(August 18, 2017) --

Dr. Alison Robertson's lab members and ADCNR team. (Courtesy Dr. Alison Robertson)

Alabama's alligator hunt delivers a great opportunity each year for Dr. Alison Robertson and her team at the Dauphin Island Sea Lab to collect tissue samples from alligators. Her team includes Alex Leynse, Clay Bennett, Grant Lockridge, and Taylor Goodie from her laboratory and volunteers Caitlin Wessel, Deryn Hill, Noel Wingers from the Dauphin Island Sea Lab.

Alligators, being resident apex predators in the Mobile-Tensaw Delta, are good bio-indicators of ecosystem health in swamps, rivers, bayous, and marshes.

Dr. Robertson gathers the tissue samples to test for the frequency of pesticides, heavy metals, natural toxins, and legacy contaminants (e.g., polychlorinated biphenyls, dioxins) in the environment. While much of this industrial waste was banned in the 1960s the chemicals are highly persistent in the watershed and can be bio-accumulated in an alligator through its diet.

"These resident species are at the top of the food web so they act as sentinels in the Mobile-Tensaw Delta" Dr. Robertson said. "If levels of these contaminants in the sediments or prey items are high, it can be detected in the tissue samples taken from these alligators."

Dr. Robertson has been collecting samples during the alligator hunts since 2014. In that time, she's also necropsied about 30 alligators donated to research each year.

PhD student Alex Leynse and Dr. Alison Robertson collecting tissue samples. (Courtesy Dr. Alison Robertson)

"The good news is that through these necropsies, we've seen an increase in the health of these animals, even over the past 3-4 years," Dr. Robertson said.

Along with health estimates, and levels of toxins and contaminants, Dr. Robertson collects samples to conduct studies on patterns of genetic variation within the Mobile Tensaw Delta alligator populations.

"We can determine how alligators are connected within and between regions," Dr. Robertson explained.

Dr. Robertson works in collaboration with Alabama Department of Conservation and Natural Resources (ADCNR) team led by Chris Nix each year. The ADCNR crew has been running the hunts for the last 12 seasons collecting data on the length, weight, and girth of all animals collected in addition to location of capture, and hunting. She also greatly appreciates the willingness of alligator hunters to assist with her research.

"These samples greatly impact our understanding of the overall health, population, and genetics of alligators, and would not be possible without the donations from hunters each year," Dr. Robertson said. “Once we have collected all of the data, we intend to contact hunters that have donated tissues so that they can find out more about the animal they brought in to the weigh station.”

One thing that is needed is a method to determine the age of alligators which Robertson is working on with Dr. Will Patterson from the University of Florida who specializes in age and growth validation.

"This is one of those things that we all want to know. Based on size and weight, we can broadly estimate an alligator's age, but by sampling and sectioning the femurs and other structures laid down annually, we may be able to get a more specific age estimate," Dr. Robertson explained.  

Dr. Robertson will collect tissue samples from more than 100 alligators during the 2017 alligator hunting season.