Marine Resources Assessment for the Marianas Operating ... - SPREP

AUGUST 2005 FINAL REPORT
and vicinity (Figure B-20). In some locales, as noted earlier, Fraser’s dolphins do approach
closer to shore, particularly in locations where the shelf is narrow and deep waters are nearby, so
there is also a low or unknown occurrence from the 100 m isobath to the shelf break. Occurrence
patterns are assumed to be the same throughout the year.
Behavior and Life History—Fraser’s dolphins are usually seen in large, fast-moving groups. Most
sightings have been of groups ranging between 100 and 1,000 individuals. Fraser’s dolphins have
been seen in mixed-species aggregations with melon-headed whales in the eastern tropical Pacific,
South Pacific, and Gulf of Mexico (Jefferson and Leatherwood 1994; Reeves et al. 1999; Gannier
2000). Very little is known of the natural history of this species, including reproduction. Available data
do not show strong evidence of calving seasonality. Sexual maturity for both sexes occurs at about 7
years of age (Jefferson and Leatherwood 1994). Fraser's dolphins feed on mid-water fishes, squids,
and shrimps (Jefferson and Leatherwood 1994; Perrin et al. 1994b). There is no information available
on depths to which Fraser's dolphins dive, but they are thought to be capable of deep dives.
Acoustics and Hearing—Very little is known of the acoustic abilities of the Fraser’s dolphin. Fraser's
dolphin whistles have a frequency range of 7.6 to 13.4 kHz (Leatherwood et al. 1993). There are no
hearing data for this species.
♦ Pygmy Killer Whale (Feresa attenuata)
Description—The pygmy killer whale is often confused with the melon-headed whale and the false
killer whale. Flipper shape is the best distinguishing characteristic⎯pygmy killer whales have rounded
flipper tips (Jefferson et al. 1993). The body of the pygmy killer whale is somewhat slender (especially
posterior to the dorsal fin), with a rounded head that has little or no beak (Jefferson et al. 1993). The
color of this species is dark gray to black, with a prominent narrow cape that dips only slightly below
the dorsal fin and a white to light gray ventral band that widens around the genitals. The lips and
snout tip are sometimes white. Pygmy killer whales reach lengths of up to 2.6 m (Jefferson et al.
1993).
Status—There are no abundance estimates for the pygmy killer whale in this area. This species is
designated as data deficient on the IUCN Red List (Reeves et al. 2003).
Habitat Preferences—The pygmy killer whale is considered to be an oceanic species. In the
northern Gulf of Mexico, this species is found primarily in deeper waters off the continental shelf
(Davis and Fargion 1996; Davis et al. 2000; Würsig et al. 2000) and waters out over the abyssal plain
(Jefferson personal communication). In some areas, pygmy killer whales are found within a few
kilometers of shore over the shelf, such as around the Marquesas Islands of French Polynesia
(Gannier 2002), off Lembata Island of the Indonesian archipelago (Rudolph et al. 1997), as well as in
some waters off the Philippines (Leatherwood et al. 1992).
Distribution—This species has a worldwide distribution in deep tropical and subtropical oceans.
Pygmy killer whales generally do not range north of 40ºN or south of 35ºS (Jefferson et al. 1993).
Reported sightings suggest that this species primarily occurs in equatorial waters, at least in the
eastern tropical Pacific (Perryman et al. 1994). Most of the records outside the tropics are associated
with strong, warm western boundary currents that effectively extend tropical conditions into higher
latitudes (Ross and Leatherwood 1994).
Information Specific to the Marianas MRA Study Area—There are no occurrence records for this
species in the Marianas study area and vicinity, but this area is within the known distribution
range for this species. Pygmy killer whales are easily confused with false killer whales and melonheaded
whales, which are two species that also have expected occurrence in the Marianas study
area. The pygmy killer whale is expected to occur from the shelf break (200 m isobath) to
seaward of the Marianas study area and vicinity (Figure B-21). There is also a low or unknown
occurrence from the 100 m isobath to the shelf break, which would take into account any
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