Over the last decade, bottlenose dolphins have become a more frequent sight north of New Jersey, as the lively mammals enjoy the warming shallow waters not far from land in New York Harbor.
A new study from Columbia University and Wildlife Conservation Society reveals that these migratory marine animals are now avid visitors to the Big Apple, frequently entering the human-traversed waters between New York and New Jersey for food and socializing. The annual return of these aquatic mammals to the city’s shore could signify improvements in coastal water quality and bring a renewed commitment to protecting local wildlife even in urban areas.
“It is kind of the million-dollar question: If there is all this human activity in the New York Harbor, why are the bottlenose dolphins coming here,” said Sarah Trabue, research assistant at the Wildlife Conservation Society and the lead author of the study. “It appears that it could be an important feeding area. The prey species here are of a quality or of a quantity that makes it worthwhile to come into these urbanized areas.”
For two years, Trabue’s team tried to find possible answers to why and how often bottlenose dolphins were in the city’s shore. They rode out in boats, dropping underwater microphones around 30 feet deep in six different locations, recording in 20-minute cycles every hour, for four months at a time, very close to the ocean floor.
The recordings were retrieved, downloaded and run through PAMGUARD, a software program that detects the sounds that dolphins make when they echolocate. Fast-paced clicks mean that a dolphin is foraging, and it’s about to get its next meal.
“The time between the clicks decreases and at a certain point, when the clicks become so close together, to our ears, it starts to sound like a buzz. That’s what we call the foraging buzz,” Trabue said.
From 2018 to 2020, there was a lot of buzz in the water. The most activity was recorded in the central harbor, right at the mouth of the estuary, where the gateway right into New York Harbor spans the area from Brooklyn to New Jersey, Sandy Hook and Breezy Point.
During peak season, late summer and fall, these microphones picked up rapid clicks almost every day. (These highly social carnivores spend their winters off the coast of North Carolina.) Experts and study authors believe the reason may be an improving habitat resulting from stricter environmental regulations such as the Clean Water Act