Causes and Trends of Harbor Seal (Phoca Vitulina) Mortality Along the British Columbia Coast, Canada, 2012–2020

Abstract

A retrospective study was conducted to categorize and describe the causes of mortality in harbor seals (Phoca vitulina) along the British Columbia coast that presented to the Vancouver Aquarium Marine Mammal Rescue Centre (MMR) for rehabilitation from 2012 to 2020. Medical records for 1,279 predominantly perinatal live-stranded harbor seals recovered in this region were reviewed. Approximately 20.0% (256 individuals; 137 males, 118 females, 1 unknown) of these animals died while at MMR. Infectious disease was the most common cause of death, accounting for 60.5% of mortality across all age classes. This was followed by nonanthropogenic trauma (7.1%), metabolic illness (5.4%), nutritional deficiency (5.0%), parasitic illness (5.0%), congenital disorders (2.5%), and human-associated trauma (0.4%). Pups were the most common age class (87.4%) amongst mortalities and predominantly died of an infectious process (62.5%). Phocid herpesvirus-1 infection was identified in 18.9% of the mortalities, with the highest prevalence occurring in 2019 (30.8%). Fungal disease was detected in six seals: three cases of pulmonary mycosis due to Cryptococcus gattii and three cases consistent with mucormycosis. In six cases, mortality was attributed to congenital disorders. Two of these cases involved axial skeletal malformities that are not currently described in the literature. This is the first study to describe the causes of mortality in harbor seals undergoing rehabilitation in British Columbia.

Videofluoroscopy of the aerodigestive tract in Phoca vitulina: reshaping perspectives on translational medicine

“…Over the past decade, thousands of infant harbor seals have been admitted to the Vancouver Aquarium’s Marine Mammal Rescue Centre (MMR) and other rehabilitation facilities worldwide ( 1 ). From 2012 to 2020, the MMR successfully rehabilitated and released 1,017 individuals – 80% of their harbor seal admissions ( 1 ).…”

“…Over the past decade, thousands of infant harbor seals have been admitted to the Vancouver Aquarium’s Marine Mammal Rescue Centre (MMR) and other rehabilitation facilities worldwide ( 1 ). From 2012 to 2020, the MMR successfully rehabilitated and released 1,017 individuals – 80% of their harbor seal admissions ( 1 ). In a retrospective review of necropsies following natural death after stranding, the highest cause of mortality in seal pups was a lack of nutrition, with sub-adults/adults dying primarily from infections secondary to bacterial pneumonia ( 2 ).…”