June (Julian Day [JD]174) to 6 August (JD219), and again for 70 d from 23 August (JD236) until cessation of monitoring (JD305). Turtles that could not be tagged were identified from mapped and/or photographed physical features (pigmentation markings, epibiotic barnacle coverage, damage, and/or injuries) and lay date (Beggs et al. 2007). A flexible measuring tape (± 0.1 cm) was used to measure curved carapace length (notch-to-tip [N–T] and notch-to-notch [N–N]) and curved carapace width (Bolten 1999).

Methods: Survey Season and Survey Effort

The project ran for 245 d between 1 March 2012 (JD61) and 31 October 2012 (JD305). During this period, 324 beach checks were conducted across all beaches. The median monthly number of visits to each beach was 1 (range  =  0–31). Body-pits or tracks can remain conspicuous for a number of weeks after a nesting emergence (Schroeder and Murphy 1999); therefore, even relatively infrequent beach checks are an effective methodology to confirm the presence of sea turtle nesting activity during the sampled period. Such checks are at worst an underestimate of abundance.

Based on the precedent of a long-term study on the adjacent island of Barbados (Beggs et al. 2007), hawksbill nesting activity is highest in the months of June to August. This agrees with local anecdotal information. For a core period of 92 d from JD153 to JD244, beach patrols were conducted on 83 d (79%) for beach HER and 84 d (80%) for beach CAM. Less frequent beach patrols were also conducted in May (15 d from JD122 to JD152) and September (4 d from JD245 to JD274). For the period of 153 d between May (JD122) and September (JD274), 186 beach patrols were conducted on the 2 index beaches.

Methods: Data from Previous Seasons

For 4 yrs (2007, 2008, 2010, and 2011), intermittent monitoring and patrolling was undertaken as part of turtle conservation and monitoring activities on various beaches within the study site. Methods were variations on beach check and patrol protocols presented above. As a consequence of mixed methodologies and recording, interannual comparisons are not possible. Also, reliable data on patrol effort are not available. The data do, however, reliably indicate species and the occurrence of nesting and poaching activity.

Results

A summary of hawksbill nesting-event data collected during both beach checks and patrols for all beaches surveyed in 2012 is presented in Table 1. Four beaches were surveyed for the first time in 2012: Waterfall Bay (WAT), Dead Man's Bay (DMB), Lovers Bay (LOV), and Kings Bay (KIN).

Table 1. Hawksbill nesting events in North East Tobago, 1 March–31 October 2012 (JD61–JD305). Index beaches are indicated by an asterisk (*). In the Total nests column, the number of estimated lays (ELs) is given in parentheses. N/A  =  not applicable (see Fig. 1 legend for definition of beach abbreviations).

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Thirty-five leatherback turtle nesting events were recorded in the region with nests at Dead Bay (DEA; n  =  8), BLO (n  =  9), and CHA (n  =  1). False crawls were recorded at DEA (n  =  6), BLO (n  =  1), CAM (n  =  4), and unknowns were recorded at DEA (n  =  5) and BLO (n  =  1). One green turtle deposited 2 clutches at beach HER and false-crawled once.

Fifty-eight individual hawksbill sea turtles were identified at index beaches during the patrol period (JD122–JD274): 31 at HER and 27 at CAM. Of these, 49 were tagged: 26 at HER and 23 at CAM. Nine other turtles were identified from unique features but were not tagged. On 5 occasions turtles seen without distinguishing features could be > 1 individual and are included as 1 individual in the reported count of untagged individuals. Only the 49 hawksbill turtles tagged during the 2012 season were encountered at the site, and no healed tag scars were recorded. Of the 58 individuals identified nesting at index beaches, 32 nested more than once on the same index beach. There were no records of a sea turtle nesting on the opposite index beach to which it was first tagged. Mean hawksbill length (± SD) was 88.95 (± 3.79) cm (N–T) and 85.64 (± 3.86) cm (N–N); width was 79.06 (± 3.65) cm (n  =  47). Mean hawksbill nesting duration (n  =  66) was 0143 (± 0031) hrs.

Female hawksbills commonly deposit 3–5 egg clutches per nesting season (Beggs et al. 2007). Beggs et al. (2007) demonstrate that 100% beach fidelity is not uncommon for nesting hawksbills. Assuming 100% beach fidelity, the observed number of nests at index site HER (Table 1) corresponds to between 68% and 114% of the expected nests (exp. 93–155) for the 31 individually identified sea turtles. At CAM observed nests (Table 1) corresponds to between 84% and 140% of expected nests (exp. 81–135) for the 27 individually identified sea turtles. The ratios of false crawls to successful nesting were 4.18∶1 (HER) and 4.82∶1 (CAM). The temporal variation in hawksbill nesting at index beaches conforms to a Gaussian distribution, with a distinct peak during the month of July (Fig. 2), indicating that the sampling period encapsulated the peak in nesting.

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Data from past seasons are presented in Table 2. All crawls resulted in a successful nesting event, with the exception of beach CHA in 2007 where only a false crawl was recorded.

