for variation in mortality on land from year to 

 year are not clear, but possibly variation is related 

 to the effect of weather on the number and in- 

 fectivity of hookworm larvae. High mortality of 

 pups on land is correlated with low survival to 

 age 3 even though mortality on land may be only 

 20 percent of the total loss. This suggests that 

 pups surviving a severe hookworm attack are left 

 in a weakened condition and are unable to with- 

 stand the rigors of ocean life. 



Little is known about the causes of death at sea. 



The killer whale and great white shark are known 

 predators of seals. Parasites probably also kill 

 seals. Evidence in the form of emaciated young 

 seals that drift ashore in winter suggests that in- 

 adequate food and violent weather are the greatest 

 hazards during the first year at sea. At this time 

 the pups make a sudden transition from nursing 

 to finding their own food in the cold, stormy, 

 winter ocean. Many perish. As high as 85 

 percent of some year classes may be lost by the 

 time they are 3 years old. 





Each year a few brown, yellow, almost white, or piebald seal pups are born. Light col- 

 ored adults are occasionally seen but true albinos rarely survive. 



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