Trends in Propeller Strike-Induced Mortality in Harbor Seals (Phoca vitulina) of the Salish Sea.

Documenting human impacts on marine mammals is critical for understanding and mitigating harm. Although propeller strike injuries in small marine mammals are often debilitating and fatal, little is known about the occurrence or demographics of these types of injuries in pinniped populations. Using data of stranded harbor seals (Phoca vitulina) in the Salish Sea from 2002-19, we identified 27 cases of fatal propeller strikes. Weaned pups were the most frequently affected (64% of cases) with a much higher rate of propeller strikes than expected for the age class. Although they do represent animal welfare concerns, harbor seals in the Salish Sea probably are not threatened by these types of injuries at the population level; nevertheless, propeller strike cases increased significantly over the time of this study period, indicating increased interactions between boats and seals in the region. Continued monitoring and increased efforts to consistently quantify vessel traffic in the area are recommended to create and monitor long-term effectiveness of mitigation measures.

Congenital Diseases in Harbor Seals (Phoca vitulina richardsii) from the Salish Sea.

Postmortem data for harbor seals (Phoca vitulina richardsii) in the Salish Sea were analyzed for epidemiologic trends in congenital diseases. Cleft palate, cleft lips, or both (n=8) and cardiac defects (n=5) were the most common congenital abnormalities, followed by cases with multiple defects (n=4). No temporal trends or spatial clusters of cases were seen from 2003 to 2019, during which time monitoring effort was consistent. Cases could not be linked to specific causes such as environmental contamination or maternal malnutrition. Our study suggests that a yearly prevalence of 2.9%±2.2 is the endemic level of congenital disease in this stable harbor seal population. Continued monitoring of birth defects and overall harbor seal population status could help to identify emerging teratogens.

Trace Element Concentrations in Livers of Pacific Harbor Seals (Phoca vitulina richardii) from San Juan County, Washington, USA.

Approximately 5,000 Pacific harbor seals (Phoca vitulina richardii) reside year-round in San Juan County (SJC), Washington (US) in the center of the binational Salish Sea. We retrospectively analyzed total cadmium (Cd), copper (Cu), iron (Fe), mercury (Hg), magnesium (Mg), manganese (Mn), lead (Pb), selenium (Se), and zinc (Zn) in livers of dead stranded harbor seals (n=57) collected in SJC between 2009 and 2012 to identify age-related and regional patterns of trace element exposure. Consistent with prior studies of contaminants in pinnipeds, Hg, Cd, and Se concentrations increased with age, and Se:Hg molar ratios approached 1:1 in adult seals. Concentrations of Cd and Hg were below putative marine mammal toxicity thresholds. Mercury concentrations were comparable among Salish Sea populations. Although SJC is less urbanized with fewer industrial inputs than South Puget Sound (SPS), SJC nonpups had greater concentrations of Cd, Cu, and Zn, and pups had greater concentrations of Zn compared to SPS seals. We hypothesize these regional differences could be due to prey preference and availability or to natural geochemical processes. Reported concentrations inform future sampling protocols and can assist in tracking long-term temporal and spatial trends of trace elements in marine organisms.

Conjoined Fetal Twins in a Harbor Seal (Phoca vitulina).

In July 2013, a stranded harbor seal (Phoca vitulina) died giving birth to conjoined fetuses. The twins were joined at the abdomen and thoracolumbar spine with the vertebral axis at 180°. The cause of this unique anomaly--a first for this species--was not identified.