Pollutants in harbour seals (Phoca vitulina)

Closeup of a harbour seal swimming in the water, looking straight into the camera.
Photo: Stein Ø. Nilsen / Norwegian Polar Institute

The harbour seal is a top predator and lives mostly on fish. This puts it at risk for high levels of pollutants. The harbour seal is a coastal seal species which has one of the widest ranges of all the seals in Norwegian waters. It is found from temperate waters in the Atlantic and Pacific oceans to arctic regions. In Svalbard, harbour seals are Red Listed and totally protected.

What is being monitored?

POPs in harbour seals

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Both PCB-153 and p,p’-DDE have greatly declined in harbour seals from 1999 to 2009.

Status and trend

Monitoring of harbour seals shows that the concentrations of fat-soluble organic pollutants (PCB-153, DDT, HCB and HCH) have declined from 1999 to 2009–10. This is in accordance with the trends for these substances seen in arctic wildlife. It is also confirmation that their regulation has been successful.

The PCB-153 levels for 2009–10 are quite like the levels found in harbour seals from California and British Columbia. Stranded harbour seals from the north-western Atlantic had more than one hundred times higher levels than the Svalbard harbour seals. The geographical differences are in keeping with the use of PCB globally, in that the highest consumption is in Europe and on the east coast of North America, followed by the west coast of North America. The levels of p,p’-DDE and α-HCH in stranded harbour seals from the north-western Atlantic were ten to one hundred times higher than in Svalbard harbour seals, whereas HCB was only two to three times higher. This may imply that the global distribution of HCB is almost in balance with the persistent organic pollutants (Cullon et al., 2012; Greig et al., 2011; Shaw et al., 2005).

Comparison with other seal species in Svalbard shows that harbour seals from 2009-10 have the same levels of PCB-153, p,p’-DDE, α-HCH and HCB as ringed seals from 2004 (Wolkers et al., 2008).

This data set is small and has few individuals, which means that the results risk being exposed to randomness where deviations can have a significant effect on the overall analysis. Notwithstanding this, the pollutants measured have declined so much that a reduction is not in doubt.

Since the data are acquired every 10th year, the analysis will not provide information on the variation in pollutant concentrations from year to year. The possibility that such variations are not being detected must therefore be taken into account when analysing the time series. It will therefore take a long time to demonstrate changes in the time series, since it is difficult to determine whether the difference between two measurement points is a consequence of genuine change, or random variation.

Causal factors

The manufacture and use of these substances are regulated nationally and internationally. The principal source for the supply of these substances has therefore stopped.

These substances are still to be found in the environment because they are stable and can be recirculated in the food chain. In addition, they leak from secondary sources like soils, lakes and glaciers in the Arctic. It is uncertain how climate change and the melting of sea ice, glaciers and permafrost will affect the pollutants.

Consequences

The levels of pollutants in harbour seals are regarded as low and do not constitute a health threat. The harbour seal is also regarded as being comparatively efficient in metabolising (breaking down) pollutants like PCB, and these metabolites (the breakdown products) have potential to disturb the hormone balance in the body, especially the thyroid hormone system.

About the monitoring

It is important to map the pollutants in this Red Listed harbour seal population in Svalbard to be able to say something about the pollutant situation in this population.

Places and areas

Relations to other monitoring

Monitoring programme
International environmental agreements
Voluntary international cooperation
Related monitoring