Occurrence and distribution of marine mammal strandings in Todos Santos Bay, Baja California, Mexico, 1998-2001

The occurrence and geographic distribution of marine mammal strandings along Todos Santos Bay, Baja California, Mexico, were investigated from 1998 to 2001. The study was carried out along 30km of coast, divided into rocky and sandy shores. During the study period we responded to calls from the public about dead stranded marine mammals (SMM), and from March 1999 to December 2001 the coast was also monitored (211km total effort). A total of 153 SMM (90 from notifications, 63 from beach monitoring) from nine different species were recorded: 76% (n=117) were California sea lions (Zalophus californianus), the most abundant pinniped on the western coast of the Baja California Peninsula. Adult males stranded more often than other age and sex classes (P<0.05). The highest frequency of California sea lion strandings was located on sandy beaches (p<0.05) because carcasses may be deposited and remain more easily there than on rocky beaches. The 1998 El Niño event influenced stranding frequencies; most SMM were recorded during that year. As to seasons of the year, most SMM were recorded during spring; this may indicate a higher abundance of marine mammals in the area during this part of the year. Probable human-induced injuries were observed in 17% (n=26) of all animals. Most of these were Z. californianus (n=24), probably due to their known interaction with fisheries; 70% were males