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Here, we provide an update regarding the ongoing nesting and population ecology research on Long Island and revisit short-term nesting population predictions provided by Richardson et al. (2006). Long Island (N 17°09’, W 61°45’), also known as Jumby Bay, is located about 2 km off the northeast coast of Antigua in the eastern Caribbean’s Leeward Islands (Figure 1). The island is roughly 300 acres (1.2 km2) in size and has a small resort and numerous private residences. Crescent-shaped Pasture Beach, a natural, calcareous sand beach situated on Long Island’s northern, windward coast, is the island’s primary nesting beach and has served as the principal study beach for the duration of the Jumby Bay Hawksbill Project research. The approximately 450-meter long beach is bordered landward by a mixed community of trees and shrubs, including the native sea grape (Coccoloba uvifera) and button mangrove (Conocarpus erectus) and the introduced Scaevola sericea, and seaward by an irregular and intermittent limestone bed. While development removed much of the beach’s native maritime forest, current beach management practices, such as planting and maintenance of vegetation beds, ensure that Pasture Beach continues to provide habitat conducive to hawksbill nesting. Beaches constructed adjacent to private residences elsewhere across Long Island (i.e., peripheral to Pasture Beach) have expanded the number of potential nesting sites in recent years.
Figure 1. Long Island (or Jumby Bay), starred in the map inset, is a 300 acre island located off the northeast coast of Antigua. GIS data set courtesy of the National Geospatial-Intelligence Agency (2005).
Saturation tagging protocols have provided the foundation for research at Jumby Bay since the inception of the project in 1987. Hourly foot patrols begin on Pasture Beach about one hour after sunset and continue to dawn, enabling the identification of every nesting hawksbill and the documentation of all nesting activities. The small, private peripheral beaches are patrolled less regularly due to logistical constraints. During egg-laying, hawksbills are fitted with two tags (Inconel Size 681; National Band & Tag Company, KY, USA) on the most proximal pads of the fore flippers and a unique pattern of holes is drilled in the supracaudal scutes with a battery-powered hand drill. These multiple marking mechanisms are highly successful in confirming an individual’s status as a new recruit (i.e., neophyte) or a remigrant to the Jumby Bay nesting population (Richardson et al. 1999; 2006). Following Richardson et al. (1999; 2006), neophytes are described as previously unmarked turtles and presumed to be first-time nesters. While we acknowledge that we are unable to confirm that ‘neophyte’ turtles have not previously nested elsewhere since laparoscopies are not conducted, the long-term assimilation of neophytes into the Jumby Bay nesting population and the high fidelity of hawksbills to the island provide compelling evidence in support of this designation (Richardson et al. 2006).
Historically, the annual research season extended from June 15 to November 16 and encompassed nearly all nesting activity at Long Island. However, to accommodate an apparent shift in the peak of the nesting season (Stapleton et al. 2010), the research season was expanded to a June 1 start date as of 2007 and continues through November 16.
Figure 2. Hawksbills documented on Long Island during the 1987-2008 research seasons. We distinguished between remigrants and neophytes in 1991, after 4 years of research, since nearly all (98%) individuals maintained a 2-4 year remigration interval (Richardson et al. 1999, 2006).
The Jumby Bay nesting population continued to exhibit signs of long-term growth during the 2005-2008 seasons, reaching a record 67 nesting hawksbills, including 29 neophytes, during 2008 (Figure 2). Although annual remigrant cohorts remained nearly constant during the past 4 years, neophyte cohorts increased relatively consistently during the period, with a marked jump from 15 to 23 neophytes between the 2004-2005 seasons. Annual neophyte cohorts represented an increasingly greater component of the total annual nesting population, and this increase in recruitment has fuelled the broader population growth at Jumby Bay in recent years.
Empirical data collected during 2005 – 2008 were remarkably consistent with the total nesting population and neophyte growth forecast by Richardson et al. (2006; Figure 3). Predicted neophyte cohort size differed by an average of 3.5% (SD: 2.3) from observed values. There was less agreement between observed and predicted values of total population size (Mean difference: 12.0%, SD: 7.8), as forecasted population growth outpaced actual growth.
Figure 3. Total nesting hawksbills (a) and neophytes (b) predicted by Richardson et al. (2006) and observed during the 2005-2008 research seasons at Long Island, Antigua, West Indies.
