Two New Publications – Pollutant levels in Scottish seals over 15 years and how these chemicals alter fat tissue function in seal pups.

Two weaned grey seal pups on the Isle of May, Scotland

Link to paper on pollutant patterns over 15 years in Scottish seals: link

Link to paper on how pollutants impact fat tissue function in seal pups: link

Or read the abstracts on this site here (pollutant levels over 15 years) and here (pollutant effects on fat tissue).

It has been a while since the last update about the PHATS team, which is led by Dr Kimberley Bennett at Abertay University, and in the time that has passed we have been busy finalising our lab work, analysing our results and of course, writing papers. We have published two studies since our previous PHATS blog about finishing our last field season on the Isle of May back in late 2017. One paper came out in October 2018 and the other came out last week as part of a special issue to celebrate the Sea Mammal Research Unit’s (SMRU) 40th birthday.

Our new paper is all about how some pollutants can stay in the environment for a very long time. We know that persistent organic pollutant (POP) concentrations fell dramatically after they were first banned decades ago. However, we know much less about pollutant trends in recent times. We compared persistent organic pollutant (POP) levels found in young seals on the Isle of May 15 years ago to the POP levels the PHATS team measured in young seals on the same island between 2015-2017. We found that there was an overall decrease in the amounts of some POPs, such as the total PCB concentrations if you add all the different types (or congeners) together. However, other types like DDT and its breakdown products had not significantly fallen over this timeframe. One complication that we found is that concentrations of some pollutant types are so low, it is difficult to detect small declines with certainty. It is clear that long term studies recording pollutant levels over many decades are needed to truly be able to say that these substances are decreasing, but such studies are very expensive, time consuming and take a long time before any results are seen. Despite this, monitoring these chemicals in the natural environment is really important, as even low concentrations of these pollutants can impact an individual’s physiology and health, which we demonstrated in our other paper…

Weaned grey seal pups on the Isle of May, ready to go to sea for the first time

Our other study (published in October last year) demonstrated how potentially disruptive pollutant effects can be, even at low concentrations. We studied blubber from the seal pups on the Isle of May and found that metabolic characteristics of the blubber was linked to the amount of POPs the seals had accumulated in their fat. These pups had been exposed to pollutants via their mother’s milk, which accumulates in their fat tissue. The seals cannot break down the POPs easily, which means concentrations inside the pups increase as they drink more milk, or as they eat more fish when they eventually go out to sea to hunt. We found out that POPs in the blubber are preventing the tissue from working correctly: the more PCBs a seal pup had in its blubber tissue, the less glucose was used by its fat cells. It is quite alarming that this is already happening in the seal pups, who have only been alive for a few weeks and have much lower levels than adult seals that have been eating fish and accumulating pollutants in their blubber their whole lives.

Visual abstract from our 2018 paper highlighting the main findings from the study, that higher PCB concentrations in seal pup blubber lead to decreases in glucose uptake rates

These two papers show us that POPs are still hanging around in the marine environment and the organisms that live there, and that even low concentrations can have significant impacts on the physiology of individuals. This might be especially important for young individuals, or for other vulnerable age groups. Currently we do not know what the potential health and energetic consequences of these changes to blubber function are, but they certainly are not helping the seal pups get the best start in life. It is really important for blubber tissue to function properly in all marine mammals, as they need a healthy blubber layer to keep them warm in the cold seas and to provide them with reserves to live off when they cannot find fish for a period of time. It is important to take into account the subtle negative effects of pollutant exposure when monitoring population dynamics and making conservation management plans, as anything that effects energy balance in individuals is likely to impact on their survival and their ability to breed. While we have found this result in grey seal pups, this problem is one that all marine mammals face as they all bioaccumulate POPs into their blubber across their lifetimes, with some of the highest concentrations occurring in top predators like killer whales. Hopefully researchers working on other marine mammals will be able to use our findings to help understand and better conserve their own study species. In fact, our work was recently included in a report made by Canadian Fisheries and Oceans exploring threats to the northern and southern resident killer whale populations.  We still have lots of data left to analyse from the PHATS project, so will continue to uncover the effects these pollutants are still having on grey seal, which will enable us to better understand the reasons some marine wildlife species are struggling to thrive.

Killer whale pod in Iceland. Killer whales have some of the highest POP levels in their blubber which could cause serious negative health consequences

Our paper on pollutants in seals was just one of the fascinating articles in the SMRU special issue. Check out the other amazing papers that were published there, including studies on monitoring grey seals, harbour seals and dolphins in the UK and further afield, research into how human activities are disturbing marine mammals physically and acoustically and novel ways to try and avoid this.

Scottish bottlenose dolphins in the Moray Firth Special Area of Conservation.

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