Originally designed to live on land, marine mammals are a diverse, charismatic group of animals that include more than 120 species. The animals share key characteristics of land mammals. They have hair, breathe air, give birth to live young, which feed off mother's milk when young. They have warm bodies and usually thick blubber to keep their body temperatures high. The bottlenose dolphin is probably the most widely recognized marine mammal, easily spotted just offshore from beaches around the world. Small groups of 20 or less can live in close proximity to shorelines, but groups living more offshore can reach several hundred. Bottlenose dolphin calves stay with their mothers for up to six years, learning how to hunt and become good dolphin citizens. Full-grown dolphins reach eight to 12 feet in length and can weigh up to 1,430 pounds. The bottlenose dolphin is protected in U.S. waters.
What makes them "marine" depends on the animal. They either live mostly in the sea or, like polar bears, depend on the ocean for food. The largest in the group are whales -- including humpback whales. These massive animals reach up to 50 feet in length and weigh up to 79,000 pounds. To maintain their weight, the animals feed on tons of krill and fish. They neared extinction due to whaling, but have recovered somewhat since a 1966 moratorium on whaling was introduced.
While polar bears live mostly on land or ice, they are excellent swimmers and have been known to swim up to 45 miles a day. The massive animals, weighing up to 1,500 pounds, hunt mostly seals. In recent years, biologists have observed that the bears are swimming now more than ever as melting stretches the distances between Arctic ice flows. Because they depend on sea ice to hunt seals, the polar bear is considered threatened as global warming melts and thins ice in this region.
This member of the weasel family is also the smallest marine mammal, with females weighing about 60 pounds and males weighing up to 90 pounds. They may be small, but they're also clever. They're the only marine mammals known to use tools. They use stones to break open clams and store food they gather in the folds of their armpits! Another feature that sets them apart is their lack of blubber. These marine mammals depend mostly on their fur to stay warm. That feature makes them particularly vulnerable to oil spills, which can compromise their fur's insulating effect.
Immediately recognizable by its long tusks and whiskers, the sea walrus is a hefty, flippered member of the Odobenidae family and is, in fact, the last living member of this group. Since both the males and females have big tusks and not much for teeth, the animals feed by sucking up shellfish from the ocean floor. So, just what are those tusks for? The longer they are (they grow to be up to four feet long in males), the higher an animal is ranked in the group. Males attack each other with their tusks to establish dominance. The ivory appendages are also handy for poking holes in the winter ice and for helping the animals pull themselves out of the water.
Manatees, also known as sea cows, are gentle herbivores that live in marshy areas in tropical and subtropical waters. The average adult manatee can weigh up 1,200 pounds and is around 10 feet long. Because of their slow metabolism, these animals can only survive in warm waters. Due to the unusually long, cold winter this year in part of the southeastern United States, populations of manatees throughout Florida were devastated. During the day, manatees usually like to stay close to the surface. At night, manatees will often sleep about three to 10 feet below sea level. This is why these gentle animals are so often accidentally injured, maimed or killed by passing boats.
Found up and down the North American coastlines, these marine mammals spend half of their lives swimming. Although they can reach up to six feet in length and weigh around 180 pounds, when on land and in plain sight harbor seals may not be easy to spot. Their spotted brown or tan fur allows harbor seals to blend in with sand and rocks. Unlike their very vocal relatives -- sea lions and elephant seals -- harbor seals are quiet creatures that make little noise. They like to hang out on beaches, sand bars and rocks during low tide to bask in the sun and sleep, but they never go far from the water. At the slightest sign of danger, they will quickly slip back under the waves. These expert swimmers have been known to plunge to depths of more than 1,600 feet and stay underwater up to 28 minutes.
Microphones submerged in the waters of the Bering Strait recorded an increasing number of whale calls from 2009 to 2012, including some from whales that normally live further south. The whales may have expanded north as the Arctic warmed and the animals’ populations recovered from hunting.
The increase in whale numbers coincided with more ship traffic in the region. More shipping could lead to whales being injured or killed in collisions and interfere with whale communications.
Along with native Arctic whales including belugas and bowheads, the microphones recorded the songs of sub-Arctic whales, such as humpbacks, minkes, fins and orcas. Oceanographer Kate Stafford of the University of Washington will present the findings Wednesday at the Ocean Sciences Meeting in Honolulu.
The microphones recorded humpbacks’ melodious songs into late autumn. And oceanographers observed fin and minke whales from July to September, and their vocalizations were recorded into early November.
“The Arctic areas are changing,” Stafford said. “They are becoming more friendly to sub-Arctic species, and we don’t know how that will impact Arctic whales. Will they be competitors for food? Will they be competitors for habitat? Will they be competitors for acoustic space, for instance these humpbacks yapping all the time in the same frequency band that bowheads use to communicate? We just don’t know.”
The northern seas provide more hospitable habitat for southern species, as the far north warms quicker than the rest of the planet and sea ice retreats.
“It’s not particularly surprising to those of us who work up in the Arctic,” Stafford said in a press release. “We are seeing and hearing more species, farther north, more often. And that’s a trend that is going to continue. These animals are expanding their range. They’re taking advantage of regions in seasons that they may not have previously.”
The trend could also be tied to the end of most commercial whaling in the Arctic and northern Pacific Oceans. Russian whaler’s ship logs record the sub-Arctic species in the region during the mid-to-late 20th century, according to the abstract of Stafford’s presentation. The whales may be returning to previously lost territory.
“The question is, are these whale populations recovering and so they’re reoccupying former habitat, or are they actually invading the Arctic because they can, because there is less seasonal sea ice?” Stafford said.
The whales aren’t the only ones increasing traffic in Arctic waters. More commercial shipping vessels now take advantage of the widespread disappearance of sea ice to navigate a northern shortcut between North America, Europe and Asia.
The warmer Arctic also makes it easier for oil and natural gas exploration of the seafloor. More cruise ships also visit the Arctic now. Ship traffic and resource extraction can pollute the waters with both chemicals and noise — the racket created by humans interferes with the whales’ vocal communications.
Using knowledge of the whale’s biology could allow ships to avoid colliding with the massive mammals. For example, tracking studies observed that bowhead whales travel north on the eastern side of the Bering Strait in spring, then return south on the western side in autumn. Seasonal shipping routes could be organized to avoid areas where whales travel.