The recent increase in total nesting activities and confirmed nests recorded on Jumby Bay largely paralleled the island’s population growth (Figure 4). Crawls and nests remained relatively stable during the first decade of research, but both have more than doubled since 2000, with 287 nests deposited and 564 total crawls recorded island-wide in 2008. The volume of activities recorded on peripheral beaches has similarly increased: the 120 nesting activities documented on peripheral beaches during 2008 represents a nearly 2-fold increase over the 63 crawls observed in 2005.
Figure 4. Hawksbill nesting activities and nests recorded on Long Island, Antigua, West Indies during 1987-2008.
Following a period of stability during the first decade of monitoring at Long Island (Richardson et al. 1999), Richardson et al. (2006) identified a significant, long-term increase in the nesting population through 2004. The 2005-2008 data are consistent with these more recent results and suggest continued population growth for the Jumby Bay population. In addition, the stability of the remigrant cohort and the growth of the neophyte cohort observed during 2005-2008 support the assertion that this population increase is largely being driven by an increase in recruitment (Richardson et al. 2006). Indeed, 102 neophytes have been documented in the last 4 years of monitoring, an encouraging sign for the Critically Endangered hawksbill.
Richardson et al.’s (2006) model forecasting Jumby Bay’s neophyte nesting numbers has proven both accurate and precise, though the total nesting population growth has been more modest than predicted. The lack of growth observed in remigrant cohorts during 2005-2008 is responsible for this diminished agreement between observed and expected values. We hypothesize that a short-term (i.e., 3-4 year) lag exists between neophyte and remigrant cohort sizes and anticipate that recent surges in neophyte cohorts will contribute to growth in remigrant numbers in the coming nesting seasons. Regardless, we recommend the continued application of statistical models to rigorously evaluate population trends and forecast Jumby Bay’s short-term population growth.
Data collected during 2007 - 2008 are minimally confounded with the extension of the monitoring season. This 2-week, early season period yielded an additional 19 records (12 nests) and 21 records (14 nests) during 2007 and 2008, respectively. During these 2 years, a total of only 1 individual would have otherwise been undetected had the research season begun at its historical June 15 start date. We also note that low levels of nesting activity may occur year-round on the island, although the vast majority of nesting activity takes place during the defined research season.
The three beaches adjacent to Pasture Beach, upon which most of peripheral beach nesting activities occur, generally are patrolled at least several mornings per week. As additional private beaches have been constructed, staff have attempted to monitor these new potential nesting sites as resources and access permitted. However, we acknowledge that an increase in monitoring intensity of peripheral beaches during the past several seasons, due to improved access and greater manpower, also may contribute to our results. We are uncertain as to whether the documented increase in crawls on peripheral beaches entirely reflects an increase in use of these beaches or is, in part, an artefact of greater monitoring intensity. It seems likely that peripheral beaches may become increasingly important to Jumby Bay’s growing nesting colony, and frequent, regular patrols of these beaches, as well as maintaining habitat conducive to hawksbill nesting, are thus research and management priorities. Although the peripheral beaches are undoubtedly important to the Jumby Bay population, few turtles appear to nest exclusively on them. For example, only two of 67 turtles were recorded crawling solely on beaches other than Pasture Beach in 2008, during which the three major peripheral beaches were patrolled nearly hourly.
The continued population growth of the Long Island nesting colony offers an encouraging sign for depleted Caribbean hawksbill stocks. While we note that this local population increase may not be indicative of trends elsewhere in Antigua or across the region (Richardson et al. 2006), some regional sites have demonstrated similar population increases [e.g., Mona Island, Puerto Rico (R.P. van Dam & C.E. Diez, pers. comm.), Barbados (Beggs et al. 2007), Guadeloupe (Kamel & Delcroix 2009)]. Fortunately, monitoring programs have been established on several beaches across mainland Antigua within the past few years (M. Clovis, pers. comm.). These data should provide valuable insight into the status of hawksbills in greater Antigua, describe population dynamics and any interchange among mainland nesting beaches and Long Island, and may clarify causal factors of the decade long population growth, including the protection of nesting females and their eggs on Jumby Bay (Richardson et al. 2006).
Acknowledgements: We thank Dr. James Richardson for his research guidance and the field research teams for data collection during the 22 years of study at Jumby Bay. We are extremely grateful for the continued support of the Jumby Bay Island Company, John and Sarah Fuller, and the Jumby Bay Resort. J. Richardson and C. Guy provided useful comments during manuscript preparation. The Jumby Bay Hawksbill Project is a member of the Wider Caribbean Sea Turtle Conservation Network.
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