Assessing Mercury Concentrations in Alligator Populations

By Alligator Research Staff

The American alligator seems, in some ways, to be one of those perfect species. It has persisted for eight million years with little change. It’s a long-lived (40-60 years) species with high adult survival and a high reproductive potential which helped it recover from once being on the endangered species list. Alligators are also a desired target of hunters for their meat and the value of their hides. And as an apex and keystone species, they play a notable role regulating prey populations and modifying their own environment in ways that benefit other wetland occupants.

Because of their longevity, position in the food chain, and tendency to reside in a limited area, alligators can serve as an indicator of local environmental conditions. Through the process of biomagnification, environmental contaminants can concentrate in their bodies and pose health risks to not only the alligators but also to humans that consume the meat. As a result, FWC’s Alligator Management Program requested that FWRI’s alligator research staff study and monitor mercury (Hg) concentrations in alligator muscle tissue from populations across the state. Our study revealed that average Hg concentrations in Florida waterways varied, but that the rate of accumulation is predictable. Based on these results, alligator research staff began a Hg monitoring program that assesses average Hg concentrations in alligator muscle tissue on harvested lakes, marshes, and river sections known as Alligator Management Units (AMUs). Approximately six or seven AMUs are sampled every year, with a goal of monitoring Hg on over 50 AMUs statewide.

The process involves capturing juvenile (3-6 ft) alligators by hand, snare, or snatch hook, and taking a 0.5-gm biopsy sample of tail muscle tissue to be tested for Hg. The alligator is marked for future identification and released. The tissue samples are sent to the Indian River Field Lab in Melbourne, where our FWRI collaborators analyze them for Hg concentrations. Based on the results and what we learned from the study, we estimate the average Hg concentration of a 7.5-ft alligator (an average-sized alligator that is harvested) on that AMU and inform the Alligator Management staff on whether health/consumption advisories need to be issued.

Advisories are issued to alligator hunters and nuisance trappers that hunt on areas with an average Hg concentration of ≥1 mg/kg. When applied, the advisories prohibit the sale of alligator meat from these areas and strongly discourage consumption. Hunters are, however, allowed to sell the alligator hide. To date, we have identified only two AMUs that meet the criteria for issuing health advisories. Both areas, Water Conservation Areas 1 and 2, are located in South Florida and are part of the eastern Everglades ecosystem. FWRI staff will continue to assess Hg levels in alligator meat to ensure that the public is informed of and protected from any potential health risk.