Wetenschap - 4 juli 2019

‘No evidence of mass seal deaths’

tekst:
Albert Sikkema

It was big news last week: Stichting ReddingsTeam Zeedieren (RTZ), a sea mammal conservation organization, sounded the alarm on seal deaths in the Netherlands. Half the young seals in the Wadden Sea had died in recent weeks, they claimed. ‘We have no evidence of that,’ responds researcher Sophie Brasseur of Wageningen Marine Research.

© Imares Researcher Sophie Brasseur from Wageningen Marine Research.

I’ve read that lots of seals are dying in the Wadden region.

‘It is the breeding season now and at this time you always see more seals getting beached. But we didn’t find more baby seals on the beaches this year than in other years.’

Oh. But WUR is being cited in the reports.

‘There is definitely something going on, but it is something else. We have been counting seals in the Wadden region for decades. Until five years ago you saw an increase in the number of seals being born, and a growth in the population. In recent years, however, the growing number of births – about 2000 per year in the Dutch Wadden Sea – has not led to a growth in the overall population. That is odd: what is happening to those baby seals? We don’t find them, they are not getting beached. Are they migrating to other areas? But there is no population growth anywhere else. So are they dying in the open sea? We don’t know.’

So how does a story about beached, dead seals get out?

‘There are a lot of groups that pick up dead and sick seals, like RTZ or First Aid for Seals. Animal ambulances pick them up too and they get cleared for municipalities without being registered. There is no central registration system for seals picked up from beaches, whether dead or alive. We do an annual count with international colleagues, but all we can say is that something is clearly changing. I would love to do more research to find out where these animals are.

Can you guess?

‘Maybe something is changing in the behaviour of seals. When we count them, we assume that a fixed percentage of them is visible on land, but maybe only a smaller number of them are ashore. We could find that out by tagging them with transmitters. But there could well be a higher death rate too.’ AS


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