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Bay Harbor Seal Health

A long-awaited study of S.F. Bay harbor seals came out in print early this October. The 150-page study, funded in part by the S.F. Estuary Project, explores the population dynamics and movements of harbor seals within and near S.F. Bay; investigates the concentration of trace elements and pollutants within individuals; and assesses the health of the population and potential sources of distress.

According to the report summary, harbor seals are an excellent indicator of the health of the estuarine ecosystem because they use bays for foraging, resting and reproduction, and because certain toxic pollutants may bioaccumulate in them. Although researchers Dianne Kopec and James Harvey were unavailable to comment on the conclusions of their study as this issue went to press, here are a few of the findings:

Between 1989 and 1992, the number of harbor seals in the Bay did not increase significantly.

Over 20% of the seals at seven of the primary haul-outs had red pelage (a scarlet hue to their coats), and at two adjacent South Bay haul- outs the level rose to over 50%. The red pelage may be indicative of the presence of selenium, which the study detected in blood from all seals.

ppDDE (a DDT derivative) was found in 88% of the seals sampled in 1989-1990. Males had higher levels (mean = 17 ppb wet wt.) than females (mean = 8 ppb wet wt.).

PCB residues were found in roughly half the seals sampled (mean = 47 ppb wet. wt.) The mean sigma PCB blood residue was higher than in blood residues in harbor seals fed fish contaminated with a mixture of organochlorines from the Wadden and Baltic seas.

More analyses of archived blood and blubber samples are needed to confirm whether contaminant-induced immune suppression is occurring in S.F. Bay seals.

All harbor seal blood mercury residues exceeded levels associated with toxicity in humans.

For details on how to get a copy of the study, contact: Dianne Kopec (415)728-5816

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