An assessment of the accidental take of sea otters, Enhydra lutris, in gill and trammel nets

Abstract

The sea otter, Enhydra 1utris, is fully protected inCalifornia by both state and federal law. Despite thisprotection the population has not grown appreciably since atleast 1976. Research efforts directed at identifying thereasons for the lack of population growth have concentratedon sources of mortality and their contribution to totalmortality.The accidental drowning of sea otters in gill and trammelnets used to take California halibut, Para1ichthysca1ifornicus, was identified as a source of mortality whichhas probably increased as the sea otter population expandedinto areas of intense fishing. As a result, an existinggill and trammel net fishery observation program in MontereyBay was expanded to assess the extent and significance ofthe accidental drownings of sea otters in the areas nearMorro Bay and Port San Luis.Three different estimates of the number of sea ottersdrowned annually in gill and trammel nets were generatedusing comparable data bases. The average of these estimateswas approximately 80 sea otters per year for the level offishing effort expended during the June 1982 through June1984 study period.Back calculations of the annual take of sea otters by thegill and trammel net fishery for California halibut weremade for each year from 1973 through 1983. Thesecalculations suggest that the level of accidental take ofsea otters during the last decade may have been high enoughto be a significant factor in the lack of sea otterpopulation growth. (31pp.)