16. Dec, 2018

California sea otter doing well, despite Great White bites.

Like other top ocean predators,  the sea otters presence helps to maintain a diverse community of animals and plants in the kelp forests. Otters eat sea urchins and other grazing animals such as crabs and abalones keeping them from devouring the kelp.  Once hunted to extinction for the fur trade, the southern  thick-haired sea otter  (Enhydra litris nereis) has had a slow road to recovery under more than a century of legal protections. Last year it even reached a number of almost 3200 species. The sea otter profited from the sea urchin boom along the  Californian coast, but now shows a jump in mortality that curtails their expansion. The reason is bites from great whites, who are also growing in number due to their pinniped food source expanding. Instead of preying on the otters (they don’t have the blubber of other sea mammals)  sharks are taking investigative bites, some of which cause severe injuries causing death

 A sea otter research program is carried out in Monterey Bay Sea Aquarium led by Michelle Staedler using data loggers to track their goings, and rescuing abandoned otters.  Because of the increased risk of shark bites, researchers as  Kerstin Wasson and Ron Eby are now exploring new shark-free habitats for the otters. One such area is  Elkhorn Slough, a major estuary system in Moss Landing that feeds into Monterey Bay. Although the swampy slough is not really a coastal area,  the otters so far seem to enjoy their new habitat where they also have more opportunities to stay on land. Captured abandoned sea otters from the Monterey coast are also released in Elkhorn Slough by Michelle Staedler and her team. 

Eelgrass beds in the Slough were being smothered by algae that grew unchecked on the leaves, absorbing the sunlight eelgrass needed for photosynthesis. Snails, slugs and other invertebrates would eat the film of algae, cleaning the grass and allowing it to get the sunlight it needs. The snails and slugs, however, tend to be devoured by the increasing number of crabs in the estuary,  which have few natural predators. Since the sea otter turned up (now counting around 150 individuals) and began feeding on the crabs  (see insert) the balance is now improving. The bay of the San Francisco is another area that Wasson and Eby are exploring as a future shark free habitat of the otters, a place where many sea otters lived in the past until they were killed by fur hunters.

Sources:

https://www.sanluisobispo.com/news/local/environment/article219016110.htmlSea otters

https://futureoftheocean.wordpress.com/2015/06/03/sea-otter-insights-monitoring-apex-predators-in-elkhorn-slough/

https://www.hcn.org/articles/sea-otter-populations-increase-but-shark-bites-stall-range-growth