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 T rue's beak ed wha le, Mesoplodon mirus; Gervais' b eaked w hale, M. europaeus; Blainville's beaked whale , M. densirostris ; and Sow erby's bea ked wh ale, M. bidens (Mead 1989). Th ese 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 sp ecies is unknown. The distribution of Mesoplodon spp. in the northwest Atlantic is known principally from stranding records (Mead 1989; Nawojchik 1994). Off the northeast USA coast, beaked whale (Mesoplodon spp.) sightings have oc curred p rincipally along the southern edge of Georges Bank (CETAP, 1982; Waring et al. 1992; NMFS un published 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; T ove 19 95; NM FS unp ublished data). True 's beaked whale is a tempera te-water species that has been reported from Cape Breton Island, Nova Scotia, to the Bahamas (Leatherwood et al. 1976; Mead 198 9). It is consid ered rare in Canad ian water s (Housto n 1990 ). Gerv ais's beaked whales are believed to be principally oceanic, and strandings have been reported from Cape C od Bay to Florida, in to the Caribbean and the Gulf of Mexico (Leatherwood et al. 1976; Mead 1989; NMFS unpublished data). This is the comm onest species of Mesoplodon stranded along the USA Atlantic coast. The northernmost stranding was on Cap e Cod. Blain ville's beaked whales have been reported from so uthwes tern No va Scotia to Florida, and are believed to be widely but sparsely distributed in tropical to warmtemperate waters (Leatherwood et al. 1976; Me ad 1989, N icolas et al. 1993). T here are tw o record s of standin gs in Nova Scotia which probably represent strays from the Gulf Stream (Mead 1989). They are considered rare in Canadian waters (H ouston 1 990). Sow erby 's beaked whales have been reported from New Englan d waters n orth to the ic e pack, an d individ uals are seen along the Newfoundland coast in summer (Leatherwood et al. 1976; M ead 198 9). Furthe rmore , a single stranding occurre d off the F lorida we st coast (M ead 198 9). This species is considered rare in Canadian waters (Lien et al. 1990).