Mangrove Saltmarsh Snake Herpetofauna Field Methods

August 9, 2018

It was my senior year and first day of a field biology course at Palm Beach Atlantic University when the opportunity of an undergraduate lifetime came my way. Our professor, Dr. Tom Chesnes, asked our class why the heck we wanted to be biologists. After hearing everyone else around the room and rehearsing it only 100 times in my head, I spoke out confidently with “Hi, I’m Rebekah, a senior zoology major and I hope to contribute to reptile conservation.” I was relieved that was over and the rest of the class carried on. The next time class came around, Dr. Chesnes pulled myself and two other students aside to ask if we’d be part of his ongoing snake conservation research that focused specifically on the mangrove saltmarsh snake, Nerodia clarkii compressicauda.

Rebekah pettit salt marsh snake

rebekah Pettit

One of those late night, mucky, musky, mosquito mangrove field sessions! Red phase mangrove saltmarsh snake.

Excited as could be, I was eager to take on this opportunity. As someone pursuing a career in an underfunded, over-competitive, male-dominated field, I knew this was a way to build my resume and pursue my passions for reptiles professionally and be part of direct conservation efforts. I was eager to learn more about this project and be a part of the team. By my professor’s suggestion and recommendation, I applied to the summer research program of the university and was accepted. Before I knew it, the semester was over and I was ready to start the internship as a field biologist for the university. Not only was it something I wanted to do and learn, but it was also a paid gig funded with grants.

Nerodia clarkii compressicauda, or the mangrove saltmarsh snake, is a semi-arboreal, semi-aquatic snake that is endemic to aquatic habitats in coastal Florida. Specifically, as the name suggests, the mangroves are its preferred habitat, and we spent countless hours and nights surveying their unique ecosystem. Partnering with published Herpetologist and Professor of Montreat College in NC, Joshua Holbrook on this project, our “Clarkii Crew” team of five included myself, Dr. Chesnes, and two other biology students, Noah Benedictus and John Foote. I was the only girl on this research team, and this made me even more eager to represent women, especially in science and herpetology.

Since not much research has been done on the mangrove saltmarsh snake, their patchy distribution makes their conservation status still questionable. Our research aimed to help bridge those gaps by presence/absence surveys in parks in which they had never been documented before. Tedious planning and permit acquisitions finally got us scheduled for May 2017 to June 2018, allowing the team to survey state parks all over Florida for this elusive species.

Mangrove salt marsh snake green phase

rebekah pettit

Green phase clarkii in habitat. 

When summer arrived, we started with pitfall surveys, aquatic trapping, and dipnet surveys of two state parks managed by the Environmental Protection Agency. The pitfall traps contained transects of drift fence with buckets dug into the ground. Each bucket contained PVC pipe for shelter and a wet sponge for water and floatation.

Every day, my partner and I would check these terrestrial traps for herpetofauna and replace materials as necessary. Aquatic traps were placed throughout shallow wetlands and dipnets were used in both fish-dominated and fishless ponds. Although none of these methods turned up our target species, we found many other herps through these techniques and still contributed to the park’s species lists.

Herping for Frogs in Florida

One of my personal favorite days was during a summer downpour when we came across a breeding group of southern spadefoot toads (Scaphiopus sp.) in a pond apple depression. These toads had never been documented in the park and spend the majority of their lives underground. It was a treat!

spadefoot toad

Rebekah Pettit

Gorgeous southern spadefoot toad in our pitfall traps!

Along with learning varied herpetological sampling methods, we quickly learned that the best method for our particular target species was simple foot hiking. This became the theme over the next year to find the mangrove saltmarsh snake. During the day we would survey the habitat area and then come back at night to do the field survey and perform various morphometric data (aka physical variation.) Morphometrics included weight, sex, color, snout to vent length, tail length, and scale counts. Over the next year we hiked the mangroves, wetlands, and estuaries, capturing and collecting data on these beautiful, yet poorly researched reptiles.

Mangrove salt marsh snake

rebekah pettit

John Foote and I doing morphometrics on a mangrove saltmarsh snake.

Due to habitat overlap and patchy distribution, hybridization was a key point in our research, which threatens the mangrove salt marsh snakes with two species of freshwater Nerodia fasciata species. Hybridization is a hot topic in conservation because it compromises the genetic purity of a species and their unique genetic variation could eventually be lost due to this interspecies relationship. Because of environmental pressures and development, we hypothesized that unnatural habitat overlap was causing increased hybridization. To confirm the genetic purity, midline scale counts were used to define the mangrove saltmarsh snake from its hybridized counterparts. With pure compressicauda, 22-23 scales were indicative against the 19-21 hybrids. Although there were exceptions to the old school rule, aside from genetic testing  (which we did not do) it was an efficient way to determine our data.

Carkii color variations


Colors vary widely in the mangrove saltmarsh snake.

Over the next year we documented hundreds of clarkii all over the state, varying in color patterns and disposition with many of the most foul-tempered individuals ended up being hybrids. We often found our target species hunting for fish within the dense mangrove prop roots. Extremely dependent on tide, we would frequently find clarkii waiting to ambush the fish that became trapped in the shallow areas. We hypothesized that if there was habitat, there was clarkii, and this was the determining factor in our survey choices. Hiking through mangrove swamps over many nights gave us hundreds of samples and the team documented the first known specimens in Broward and Martin county. Our Broward county finds got published in the newspaper introducing these elusive snakes to the public!

Mangrove salt marsh snake

Joshua Holbrook

Mangrove saltmarsh snake found in Broward County.

Although the permits expired in June of 2018, the research and field work surely have not and I am forever a part of the clarkii crew! This ongoing scientific research in the works by Chesnes and Holbrook was a privilege for me to be part of in my last year of undergrad studies as a zoology student. It gave me opportunity, experience, and discovery in the field of herpetology and a greater appreciation for my own backyard in Florida. By communicating the conservation status of the mangrove salt marsh snake, development and conservation efforts can be properly distributed and planned for when the distribution of a species’ population is understood. Without knowing established numbers, understanding the impact of their loss on a threatened ecosystem such as mangroves is almost impossible!

clarkii salt marsh snake

rebekah pettit

Color variation in mangrove saltmarsh snakes! Noah Benedictus, John Foote, Rebekah Pettit, Joshua Holbrook, John Foote, Rebekah Pettit, Dr. Tom Chesnes with handfuls of clarkii!

Red phase mangrove salt marsh snake

rebekah pettit

Red phase mangrove salt marsh snake.

Upon graduating with my zoology degree, my team and I did multiple presentations at university conferences to showcase this beautiful species and emphasize the importance of field work and herpetological research. As an undergrad and now beginning zoologist, I would absolutely recommend getting involved with professors and research! This will set you apart from your competitors, provide experience, technique, and a greater understanding for the natural world conservation aims to protect. The variation of color the mangrove saltmarsh snake comes in naturally is just another indication there is still much to be known about one of the mangrove’s most elusive predators. 

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