International Movements of Adult Female Hawksbill Turtles (Eretmochelys imbricata): First Results from the Caribbean's Marine Turtle Tagging Centre
Abstract
Effective management of migratory sea turtles requires informed and sustained collaboration among range states. The primary objective of the Wider Caribbean Sea Turtle Conservation Network's regional Marine Turtle Tagging Centre at the University of the West Indies, Barbados, has been to encourage and enable such collaboration, uniting otherwise isolated sea turtle tagging programs to benefit from information on the geographic range of sea turtles tagged in one country and captured, sighted, or stranded in another country. We present the first summary of information gleaned from international tag returns of adult female hawksbill sea turtles (Eretmochelys imbricata) marked with Marine Turtle Tagging Centre tags. Twenty-one sea turtle projects in 19 countries and overseas territories received Inconel 1005–681 tags from the Marine Turtle Tagging Centre between January 2002 and June 2009, and 12 of these projects have reported tagging adult female hawksbills, for a combined total of 2261 tagged individuals. Sixty-three of these individuals (2.8%), sighted at least once in another country since being tagged, have been reported to the Marine Turtle Tagging Centre; the majority of them (96.8%) were originally tagged while they were nesting in Barbados. Based on minimum straight-line distance traveled, the point of capture averaged 343.9 ± 69.7 km standard error (SE), (median 175 km) from the nesting beach. The average number of days between tagging and the first recapture was 835 ± 67.9 days SE, median 860 days). Although the majority of returns came from within a few hundred kilometers of the tagging site, tagged animals often passed through multiple exclusive economic zones and were exposed to conflicting management regimes, which include legal and illegal sea turtle fisheries. The shallow continental shelf off the coasts of Nicaragua and Honduras was confirmed as a foraging ground for Eastern Caribbean hawksbills.
Hawksbill sea turtles (Eretmochelys imbricata) forage in coastal waters, mainly on sponges in reef and other hard bottom habitats (e.g., Meylan 1988; Bjorndal 1997; León and Bjorndal 2002; Blumenthal et al. 2009; but see Bjorndal and Bolten 2010) and nest on sandy beaches throughout the Wider Caribbean Region (WCR) (Dow et al. 2007). Although now protected from harvest by a large majority of WCR governments (Dow et al. 2007), the species has been heavily exploited in this region for meat, eggs, and shell (Milliken and Tokunaga 1987; Fleming 2001; Godley et al. 2004; Bräutigam and Eckert 2006; Mortimer et al. 2007) for more than 1000 years (Frazier 2003). Hawksbills were listed as endangered on the International Union for Conservation of Nature (IUCN) Red List of Threatened Animals in 1968, a status retained until their listing as critically endangered in 1996 (IUCN 1996). The critically endangered listing was reaffirmed in the most recent Red List assessment (Mortimer and Donnelly 2007).
Long-term tagging at the nesting beach confirms that individual hawksbills nest at regular intervals, typically 4–5 times, during a reproductive season (Richardson et al. 1999) before leaving the vicinity of the nesting beach and returning to nonbreeding foraging grounds, often located in the waters of a distant country. Information on postnesting movements becomes available when tagged animals are subsequently captured by fishers, stranded, or otherwise encountered away from the point of origin (Meylan 1999). Although data accrued from satellite telemetry studies (Hillis-Starr et al. 2000; Horrocks et al. 2001; Troëng et al. 2005; Cuevas et al. 2008; van Dam et al. 2008) can yield more detailed information on WCR migratory pathways, flipper tagging continues to provide a cost-effective means to obtain information over longer periods of time on dispersal patterns and animal fate. Furthermore, flipper tagging encourages a level of communication and collaboration among stakeholders that does not ordinarily occur with satellite telemetry.
