We are seeing an unprecedented number of CA Sea Lion strandings off the CA coast right now.  NOAA provides insights into this Unusual Mortality Event. 

Description

California Sea Lions are best known for their playfulness, intelligence, and loud barking.  They range in color from dark brown in males to a golden brown in female.  They have obvious external ears and long narrow forelimb flippers, used for incredibly graceful swimming and “walking” on land. California Sea Lions are “sexually dimorphic”, meaning, there is a significant difference between males and females, in this case related to size: Adult males can be 8 feet long and can weigh up to 900 lbs. Females are much smaller, reaching 6 feet long and weighing only 250 lbs.  At about age 5, adults males have a distinctive boney “bump” on their forehead, which is absent on females.  California Sea Lions have a life span of 20-30 years.

Behavior

California sea lions are very social animals and form groups of several hundred individuals onshore. They generally haul out on rocky islets, unused floating piers, and buoys. When hauled out, they almost constantly make a barking sound that is distinctive to this species.  In the water, they float together on the ocean’s surface in “rafts.”  They can travel some distance to find their favorite foods, anchovies, sardines, salmon, squid, rockfish and other schooling fish, but feed mostly in upwelling areas. They are very fast, agile swimmers (reaching speeds up to 9 mph) and are often seen porpoising and wave riding. They are sometimes seen a few miles offshore. The deepest dive ever recorded for a California sea lion is 1,760 feet!

Breeding

California Sea Lions breed primarily from the Channel Islands in southern California to Central Mexico. Most pups are born from May to July and weigh 13 to 20 pounds.  At about a week after birth the moms swim out to sea to feed for a day or two, leaving the pups onshore, in the male’s territory, in groups. When the female returns, she finds her pup by their smell and distinctive voice. Females nurse pups for 6 months to 1 year, but after only 3 weeks from giving birth, she is ready to breed again.

Male California Sea Lions are polygamous, and on breeding grounds, can defend territories with up to 14 females. They defend their territories with aggressive physical displays and vocalization, sometimes lasting weeks. In the post-breeding season, males migrate north as far as British Columbia, Canada. Females generally stay around the breeding colonies in the non-breeding season. So off our coast, we see almost exclusively males, the smaller ones being young animals.