Grey Seals Predation

Last month I participated on the 89th annual meeting of the German Society for Mammalian Biology in Hannover. I heard lots of interesting talks and want to give a little glimps of it here.

The first will be a short overview of new scientific findings from Abbo van Neer about the predation behavior from grey seals in the north sea. If you like to take a deeper view into the topic, I recommend his paper.

– German version (will be added soon) –

The grey seal (Halichoerus grypus) lives in the same habitat and region, occupying the same spaces as the harbour seal and both seem use the habitat cooperative. They mainly prey on fishes but it was shown that they have different preferences, therefore have different ecologically niches for food preference.

Although young grey seal males seem to sometimes have sexual encounter with female habour seals (for which the body contact can be rough) there were no documented killing between these two species so far.

The Working group at the „Institute for terrestrial and aquatic wild life research“ was now able to document predation behavior of grey seals on harbour seals. The grey seal are young sub adult males in the age of two to three years and they not only attack the harbour seal, they also feed on them. Having other marine predators, like e.g. Orcas, feeding on smaller mammals this behavior seems surprising but not unnatural. The predation behavior is not limited to harbour seals, but also on young grey seals as well, therefore these sub adult males show cannibalistic behavior.  The cannibalistic behavior seams really irritating and was therefore taken under closer focus.

Not only the grey seals of the North Sea shown these behavior, but also individuals from Scotland.

Although this behavior is very rare and only performed by young males the question remained, why?

Some first thoughts were oblivious the question for other prey availability, stress in-between the population of grey seal or in-between the two seal species. But further investigations negate both hypotheses. Perhaps some human impact on the habitat leads to stress on the animals and therefore they show unnatural behavior? To answer this question it has to be investigated if this behavior is really a new behavior or if its perhaps a very old behavior which was not recognized as such due to humanization of theses animals.

Detailed analyses of the tracks on carcasses that were identified as predatored by grey seals were made and it got clear that cases of “shark kills” as well as “Boat accidents” were actually grey seal attacks.

These results suggest that this behavior is not new, not caused by human impact and not so unnatural as on first glance thought.
The research group around Abbo van Neer are still on this project and work hard to resolve the unclearness and get a good view into this topic. It stays thrilling and I’m looking forward for the next results!

Again, if you want to get more details on the story and research behind please access the paper or contact the author.

 

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