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.
The conservation organization Clean Ocean Action is circulating a petition to stop the planned firing of loud air guns into the Atlantic Ocean off the coast of New Jersey. Whales, fish and other marine animals could be injured, seriously disturbed or driven away by the air guns.
A team of geologists plans to use the air guns to map ancient changes of the coastline of the Eastern United States. With that map the geologists, led by Gregory Mountain of Rutgers University, hope to measure how sea levels have changed during the past 60 million years in response to dramatic natural climate changes, such as the Ice Ages.
However, Clean Ocean Action charges that the experiments will hurt the local tourism and fishing economies, along with the wildlife. The organization also noted that the geologists’ data could benefit the fossil fuel industry, according to the National Science Foundation award abstract for the air gun study.
The air guns blast sound at levels of from 246 to 253 decibels, according to the Office of the Federal Register documentation related to the Rutgers study. A chart on the Dangerous Decibels website shows that level is approximately twice the level of a jet plane engine at 100 feet. The EPA considers exposure to 70 decibels per 24-hour period to be the acceptable level to avoid hearing loss in humans.
The 240+ decibel blasts in the Rutgers study would continue every few seconds, 24/7 for 30 days. However, the geologists have filed for a permit to, “disturb a marine mammal or marine mammal stock in the wild by causing disruption of behavioral patterns, including, but not limited to, migration, breathing, nursing, breeding, feeding, or sheltering,” per the Marine Mammal Protection Act of 1972.
Five marine animal specialists will be on board the Rutgers’ research vessel to monitor for mammals or turtles with a designated radius of the ship, according to a project summary. The specialists will stop the air gun firing if they spot wildlife. The summary also stated that the study was timed to minimize disruption of animal behaviors.
Clean Ocean Action accused the geologists of misrepresenting how the timing of the study would affect the marine wildlife.
A growing body of research has documented how loud sounds created by human activities harm marine animals. For example, one study published in PLOS ONE earlier this year found that humpback whales dramatically reduced their singing when air guns were in use nearby. As far back as 1986, biologists observed bowhead whales avoiding underwater air gun blasts that reached over 160 decibels in a study published in the Journal of the Acoustical Society of America.
Photo: A humpback whale leaps. Credit National Oceanic and Atmospheric Administration, Wikimedia Commons