New England Aquarium survey spots rarely seen Chilean devil rays off Cape Cod

"The Monument's deep sea canyons, complex oceanographic conditions, and productive waters support a remarkable diversity of marine life, especially in the summer months when warm water protruding from the Gulf Stream draws in seasonal visitors like Chilean devil rays," McKenna said ^[10]. We think the explanation is plausible. A ray of tropical and warm seas ^[4] turning up southeast of Cape Cod as summer closed ^[1] is what a reach of Gulf Stream water into the area would predict.

The survey's headline figure, more than 2,000 animals across 15 species ^[1], covers everything the observers logged. The aquarium did not report how many of those animals were devil rays, or which of the 15 species were the seasonal warm-water visitors McKenna describes ^[10]. Her word "rarely" ^[3] is the only measure of how unusual the sighting was.

Counting from the air has a specific limit with this species. Chilean devil rays are the deepest-diving rays, reaching almost 6,000 feet ^[8]. They are also frequently solitary and usually found offshore ^[7]. We'd expect observers in an aircraft to log only the animals near the surface during each pass. A low sighting rate from the air therefore reflects the survey as well as the rays. Those dives rely on "a specialized network of blood vessels surrounding their brain that allows them to keep their brain warm even at very cold water temperatures at deep depths," McKenna said ^[9].

Cold water at depth does not stop those dives ^[9]. In our view, the warm-water link McKenna describes is about where the rays spend time near the surface in summer, the same layer of ocean an aerial survey can observe ^[1].