What's going on down there? 2,000 ocean scientists do the biggest, wettest census ever

Science News,  Feb 17, 2007  by Susan Milius

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Older tracking systems for fish could cover just 100 square meters at a time. Those systems gave only rough ideas of the size of huge fish clusters that moved, spun off satellites, split, fused, and swerved this way and that. In a test off the coast of New Jersey, the new tool detected what may be the largest fish school ever recorded in one image, the researchers report in the Feb. 3, 2006 Science. It covered an area the size of Manhattan and included some 20 million fish.

On a very different scale, fish biologist Tracey Sutton has been considering the rare fish that he has pulled out of collecting nets lowered to the deepest waters of the Mid-Atlantic Ridge. Based at Harbor Branch Oceanographic Institution in Fort Pierce, Fla., Sutton has cruised on census expeditions along almost the entire length of the ridge. "It's a beautiful place," he says.

There he found tubeshoulders that when prodded squirt blue, luminescent clouds out of tubes on their shoulders. Sutton speculates that a fish living in velvet-black darkness might use a sudden blue glow to illuminate prey or to startle a predator.

On the ridge, Sutton found 10 or 20 tubeshoulders at a time instead of the one or two tubeshoulders that have shown up in samples from deep water elsewhere. He suggested at the Ocean Sciences conference in Honolulu last year that these supposedly nomadic loners gather at seamounts, which may be spawning grounds.

Sutton also collected hundreds of normally hard-to-find stoplight loosejaws (Malacosteus niger). These fish emit red light from a comma-shaped patch beside each eye, one of the few animals known to glow red. Despite having big fangs and a jutting jaw, the stoplight loosejaw feeds mostly on little crustaceans about as difficult to subdue as alphabet soup.

"I couldn't for the life of me figure out why it would do that," Sutton says. In the past 2 years, though, he and several other biologists have concluded that the wimpy diet of these loosejaws supplies them with the materials for the eye pigments that let them see red.

Seamounts and ridges may attract other deep-sea species that otherwise would be widely dispersed, Sutton speculates. If so, as state-of-the-art fishing fleets push into deep frontiers, fisheries managers need to watch out for damage to such exotic creatures.

The census is finding where fish aren't as well as where they are. Sharks don't seem to frequent the ocean's abyss, below 3,000 m, say Imants G. Priede of the University of Aberdeen in Scotland and his colleagues. They looked at world-wide fish-sighting records and their own sampling data from five cruises in the northeastern Atlantic. Shark species ply the waters down to 2,000 m, they report. In the depths though, sharks rarely appear, although bony fish live there. Sharks are "apparently confined to about 30 percent of the total ocean," the researchers reported in the June 7, 2006 Proceedings of the Royal Society B. That puts all of them within the reach of fishing fleets, so "sharks may be more vulnerable to over-exploitation than previously thought," the researchers concluded.