NMFS Biological Opinion on U.S. Navy training ... - Govsupport.us

FINAL PROGRAMMATIC BIOLOGICAL OPINION ON U.S. NAVY ACTIVITIES IN THE HAWAII RANGE COMPLEX 2008-2013
Whitehead 1997). Sexually mature males join these groups throughout the winter. During the summer, mature male
sperm whales are thought to migrate into the Aleutian Islands, Gulf of Alaska, and the Bering Sea.
Sperm whales commonly concentrate around oceanic islands in areas of upwelling, and along the outer continental
shelf and mid-ocean waters. Because they inhabit deeper pelagic waters, their distribution does not include the broad
continental shelf of the Eastern Bering Sea and these whales generally remain offshore in the eastern Aleutian
Islands, Gulf of Alaska, and the Bering Sea.
Sperm whales have a strong preference for the 3,280 feet (1,000 meters) depth contour and seaward. Berzin (1971)
reported that they are restricted to waters deeper than 300 meters (984 feet), while Watkins (1977) and Reeves and
Whitehead (1997) reported that they are usually not found in waters less than 1,000 meters (3,281 feet) deep. While
deep water is their typical habitat, sperm whales have been observed near Long Island, New York, in water between
41-55 meters (135-180 feet; Scott and Sadove 1997). When they are found relatively close to shore, sperm whales
are usually associated with sharp increases in bottom depth where upwelling occurs and biological production is
high, implying the presence of a good food supply (Clarke 1956).
Population Structure
The population structure of sperm whales is largely unknown. Lyrholm and Gyllenstein (1998) reported moderate,
but statistically significant, differences in sperm whale mitochondrial (mtDNA) between ocean basins, although
sperm whales throughout the world appear to be homogenous genetically (Whitehead 2003). Genetic studies also
suggest that sperm whales of both genders commonly move across over ocean basins and that males, but not
females, often breed in ocean basins that are different from the one in which they were born (Whitehead, 2003).
Sperm whales may not form “populations” as that term is normally conceived. Jaquet (1996) outlined a hierarchical
social and spatial structure that includes temporary clusters of animals, family units of 10 or 12 females and their
young, groups of about 20 animals that remain together for hours or days, “aggregations” and “super-aggregations”
of 40 or more whales, and “concentrations” that include 1,000 or more animals (Peterson 1986, Whitehead and
Wiegart 1990, Whitehead et al. 1991). The “family unit” forms the foundation for sperm whale society and most
females probably spend their entire life in the same family unit (Whitehead 2002). The dynamic nature of these
relationships and the large spatial areas they are believed to occupy might complicate or preclude attempts to apply
traditional population concepts, which tend to rely on group fidelity to geographic distributions that are relatively
static over time.
Atlantic Ocean
Based on harvests of tagged sperm whales or sperm whales with other distinctive marking, sperm whales in the
North Atlantic Ocean appear to represent a single population, with the possible exception of the sperm whales that
appear to reside in the Gulf of Mexico. Mitchell (1975) reported one sperm whale that was tagged on the Scotian
Shelf and killed about 7 years later off Spain. Donovan (1991) reported five to six handheld harpoons from the
Azore sperm whale fishery that were recovered from whales killed off northwest Spain, with another Azorean
harpoon recovered from a male sperm whale killed off Iceland (Martin 1982). These patterns suggest that at least
some sperm whales migrate across the North Atlantic Ocean.
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