Assessment of the American crocodile (Crocodylus acutus) population in Ambergris caye, Belize

Ó Mórdha, Ciarán

Assessment of the American crocodile (Crocodylus acutus) population in Ambergris caye, Belize

dc.contributor.advisor	Collins, Courtney
dc.contributor.advisor	Ramsay, Ruth
dc.contributor.advisorexternal	Summers, Chris
dc.contributor.advisorexternal	Manzi, Christina
dc.contributor.author	Ó Mórdha, Ciarán	en
dc.contributor.funder	Crocodile Specialist Group	en
dc.contributor.funder	European Crocodile Network	en
dc.date.accessioned	2025-02-12T16:13:53Z
dc.date.available	2025-02-12T16:13:53Z
dc.date.issued	2024
dc.date.submitted	2024
dc.description.abstract	American crocodiles (Crocodylus acutus) have the second largest global distribution of all extant crocodilians, ranging from South Florida through Hispaniola, Cuba, and Jamaica, along the Caribbean coast from southern Mexico to Venezuela, and along the Pacific coast from Mexico to Peru. The species is considered Vulnerable by the IUCN throughout its range, with habitat loss currently a major threat facing the species in parts of its range, including Belize. In Belize, C. acutus is found throughout the coastal zone. Ambergris caye, the country’s largest and most densely populated caye, is inhabited by C. acutus, but its present status there is poorly understood. The aim of this study was to address these data gaps by assessing the status and life history of C. acutus on Ambergris caye and comparing this information with that from other areas within the species’ range to inform the development of a local American crocodile management plan. During 19 nocturnal eyeshine surveys covering 171.5 km of shoreline on Ambergris caye carried out between May and September 2023, 199 American crocodiles were observed, an encounter rate of 1.16 crocodiles/km consisting of 22% adults, 10% subadults, 16% juveniles, 22% yearlings/hatchlings and 30% whose size class could not be determined. These results were similar to those of previous surveys carried out in 2010-2011, but with a higher encounter rate in 2023, suggesting a stable, if not slowly increasing, population. Crocodile nests were located by visiting previously identified nest sites, conducting additional surveys by boat and drone, and utilising social media to investigate reports of nesting activity by residents. A total 9 nests were found during the study. More than half (56%) of these were concentrated along the sand banks adjacent to the caye’s three sewage treatment ponds. Utilizing the 13 years of crocodile capture data (n=865) collected by ACES Wildlife Rescue in Ambergris caye, this study investigated growth rates, morphometrics, and sexual size dimorphism of the local crocodile population. Analysis revealed the growth rate (total length [TL]) of 115 crocodiles averaged 0.045 ± 0.027 cm/day. The growth rates found in adults differed by sex, with females (n=20) exhibiting a slightly lower average growth rate (0.039 ± 0.028 cm/day) compared to males (n=47) (0.048 ± 0.028 cm/day); however, the difference was not statistically significant. Notably, as total length (TL) increased with age, growth rates slowed more significantly in females than in males, with no significant relationship observed between TL and growth rates in males. Morphometric analysis encompassed 332 juveniles (TL<120cm), 25 female sub-adults (120≤ TL<180 cm), 31 male sub-adults (120≤ TL<180 cm), 40 female adults (TL≥180 cm) and 62 male adults (TL≥180 cm). Allometric relationships between TL and dorscal cranial length (DCL), snout length (SL), snout vent length anterior (SVLa) and snout vent length posterior (SVLp) revealed both positive and negative associations, all of which followed linear regressions. The dorsal cranial length to cranial width ratio (DCL: CW) of 2.7 to 4.2 indicates a broad-snouted skull morphotype akin to that observed in other island populations of C. acutus in the Yucatan region. The sexual dimorphism index of 1.07 toward males suggests a relatively minor disparity between the TL of males and females on Ambergris caye, indicating less pronounced sexual dimorphism compared to other populations of C. acutus. The sex ratio 2.39(M):1.0(F) was biased towards males. While Ambergris caye, likely the most human-populated caye in Belize, faces increasing development, pollution, and human-crocodile interactions, it may harbor one of the largest and most stable American crocodile populations in the country. The encounter rate of 1.16 on Ambergris caye is notably higher than that reported for nearby Turneffe atoll (0.34 in 2009) and the Belizean cayes overall (0.43 in 2000), suggesting this population is among the most robust in Belize. However, the study’s findings indicate that insufficient nesting habitat could pose a risk to the long-term stability of the population if not addressed through targeted conservation efforts. To mitigate this risk, it is imperative to conduct annual surveys to ascertain long-term population trends. Additionally, implementing protective measures for nests and intensifying surveys within the Bacalar Chico National Park and Marine Reserve to investigate nesting activity are vital steps in formulating a robust species management plan. Addressing these research gaps will not only enhance our understanding of the ecology of C. acutus in Belize but also inform targeted conservation efforts essential for safeguarding this population's viability and ecological role in the region.	en
dc.description.status	Not peer reviewed	en
dc.description.version	Accepted Version	en
dc.format.mimetype	application/pdf	en
dc.identifier.citation	Ó Mórdha, C. 2024. Assessment of the American crocodile (Crocodylus acutus) population in Ambergris caye, Belize. MRes Thesis, University College Cork.
dc.identifier.endpage	124
dc.identifier.uri	https://hdl.handle.net/10468/17031
dc.language.iso	en	en
dc.publisher	University College Cork	en
dc.rights	© 2024, Ciarán Ó Mórdha.
dc.rights.uri	https://creativecommons.org/licenses/by/4.0/
dc.subject	Crocodile	en
dc.subject	Growth rate	en
dc.subject	Population	en
dc.subject	Morphometrics	en
dc.title	Assessment of the American crocodile (Crocodylus acutus) population in Ambergris caye, Belize	en
dc.type	Masters thesis (Research)	en
dc.type.qualificationlevel	Masters	en
dc.type.qualificationname	MRes - Master of Research	en