Haro-Garay, Martha J., Department of Earth and Ocean Sciences, University of British Columbia, 6270 University Blvd.,Vancouver, B.C., Canada V6T 1Z4. e-mail: mharo@cibnor.mx Present address: Centro de Investigaciones Biológicas del Noroeste (CIBNOR), Mar Bermejo 195, Col. Playa Palo de Santa Rita, La Paz, Baja California Sur 23090, México.