Sighting Characteristics and Photo-Identification of Cuvier's Beaked Whales (Ziphius Cavirostris) Near San Clemente Island, California: A Key Area for Beaked Whales and the Military?

The relationship between beaked whales and certain anthropogenic sounds remains poorly understood and of great interest. Although Cuviers beaked whales Ziphius cavirostris are widely distributed, little is known of their behavior and population structure throughout much of their range. We conducted a series of five combined visual-acoustic marine mammal surveys from 2006 to 2008 in the southern San Nicolas Basin, a site of frequent naval activity off the southern California coast, west of San Clemente Island. The study area was defined by a 1,800 km2 array of 88 bottom-mounted hydrophones at depths up to 1,850 m. The array was used to vector visual observers toward vocalizing marine mammal species. Thirty-seven groups of Cuviers beaked whales were encountered during the study period. The overall encounter rate was one group for every 21.0 h of survey effort, and was as high as one group per 10.2 h of effort during the October 2007 survey. Whales were encountered in the deepest portion of the study area, at a mean bottom depth of 1,580 m SD 138. The average group size was 3.8 individuals SD 2.4, which was higher than has been reported from other studies of this species. Twenty-four groups were observed over multiple surfacings median 4 surfacings, range 2-15. The mean encounter duration of extended sightings was 104 min SD 98, range 12-466 min and the mean distance moved over the course of sightings was 1.66 km SD 1.56, range 0.08-6.65 km. Temporal surfacing patterns during extended encounters were similar to dive behavior described from Cuviers beaked whales carrying time-depth recording tags.