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

AUGUST 2005 FINAL REPORT
though off the Florida panhandle, they can be found over the continental shelf (Fulling et al. 2003). In
some regions, this species may regularly frequent coastal waters and areas with shallow bottom
depths. For example, there are reports of rough-toothed dolphins over the continental shelf in shallow
waters around La Gomera, Canary Islands (Ritter 2002), Puerto Rico and the Virgin Islands
(Mignucci-Giannoni 1998), and in coastal waters off Brazil, including even in a lagoon system (Flores
and Ximenez 1997; Lodi and Hetzel 1999). At the Society Islands, rough-toothed dolphins were
sighted in waters with a bottom depth less than 100 m to over 3,000 m, although apparently favoring
the 500 to 1,500 m range (Gannier 2000).
Distribution—Rough-toothed dolphins are found in tropical to warm-temperate waters globally, rarely
ranging north of 40ºN or south of 35ºS (Miyazaki and Perrin 1994).
Information Specific to the Marianas MRA Study Area—As an oceanic species, the rough-tooth
dolphin is expected to occur from the shelf break to seaward of the Marianas study area (Figure
B-12). There is also a low or unknown occurrence of rough-toothed dolphins from the coastline
(including harbors and lagoons) to the shelf break (Figure B-12), which takes into consideration
the possibility of encountering this species in more shallow waters, based on distribution patterns
for this species in other tropical locales. Occurrence patterns are expected to be the same
throughout the year.
Behavior and Life History—Small groups of 10 to 20 rough-toothed dolphins are most common,
with herds up to 50 animals reported (Miyazaki and Perrin 1994; Reeves et al. 1999). Rough-toothed
dolphins often associate with other cetacean species (Miyazaki and Perrin 1994; Nekoba-Dutertre et
al. 1999; Ritter 2002; Wedekin et al. 2004). In the Society and Marquesas Islands, rough-toothed
dolphins are sometimes sighted in association with large schools of melon-headed whales and
Fraser’s dolphins, short-finned pilot whales, as well as with humpback whales (Gannier 2000, 2002;
Gannier and West 2005). Rough-toothed dolphins tend to associate with floating objects in the
eastern tropical Pacific and Gulf of Mexico (Pitman and Stinchcomb 2002; Fulling et al. 2003).
Cephalopods and fish, including large fish such as dorado, are prey (Miyazaki and Perrin 1994;
Reeves et al. 1999; Pitman and Stinchcomb 2002). Reef fish are also preyed upon; Perkins and Miller
(1983) noted that parts of reef fish had been found in the stomachs of stranded rough-toothed
dolphins in Hawai’i. Gannier and West (2005) observed rough-toothed dolphins feeding during the
daytime on epipelagic fishes, including flying fishes. Rough-toothed dolphins are known to interact
with fisheries in tropical areas, for example, pulling fish from longlines (Nitta and Henderson 1993;
Nekoba-Dutertre et al. 1999; Poole personal communication). Female rough-toothed dolphins reach
sexual maturity between 4 and 6 years of age; males attain sexual maturity between 5 and 10 years
(Mead et al. 2001). Rough-toothed dolphins may stay submerged for up to 15 min and are known to
dive as deep as 70 m, but can probably dive much deeper (Miyazaki and Perrin 1994).
Acoustics and Hearing—The vocal repertoire of the rough-toothed dolphin includes broad-band
clicks, barks, and whistles (Yu et al. 2003). Echolocation clicks of rough-toothed dolphins are in the
frequency range of 0.1 to 200 kHz, with a peak of about 25 kHz (Miyazaki and Perrin 1994; Yu et al.
2003). Whistles show a wide frequency range: 0.3 to >24 kHz (Yu et al. 2003). There is no published
information on hearing ability of this species.
♦ Common and Indo-Pacific Bottlenose Dolphins (Tursiops truncatus and Tursiops aduncus,
respectively)
Description—Bottlenose dolphins (genus Tursiops) are medium-sized, relatively robust dolphins that
vary in color from light gray to charcoal. Tursiops is named for its short, stocky snout that is
distinctively set off from the melon by a crease (Jefferson et al. 1993). There is striking regional
variation in body size; adult body length ranges from 1.9 to 3.8 m (Jefferson et al. 1993).
The taxonomy of Tursiops continues to be in flux; two species are currently recognized, the common
bottlenose dolphin (Tursiops truncatus) and the Indo-Pacific bottlenose dolphin (Tursiops aduncus)
(Rice 1998; IWC 2004), with additional species likely to be recognized with more genetic analyses
3-38