Studying Bottlenose Dolphins in the Gulf of Mexico

Nikki Vollmer is an assistant scientist with CIMAS at NOAA’s Southeast Fisheries Science Center, where she studies the genetic population structure of marine mammal species in the U.S. Gulf of Mexico and western North Atlantic.

Common bottlenose dolphins (Tursiops truncatus, referred to herein as bottlenose dolphins) are one of the most common marine mammal species living off the U.S. coast. In fact, if you go to the beach and see a bunch of dolphin fins in the distance it is most likely a group of bottlenose dolphins passing by. This species is found close to shore in estuarine and coastal habitats and in the deeper waters of the continental shelf.

Unfortunately, because these dolphins are found in the same waters that humans use, they sometimes face negative impacts, such as injuries or even death, from human-related activities associated with fishing gear, illegal feeding, and collisions with boats. In the U.S., NOAA’s National Marine Fisheries Service is in charge of protecting and conserving the bottlenose dolphins in our waters. To do this, they try to identify unique populations and set up regulations and guidelines to help manage each one separately.

dolphin mom and calf

Common bottlenose dolphin mom and newborn calf. Photo: NOAA Fisheries ESA/MMPA Permit No. 779-1633.

A major human-related event that significantly impacted bottlenose dolphins in U.S. waters of the northern Gulf of Mexico (GOMx) was the oil spill resulting from the Deepwater Horizon explosion in April 2010. In the months that followed, hundreds of bottlenose dolphins were found dead washed up on the shores off Louisiana, Mississippi, Alabama and the panhandle of Florida.

In the years since the spill, scientists that are part of the Consortium for Advanced Research on Marine Mammal Health Assessment (CARMMHA) have gone into the waters of some of the most heavily oiled habitats, like Barataria Bay, Louisiana and Mississippi Sound, and captured live bottlenose dolphins to assess the health of those living in these impacted areas. Two important questions researchers want to understand are: 1) how many unique populations of bottlenose dolphins live in the northern GOMx, and 2) how significantly were those populations impacted by the oil spill? Recently, myself and colleagues at NOAA and CARMMHA have been working to try and answer these questions using DNA.

dolphin with oil on head

Common bottlenose dolphin in Barataria Bay, Louisiana with oil on its head. Photo: Louisiana Department of Wildlife and Fisheries

When DNA is collected from many individuals from the same species, it can be used to determine how many populations there are and which individuals belong to each population. We get DNA from bottlenose dolphins by sampling a small bit of their skin and using special chemicals and laboratory techniques to extract the DNA.

To investigate the population structure of bottlenose dolphins in the northern GOMx, we extracted the DNA from over 500 skin samples collected from live animals in these waters and have been using many different statistical analyses to interpret the genetic data. We are also incorporating additional data (e.g., location of sample collection, cumulative surface oil) to better understand how much each genetically distinct population we identify overlapped with the oil as it spread throughout the northern GOMx. With this information, we will be able to estimate what percentage of each population was exposed to, and likely impacted by, the oil resulting from the Deepwater Horizon explosion. Our findings will soon be published in a peer-reviewed scientific journal and will provide important baseline data that will be key to planning future restoration projects and developing successful conservation strategies for bottlenose dolphins in the GOMx.

This work was partially funded by the Gulf of Mexico Research Initiative (GOMRI) through a consortium grant to the National Marine Mammal Foundation.

By Nikki Vollmer, April 28 2021