MESOPLODONT 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. 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). Off the northeast U.S. coast, beaked whale (Mesoplodon spp.) sightings have occurred principally along the southern edge of Georges Bank (CeTAP, 1982; Waring et al. 1992; Palka and Waring, in prep.). 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; Palka and Waring, in prep.). 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's beaked whales are believed to be principally oceanic, and strandings have been reported from the mid-Atlantic Bight to Florida, into the Caribbean and the Gulf of Mexico (Leatherwood et al. 1976; Mead 1989). This is the commonest species of Mesoplodon stranded along the U.S. Atlantic coast. The northernmost stranding was off New York (Mead 1989). 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). There are two records of standings 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).