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

Bolaños Montero, Juan Rafael; Sánchez Ramírez, Juan José; Sigler, Luis; Barr, Brady Robert; Sandoval Hernández, Iván

Dos especies de cocodrilianos han sido descritas en Costa Rica, el cocodrilo americano, Crocodylus acutus (Cuvier, 1807) y el caimán, Caiman crocodilus (Linnaeus, 1758). En Costa Rica se ha generado información de ambas especies, pero con énfasis en la vertiente del Pacífico, presumiblemente debido a su mayor desarrollo, lo cual ha acarreado mayor presión social hacia la atención de incidentes generados por el encuentro entre humanos y cocodrilos. El estudio se desarrolló durante el 2017 y en un área de aproximadamente 400 km2, caracterizada por tener una amplia densidad de cursos de agua que incluyen a los ríos: Matina, Pacuare, Reventazon y Parismina. En estos ríos se recorrió un promedio de 25 km desde la línea de costa hasta el interior del territorio, incluyendo los canales de Tortuguero, así como otros cuerpos de agua que conectan a estos ríos, lagunas importantes, y canales secundarios. Se realizaron tres repeticiones por segmento. Una población de 1 084 caimanes y 503 cocodrilos fue estimada, para una abundancia relativa de 8.64 y 2.80 ind/km respectivamente. Con respecto a caimanes poco más del 12 por ciento de los animales observados estaban en edad reproductiva, mientras que para cocodrilos sólo un 2 por ciento. La abundancia en los diferentes segmentos resultó ser significativamente diferente para ambas especies (Kruskal-Wallis, P 0.000). Mientras que la distribución por tallas de cocodrilos fue similar en todos los segmento (Kruskal-Wallis, P 0.15). Con 9 cocodrilos y 18 caimanes, reclutas o juveniles capturados, se calculó una proporción de sexos de 1.25 y 0.83 machos a hembras, para cocodrilos y caimanes respectivamente.

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; presumably 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 1 084 caimans and 503 crocodiles is estimated; for a sight count of 8.64 and 2.80 ind/Km respectively. Speaking of caimans, up to 12 por ciento of individuals of reproductive age were observed, while for crocodiles that number was only 2 por ciento. The abundance of both species in the different places studied, turned out to be significantly different for crocodiles and for caimans (Kruskal-Wallis, P 0.001). 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 0.001), 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 recruit and juvenile sizes.