Causes of mortality in marine-foraging river otters

North American river otters (Lontra canadensis) inhabit inland freshwater environments; however, from Alaska to California they also occur in coastal marine waters where they forage on a variety of marine fish and invertebrates. Little is known about mortality factors in marine-foraging river otters. Among 30 otter carcasses collected in San Juan County, Washington, analysis indicates that car collisions and gunshots were the most common causes of mortality.

Otter crossing street sign. Photo: Joe Gaydos
Otter crossing street sign, Whidbey Island. Photo: Joe Gaydos


Retrospective analysis of diagnostic findings from 30 marine-foraging river otter (Lontra canadensis) carcasses opportunistically acquired between 2003 and 2013 revealed trauma as the most common cause of mortality (47%). Within this focal population, causes of trauma included vehicular, gunshot, and one case of suspect intraspecific aggression. Other causes of death included idiopathic (20%), infectious (13%), metabolic (10%), nutritional (7%), and neoplasia (3%). One case of neoplasia, a pancreatic islet cell adenoma, was identified in a 12–yr old female. In six animals, diffuse renal interstitial fibrosis and multifocal glomerulosclerosis of unknown clinical significance were noted.


Joseph K. Gaydos, Martha A. Delaney, and Stephen Raverty (2020) Causes of Mortality in a Population of Marine-Foraging River Otters (Lontra canadensis). Journal of Wildlife Diseases In-Press.

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About the Author: 
Joseph K. Gaydos,1 Martha A. Delaney,2 and Stephen Raverty3 1The SeaDoc Society, University of California at Davis, Eastsound, Washington; 2Zoological Pathology Program, University of Illinois, Brookfield, Illinois; 3Animal Health Center, Abbotsford, British Columbia