Dauphin Island Sea Lab Study Sheds Light on Bottlenose Dolphin Populations in Alabama Waters

by Dauphin Island Sea Lab
dolphin surfaces in bay
(Courtesy DISL/MSN)

A comprehensive study by a team of researchers from the Dauphin Island Sea Lab and the NOAA Southeast Fisheries Science Center provides the first directly measured abundance estimates of bottlenose dolphins in the Mobile Bay and Perdido Bay waters of Alabama. The study provides crucial insights into Mobile Bay and Perdido Bay dolphin ecology and a solid database to support long-term monitoring to determine if the dolphin population in Alabama waters is stable or under threat.

As apex predators, bottlenose dolphins are sentinels of ecosystem health. Understanding the multiple stressors that impact the population and abundance can inform conservation management and strategies.

“In the northern Gulf of Mexico, the species is divided into 32 distinct bay, sound, and estuary stocks from Texas to the Florida Keys, and several of these are poorly monitored, with no recent abundance estimates available,” said the paper’s first author, Dr. Thibaut Bouveroux. “So, the research we conducted is crucial to understand how many animals use these two embayments and how many are residents. “

The study, conducted between January 2020 and June 2022, used mark-recapture photo-identification surveys pioneered by NOAA and other field experts to identify 673 distinct individual dolphins regularly encountered in Mobile Bay and 189 individuals in Perdido Bay.

dorsal fins of two dolphins are visible above the water surface
The unique markings, notches, and curvature of a dolphin's dorsal fin allows researchers to distinguish them from one another. This study used photo-identification surveys to determine the abundance of dolphins in Mobile Bay and Perdido Bay. (Courtesy DISL/MSN)

Using statistical modeling, the team investigated the seasonal variation in dolphin abundance in both areas, and their findings revealed that the dolphin population in Mobile Bay strongly varied between seasons, with an estimated 1,500 dolphins using Mobile Bay in summer and about 740 dolphins utilizing the area in winter.

In contrast, in the smaller-sized Perdido Bay, they estimated that about 100-200 dolphins use the area, which is similar but slightly more used in winter. Dolphins also showed higher residency in Perdido Bay than Mobile Bay, meaning they tended to stay in the Bay rather than move to other areas, likely due to the smaller embayment size and narrower connections with adjacent waters, such as the Gulf of Mexico.

dorsal fins of two dolphins are visible above the water surface
The unique markings, notches, and curvature of a dolphin's dorsal fin allows researchers to distinguish them from one another. This study used photo-identification surveys to determine the abundance of dolphins in Mobile Bay and Perdido Bay. (Courtesy DISL/MSN)

The study also highlights the value of photo-ID surveys to assess dolphin populations. This work allowed researchers to establish a comprehensive photo-ID catalog that can be used to monitor changes in the numbers and residency patterns of dolphins through time among these different areas relative to environmental conditions or pulse stressors.

This study was featured on the front cover of the journal Aquatic Conservation: Marine and Freshwater.

Aquatic Conservation: Marine and Freshwater cover
(Courtesy DISL/MSN)

The research was funded by the Deepwater Horizon natural resource damage settlement funds provided by the Alabama Trustee Implementation Group. Additional support was received from the Alabama Department of Conservation and Natural Resources (ADCNR), underscoring the collaborative effort required to advance marine conservation efforts.