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

AUGUST 2005 FINAL REPORT
(Natoli et al. 2004). Indo-Pacific bottlenose dolphins can be distinguished from the common
bottlenose dolphin using genetic, osteological, and external morphology data (Wang et al. 1999,
2000a, 2000b). Both species occur as two morphotypes (or forms): a nearshore (coastal) and an
offshore form (Hersh and Duffield 1990; Hoelzel et al. 1998). There is a clear distinction between the
nearshore and offshore form of the bottlenose dolphin in the western North Atlantic and western
North Pacific suggesting that the two forms may be eventually considered two different species (Curry
and Smith 1997; Hoelzel et al. 1998; Kingston and Rosel 2004).
Status—Bottlenose dolphins are designated as data deficient on the IUCN Red List (Reeves et al.
2003). Nothing is known of stock structure around the Marianas. The only estimate of abundance of
bottlenose dolphins for the region around the study area is an estimate of 31,700 animals for the area
north of the Marianas (Miyashita 1993), which may possibly coincide with the stock of offshore
bottlenose dolphins that occurs around the Marianas.
Habitat Preferences—Tursiops live in coastal areas of all continents (except Antarctica), around
many oceanic islands and atolls, and over shallow offshore banks and shoals. In the eastern tropical
Pacific and elsewhere there are pelagic populations that range far from land (Scott and Chivers 1990;
Reeves et al. 2002). The common bottlenose dolphin has a wider range than the Indo-Pacific
bottlenose dolphin; it ranges beyond the tropics and subtropics into temperate waters (Reeves et al.
2002). One satellite-tagged common bottlenose dolphin in the western North Atlantic moved into
waters with a bottom depth greater than 5,000 m (Wells et al. 1999). The Indo-Pacific bottlenose
dolphin is common in shallow water within 1 km of shore; individuals are seen regularly just seaward
of the surf zone and in clear water just outside turbid estuarine plumes (Reeves et al. 2002).
Risk of predation and food availability influence bottlenose dolphin habitat use (Shane et al. 1986;
Wells et al. 1987; Allen et al. 2001; Heithaus and Dill 2002). Predation risk is determined by the
number of predators in an area, the ability of predators and prey to detect each other, and the
probability of capture after detection; predation risk can be influenced by a suite of habitat attributes,
such as water clarity and depth (Heithaus 2001).
Distribution—The overall range of Tursiops is worldwide in tropical to temperate waters. Tursiops
generally do not range poleward of 45º, except around the United Kingdom and northern Europe
(Jefferson et al. 1993). The common bottlenose dolphin has been recorded in tropical to temperate
regions throughout the world. The Indo-Pacific bottlenose dolphin is reported throughout much of the
warm temperate and tropical Indian Ocean and western Pacific Ocean. In the western North Pacific,
this species occurs from southern Japan southward (including the Taiwan Strait), in the subtropical
western South Pacific, in much of the Indonesian archipelago, along the north coast of Australia
between New South Wales and Western Australia, and along the entire rim of the Indian Ocean to
South Africa, including the Persian Gulf and Red Sea (Reeves et al. 2002). Both the common
bottlenose dolphin and the Indo-Pacific bottlenose dolphin occur in the Indo-Pacific region.
Bottlenose dolphins found in nearshore waters around the main Hawaiian Islands are islandassociated,
with all sightings occurring in relatively nearshore and shallow waters (