A Dolphin’s tale

Please consider the images to be copyrighted and ask permission before copying or using. Thank you. DEClapp

Here in New England the coast varies from a southerly sandy beach to a rocky northern beach. The state of Rhode Island is quite rocky along its coast and north of Boston it is pretty much all exposed rock. South of Boston there is a great deal of glacial sand that forms both the substrate of the ground and the soft, sandy, and malleable, stuff of the beaches, all the way past the Carolinas to Florida – excepting the Rhode Island shoreline. This sand moves easily with storm-driven waves, the pummeling by rain drops, and the twice daily energy of the rising and ebbing tides. The olden days glaciers came down from the north and ended for the most part somewhere near a line from Boston to Albany, an east-west boundary that marks the lower edge of the icy invasion. Out on the eastern end of that line is now Cape Cod; a seventy mile long arm of glacial deposited and sifted sand reaching east and then north and finishing with a curled hand out at Provincetown. Just to the south of the Cape are the Islands of Martha’s Vineyard and Nantucket.

The very shape of this sand bar presents a protective barrier to the populated coast line and also serves as a trap for marine creatures that don’t carry Google-Earth maps. We get a lot of wind from the northeast; much of our weather driven catastrophes are northeasters. These winds drive water into the bended arm of the Cape and deposit all sorts of birds, reptiles and mammals for us to be amazed by. A northeaster will have bird watchers out in the storm looking for sea birds driven to land and into Cape Cod Bay; birds that fly in a big loop looking to exit this constraining land. This is when murres, guillemots, razorbills, jaegers, puffins, and a few others are likely to be seen from shore. At the same time sea turtles that have been feeding along the Gulf Stream and following warm patches of water in all directions can be driven in along the beaches. In late fall we see dozens and dozens of Kemps Ridley, Green and an occasional Leatherback forced up onto the cold beach.

The marine mammals we see in this area (Harbor and Gray Seals; Atlantic White-sided and Short-beaked Dolphins; Fin, Humpback, Minke, Atlantic Right, and the occasional Sei Whales) are all good swimmers and not directly impacted by the movements of the ocean’s surface water. However, the water does move, the prey often travels with the water, many of these mammals are migratory and arrive here coincidentally with a burgeoning food supply. It is the migratory ones that get trapped inside the reach of Cape Cod. They might be headed down the coast, past Boston Harbor and Minot Light and then unknowingly into Cape Cod Bay. They hit the southerly end and I suppose many turn around and swim out, but many follow shallow water and get isolated on sand bars as the tide drops, especially within another hook that reaches westward from the eastern edge of Cape Cod Bay in Wellfleet kind of a fish-hook like barb within Cape Cod Bay. In much of this area you can be standing on quartz sand at low tide and have about eight feet of water at high tide. Maybe the term migratory isn’t quite appropriate for some marine mammals – the dolphins move a lot following food. The whales we see are really migratory as they head south in the fall and return in the spring. They are predictable where the dolphins are not.

Below are a few of the dolphin types that I have encountered and a story or two about Cape Cod dolphins – maybe whales and sea turtles will follow. The image at the head of this post shows a Short-beaked Common Dolphin with the letters IFAW painted on its side. IFAW stands for the International Fund for Animal Welfare. It is a truly international organization with a string of wonderful successes in the conservation/wildlife arena. It may be marine mammals in Cape Cod but it is also elephants in Uganda, and habitat in Kenya, and tigers, penguins, seals, and more and more elephants. Here on the Cape where we may have 400 strandings in a year IFAW is ever alert to get the animals safely back into the water away from sand bars and shallows.

