STOCK DEFINITION AND GEOGRAPHIC RANGE
The dwarf sperm whale appears to be distributed worldwide in temperate to tropical waters (Caldwell and Caldwell 1989). Sightings of these animals in the northern Gulf of Mexico occur primarily along the continental shelf edge and over the deeper waters off the continental shelf (Mullin et al. 1991;...
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| Format: | Text |
| Language: | English |
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1999
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.294.8882 http://www.nmfs.noaa.gov/pr/pdfs/sars/ao1999whds-gmxn.pdf |
| Summary: | The dwarf sperm whale appears to be distributed worldwide in temperate to tropical waters (Caldwell and Caldwell 1989). Sightings of these animals in the northern Gulf of Mexico occur primarily along the continental shelf edge and over the deeper waters off the continental shelf (Mullin et al. 1991; Southeast Fisheries Science Center, SEFSC, unpublished data). Dwarf sperm whales and pygmy sperm whales (Kogia breviceps) are difficult to distinguish and sightings of either species are often categorized as Kogia sp. Sightings of this category were documented in all seasons during seasonal GulfCet aerial surveys of the northern Gulf of Mexico during 1993-1995 (Hansen et al. 1996). The few reliable sightings of dwarf sperm whales during those surveys were more numerous in spring, probably a result of greater survey efforts in that season (Jefferson and Shapiro 1997). Pygmy and dwarf sperm whales have been sighted in the northwestern Gulf of Mexico in waters 1000 m deep, on average (Davis et al. 1998). However, these authors cautioned that inferences on preferred bottom depths should await surveys for the entire Gulf of Mexico. The difficulty in sighting pygmy and dwarf sperm whales may be exacerbated by their avoidance reaction towards ships, and change in behavior towards approaching survey aircraft (Würsig et al. 1998). In a recent study using hematological and stable-isotope data, Barros et al. (1998) speculated that dwarf sperm whales may have a more pelagic distribution than pygmy sperm whales, and/or dive deeper during feeding bouts. There is no information on stock differentiation. POPULATION SIZE Estimates of abundance of Kogia sp. were derived through the application of distance sampling analysis (Buckland et al. 1993) |
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