Diet analysis of the introduced Spectacled Caiman ( Caiman Crocodilus) in Tortuguero Lagoon, Puerto Rico

Abstract

The spectacled caiman (Caiman crocodilus) was introduced to Puerto Rico over 50 years ago with the Tortuguero Lagoon Natural Reserve (TLNR) as its epicenter, where it is now established as an apex predator. Although concerns have been raised regarding the potential impact of this naturalized predator on Puerto Rico’s native fauna, little was known of the caiman’s diet on the island. Therefore this study was conducted to determine the diet of the spectacled caiman and its potential impact on island animals. For this study, measurements were obtained from 138 caimans across all life stages (12–94 cm snout–vent length; SVL) from October 2014 to May 2015 within the TLNR. Stomach contents were retrieved and analyzed based on prey category occurrence frequency. Caiman muscle samples were obtained to conduct a stable isotope analysis. Representative prey species were collected based on principal prey groups observed in stomach contents. Isotopic signatures of both predators and prey were analyzed using the Bayesian mixing model (SIAR) to determine nitrogen and carbon source proportions from the different life stages. Insects were the most abundant prey items encountered with 90.7% and 68.8% in hatchling (SVL < 20 cm) and juvenile (SVL = 20 – 59.9 cm) stomach respectively. In adult (SVL > 60 cm) caimans, fish remains were the most significant prey items with 38.3% frequency of occurrence. Fish, insects, and gastropods were the only categories of ten designated prey categories to show significant variation among the three caiman age classes. This study provides novel information on dietary habits of spectacled caimans in Puerto Rico relevant to the design of management strategies and further promotes the use of stable isotopes in diet studies.