by Corinne Johnston
It can be a big surprise for summer visitors on Bald Head Island to find a large alligator sunning itself on a BHI Club putting green or a lagoon shoreline. Sometimes alligators can be seen in the marsh using brackish water to clean their skin, or even walking down the beach. The American alligator ( Alligator mississippiensis) is native to the southeastern United States, but North Carolina is at the northern end of its range. Alligators have inhabited freshwater rivers, lakes, and marshes for 150 million years. They are the largest reptile in the U.S. and can grow between 10-15 feet. Alligators are a keystone species and an apex predator. They provide ecosystem services for other species such as keeping the balance among trophic levels and providing habitats by creating dens along the banks. By being at the top of the food chain, alligators balance older and sick animals.
In the summer, the Bald Head Island Conservancy conducts weekly spotlight surveys to track the size of the island population. In 2019, an average of 17 alligators were spotted per night. Alligators tend to be territorial which generally leads to one alligator per lagoon. Occasionally there could be multiple but it depends on the time of year. Alligators are more dormant in the colder months and more active during mating season, starting in April and lasting until June.
The Conservancy partnered with Dr. Scott Belcher from NCSU in 2019 to capture BHI alligators and test their blood for per- and polyfluoroalkyl substances (PFAS). PFAS are toxic, forever chemicals found throughout our environment. They are not susceptible to degradation, and are common in household items (non-stick/water resistant surfaces), industrial sites, food, and drinking water . These substances cause health concerns in humans and wildlife. PFAS exposure is also a local concern. Brunswick County is leading with the highest PFAS concentration in the nation. The Belcher Lab is examining the effects of PFAS exposure on the health of striped bass and American alligators in the Cape Fear River watershed. Being a long- lived species that can live between 35-50 years, alligators are a valuable indicator for human health. The Belcher Lab noticed that within the Wilmington area, alligators had poorer body condition scores and unhealed lesions than alligators outside of this area. Bald Head Island is unique because a captured individual had a PFAS concentration of 4700 parts per billion (ppb). The other island alligators did not exceed 41 ppb. We wanted to determine why this alligator had such high PFAS concentrations by investigating its diet using chemical indicators. For my intern project, I analyzed these indicators of food sources (stable isotopes) and PFAS exposure from the captured island occupants. Stable isotope analysis (SIA) can be used to examine individual habits and movement by comparing the “chemical fingerprint” of an animal to its food or environment. By understanding alligator habits and movements we hoped to help discover how PFAS accumulates in the body.
Alligators are opportunistic feeders and can eat anything from turtles to pets. By conducting SIA, we can see if BHI individuals are utilizing terrestrial or marine dietary sources. My findings support that most of our individuals are foraging in terrestrial habitats. One individual found near the creek shows more of a marine diet. We can determine that its habitat range includes the nearby Bald Head Creek. This information can help us investigate ways in which alligators reflect their environment. To ensure the safety of residents and our American alligator population, it is important to reduce negative human-alligator interactions. This includes not feeding any individuals you may come across, but also not fishing in the golf course lagoons, feeding turtles or birds in lagoons, and keeping pets on a leash. Feeding alligators can cause them to rely on those behaviors and act aggressively around humans. We want to protect the unique wildlife that call BHI home!