In European shelf seas, harbour porpoises are considered particularly vulnerable, with negative
impacts from high levels of pollutants, which can harm many aquatic organisms. Higher trophic
species, such as porpoises, are particularly at risk due to bioaccumulation of pollutants.
Negative effects on reproduction and resistance to disease have been demonstrated for
porpoises in the region. Identifying locations where high densities of porpoise and
concentrations of pollutants co-occur would identify where mitigation is most needed. This
study attempts to address this gap in our knowledge by producing maps of key pollutants and
of porpoise abundance at a regional scale.
This study sets out to identify where in European waters harbour porpoises are at higher risk
from Cadmium, Lead, Mercury, PAHs and PCBs – by producing maps of pollutants to compare
with porpoise abundance, identifying overlap. Relationships between recorded concentrations
of pollutants and relevant environmental variables were established and used to predict spatial
variations in concentrations of sedimentary pollutants across European waters. These were
then compared with the lethal dosages (LD50) for mammals, and pollutant concentrations in
sediment above the LD50 were plotted to show the regions of concern.
This study found that large areas of the North Sea pose a risk to harbour porpoises with
sediment pollutant levels above the LD50 values for marine mammals around the Orkney and
Shetland Isles (Cadmium), along the mainland European coastline (Mercury) and even across
the entire North Sea region (Lead). No predicted PAH and PCB concentrations were above the
LD50 values. When these predictions were overlapped with porpoise abundance, the southern
North Sea was predicted to be a region of risk for harbour porpoise populations.
Further work is required to eliminate erroneous results and to improve the accuracy of the
maps, and to incorporate data from the water column and within biota. However, this study
provides a solid starting point in assessing risk from pollutants on a greater spatial scale than is
possible by point sampling (which is logistically and financially impossible at the same scale).