NATURE Death of a harbour seal

Seal CSI Mayo


Marine life
John Paul Tiernan

A stinking bloated corpse was the most interesting life on the beach this week. Beheaded by God knows what, the only clue to its identity was its flippers, now even more human-like as the fur, skin and fat had been stripped away to reveal the bones of a five digit ‘hand’.
Around the headland, on an isolated stretch of coastline accessible only by foot or by sea, is this female’s former colony, where she spent many a low-tide afternoon hauled-out on a rock, full of fish and warming in the sun.
Was this just natural seal mortality we were asked, or is there a reason or pattern? Local knowledge does tell that there is usually an increase in seal corpses on the beach at this time of year. Of course, February is peak season for storm swells and mountainous seas. A navigation home to the colony after a fishing trip is an arduous task for an older seal (30-35 years) when the shallow waters close to shore become a cauldron of violent, fast-moving white-water.
It being spring, mortality during pupping (giving birth) was offered as a possibility. Mortality does increase during pupping and although the harbour seal usually births from May onwards, they can start as early as February and especially so for older females. A study last year in the North Sea found that harbour seals were pupping up to a month earlier compared to 30 years ago due to an increase in the number of smaller bottom-dwelling fish, which boosts the seals’ diet. This increase in smaller fish was due to the overfishing of larger predatory fish in the last few decades. No such study exists yet for Ireland. This seal however, judging by its yellowing dismembered state, was dead since January, ruling out mortality due to pupping.
This harbour or ‘common’ seal did not look like it was culled (shot), but a few hours south of here on the Dingle Peninsula, there are reports of fishermen calling for a cull on the local grey seal population, turning to them as a culprit for salmon declines as well as bothering hake and pollack nets.  Wild fish stocks are certainly falling and there are a number of reasons, some close to home and others beyond our control – in the case of salmon – when they go to sea.
Shooting seals won’t bring fish stocks back though; let’s hope that in Mayo at least, the seals’ corpses we do find on the beach continue to get there naturally.