1. University of Rhode Island, Graduate School of Oceanography; Narragansett RI 02882 U.S.A.
2. Marine Biological Laboratory, Program in Sensory Physiology and Behavior; 7 MBL Street Woods Hole MA 02543 U.S.A.
3. Brown University, Department of Ecology and Evolutionary Biology; Providence RI 02912 U.S.A.