Meylan (1999) first summarized international tag return data for hawksbills in the WCR. She listed only 7 Caribbean nesting beach locations at which adult female hawksbills were regularly tagged (Tortuguero, Costa Rica; Buck Island, St Croix; Jumby Bay, Antigua; Campeche, Las Coloradas, and Isla Holbox, Mexico; Mona Island, Puerto Rico) and estimated that 2503 nesting hawksbills had been tagged over the previous 40 years. Of these animals, 18 (0.72%) were recaptured or resighted internationally, most of which came from the long-term tagging program at Tortuguero. Despite the paucity of recapture data, Meylan was able to convincingly demonstrate the migratory behavior of hawksbills, which reversed a previously held opinion that the species was nonmigratory or even sedentary (Hendrickson 1980; Witzell 1983).
In 2001, the Wider Caribbean Sea Turtle Conservation Network (WIDECAST) established a regional Marine Turtle Tagging Centre (MTTC). The MTTC is hosted by the Barbados Sea Turtle Project of the University of the West Indies, Cave Hill Campus. Since then, the MTTC has assisted the region in the development of data collection and record-keeping protocols (Eckert and Beggs 2004, 2006) and database management software (Eckert and Sammy 2008), as well as provided training, tags and tagging equipment, assistance in the purchase of more specialized tags and equipment, and rewards (T-shirts, bags, hats) to those who contribute information on tagged turtles. Finally, the MTTC has provided a secure location for participating field projects to archive tagging and other population data, if desired.
Effective management of migratory sea turtles requires informed and sustained collaboration among range states (e.g., Santo Domingo Declaration: Eckert and Abreu-Grobois 2001). The primary objective of the MTTC has been to encourage and enable such collaboration. Before its establishment, the region had little capacity to benefit from information about the geographic range, movement, growth, and fate of sea turtles tagged in one country and killed or otherwise recaptured or observed in another country. Through the MTTC, and for the first time in the WCR, the efforts of previously isolated sea turtle tagging projects to understand “their” sea turtle populations have been strengthened and united through harmonized tagging programs and centralized record keeping and reporting. The purpose of this article is to provide the first report of international tag returns from adult female hawksbills marked with MTTC tags over the period January 2002 to June 2009.
METHODS
In 2001, the MTTC purchased from National Band and Tag (USA) an inventory of flipper tags suitable for use on both hard-shelled and leatherback (Dermochelys coriacea) sea turtles, began development of database management software and a manual of recommended practices for sea turtle tagging, and convened the first of a series of regional training workshops. To be eligible to receive complimentary tags from the center, participating projects completed a standardized application form that indicated, inter alia, the target species and size class(es) and the estimated number of sea turtles tagged per year. Target species and size class determine the tag type received. Inconel 1005–681 tags (prefix WE or WH) are typically applied to juvenile sea turtles and adult hawksbills, whereas Monel 1005–49 tags (prefix WC) are reserved for adults of other species.
Applicants to the MTTC must demonstrate that tagging staff have received training on standard field protocols (Eckert et al. 1999; Eckert and Beggs 2004, 2006) from WIDECAST and document that appropriate permits to handle and tag sea turtles have been received from their government. In return for free tags, tagging equipment, training, and other resources provided, participating projects agree to submit to the MTTC an annual report on tag fate. The annual report details a roster of tag numbers deployed, the identity of the species on which the tags were placed, the geographic location (and whether on the nesting beach or at sea) where the animal was tagged, and the date that the tag was attached. This information is archived by the MTTC, thereby ensuring that tag fate data are centrally compiled and maintained at a secure location and accessible for retrieval when tagged animals are resighted.
Each tag dispensed by the MTTC is inscribed with a return address (Reward Premio Send, UWI Dept. Biology, Barbados), and tags from animals subsequently recaptured (a term we use to refer generally to animals killed, captured, sighted, or stranded outside the country where they were originally tagged) are returned or reported to this address. Colorful posters that explain the importance of reporting information on tagged sea turtles are posted throughout the WCR by WIDECAST country coordinators to increase likelihood of reporting. Information received by the MTTC from an informant is immediately communicated to the project that tagged the animal, and a reward is sent to the informant. Informants are put in communication with the project that undertook the tagging to further opportunities for exchange of information and collaboration.