The eastern edge of Massachusetts ends in the curled arm of Cape Cod. If you are a marine mammal swimming south along the coast you may swim into the northern gape of the Cape. If you are a bird caught up in a storm with northeast winds you can be blown into the Bay and then have to fly south and east and then north to get out. This Wikipedia map shows the sandy hook on the north/south part (eastern edge) of the Cape that further confuses and stymies swimming marine mammals. In 2019 there were over 400 strandings inside Cape Cod Bay.
Dolphins are usually longer-snouted than the similar porpoises. This cute little marine mammal (perhaps just a very small whale) is a Commerson’s Dolphin. This is an animal with two very separate populations, one around Tierra del Fuego and the Falklands and the other half a world away in the Indian Ocean. Porpoises are small, with almost no beak and a small rounded dorsal fin. Though this dolphin is also small it qualifies as a dolphin.
The White-sided Dolphins are widespread in the North Atlantic. It is the common dolphin from the Carolinas to the Canadian Maritimes and then eastward to the Scandinavian shores. It is also a rather large dolphin as it can grow to over nine feet in length (2.8m) and weigh up to 500 pounds (227kg). Though these dolphins don’t migrate in any predictable way they do move significantly as large social groups so that they stay near the food sources they require. They eat fish (herring and hake mostly) and lots of squid as well. These animals are often seen from whale-watching boats off Cape Cod.
The Common Dolphin is in fact the most common dolphin on the planet. They are seen all around New Zealand and Australia and throughout the warm and temperate waters of both the Pacific and Atlantic Oceans. Here in the northeastern part of the US we see them associated with the great flow of the Gulf Stream. It may be the most abundant dolphin but the most common one in aquaria displays is the Bottle-nosed Dolphin; the next image down.
Bottlenose Dolphins are also common and widespread. They are also found in most warm or temperate waters. Molecular studies are seeing that there are three types of Bottlenose Dolphins and these may soon be categorized as separate species. They are gregarious, as are many dolphins, and are often seen in groups of hundreds and sometimes thousands. We have seen these mammals in water shows and on television. Flipper was a Bottlenose Dolphin. They are chunky and most weigh well over 600 pounds. They can live for more than 40 years and are constantly on the move. Tuna nets (commercial fishing) are a threat to pods of dolphins but at the moment there are lots of these creatures around.
The next three images are of a Short-beaked Common Dolphin that was at the top of the wrack line on a local beach. It was one of three that succumbed on sandy flats exposed at low tide. In this case the low tide flats extend almost half-a-mile from the high tide wrack line. The animals got in to far when there was water and were left high and dry when the tide ebbed. Over the past few years this has happened locally to Minke Whales, Harbor Porpoise, Atlantic White-sided Dolphins, Grampus (Rizzo) Dolphins, as well as The Short-beaked Common Dolphins. And sea turtles as well. It is quite common and always heart-wrenching. The bird next to the dolphin is an immature great Black-backed Gull. Gulls, coyotes, and vultures will help dispose of a carcass, but many marine mammal carcasses are towed back into the water and then well away from shore.
The teeth of dolphins are conical and one of the taxonomical characteristics that tell you that they are really dolphins. They can swing their head and jaws as they swim through schools of fish sometimes catching them outright and other times damaging and wounding the prey. They are strong swimmers and have little trouble catching food.
This one has the letters IFAW painted on it. This is the mark of the International Fund for Animal Welfare. On a worldwide basis they work to protect and secure threatened and endangered species and habitats of all sorts. Here on Cape Cod they are the marine mammal EMTs. They can respond, triage, then elevate, and wheel off the beach, and then drive to the ocean side of the Cape to release stranded animals. It is heavy hard work and due to the numbers and difficulty in gathering information it is an effort that isn’t always rewarded by watching the mammals swim away.
I thought I’d stick in a couple images of the larger marine mammals (Humpback Whales) at work. Around the world the marine mammals either chase and catch fish (toothed whales) or gulp in huge quantities of water and strain the smaller stuff as they “exhale” the water back through their baleen sieve (baleen whales). That is the baleen reaching down from the lid-like top jaw of the whale. In most waters there are creatures of great abundance; here in the western Atlantic it is Sand Lance our whales seek out, but there are sardines in some places and capelin in other waters. These are fish that swarm in schools of thousands or hundreds of thousands. Krill, squid, mackerel, menhaden and a few others are schooling creatures and are also sought out.
Though many of the whales eat fish, as we see here, there are other whales (and a seal or two as well) that strain plankton bits from the water. Imagine the largest animals on earth living on food items smaller than popcorn.
The whales in the picture above are feeding on Sand Lance, a fish about the size of a small pencil. The whales will circle around underwater exhaling air as they swim. The bubbles rise and the fish are confused and stay inside the “bubble net” or ring. The whales then swim up through the net taking in lots of water and fish. As you saw in the image above, the top jaw is a rather flat lid where the bottom jaw has the world’s largest double chin. The throat is pleated and expands greatly as the whale takes in the food-rich water. Once at the surface the whale will swim slowly forward allowing the pressure of the motion to force the rorquals (pleats) to close, the water to pass out through the mostly closed mouth. A baleen whale with a mostly closed mouth presents a baleen, sieve-like, barrier to any fish that were brought in by the big gulp.

3 thoughts on “A Dolphin’s tale

  1. Interesting as usual mr Clapp. Here in Hawaii.the mothers and.baby Humpbacks have started their migration back to Alaska for the summertime buffet and just this morning I had a large ( 40-60 ) pod of Spinner Dolphins, so called because they often jump out of the water and spin around as they do so. There are still quite a few adult Humpbacks here and today I have seen about 15 full body breaches.

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