What is a Successful Head-start Program? Investigating Head-start Methods and Life History of American Crocodile (Crocodylus acutas) to Improve Management Techniques of Declining Crocodilian Populations

Crocodilians suffered global declines due to overhunting and habitat loss throughout the 20th century. Legal protections and conservation management plans were implemented for many crocodilian species, with some, such as American alligators (Alligator mississippiensis) and the Indo-Pacific crocodile (Crocodylus porosus), experiencing successful recovery. Various conservation management methods have been used on crocodilians to increase population numbers. Head-start has been used with many species of crocodilians worldwide. 

Though there have been many different crocodilian head-start programs globally, little information is available in the literature. In most of the literature, the methods of head-starting are not detailed and, therefore, hard to replicate. Additionally, only a few accounts in the literature assess the head-start's success quantitatively. Furthermore, head-starting is rarely the central theme of the papers available. However, recovery and management programs for C. acutus in the Caribbean could provide valuable information to fill knowledge gaps on head-starting crocodilians.  

The American crocodile (Crocodylus acutus) is a sizeable neotropical crocodile that occurs from the southern tip of Florida down into the Greater Antilles and the Caribbean and Pacific coasts of Mexico, Central America, and northern South America. Crocodylus acutus is predominately a coastal species that inhabits a variety of freshwater, brackish, and marine habitats, including estuarine sections of rivers, freshwater lakes, and reservoirs, mangrove swamps, coastal lagoons, offshore islands, and atolls. The IUCN lists C. acutus as "Vulnerable," and the Convention on Trade in Endangered Species of Flora and Fauna (CITES) lists them under Appendix I (Rainwater et al., 2021). Though IUCN reports that the overall population trend is increasing, many populations throughout the range are still declining and threatened with extirpation due to overhunting, pollution, and habitat loss and degradation (Rainwater et al., 2021). In the Caribbean, multiple species recovery projects have been implemented using head-starts or captive breeding in their recovery plans for C. acutus. 

One population of C. acutus that is declining and threatened with extirpation is in Lago Enriquillo, Dominican Republic. Population surveys conducted by Greco et al. (2023) found that there were likely only 40–60 breeding adults left in a population that used to have 300–600 breeding adults in the 1970s and 1980s (Schubert and Santana, 1996). These findings made key stakeholders reconsider the long-term management plan for C. acutus in Lago Enriquillo. The Dominican Ministry of Environment and Natural Resources (MENR) and its collaborators decided that a head-start program would be beneficial for increased recruitment and population recovery. The implementation of a head-start program in Lago Enriquillo has provided us with a unique opportunity to research head-start individuals, their Ex-situ environments, and the natural system into which they will be released.  

We are investigating the various methods that have been used for crocodilian head-start programs, different methods of quantifying success, some of the challenges that come with head-start and set some general research recommendations for managers to consider before deciding if head-starting is the proper method for population recovery. Specifically, the goals of our project are to: 1) do a literature review on crocodilian head-start programs to provide the various methods of head-start, methods of quantifying success pre- and post-release, and general management recommendations; 2) identify and quantify Ex-situ techniques that prove successful on head-start individuals with C. acutus from Lago Enriquillo; 3) conduct In-situ research on resource selection, home range selection, ecotoxicology, and community dynamics with wild C. acutus in Lago Enriquillo (with an emphasis on individuals from the same cohort as head-start individuals) to provide critical life history information, prioritize areas best suited for releasing head-started individuals, and optimize captive conditions for head-start crocodiles; 4) and analyze data to elucidate which techniques work best for head-start, quantify head-start success, and reveal In-situ patterns of crocodiles in Lago Enriquillo with consideration for long-term management. 

We recently finished our first field season in June 2024. We collected Head-start crocodile hatchlings, administered an initial health assessment, placed them in enclosures, and monitored them daily. Simultaneously, we conducted two nocturnal eyeshine surveys by boat (one in May and one in June), captured four crocodiles and performed gastric lavage to analyze diet, collected blood and scute samples for mercury analysis, and conducted bird and aquatic biodiversity surveys. Currently, we are analyzing our data with plans to have preliminary results by the Fall 2024 semester.