Studies of beaked whale diving behavior and odontocete stock structure in Hawai'i in March/April 2006
Baird, R.W., G.S. Schorr, D.L. Webster, D.J. McSweeney, and S.D. Mahaffy. 2006. Studies of beaked whale diving behavior and odontocete stock structure in Hawai'i in March/April 2006. Report prepared under contract No. AB133F-06-CN-0053 to Cascadia Research from the Southwest Fisheries Science Center, NMFS, La Jolla, CA.
Small-boat surveys were undertaken in March/April 2006 off the west side of the island of Hawai‘i for the purposes of obtaining dive data from Blainville’s (Mesoplodon densirostris) and Cuvier’s (Ziphius cavirostris) beaked whales, as well as collecting biopsy samples and photo identification of these and other species of odontocetes for studies of stock structure and residency patterns. There were 157 sightings of 13 species of odontocetes in 4,264 km of effort, with 120 genetic samples from seven species and over 29,000 photographs from 13 species obtained. Photographic matching to existing catalogs is currently underway for eight species. Site fidelity of dwarf sperm whales (Kogia sima) was evidenced by a high rate of both within- and between-year photographic re-sightings. Photographs of distinctive individual Cuvier’s (3) and Blainville’s (11) beaked whales were obtained from 8 encounters (2 with Cuvier’s, 6 with Blainville’s). One of the three Cuvier’s and three of the 11 Blainville’s had been previously documented in the area, with matches for two individuals (one of each species) spanning a 15 year period, demonstrating long-term site fidelity for both species. Time-depth recorder/radio tags were deployed on three Blainville’s beaked whales, with 30.65 to 64.53 hours of data collected from each individual (sum = 135 hours). Overall dive patterns were similar to the smaller sample of dive data for this species presented by Baird et al. (2006), with dives >800 m occurring an average of once every 2.49 hour and averaging approximately 1,100 m in depth and 54 minutes in duration (maximum 1,520 m, 83.4 minutes). One Blainville’s beaked whale was tagged in deep water (>3,000 m) and regularly dove to 1,100 – 1,500 m. Diel patterns were assessed using data from these individuals and from one tagged in 2004 by Baird et al. (2006). Deep (>800 m) dives occurred slightly more often at night (mean = 0.46 h-1, SD = 0.11) than during the day (mean = 0.35 h-1, SD = 0.08), though this difference was not significant, and deep dive depths and durations were similar between the day and night. Dives to mid-water (100-600 m) occurred more than five times as often during the day (mean = 1.74 h-1, SD = 0.44) than at night (mean = 0.32 h-1, SD = 0.23), and whales spent more time in the top 100 m at night than during the day. Dive data collected simultaneously from two individuals in the same group (one adult male, one adult female) indicated whales closely coordinated their dive depths in the top 600 m of the water column (average vertical distance between the pair of 10 m), while below 600 m the whales diverged and likely foraged independently (average vertical distance of 95 m).