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The Northern Fur Seal: Insights on Breeding and Survival

The Northern Fur Seal (*Callorhinus ursinus*) showcases remarkable sexual dimorphism, with males reaching lengths of 2.1 meters and weights between 175-275 kg, while females average 1.4 meters and weigh 30-50 kg. Males establish dominance at rookeries by fiercely battling for territory and guarding up to 40 females, losing up to 20% of their body weight in the process. These seals consume a diverse diet of over 50 fish species and 10 cephalopods. Despite a population of over 1.75 million in 1976, threats from predators like sharks and entanglement in fishing gear remain pressing issues.

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The Northern Fur Seal: Insights on Breeding and Survival

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  1. Species of the Day The Northern Fur Seal Callorhinus ursinus

  2. Breeding/Mating • Pronounced Sexual Dimorphism • Males 2.1 meters long and weigh 175-275 kg • Females 1.4 meters long and weigh 30-50 kg • Males establish dominance at the rookeries • Fight by biting flippers • Guard up to 40 females • Will lose 20% of body weight while guarding

  3. Interesting Facts • Feed on 50 different fish species (many are commercially important to humans) • Also feed on 10 different cephalopods (squid) • Lactating females eat 1.6 times more than non-lactating females • Thick fur has over 46,000 hairs per square centimeter ( that’s over 225,000 per square inch!) • Hunted for their fur from the 1800s until today. Some of the warmest on the planet.

  4. Known Predators/Problems • Sharks • Killer Whales • Northern Sea Lions • Kill up to 7% of all young • Pollution • 5% of all young become entangled and die in fishing gear every year.

  5. Population Statistics • Over 1.75 million estimated in 1976 • North American Fur Seal Convention protected herds until 1984. • Aleuts allowed to harvest 2000 sub-adult males per year. • With no protection, many fur seals killed by fisherman • Removes competition for fish

  6. Bibliography • Reeves, Randall, Brent Stewart, & Stephen Leatherwood, 1992. The Sierra Club Handbook of Seals and Sirenians. Sierra Club Books, CA. • http://nmml.afsc.noaa.gov/AlaskaEcosystems/nfshome/nfsdescription.htm • http://ip30.eti.uva.nl/bis/marine_mammals/pictures/callorhinus_ursinus.jpg

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