Boat noise in Bocas "potentially harmful"
to dolphins: researchers
STRI Panama

Tourists in Bocas Del Toro’s Dolphin Bay get a good look at a bottlenose dolphin in July 2012. Credit: (STRI/Sean Mattson).

Panama’s once-sleepy Bocas del Toro Archipelago is an increasingly popular destination for tourists. Attractions include dolphin-watching tours around the mangrove cays of the Caribbean getaway. While the dolphin population of Bocas is relatively small — about 200 individuals — a boat tour can almost guarantee a close encounter with the charismatic creatures. Not surprisingly, dolphin-watching boat traffic has increased exponentially in recent years.

New research by visiting scientists at STRI’s Bocas del Toro Research Station shows that noise from boat motors alters the way bottlenose dolphins communicate while foraging, one of their most noise-sensitive activities. Dolphin whistles become lower in minimum -ending- and peak frequencies, but longer in duration. Lower and longer whistles can travel longer distances allowing dolphins to avoid or reduce their signals to be masked by boat engine noise. However, this also means that dolphin acoustic communication space is drastically reduced by the roar of boat motors prompting them to make these changes.

The findings, published in the Journal of the Acoustical Society of America in April, “clearly suggest that interactions with dolphin-watching boats are potentially harmful.” Authors Laura May-Collado, of the University of Vermont, and Shakira Quiñones-Lebrón, of the University of Puerto Rico, wrote: “Our results also indicate that intrusive dolphin-watching activities and associated engine noise may be negatively impacting individual fitness in this small dolphin population.”

Between 2004 and 2012, May-Collado and team collected 56 hours of dolphin whistle recordings from 47 individuals, all photo-identified. The recordings were made in the presence of two to 17 dolphin-watching boats, with an hourly turnover of 34 boats. These are low-season figures. During the peak of the tourist season, up to 100 boats can interact with dolphins in a single day.

Aggressive dolphin watching can have other negative effects. “Dolphins reduce their feeding and socializing time, two very important activities for their survival, when the number of boats increases,” said May-Collado. Her team has also documented boat strikes, which killed at least 10 dolphins between 2012 and 2013. They also observed calves separated from their mothers, which can reduce the chances of survival of offspring. “All in all, this is an industry that is far from being sustainable in Bocas. So we are trying to increase education, training, and outreach activities and use the information we have to propose a management plan that minimizes risk of population extinction in Bocas.”

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