Abstract
The American crocodile, Crocodylus acutus, is widely distributed in the American neotropics. It is endangered throughout most of its range and is listed as vulnerable by the International Union for the Conservation of Natural Fauna and Flora (IUCN) and on Appendix I of the Convention for the International Trade in Endangered Species of Wild Flora and Fauna (CITES). Despite this listing, there are few published reports on population status throughout most of its range. We investigated the status of the C. acutus, at several locations along the Pacific coast of Costa Rica. We carried out spotlight and nesting surveys from 2007-2009 along the Costa Rican Pacific coast in four distinct areas, coastal areas of Las Baulas (N=40) and Santa Rosa (N=9) National Parks and the Osa Conservation Area (N=13), and upriver in Palo Verde National Park (N=11). We recorded crocodile locations and standard environmental data at each observation. Encounter rates, population structure, distribution within each area and data on successful nesting (presence of hatchlings, nests, etc) were determined. We attempted to capture all crocodiles to record standard morphometrics. A total of 586 crocodiles were observed along 185.8km of survey route. The majority of animals encountered (54.9%) were either hatchlings (<0.5m) or juveniles (0.5-1.25m). The average non-hatchling encounter rate per survey for the Pacific coast was 3.1 crocodiles/km, with individual encounter rates ranging from 1.2 crocodiles/km to 4.3 crocodiles/ km in Las Baulas National Park and the Osa Conservation Area respectively. Distribution of size classes within the individual locations did not differ with the exception of Santa Rosa and Las Baulas National Parks, where hatchlings were found in water with lower salinities. These were the first systematic surveys in several of the areas studied and additional work is needed to further characterize the American crocodile population in Costa Rica.
Highlights
Populations of C. acutus were severely depleted throughout the range during the 20th century due to hunting and over-harvesting (Thorbjarnarson et al 2006)
We conducted 73 crocodile surveys on the Pacific coast of Costa Rica covering 185.8km of crocodile habitat (Tables 2 and 3). 50% of surveys were conducted in the Tamarindo Estuary of Las Baulas National Park; the remainder of the surveys were spread between Palo Verde National Park (Tempisque River), Santa Rosa National Park (Naranjo Estuary and Laguna el Limbo) and the Osa Conservation Area (Tables 2 and 3)
The spectacled caiman, Caiman crocodilus, was encountered in the areas throughout the Osa Conservation Area (ACOSA) making up 17% of all encounters with the remainder C. acutus or eye shine
Summary
Populations of C. acutus were severely depleted throughout the range during the 20th century due to hunting and over-harvesting (Thorbjarnarson et al 2006). Suitable coastal habitat is more disjunct along the Pacific coast, which has resulted in a series of smaller, isolated populations of C. acutus (Thorjarnarson et al 2006). This makes the estuary system of the Pacific coast of Costa Rica an ideal place to study metapopulation structure of crocodiles. The data obtained during surveys were used with an ongoing study examining the genetic structure of crocodile populations in Pacific Costa Rica. Understanding linkages between these potential metapopulations is crucial in developing management plans for C. acutus within Costa Rica
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