Population status of the American crocodile, Crocodylus acutus (Reptilia: Crocodilidae) and the caiman, Caiman crocodilus (Reptilia: Alligatoridae), in the Central Caribbean of Costa Rica

Abstract

American crocodile (Crocodylus acutus)(Reptilia:Crocodilidae) and caiman (Caiman crocodilus)(Reptilia:Alligatoridae) population status, in the Costarican Central Caribbean. Two species of crocodilians have been described in Costa Rica, american crocodile (Crocodylus acutus: Cuvier 1807), and caiman (Caiman crocodilus: Linnaeus 1758). In Costa Rica, data has been generated on both species, but populations in the Pacific have received more attention from researchers; due to the fact that the Pacific slope has a greater development, which brings greater social pressure on the attention of the incidents generated by the encounter between humans and crocodiles. This study, performed during 2017, was done in an area of approximately 400 km2, characterized by having a wide and dense network of water courses, which includes the Matina, Pacuare, Reventazón and Parismina rivers. In these rivers, an average of 25 kilometers were traveled from the coastline up stream to the interior of the territory, including the Tortuguero canals, and other water bodies that connect these rivers, as well as in the most important lagoons and secondary channels. Three repetitions were made per segment. A population of 1084 caimans and 503 crocodiles is estimated; for a relative abundance of 8.64 and 2.80 ind/Km respectively. Speaking of caimans, up to 12% of individuals of reproductive age were observed, while for crocodiles that number was only 2%. The presence of both species in the different places studied, turned out to be significantly different for crocodiles and for caimans (Kruskal-Wallis, p≤0,000). Likewise, the size distribution is similar for crocodiles reported in all environments (Kruskal-Wallis, p≤0.15), while for caimans it indicates that there is a different distribution for sizes, according to the environment in which they are found (Kruskal -Wallis, p≤0,000), with a bias against of the Pacuare and Matina rivers. It was possible to estimate a sex ratio of 1.25 and 0.83 males to females, in crocodiles and caimans respectively, with 9 and 11 captures in that same order, in individuals of recruits, juvenile and subadult sizes. The Matina River and the Jalova Lagoon are the two main sites for the observation of crocodiles, their abundances are lower than those reported for the Pacific of Costa Rica, in whereas caimans, with a more homogeneous distribution throughout the sampling area, have a relative abundance considerably more than that reported in Honduras (2.2 ind/km), but lower than the 12.5 reported forLa Rambla de Sarapiquí, in the Northern Zone of Costa Rica.

Population status of the American crocodile, <em>Crocodylus acutus</em> (Reptilia: Crocodylidae) and the spectacled caiman, <em>Caiman crocodilus</em> (Reptilia: Alligatoridae) in the Costa Rican North Caribbean

“…During the nocturnal surveys, size estimates were made using the following parameters: (a) distance from the eyes to the tip of the snout; (b) the distance between the eyes; (c) the total length of the animal; (d) any animals that hid before their size could be assessed were noted as "undetermined" and were included in the general count of crocodilians present at a given location, without verification of size or species (Bolaños et al 2019).…”

“…Crocodylus acutus individuals were classified using eight size classes (Bolaños et al 2019), based on 50 cm intervals (Table 2). This classification allows for size estimates with minimum error and the comparison of data with those obtained in different censuses performed in Costa Rica, especially those reported for the Central Caribbean by Bolaños et 2).…”

“…A grouping control was applied to the sightings performed, by placing a number "1" beside each observation for those individuals considered as "grouped", in that they were observed within 50 m of other individuals. Conversely, a number "2" was assigned to those individuals observed at greater distances apart, these considered as "dispersed" (Bolaños et al 2019).…”

“…In the Caribbean watershed, a physical limit that divides this region into two large subregions can be distinguished: the North Caribbean, from Limón city to the San Juan River, and the South Caribbean, from Limón city to the Sixaola River. Between the North and South Caribbean subregions, a third subregion can be delimited, corresponding to what Bolaños et al (2019) described as the Central Caribbean. The authors defined this subregion as the area in-between the city of Limon and the mouth of the Parismina River, at the Jalova Station of Tortuguero National Park.…”

“…As part of a limited group of researchers who have studied the crocodilian populations in the Caribbean region, Bolaños et al (2019) found that C. crocodilus and C. acutus are commonly encountered, though they recommended increasing the level and effort of investigation. Bolaños et al (2019) reported a C. crocodilus density of 8.64 ind./km, while for C. acutus, the density was lower, 2.80 ind./km; these authors found a male-to-female sex ratio of 1.25 and 0.83 for caimans and crocodiles, respectively, in the Central Caribbean. Given the fact that there is generally little information about the crocodilian populations in the Caribbean watershed, and practically nothing known about them for the North different (Χ 2 =7.34, p≤0.026) from the studied subareas.…”