NOAA Teacher at Sea
Maggie Prevenas
Onboard US Coast Guard Ship Healy
April 20 – May 15, 2007
Mission: Bering Sea Ecosystem Survey
Geographic Region: Alaska
Date: May 1, 2007
Species Profile: Dall’s Porpoise and Northern Fur Seal
The place to be on the ship is up in the bridge. That is the place to see all the animals. We have two different groups of scientists up there from sunrise to about nine at night. We have scientists looking for different kinds of birds and we have scientists looking for ice seals. Sometimes they see other animals. Like today. They saw another kind of cetacean, a porpoise. If you’d like to learn more about them, read on.
Dall’s Porpoise: Phocoenoides dalli
Where do Dall’s porpoises live? Dall’s porpoises only live in the North Pacific Ocean from Japan to Southern California and as far north as Bering Sea.
How many Dall’s porpoises are there? We don’t know. Although population numbers are unknown, Dall’s porpoises appear abundant through their range. Dall’s porpoises are not considered endangered.
How can I identify a Dall’s porpoise? Dall’s porpoises are beautiful! Though individual animal coloring varies slightly, Dall’s porpoises are easy to identify as they are mostly black with white along their sides, on the top half of their dorsal fins and on the trailing edge of their flukes. Dall’s porpoises mature to around 7 feet (2.1 meters) long and have 19-23 spade-shaped teeth. When swimming, Dall’s porpoises leave a characteristic splash called a ‘rooster tail.’
How well can a Dall’s porpoise see or hear? Scientists don’t really know. Captive Dall’s porpoises emit low frequency clicks that are presumably used for echolocation.
What do Dall’s porpoises eat? Dall’s porpoises are thought to have a rather varied diet consisting of hake, squid, lanternfish, anchovy, sardines and small schooling fish.
How do Dall’s porpoises have babies? Female Dall’s porpoises reproduce at approximately six years of age while male Dall’s porpoises mature at 8 years of age. Dall’s porpoise calves are born in mid-summer after a 12 month gestation period. They are about 3 feet (0.9 meters) long. Calves and their mothers live separate from main porpoise herds for a time. Dall’s porpoise mothers usually have calves every 3 years.
How long do Dall’s porpoises live? How do they die? Dall’s porpoises usually live about 16-17 years. Very little is known about their mortality however many believe that Dall’s porpoises are very susceptible to “incidental” capture by certain types of fishing gear. These porpoises become so intense upon the pursuit of their food that they fail to anticipate or see gill nets set for fish. Porpoises that get entangled in nets usually drown.
Northern Fur Seal: Scientific name: Callorhinus ursinus
The Healy made a stop at St. George and St. Paul Island this past week. Collectively, they are called the Pribilof Islands. The history of these two islands is very interesting. There is a deep Russian influence as well as Native Alaskan Aleut. The animal that the islands based their economy on was the Northern Fur Seal. Read on if you’d like to learn more!
Northern fur seals range extends from Southern California, up the North American coast, west along the Alaskan coastline, across the sub Arctic sea to the Russian coast and down to waters of northern Japan.
How many Northern fur seals are there? The estimate of the world’s population of Northern fur seals is 1,130,000. There are about 880,000 northern fur seals in U.S. waters and most breed on the Pribilof Islands. A smaller population of Northern fur seals are found on San Miguel Island off the California coast. But in 1909, there were only 200,000 to 300,000 left to breed on the Pribilof Islands because of commercial seal harvests. The seal hunters harvested the Northern fur seals for their fur.
How can I identify a Northern fur seal? Males are gray to black, and females are light gray on the back and reddish-brown on the chest with a light patch. Both have extremely dense fur, so dense that it keeps the cool ocean water from the skin, thereby preserving body heat; but it is not waterproof. Because of this dense fur they have large, hairless flippers to keep them cool. The females weigh 90 to 110 pounds on average, and the males between 300 and 615 pounds. Like all fur seals and sea lions, the Northern fur seal has ears that stick out from its head. By rotating their flippers forward, they can walk, run and climb out of the water.
What do Northern fur seals eat? Northern fur seals feed mainly at night and may dive to depths of 600 feet (180 m) in search of small schooling fish and squid and prey are typically eaten underwater. Larger fish are brought to the surface and eaten there.
How do Northern fur seals have their young? After giving birth on one of the rookeries, the mother nurses her pup for 8-10 days. She then begins a pattern of leaving to feed at sea for 4 to 10 days, and returning for 1 or 2 to nurse her pup. During this time she usually makes short shallow dives at night to feed. The pups are weaned after 4 months.
How long do Northern fur seals live? How do they die? The Northern fur seal can live for 25 years, but most females live to be 18-20 years old and the males to their low teens.
Natural predators of the fur seals include sharks, foxes, killer whales and Steller sea lions. El Ñino and entanglement also are hazardous to the Northern fur seal.
Do you know what is really cool about Northern fur seals? A Northern fur seal bull, that has territory, will defend it against any intruding bulls, and even humans!!
The Northern fur seal can spend extremely long periods in the open ocean. Before returning to the breeding colonies many pups will remain at sea for up to 22 months!
A Northern fur seal mother find her pup by moving through the breeding colony and listening for the pup’s distinctive voice!
Northern fur seals mainly feed at night, when prey species are closer to the ocean surface!
Northern fur seals have huge flippers, proportionally bigger than a Steller sea lions. They help keep them cool.
Northern fur seals are famous for the dense fur that covers all but their flippers. That fur consists of approximately 46,500 hairs per square centimeter.