The distance between the location of each tag sighting or tag return and the location where the animal was tagged was calculated by using the Great Circle Route formula by Google Maps Distance Calculator (http://maps.google.com/maps?showlabs=1&ftr=misc.distance).
RESULTS
Twenty-one projects in 19 countries and overseas territories have received Inconel 1005–681 tags from the MTTC between January 2002 and June 2009. Twelve of these projects have reported tagging adult female hawksbills with MTTC tags, for a combined total of 2261 tagged individuals (Table 1), and most (99.8%) were tagged in Eastern Caribbean islands (Fig. 1).
Citation: Chelonian Conservation and Biology 10, 1; 10.2744/CCB-0875.1
Sixty-three tagged adult female hawksbills (2.8%) subsequently captured (deliberately or incidentally), sighted, or stranded have been reported to the MTTC. The majority of these (96.8%) were animals originally tagged while nesting in Barbados, where 79.4% (n = 1795) of adult female hawksbills tagged with MTTC tags have been tagged to date. Two others were from an animal tagged while nesting in Nevis (St Kitts and Nevis), which later stranded dead in Guadeloupe, and from an animal caught at sea close to Palm Island (St Vincent and the Grenadines), tagged, and released, and that nested in Barbados a few months later. Most reports (93.7%) were of animals captured and killed by fishers, but there also were 2 live sightings by divers and 5 dead strandings (see Table 2 and Fig. 2 for locations). In some cases when tags were returned by fishers to government fisheries departments, the exact locations and dates of capture were not reported.
Citation: Chelonian Conservation and Biology 10, 1; 10.2744/CCB-0875.1
Based on minimum distances travelled, the point of recapture or sighting was a mean of 343.9 ± 69.7 km standard error (SE) (range, 150–2620 km; Table 2) from the point of tagging, with a median distance of 175 km. Tagged animals could have travelled greater distances if they skirted land masses during their postnesting migrations or if they did not move directly to the point of recapture. The average number of days between tagging and distant recapture was 835 ± 67.9 days SE (range, 41–2305 days), with a median of 860 days (Table 2). There was no correlation between days free and distance travelled (r = 0.238, p > 0.05). Between tagging and recapture, turtles journeyed through multiple political jurisdictions with varying levels of legal protection (Fig. 3).
Citation: Chelonian Conservation and Biology 10, 1; 10.2744/CCB-0875.1
DISCUSSION
A total of 2261 adult female hawksbills have been tagged with MTTC tags since the first tags were disbursed in 2002: nearly as many over a period of 7 years as were included in the 40 year data set (n = 2503) analyzed by Meylan (1999). Not only has the MTTC facilitated the tagging of a large number of critically endangered (cf. IUCN) hawksbills in a short period of time, but most of these animals have been tagged in the insular eastern Caribbean, thereby complementing Meylan's (1999) emphasis on recaptures of adult females originally tagged in Mexico and Costa Rica, and providing a more comprehensive picture of the range and movements of reproductively active adult females at a regional scale.
Most tag returns involved animals tagged in Barbados, one of the largest hawksbill rookeries in the WCR (Beggs et al. 2007), and recovered in countries northwest of the island, less than 200 km away, and with legal fisheries that seasonally target large juvenile and adult sea turtles (Table 2). Other countries, also within a few hundred kilometers of Barbados, which conduct in-water sea turtle monitoring and/or have a stranding response effort (e.g., Martinique, Guadeloupe) contributed sighting or stranding data (Table 2). Satellite tracking (Horrocks et al. 2001) supports the conclusion that most postnesting movements from Barbados are typically in the order of several hundred kilometers and terminate in preferred foraging habitats.
