MESOPLODON BEAKED WHALES (Mesoplodon spp.): Western North Atlantic Stock

STOCK DEFINITION AND GEOGRAPHIC RANGE Within the genus Mesoplodon, there are four species of beaked whales that reside in the northwest Atlantic. These include True's beaked whale, Mesoplodon mirus; Gervais' beaked whale, M. europaeus; Blainville's beaked whale, M. densirostris; and Sowerby's beaked whale, M. bidens (Mead 1989). These species are difficult to identify to the species level at sea; therefore, much of the available characterization for beaked whales is to genus level only. Stock structure for each species is unknown. The distribution of Mesoplodon spp. in the northwest Atlantic is known principally from stranding records (Mead 1989; Nawojchik 1994; Mignucci-Giannoni et al. 1999). Off the northeast USA coast, beaked whale (Mesoplodon spp.) sightings have occurred principally along the southern edge of Georges Bank (CETAP, 1982; Waring et al. 1992; NMFS unpublished data). Most sightings were in late spring and summer. In addition, beaked whales were also sighted in Gulf Stream features during NEFSC 1990-1995 surveys (Waring et al. 1992; Anon 1994; Tove 1995; NMFS unpublished data). True's beaked whale is a temperate-water species that has been reported from Cape Breton Island, Nova Scotia, to the Bahamas (Leatherwood et al. 1976; Mead 1989). It is considered rare in Canadian waters (Houston 1990). Gervais' beaked whales are believed to be principally oceanic, and strandings have been reported from Cape Cod Bay to Florida, into the Caribbean and the Gulf of Mexico (Leatherwood et al. 1976; Mead 1989; NMFS unpublished data). This is the most common species of Mesoplodon to strand along the USA Atlantic coast. The northernmost stranding was on Cape Cod. Blainville's beaked whales have been reported from southwestern Nova Scotia to Florida, and are believed to be widely but sparsely distributed in tropical to warm-temperate waters (Leatherwood et al. 1976; Mead 1989, Nicolas et al. 1993). There are two records of strandings in Nova Scotia which probably represent strays from the Gulf Stream (Mead 1989). They are considered rare in Canadian waters (Houston 1990). Sowerby's beaked whales have been reported from New England waters north to the ice pack, and individuals are seen along the Newfoundland coast in summer (Leatherwood et al. 1976; Mead 1989). Furthermore, a single stranding occurred off the Florida west coast (Mead 1989). This species is considered rare in Canadian waters (Lien et al. 1990).