Reproductive dysfunction (including a longer calving interval, lower pregnancy rate and later maturation and higher rates of reproductive abnormalities) in UK harbour porpoises may be related to Polychlorinated Biphenyls (PCB) exposure, according to a new report. So man-made chemicals that have been heavily restricted in Europe for 30 years are still having terrible impacts on harbour porpoises, and previous research shows that other cetacean species are also susceptible.
Reproductive abnormalities, occurring either through endocrine disrupting effects or via immunosuppression and increased disease risk, were identified in the NE Atlantic (UK) harbour porpoise population, compared to porpoise populations in much less PCB-polluted regions, using samples from stranded and bycaught porpoises.
Half of mature female harbour porpoises that were found to be resting (neither pregnant nor lactating) had not offloaded their pollutant burden via gestation and primarily lactation. Where data were available, these non-offloading females were previously pregnant, which suggests foetal or newborn mortality. Further, direct observations of reproductive failure (abortions, foetal death or stillbirth) were observed in a fifth of necropsied mature female UK porpoises.
Data show both direct and indirect (PCB burdens) evidence of reproductive dysfunction, and reproductive failure could have occurred in almost 40% of mature females sampled. PCBs may have reduced foetal or newborn survival, something which has also been observed in other mammals. UK harbour porpoises are part of a larger north-east Atlantic population and this research suggests a population-level risk from PCB exposure.
We don’t know what size the harbour porpoise population was before chemical pollutants were dispersed into the ocean. Evidence exists of large‐scale incidental captures of porpoises in fishing gear prior to July 1994 and so it would make sense that the harbour porpoise population in this region is depleted. The existence of a “younger” porpoise NE Atlantic population, where most individuals do not live beyond 12‐years of age (as presented in this study) suggests other factors are at play. This is very worrying indeed.
In order to continue to monitor what is happening in the future we need the UK and devolved governments to continue monitoring PCB levels in porpoises, including their life histories (e.g. age and reproductive rates). We also need to know what is happening within the rest of the NE Atlantic population.
These should be assessed on a sub-population management unit level, including through collaborative projects between the UK and neighbouring countries. A cetacean PCB indicator, under Descriptor 8 of the EU Marine Strategy Framework Directive, might enable assessment on the appropriate management unit level, and so will require collaborative projects between the UK and neighbouring countries, and to incorporate these data somehow within management frameworks.
Although banned, PCBs are still a problem. And as some of them have half-lives for up to 100 yrs, they may be for some time yet. There is little we can do about this now, except learn from it.
As a result, we need to carefully manage all other threats that whales and dolphins face, because they are less able to deal with these other threats due to these burdens.
Another paper that came out last week analysed the environmental risks posed by 22 priority pollutants: 6 metals, 10 PAHs and 6 PCBs, in UK estuaries and coastal waters. The authors found that contaminants banned more than 20 years ago could be re-suspended in sediment to pose an ongoing environmental risk.