A BALANCE OF MARINE RESOURCES
Congress enacted Public Law 99-625 to conserve
The Truth About Sea Otters
Lacking the insulating blubber of other marine mammals, sea otters rely on their dense fur and a galloping metabolism to survive in the ocean. The comic antics of otters, rolling and patting in apparent perpetual motion, aerates their fur, insulating them from the water's chill. Otter energy is fueled by a voracious appetite: an adult can eat 20 pounds or more of shellfish meat a day.
In food-rich areas, otters feed selectively on their preferred prey - shellfish - selecting large items first. Depleting those, they diversify their diet, foraging down the food web, devouring clams, mussels, even worms and starfish, until food becomes scarce. Because sea otters seem to have few natural predators, food scarcity may be the biggest factor limiting population growth when a herd reaches equilibrium density. Food depletion causes die-offs or spurs emigration to new areas. This is the largest threat to shellfisheries.
As food competition increases, subdominant male otters are forced to the outskirts of their established range. These peripheral male groups, the "migrant front", often numbering more than 100 animals, colonize unoccupied food-rich areas. Eventually females spread into the vacated male areas, the population builds, and the cycle repeats, wavelike. Large male otter groups sharply reduce shellfish numbers; recruitment of other otters into the area keeps prey abundance depressed. While sea otters don¹t remove all shellfish, leaving very small individuals and those hidden increvicesbeyond their reach, they do preclude nearshore fisheries. Human harvest is regulated by size limits, season and gear restrictions, even sex of the species. Sea otters don't observe these rules; they take every shellfish they can catch.
Otter Impacts on Shellfish Resources and Fisheries
The initial direct effects of sea otter foraging are indisputable. Soon after moving into new areas, otters drastically reduce exposed populations of their preferred prey -- sea urchins, abalone, crabs -- leaving the cast shells as evidence of their activity. Biologists have documented the impacts of sea otter foraging on fisheries. Examples:
€ In Prince William Sound, Alaska, individual otters were observed eating over 80 clams and 12 Dungeness crabs daily, altering their habits to forage at night, when crab are active. The Alaska Department of Fish and Game closed the Orca Inlet Dungeness fishery for the first time in 1980. It remains closed today.
€ California Fish and Game biologists recorded the drastic reduction of abalone and sea urchins on the central coast following recolonization by otters. They also noted a marked decline in shellfish-eating fish such as cabezon. Abalone and sea urchin fisheries on the central coast ended in the early 1970s.
€ Biologists documented the rapid decline of Pismo clams from Pismo Beach following colonization by otters, precluding a recreational fishery.
€ Sea otter emigration to Little Cojo Bay, in the management zone, eliminated virtually all harvestable shellfish after just two months.
Shellfish vs. Sea Otters
Although popular sentiment argues that sea otters are keystone species essential to the health of the nearshore ecosystem, scientists are finding that relationships between sea otters, urchins, kelp forests and their inhabitants are extremely complex. California¹s nearshore ecosystems are not simple. Kelp forests change in response to a multitude of factors storms, water temperature, light levels, local pollution with or without otters. It¹s called patchwork dynamics.
The bottom line is this:
Commercial shellfish landings and value were compiled
from Department of Fish and Game (CDFG) Table 15. Northern California
sport abalone landings were compiled from CDFG estimates based on creel
census and telephone surveys.
Shellfish Industry Recommendations on California Sea Otters
The sea urchin industry has promised funding
For more information: The Community Ecology of Sea Otters (Ecological Studies v.65) Editors, G. VanBlaricom & J. Estes