Temporal Trends in Contaminants in Puget Sound Harbor Seal

Harbor seals (Phoca vitulina) are the most abundant marine mammal species in Washington State and occur throughout the marine waters including Puget Sound (Osborne et al. 1988). Extremely high concentrations of some chlorinated hydrocarbon contaminants, especially PCBs, were found in Puget Sound harbor seals in the 1970s and 1980s (Arndt 1973, Calambokidis et al. 1978, 1984). There has been increasing evidence of contaminant-associated adverse effects including reproductive impairment and immunotoxicity and endocrine disruption caused by some chlorinated hydrocarbons in controlled captive feeding studies with PCBs being implicated in the observed effects (Reijnders 1986, Brower et al. 1986, Addison 1989, Ross et al. 1995, 1996, De Swart et al. 1994).

One of the longest-term datasets on trends in contaminants in the Puget Sound region comes from harbor seals. Harbor seal pups from Puget Sound have been collected and tested for concentrations of PCBs and DDT compounds at 4-5 year intervals from 1972 to 1990 at several Puget Sound sites (Arndt 1973, Calambokidis et al. 1978, 1984, 1991). Analyses were last completed for 14 pups collected in 1990 from Gertrude Island in southern Puget Sound and Smith Island in the Strait of Juan de Fuca. Clear temporal and spatial trends in chlorinated hydrocarbons have been documented in harbor seal neonates in Puget Sound (Calambokidis 1995). Samples from harbor seals are ideally suited for trend analyses because they are highly contaminated, represent an integration of concentrations in a broad selection of prey in a region, and, with the utilization of non-emaciated pups, provide limited inter-sample variability allowing sensitive detection of changes over time.

Additional blubber samples from dead harbor seal neonates at Gertrude Island were obtained in 1996 and 1997, and biopsy samples of blubber were obtained from weaned harbor seal pups in 1993 and 1996. Biopsy samples from weaned pups have not been used in the past trend analysis but may be a valuable alternate source of samples. For these samples to be suitable for use in the trend analysis, information is needed on the degree of inter-sample variability, factors responsible for variability, and the comparability of these samples to the past analyses on dead harbor seal neonates.

Primary objectives of the study were:

1. Determine current levels of a broad range of chlorinated hydrocarbon contaminants in Puget Sound harbor seals including congener-specific concentrations of PCBs, DDTs and other pesticides, and the first analyses of polychlorinated dibenzo dioxins and furans (PCDDs and PCDFs).
2. Determine trends in concentrations of some of these contaminants including long-term trends in PCBs and DDT compounds in blubber of harbor seal pups in southern Puget Sound .
3. Determine how concentrations in blubber vary between biopsies of weaned seal pups and those from dead neonates.
4. Identify the degree of inter-sample variability and potential factors responsible for variation (date, length, weight, etc.) in samples from pups and evaluate use of weaned pups in future trend analyses.

This report summarizes the results of the analyses conducted on Puget Sound harbor seals to address the above objectives. These results and those of related studies in British Columbia will be the focus of several planned manuscripts for publication in scientific journals.