I used to live on a 38ft sailboat, a Downeaster cutter to be exact. Nice boat. It was parked in a floating “trailer park” in St Augustine where a tidal channel cut thru an expansive salt marsh. The wetlands there are rich in aquatic and semi-aquatic life – invertebrates, fishes and birds. Not far away a friend had a house in the marsh where a hundred or so roseate spoonbills roosted at nights during the summer, and large fish would bang loudly on the bottom of my boat at night as they cornered and rushed at their smaller prey.
One evening I was sitting out on the stern deck and noticed a double-crested cormorant engaged in peculiar behavior. From a swimming position it would swim down under water until it caught a gafftopsail catfish, then pop back up to the surface for a breather and to orient the fish headfirst toward its gullet. These catfish looked like they might be too large for the bird to swallow, especially considering the catfish’s three long, poisonous spines.
The cormorant would then dive back under water with the catfish and evidently swim to and fro over an oyster bar, based on the long, thin lines of turbidity rapidly left behind. Then the cormorant would surface and swallow the catfish. All I can deduce is that the cormorant was using the hard bottom of the oyster bar to break the catfish’s spines so that it could be safely eaten.
If so, could the oyster bar be considered a “tool” of the cormorant?