Indian River Lagoon's Dolphins May Face Increased Risk of Choking to Death: A Study

With Florida's Indian River Lagoon (IRL) earning a reputation as a dolphin graveyard, researchers recently published an examination on one of the threats facing the area's dolphins.

The IRL comprises 40 percent of the Florida coastline and is the most biodiverse estuary in the United States. Moreover, it is home to a group of approximately 700 dolphins that never venture outside of lagoon.

Because of multiple single cases of asphyxiation in dolphins caused by fish lodged in the esophagus being reported, the researchers decided to pursue the overall significance this specific cause of death had on the local population.

To do this, the scientists performed a retrospective evaluation of pathology records from stranded bottlenose dolphin, discovering that from 1997 to 2011, asphyxiation due to choking was identified as the cause of death in 14 of the 350 cases, or just 4 percent.

Sampling an unrelated but adjacent population over the same period, however, yielded no cases of asphyxiation out of a total of 186 necropsies.

Furthermore, in nearly half of the cases a dolphin living in the IRL died after choking on a fish, recreational gear was also present.

Detailed examinations of the specific kinds of fish lodged in the dolphins yielded positive identification in for eight of the 14 fish. Among those identified was the sheepshead fish, which are considered native and common throughout the southwestern Atlantic states and the IRL, but are not a normal or important prey for bottlenose dolphins due to the fish's sharp spines. And while tilapia, which was also identified in addition to boasting strong spines, are non-native to the area, evidence shows they are becoming increasingly common in the IRL.

For this reason, the scientists hypothesize that the differences in choking deaths between the two adjacent populations may be a result of differences in the prey abundance and distribution or differences in foraging ecology between dolphin groups.

One thing that is clear to the researchers is that if future changes in environmental conditions produce changes in fish abundance or prey preference in dolphins of the IRL, the dolphins will likely be exposed to more risk.

"Because they are so tied to home, when things change in the environment, they are vulnerable to the changes every time," Judy St. Leger, director of pathology and research at SeaWorld and co-author of the study, told Discovery News.