Shark etiquette

Natural History, March, 2007 by Jennifer McIntosh, R. Aidan, Anne Martin

R. Aidan and Anne Martin's amazing article on white sharks ["Sociable Killers," 10/06] prompts me to ask about shark behavior I witnessed on a scuba diving trip in Palau. At a seamount, one shark was hanging vertically in the water over the peak while so-called cleaner fish cleaned it. Off to one side, at the base of the seamount, ten or fifteen other sharks swam in a circle. As soon as the cleaned shark swam away, one shark peeled away from the circle and swam up to be cleaned. We never saw any sign of conflict among the sharks about taking turns. Did size prevent the conflict?

Jennifer McIntosh

Pacific Palisades, California

R. AIDAN AND ANNE MARTIN REPLY: Cleaning stations are remarkable places on reefs, where many species of fishes suspend aggression and predation, and each individual waits its turn for tiny cleaners to pick off parasites or dead skin. Many species of sharks and rays queue and take their turn; size seems to have no effect on preferred access.

What intrigues us about Jennifer McIntosh's report is the vertical orientation of the sharks (which were most likely gray reef sharks). Many bow-fish clients adopt unusual postures while they are being cleaned, but sharks typically either lie on the bottom or swim more slowly so that the cleaners can keep up. Because sharks rely on dynamic lift to maintain position in the water column [see "No Bones About 'Em," by Adam Summers, page 36], it is not easy for them to reduce speed; where there are strong currents, it may be easier.