Ebb and Flow

Photo-ID of our individual seals can be difficult when grey seals have a habit of rolling around in the sand, the mud, and the sandy-mud. As such, there have been plenty of days where all of us wished for a little extra water in the study sites for the seals to wash off. Well, last night was the new moon and with it came the high spring-tide. This means that at one site, the flat expanses of sand enabled the actual sea water to come almost all the way to the door of our hide! At the other, the marsh grass helped slow down the waters a bit, but every available muddy patch or ‘wallow’ has been converted into a grey seal pup swimming pool.

The part underwater is usually marsh-flats. During high-tide however the sea completely covers it and many ‘pools’ of water form.

While this was somewhat helpful for cleaning the seals off, the ecological implications are the really interesting part. Grey seals breed on many substrates from rocky shores to sandy beaches, but even for this terrestrial portion of their lives, the sea can still impact their breeding ecology.

Distribution of seals after the high-tide.

Last year was a particularly dry year with little to no rain. From initial data and observations, this seemed to impact how the seals used the area. At the study site comprised primarily of sand-flats, we saw very spatially spread out seals with females as far as 150m from the dune line. However, after a storm-surge event that occurred at the same time as a spring tide (the highest tides of the month) we arrived at the site to find the seals all squished in to about 20m worth of beach between the dunes and the water line. This made for interesting changes in male fighting, female-female aggression and a few mum-pup separations. We were keen to see how the seals distributed themselves this year (as there has already been quite a bit more precipitation) and to pay closer attention to how the seals respond to normal tide fluctuations spatially and behaviourally. Does aggression between males and females peak as density increases with high-tides? Do turn-overs in male territories occur more often during the reshuffle of space? Does the constricted space used by females allow for a fewer number of males to monopolize the majority of matings? Why do some females seem to prefer being close to the dunes while others like to rest on the waterline?

While we strive to look into these questions, it seems the pups are simply happy to have a bit of swimming practice!


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