Feature photo: October 13, Common dolphin jumping a boat wake in the Atlantic Ocean. Artie Raslich/Gotham Whale
The Gulf of Maine is traversed by many species of marine mammals, from soulful harbor seals to the greatest of whales, either as local residents or tourists on their breeding and feeding voyages. Among the most charismatic of all are dolphins. Besides spotting them from whale-watching boats, how much do you actually know about New England’s native dolphins?
“When people think of dolphins, they think of tropical animals,” says Brian Sharp, stranding director for the International Fund for Animal Welfare, located in Yarmouth Port on Cape Cod. “But you’ve really not seen a dolphin until you’ve seen one of the species endemic to New England waters.”
The two species of dolphin most frequently sighted around Cape Cod Bay have one thing in common: their markings look like custom paint jobs. And although striped dolphins, Risso’s dolphins, and the occasional bottlenose will sometimes pass through, it’s these two species of streamlined wave-riders that New Englanders most often spy skirting the edge of the continental shelf.
Common Dolphins (Delphinus delphis)
At 6 to 7 feet long and a svelte 165 to 300 pounds, common dolphins are like “wide receivers” in build, says Tony LaCasse, media relations director of the New England Aquarium and a longtime dolphin rescuer. Even when stranded, common dolphins are communicative, chattering to the other members of their pod through clicks, whirrs, and whistles. Rescuers will often point them towards each other in order to reassure them. They are dark grey and tan with white countercolored bellies, an hourglass shape on their side, and a stripe from their eye to their mouth giving them a masked appearance. They have a long rostrum, or snout.
Atlantic White-Sided Dolphins (Lagenoryhnchus acutus)
Even salty, seasoned boat captains describe Atlantic white-sided dolphins as “beautiful.” These cetaceans sport natural detailing of bold white and silver patches on their sides, with a yellow or tan stripe that leads to their tail. At 7 to 9 feet long, and weighing in at more than 500 pounds, they are “girthier” than common dolphins, a look accentuated by their short rostrum. LaCasse compares them to “linebackers:” brawny, husky, and stoic while awaiting rescue at the beach
Most dolphins skim the continental shelf and shelf edge, swimming closer to the coastline if they are hot on the trail of prey such as a school of herring, hake, mackerel, smelt, or anchovies.
Unfortunately, coming near to shore makes dolphins vulnerable to running aground. It’s really impossible to talk about dolphins in New England without giving attention to strandings. Knowing how this phenomenon occurs can help us understand even more about our endemic dolphin species.
Mass strandings in New England have happened longer than humans can remember. Cape Cod Bay, a hooked sandbar with a gently sloping shore, is a notorious trap for dolphins. Anyone who has combed the beaches of the Cape knows that when the tide goes out, it runs out far and fast—so if you are a dolphin who has pursued your prey close to shore, that shallow beach profile with its hidden sandbars can leave you high and dry before you even know what’s happening.
Along the New England coast, “as far as we know, the commonest mass strandings are behaviorally driven, without a human cause,” says Michael Moore, Director of the Marine Mammal Center at Woods Hole Oceanographic Institution. Dolphins, the highly social animals that they are, may follow a sick lead animal inland. Even healthy lead animals can have their echolocation disoriented by mucky water caused by a turn of the tide, or the cloudy aftermath of a nor’easter.
Once dolphins are stranded, time is of the essence in a rescue. Gravity on land presses hard on marine mammals whose skeletons have not evolved to resist its force and protect their internal organs (seals are built to spend significant periods on land, but not so cetaceans). They can suffer significant internal trauma if out of the buoyant salt water for too long. Also, the hot sun can burn dolphin skin in summer, and frostbite can singe it in the winter. There is little temporal margin for error if dolphins are going to be viable again back at sea.
Mass dolphin strandings (from 2 to 20 individuals) occur most often in the winter, from December through April. With the lack of daylight on short winter days, the Northeast Regional Stranding Network monitors and patrols beaches in order to stay ahead of a potential crisis.
Imagine a stranding like a military triage situation. The Cape’s tidal flats can go out a long way, so a dolphin might be stranded as much as a mile from the road. They might be in three feet of tidal mud, or beached on a sand bar far from the water’s edge. Rescuers have refined the use of all-terrain dolphin carts, stretchers with cut-out holes for pectoral fins, and transport trailers that are enclosed and lined to make rescue faster, more efficient, and less traumatic. Even with all that technology, it still can take six people to carry and load a slippery, unwieldy dolphin, so rescuing is muddy, strenuous, and emotional work!
Rescued dolphins are tagged and then released from Herring Cove or Race Point in Provincetown, MA where there are fast drop-offs into deep water. The Provincetown Fire Department sets up lights on the beach to aid rescuers, and trained response volunteers in drysuits walk the dolphins out into the water.
The satellite tags reveal that after a day or two of getting their bearings, even single dolphins usually find their way back to the pod. They will link up with other released dolphins in their family group and then travel together, often heading out towards Georges or Stellwagen Bank… staying well clear of land!
While little can be done to prevent geographically-caused mass strandings, you can support your local rescue network to make sure that stranded animals have a viable chance at survival. Single animal strandings often caused by illness, injury, or entanglement in fishing gear are more complex. In that case, advocating for responsible, sustainable fishing practices will help dolphins and other pelagic species avoid becoming bycatch casualties.
Dolphins are very much residents of New England waters, and there are more of them out there than we might realize: “When you see four or five dolphins at the surface,” says Brian Sharp, “it can be an iceberg effect: that really is a small portion of the number of animals actually around you, below the water and beyond your vision.”
Hopefully what you have learned here will help expand your vision so that you will see our endemic dolphin species even more clearly!
If you find a dolphin stranded south of Boston, please telephone IFAW’s stranding hotline at 508-743-9548. From Boston on north, please dial the New England Aquarium’s Marine Animal Hotline at 617-973-5247. For entanglements or by-caught cetaceans, please call the Provincetown Center for Coastal Studies at 1-800-900-3622.