First Mass Stranding of Killer Whales (<I>Orcinus orca</I>) in the Gulf of California, Mexico

Abstract

We present the first report of a mass stranding of killer whales (Orcinus orca) in Mexican waters. This species is a temporal inhabitant of the region. On 31 July 2000, eight killer whales stranded alive at the southern tip of Isla San Jose in Bahia de La Paz (24o 54' N, 110o 35' W). All the individuals died despite the attempts performed by local fishermen to return them to sea. The group consisted of an undetermined number of females, immature males, and two calves. Skin and blubber samples were collected, as well as a skull on 2 August from a 4.6-m immature male. A second skull was collected on 19 August, which belonged to an individual of undetermined sex that measured 5 m in length. The teeth from both individuals were completely worn down. A couple of months later, two other skulls were collected. Individual strandings of killer whales are rare, and six records have been documented in the Mexican Pacific and Gulf of California. This report represents the first mass stranding of killer whales in Mexico. Since 1972, more than 160 killer whale sightings have been collected in the Gulf of California, with more than 90 photo-identified killer whales; nevertheless, no matches with the stranded individuals were found. There are few cases of killer whales found stranded live, probably as a result of whales chasing or following prey, or as a result of an outgoing tide. Causes of this stranding remain unknown.