Beluga whales probably live about 25 to 30 years.
B. Aging studies.
1. As a beluga whale ages, it periodically produces growth layer groups of dental material. Age can be estimated by examining a sliced section of a tooth and counting these layers. These estimations are most accurate in young whales, before the tooth's pulp cavity fills in. Researchers are currently investigating new tooth-aging methods. Scientific evidence indicates that belugas may deposit up to two growth layer groups annually (Goren, et al, 1987).
In beluga whales, age can be estimated by examining a sliced section of a tooth and counting growth layer groups.
2. Researchers use size and coloration to estimate relative ages of belugas. Because immature belugas lighten as they approach maturity, paler belugas are likely to be older than darker ones.
Killer whales and polar bears prey on beluga whale adults and calves (Ridgway and Harrison, 1981).
D. Human interaction.
1. Beluga whales have been hunted for centuries.
a. Since ancient times, indigenous Arctic peoples of Canada, Alaska, and Russia have hunted beluga whales for their meat, blubber, and skin. Tanned beluga skin, often referred to as "porpoise leather," is the only cetacean skin thick enough to be used as leather (Ellis, 1991).
b. Arctic natives still subsistence hunt belugas for food and other raw materials. This practice is an important part of their culture, but there is some concern that the current harvest may be too high for the population to withstand (Dold, 1993). The annual harvest is about 200 to 550 in Alaska and about 1,000 in Canada (Nowak, 1991; Dold, 1993).
c. In the 18th and 19th centuries, commercial hunting of belugas by Europeans and Americans caused a drop in the Canadian Arctic beluga population. In addition to using the meat and blubber, Europeans also used the beluga whales' fine melon oil to lubricate watches and machinery, and to illuminate lighthouses (Ellis, 1991). From 1868 to 1911 Scottish and American whalers took more than 20,000 belugas in Lancaster Sound and Davis Strait (Ellis, 1991).
d. In the 1930s belugas along the St. Lawrence River were killed by fishermen who believed the whales were a threat to the fishing industry (Ellis, 1991).
2. Industrial run-off in the St. Lawrence River has resulted in high levels of toxic chemicals such as polychlorinated biphenyls (PCBs) and dichlorodiphenyltri- chloroethane (DDT); and heavy metals such as lead, mercury, and cadmium in the water. These toxins are thought to be responsible for the deaths and strandings of many belugas in the St. Lawrence River. Levels of these toxins in St. Lawrence belugas were found to be significantly higher than in Arctic belugas (Smith, St. Aubin, and Geraci, 1990).
a. These toxins become more concentrated as they are passed up the food chain.
b.PCBs and DDT are lipophilic; that is, they are readily stored in animal fat. Heavy metals are generally concentrated in other body tissues including the liver, kidneys, and muscles (Smith, St. Aubin, and Geraci, 1990).
c. These toxic chemicals also may cause a decline in a beluga's immune system, making it susceptible to pneumonia, ulcers, cysts, lesions, tumors, and bacterial infections (Smith, St. Aubin, and Geraci, 1990).
d. Low birth rates in the St. Lawrence River also may be linked to industrial pollution (Nowak, 1991).
3. Oil exploration and hydroelectric development cause significant alterations to beluga habitats (MacDonald, 1993).
E. Disease and parasitism.
1. As in any animal populations a variety of diseases can be responsible for beluga whale deaths. These include viral, bacterial, and fungal infections; skin diseases; tumors; heart disease; urogenital disorders; and respiratory disorders. Some of these disorders may be brought on or compounded by toxic contamination.
2. Beluga whale parasites include tapeworms, roundworms, and flukes.
F. Entrapment in ice.
Beluga whales trapped by ice are often susceptible to predation by polar bears, starvation, and suffocation (Ridgway and Harrison, 1981).
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