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Mortal Entanglement

On Wednesday 10 May 2023, some regular Arran visitors came across an unusual sight on the tideline of Blackwaterfoot beach. The photo taken by Al Ballantine was shared with me. The Gannet had obviously choked on the Dogfish it had been trying to swallow. Both were dead.

Gannet is a familiar bird round our shores diving in pursuit of near-surface pelagic fish like mackerel. Dogfish is a common bottom dwelling species not normally part of the Gannet diet. Whether the Dogfish was in shallow water or a discard from a fishing boat, we will never know.

Gannets tend to avoid fish that are difficult to swallow. Dogfish skin is particularly rough with numerous backward pointing denticles. It has uses including as sandpaper for burnishing. The inside of the Gannet beak is serrated to better grip slippery fish. This combination may have contributed to the Gannet’s inability to swallow the Dogfish and for the Dogfish’s inability to extricate itself from their mortal entanglement. In addition, the Dogfish seen in the photo is not the commonest local Dogfish Scyliorhinus canicula, but is more likely a juvenile Spurdog, Squalus acanthias, which has venomous spines, one of which can seen in the photo beside the dorsal fin.

A search on the internet provided only a handful of similar incidents. An article from 2014 in the journal “Irish Birds” :  Morus bassanus choked by lesser spotted dogfish Scyliorhinus canicula. Irish Birds 10: 124-126. D.T.G Quigley and E. O'Flynn. was informative.

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