Sightings of Dwarf (Kogia sima) and Pygmy (K. breviceps) Sperm Whales from the Main Hawaiian Islands

Sightings of dwarf (Kogia sima) and pygmy (K. breviceps) sperm whales in Hawaiian waters have only rarely been reported. As part of boat-based surveys of odontocete cetaceans around the main Hawaiian Islands between 2000 and 2003, Kogia were observed on 18 occasions. Kogia were sighted most frequently in deeper portions of the study area (mean depth, 1,425 m) and in calm sea conditions (mean Beaufort sea state, 0.8). Thirteen of the 14 groups identified to species were dwarf sperm whales, the sixth most common species of odontocete documented around the main Hawaiian Islands. One group of six dwarf sperm whales containing two mother-infant pairs did not dive for more than a few minutes at a time. Most groups were difficult to approach, but photographs of several individual dwarf sperm whales showed distinctive marks on the dorsal fins, demonstrating that individual photo-identification is possible with this species. Sightings of dwarf (Kogia sima) and pygmy (K. breviceps) sperm whales in the wild are uncommon. Both species tend to live in deep water usually far from shore, may dive for long periods, typically show a very low profile at the water’s surface, only very rarely engage in any obvious aerial or surface-active behavior, and tend to avoid vessels (see reviews in Willis and Baird 1998 and McAlpine 2002). For all of these reasons, most of what is known about these species tends to come from beach-cast, or stranded, animals. Only a few geographical areas, such as parts of the Bahamas (MacLeod et al. 2004), have been identified where conditions (depth, sea state, distance to shore) are suitable for small-boatbased research on these species. Around the main Hawaiian Islands, few records exist of either species, and most are of strandings (Edmondson 1948, Shallenberger 1981, Mazzuca et al. 1999). Stranding records suggest that pygmy sperm whales are most common around the main Hawaiian Islands (Shallenberger 1981), though aerial surveys for marine mammals around the main islands over 3 yr resulted in only two sightings of Kogia (Mobley et al. 2000). Barlow (2003) noted that both species of Kogia are quite abundant in offshore Hawaiian waters, but he had no ‘‘on-effort’’ sightings of either species within several hundred kilometers of the main islands during a recent large-vessel survey. In this paper I summarize Kogia sightings in the main Hawaiian Islands during 2002 and 2003. These sightings resulted from an ongoing study of odontocete stock structure, population sizes, and ecology in the main Hawaiian Islands (see Baird et al. 2003, 2004). Boat-based field operations were undertaken from 2000 to 2003. Vessels used ranged in size from 6 to 18 m and transited the study area at speeds from 16 to 30 km/hr, carrying two to six observers, scanning 360 degrees around the vessel. Apart from a period in 2003, boat observations involved 6to 9-m vessels. During 2000–2001 one vessel was used at a time, but during some portions of fieldwork in 2002 and 2003 two boats were used simultaneously in different portions of the study areas (when two boats operated siPacific Science (2005), vol. 59, no. 3:461–466 : 2005 by University of Hawai‘i Press All rights reserved 1 Field research was supported by the Southwest Fisheries Science Center of the National Marine Fisheries Service and by the Wild Whale Research Foundation. Manuscript accepted 1 September 2004. 2 Cascadia Research Collective, 218 1 2 West 4th Avenue, Olympia, Washington 98501 (e-mail: rwbaird@dal .ca or [email protected]). multaneously effort is referred to as vesseldays). Locations of sightings and 5or 10min effort locations were determined using a Global Positioning System. Bottom depths of sightings and effort locations were estimated using a kriging interpolation (Golden Software 2003) of digital bathymetry data (obtained from National Oceanic and Atmospheric Administration). The two species were distinguished in the field based on the relative size and positioning of the dorsal fin: in dwarf sperm whales the fin is positioned approximately midway along the back and is relatively tall (>5% of the body length); in pygmy sperm whales the fin is positioned posterior to the midpoint of the back and is relatively short (<5% of the total body length [see Willis and Baird 1998, McAlpine 2002]). When possible, photographs were obtained to confirm field identifications. Table 1 summarizes research effort from 2000 through 2003. During 2000 and 2001 all search effort was in shallow waters, defined to be less than 500 m in depth. In 2002 search effort was in shallow waters off Maui/Lāna‘i, as well as in both shallow and deep waters off the Wai‘anae and south coast of O‘ahu, and in shallow and deep waters off the island of Hawai‘i. In 2003 search efforts covered both shallow and deep areas off all the main Hawaiian Islands. A total of 340 groups of odontocetes was seen during the surveys, and 15 species were documented. Kogia were observed on 18 occasions (Table 2, Figure 1), and groups were identified to species on 14 occasions (13 groups of dwarf sperm whales and one group of pygmy sperm whales). Photographs obtained from 8 of the 13 dwarf sperm whale sightings were used to confirm species identifications. Half of the Kogia sightings were off the island of Hawai‘i, and 8 of the remaining 9 sightings were off Kaua‘i or Ni‘ihau (Table 2). Water depth was available for 17 of the 18 sightings; mean water depth was 1,425 m (SD 1⁄4 954 m), with a range from 450 to 3,200 m. For positively identified groups of dwarf sperm whales, mean water depth was 1,565 m (SD 1⁄4 1,017 m). Quantitative information on depth of search effort was only available for effort from O‘ahu east to Hawai‘i and differed between island areas. The deepest average depth of search effort was off Hawai‘i (median 1⁄4 1,142 m, 50% of effort between 500 and 1,400 m), and the shallowest average depth of search effort was off Maui and Lāna‘i (median 1⁄4 100 m, approximately 50% of effort between 1 and 100 m). The average depth of search effort off O‘ahu was intermediate (median 1⁄4 549 m, with approximately 50% of effort between 200 and 600 m). Group sizes for dwarf sperm whales ranged from 1 to 6 (mean 1⁄4 2.33, SD 1⁄4 1.56). Behavior of individuals in most groups was similar: animals logged at the water’s surface for periods of up to a few minutes, then slowly sank or slow rolled out of sight and were not resighted. In contrast, healthy captive animals are often active and even breach at times (Manire et al. 2004). The largest group obTABLE 1 Distribution of Search Effort Year Islands No. of days No. of hours on effort No. of km on effort 2000–2001 Maui/Lāna‘i 72 486 5,78