Island nations with active sea turtle fisheries within a few hundred kilometers to the south and southwest of Barbados report few or no sightings of Barbados-tagged turtles (i.e., Grenada, Trinidad, and Tobago) compared with islands to the west and northwest (e.g., St Vincent, St Lucia; see Table 2). This may reflect a tendency for postnesting females to make use of prevailing west-north-westerly currents to journey back to preferred foraging grounds (see van Dam et al. 2008).
Notably, 5 longer-distance movements were also recorded from the tag return data. These were from Barbados to Nicaragua (two females, 2600+ km), to Honduras (2250+ km), to Cuba (1850+ km), and to the Dominican Republic (1350+ km). A second tag return from Cuba and one from Panama have also been received from adult hawksbills tagged in Barbados before 2002 (BSTP, unpubl. data, 2009). The movements from Barbados to Central American foraging grounds exceed the previous WCR record of 1936 km for a postnesting hawksbill departing from St Croix, US Virgin Islands, and recovered in the Miskito Cays, Nicaragua (Hillis 1994), and also exceed the previous record for travel of an adult female hawksbill in the Pacific Ocean (2425 km between foraging in Vanuatu and nesting in Queensland, Australia: Miller et al. 1998).
Although the data reported here suggest that movements of more than 1000 km are less common than movements of hundreds of kilometers, long-distance migrations do occur, and shallow water habitat off Nicaragua and Honduras may be important foraging grounds for adult hawksbills that originate throughout the Caribbean (see also Troëng et al. 2005; van Dam et al. 2008; Nevis Turtle Group and The Ocean Conservancy, unpubl. data, 2007). Moreover, long-distance migration from rookeries at low but consistent frequencies is likely to be an important factor in the long-term survival of nesting populations still subject to heavy exploitation in the eastern Caribbean subregion (Bräutigam and Eckert 2006; Grazette et al. 2007), as well as an important influence on population genetic structure on hawksbill foraging grounds (Abreu-Grobois et al. 2006; Browne et al. 2008; Velez-Zuazo et al. 2008).
Although tag returns are more likely from countries with legal sea turtle fisheries (fishers would be less likely to report a tagged turtle captured illegally), the large number of tags returned from active eastern Caribbean fisheries is indicative of the potential impact of legal and illegal fisheries on conservation efforts in the country of origin. The data reiterate the serious challenges, aptly described by others (e.g., James et al. 2005; Blumenthal et al. 2006; Bräutigam and Eckert 2006), posed to migratory sea turtles in the WCR by an inconsistent regulatory framework. As efforts to monitor hawksbill populations on foraging grounds increase (e.g., van Dam and Diez 1998; Diez and van Dam 2003; Blumenthal et al. 2009; Bjorndal and Bolten 2010), the number of sightings and nonlethal capture of tagged animals (as part of these monitoring programs) will also increase and provide additional information on the spatial relationship between preferred foraging habitat and nesting grounds and the shared management responsibilities of constituent states.
In conclusion, the MTTC has been an uniquely positive factor in facilitating sea turtle tagging efforts in the WCR, building capacity among community-based field staff and volunteers, ensuring that tagging is conducted in accordance with best practices, maintaining a shared database at a regional scale, encouraging collaborative analysis and publication of tag return data, and providing explicit support for a more unified framework aimed at sustainably managing this highly migratory marine resource.
Wider Caribbean countries where adult female hawksbill sea turtles (Eretmochelys imbricata) were tagged with MTTC tags during the period January 2002 to June 2009.
International tag returns for adult female hawksbill sea turtles (Eretmochelys imbricata) tagged in Barbados, as well as in Palm Island and Nevis (insert), using MTTC tags during the reporting period (January 2002 to June 2009). Arrows point to the location of recapture.
Protection regimes for the hawksbill sea turtle (Eretmochelys imbricata). The nations and overseas territories of the Wider Caribbean Region offer varying levels of legal protection, with the majority protecting this species at all times. Belize, Honduras, and Guatemala can legally grant exemptions for bona fide traditional or subsistence use. In nations where legal fisheries persist, size restrictions and seasonal closures generally apply. Figure 3 was adapted from Dow et al. (2007).
