Dolphin Deaths in Florida Linked to Choking on Fish and Fishing Gear

Dolphins in Florida may be in trouble--and it could be because of humans. Scientists have found that mass dolphin deaths in the Indian River Lagoon may have been partly caused by fishing hooks and lines that choked them to death.

The Indian River Lagoon is a unique ecosystem. Closed off from other areas, the population of dolphins that lives there does not leave the lagoon. Only numbering 700, the bottlenose dolphins began to die off in 1997, choking to death on spiny fish. In 2011, further changes to the lagoon sparked more deaths. An algae superbloom killed off 60 percent of the sea grass, which may have helped cause the deaths of 46 more dolphins.

Despite the fact that several of these dolphin deaths were due to asphyxiation, the researchers still weren't sure what the significance of this cause of mortality in a single population was. In order to investigate these deaths a bit further, the researchers performed a retrospective evaluation of pathology records from stranded bottlenose dolphins from the Indian River Lagoon. The scientists found that 14 out of 350 deaths were caused by asphyxiation due to choking. They found that most of these animals choked on fish species with strong dorsal spines, but also found that many of the cases were associated with fish attached to fishing gear.

The researchers then sampled an unrelated but adjacent population over the same period in the Atlantic Ocean. None of them had died of asphyxiation, which suggested that the dolphins living in the lagoon were more likely to encounter fish that posed a risk.

While many factors contributed to the lagoon deaths, though, the study highlights an important issue: fishing lines and gear can cause dolphin deaths. By limiting the amount of gear being used and by encouraging safe fishing practices, these deaths could be lowered in the future. By that same token, an increase in fishing and gear use could see more deaths.

"Environmental alterations leading to changes in prey availability or increased interactions with fishing gear may change the significance of fatal choking in dolphin populations," warned the authors in an interview with Discovery News.

The findings are published in the journal PLOS One.