Dolphins in Massachusetts
More than a dozen species of dolphins and porpoises are known to have inhabited Massachusetts waters. Some of the more commonly seen ones are the Atlantic white-sided dolphin (Lagenorhynchus acutus), the short-beaked common dolphin (Delphinus delphis), and the harbor porpoise (Phocoena phocoena). These species are found throughout the waters off Massachusetts. Short-beaked common dolphins, long-finned pilot whales, Atlantic white-sided dolphins, striped dolphins, and Risso’s dolphins are mainly seen off the coast of Essex, Barnstable, and Nantucket counties (although not necessarily near the shore itself). Dolphins are also seen on Stellwagon Bank and Jeffries Ledge in Cape Cod Bay (especially July through December), and in deep water along the edge of the continental shelf. Harbor porpoises can be found anywhere along the coast, and are often seen near the shore.
The life cycles of dolphins and porpoises vary depending upon the species. For example, the Atlantic white-sided dolphin becomes sexually mature between 6 to 12 years of age and following a gestation period of 10 to 12 months, females give birth to a single calf who may go on to live 27 years. The short-beaked common dolphin becomes sexually mature at 5 to 12 years of age and females give birth to a single calf every 2 to 3 years. These offspring can live up to 35 years. In comparison, the harbor porpoise becomes sexually mature relatively early, at 3 to 4 years of age and females may give birth every year for several consecutive years. However, these porpoises have a relatively short lifespan, living an estimated 24 years.
Where these animals live and what they eat varies depending upon the species:
- Atlantic white-sided dolphins are found in the colder waters of the North Atlantic Ocean. They tend to move with the seasons, moving closer inshore and north during the warmer months and more offshore and south during the winter. Their diet consists of small schooling and bottom fish such as cod, hake, herring, mackerel, smelt, and sand lace, as well as shrimp and squid. They are known to be cooperative feeders.
- Short-beaked common dolphins are found in most warm tropical and cool temperate waters in both the Atlantic and Pacific Oceans. Their habitat includes not only coastal and offshore waters but also enclosed seas such as the Mediterranean Sea. Their diet largely consists of schooling fish like mackerel and herring but they also consume cephalopods such as squid.
- Harbor porpoises are most often found in coastal and offshore waters of the sub-Arctic, North Atlantic, and North Pacific, and are frequently located in shallow waters of bays, estuaries, tidal channels, and rivers. Because of their preference for cooler temperature waters, harbor porpoises have a high metabolic rate and must feed both day and night to ensure they have sufficient energy. In fact, it’s been estimated that they will consume up to 10 percent of their body weight—mainly consuming schooling fish such as herring, sprat, and sand eels, but also octopus and squid—each day.
Like all marine mammals, all species of dolphins and porpoises are protected under the Marine Mammal Protection Act. None of the dolphins or porpoises identified in Massachusetts waters are currently classified as endangered. However, as of 2022, nine of the world’s estimated 41 dolphin species are classified as endangered by the International Union for Conservation of Nature’s Red List of Threatened Species, the Endangered Species Act, or both. Tragically, the baiji dolphin is now believed to be functionally extinct, becoming the first whale or dolphin driven to extinction by human activity (primarily habitat destruction and entanglement in fishing equipment). Similarly, the vaquita, the smallest of the world’s seven porpoise species, is now the most threatened porpoise. Because of entanglement in fishing nets, perhaps only 10 members of this “critically endangered” species survive in Mexico’s Gulf of California, and like the baiji dolphin, its extinction may be imminent.
Threats to Dolphins
Dolphins and porpoises in Massachusetts and elsewhere are confronted with a number of human-caused and natural threats and stressors, with the main threat being entanglement in commercial fishing gear. Research suggests that more than 300,000 whales and dolphins are killed each year as a result of entanglement in fishing gear and even more in fishing debris; however, this likely severely underestimates the true losses, as most entanglements are not observed or recorded. Marine mammals including dolphins and porpoises can become entangled or caught in driftnets, gillnets, seines, trawls, trap pots, and longlines. Entanglement can result in a prolonged and painful death when marine animals cannot reach the ocean’s surface to breathe, suffer cuts and infections to their skin when fishing ropes lacerate their skin, or slowly starve to death if they cannot feed because they are towing heavy fishing gear.
Other threats to dolphins include encounters with rod-and-reel gear, vessel collisions, habitat destruction and degradation, extreme weather events and changes in climate, underwater noise pollution, chemical spills and biotoxins, and hunting by humans. Dolphins and porpoises are hunted both legally and illegally throughout the world, and it has been estimated that more than 100,000 small whales, dolphins, and porpoises are intentionally killed each year. The most well-known of these—documented in the 2009 Academy Award-winning film The Cove—is the annual “drive” hunt which occurs each year from September through March in Taiji, Japan. During the 2021-2022 Taiji hunting season, an estimated 498 dolphins were slaughtered and 65 were captured to be sold to aquariums and amusement parks. However, the most recent hunting season that ended Feb 29, 2024, resulted in an estimated total of 415 dolphins slaughtered or captured. This decline could be due to increased awareness of the cruelty of dolphin captivity and partially due to increased understanding of the dangers of mercury poisoning.
Strandings are a particular problem for dolphins in Massachusetts. Cape Cod’s tidal range is massive, and every low tide reveals nearly 20 square miles of sand flats; for dolphins hunting food, this can quickly turn shallow waters into a maze of draining water. As a result, more dolphins become stranded on Cape Cod than almost any other place in the world. The International Fund for Animal Welfare announced that 2024 has been record-breaking in terms of the large quantity of dolphin strandings. On June 28, 2024 alone, the largest mass stranding of dolphins in US history took place on Cape Cod, consisting of a total of 146 dolphins, only 102 of which survived. Fortunately, however, thanks to improvements in technology and rescue protocols and techniques, the survival rate of animals discovered stranded has improved significantly in the last few decades. Researchers are now working to develop technology that could recognize the whistle sounds dolphins seem to make before a stranding and send real-time alerts to rescuers in stranding hot spots like Wellfleet Harbor, which could help improve survival rates even more.
How is Massachusetts Helping?
Several organizations operate hotlines and have staff and volunteers who are trained to respond to sick, injured, entangled, or stranded marine mammals in Massachusetts:
At the federal level, NOAA Fisheries operates a Dolphin & Whale 911 app which concerned individuals can use to report a sick, injured, entangled, stranded, or dead marine mammal or sea turtle. It also maintains the Northeast Marine Mammal and Sea Turtle Stranding and Entanglement Hotline ((866) 755-NOAA).
Fun Facts:
- Dolphins, porpoises, and whales are all “cetaceans.”
- All dolphins are whales but not all whales are dolphins.
- The largest member of the dolphin family is the orca, or killer whale.
- Dolphins are among the most intelligent animals on the planet.
- Dolphins and porpoises are social and live in groups called pods.
- Dolphins and porpoises communicate by making squeaks, buzzes, whistles, and clicks and these sounds can be heard from miles away.
- While dolphins tend to have long noses, large mouths, and cone-shaped teeth, porpoises have smaller mouths and spade-shaped teeth. The dorsal fin of a dolphin is hooked or curved, while that of the porpoise is shaped more like a triangle. As a general rule, dolphins have long and lean bodies, while porpoises tend to be more portly.
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