Table 2. Data from previous seasons indicating presence (x) of hawksbill nesting and number of crawls (C) and poachings (P) for 9 beaches in North East Tobago. An empty cell does not distinguish between no patrols and patrols but no events (see Fig. 1 legend for definition of abbreviations).

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Poaching events are presented in Tables 1 and 2. One instance of attempted egg poaching was reported for beach CAM and 2 dead turtles (1 hawksbill and 1 leatherback) were found buoyant in Man O'War Bay adjacent to index sites during the 2012 season.

Discussion

The 2012 results (Table 1) reveal that the North East Tobago site hosts a population of hawksbill turtles that is of regional and local conservation relevance. Regional comparisons are difficult because reported categories of geographic aggregation vary widely. We refer to North East Tobago as a site composed of a series of proximal beaches available for sea turtle nesting, based on the strong nesting fidelity exhibited by the species toward 1 or 2 adjacent beaches (Beggs et al. 2007). Dow et al. (2007) identify only 3 hawksbill nesting sites with > 1000 crawls/yr in the wider Caribbean region: Punta Xen in Mexico (30 km), the beaches of Puerto Rico (9 km), and the West coast of Barbados (32 km). By comparison, 427 events were documented in 2012 at the North East Tobago site (3.185 km). Based on the survey methods used in this study, these events are most likely an underestimate of actual hawksbill nesting activity. This result demonstrates that there is a significant concentration of hawksbill nesting activity in North East Tobago, which warrants increased patrols and on-going conservation efforts.

Further, with > 100 crawls beaches HER and CAM have regional significance and are appropriate index beaches. Only 36 of 817 beaches reported by Dow et al. (2007) support this level of nesting activity in the Caribbean. Based on this single year of data, the number of turtles at the North East Tobago site compares with the mean annual abundance reported by projects in Jumby Bay Island Antigua (Tilley et al. 2012), Guadeloupe (Kamel and Delcroix 2009), and Martinique (La Gazette des Karets 2006).

Data from previous years (Table 2) indicate that the 2012 survey results represent persistent hawksbill sea turtle nesting activity at the North East Tobago site. Reports of nesting activity on 4 previously unsurveyed beaches (WAT, DMB, LOV, and KIN) reveal that hawksbill nesting activity is more widespread than was previously reported at the North East Tobago site.

Fifty-eight untagged turtles observed at index beaches in 2012 provide evidence that there is a significant population of hawksbill turtles at the site. No tags or tag scars were recorded; therefore, these individuals likely represent novel encounters with previously unknown females.

Our surveys were not comprehensive enough to allow definitive statements about within-season nesting beach fidelity. Our results, however, show no evidence of a sea turtle nesting on > 1 beach, which agrees with the high beach fidelity recorded by Beggs et al. (2007). Based on our model of 3–5 clutches per female with 100% beach fidelity, the number of nests observed versus expected at index beaches reveals that saturation monitoring was likely achieved and that 2012 results reflect the true level of activity. At nonindex beaches, where monitoring was undertaken irregularly, abundance counts are likely underestimated.

Hawksbill nesting showed a marked increase during summer months, which is a pattern generally repeated in the Caribbean region (Barbados, Beggs et al. 2007; Mexico, Perez-Catañeda et al. 2007). The temporal variation in nesting (Fig. 2) indicates that an extension to the patrol period is warranted in order to capture the later activity peak observed in hawksbill nesting activity (JD211) compared with leatherback nesting activity, which may occur 2 mo earlier in the season (JD136; Forestry Division et al. 2010) and from which survey effort was set.

Eighty-six poaching events (Tables 1 and 2) demonstrate that sea turtles are consistently and heavily exploited at the North East Tobago site despite full protection mandated by national legislation (Conservation of Wildlife Act 1958, amended 1963; Fisheries Act of 1916, amended 2012). A dramatic reduction in recorded poaching events at index beaches from 2011 to 2012 may be due to intensive patrols in 2012. Conversely, reductions in recorded poaching events from 2011 to 2012 at some of the nonindex beaches are likely artefacts of limited patrol effort. Temporary shelters constructed on some of these beaches during peak nesting months in 2012 suggest substantial effort by poachers. Patrollers also encountered elaborate methods of carcass disposal and destruction of indirect evidence such as obscured sea turtle tracks and drag-marks. These observations, coupled with anecdotal accounts of sea turtle poaching and of readily available sea turtle meat, locally suggest that a high proportion of the annual nesting cohort may be taken at some beaches. Unconfirmed reports of capture in illegally set gill nets within the site, as well as 2 dead sea turtles found floating nearby during the 2012 season, suggest that capture at sea may also constitute a significant poaching threat.

The results of this study quantify a previously undocumented, regionally important rookery for the globally critically endangered hawksbill sea turtle, consisting of untagged reproductive females. The amount of nesting activity at the 2 index beaches suggests that Man O' War Bay, where both are situated, is critical habitat for this species, which may also extend to coastal waters and beaches throughout the site.

Results also indicate a consistently high and likely unsustainable level of poaching at beaches throughout the site. Limited law enforcement (Forestry Division et al. 2010) and limited capacity to consistently patrol all nesting beaches within the site mean that there is little deterrent to poaching. The rookery may therefore be at critical risk.