Harbor Porpoise, Phocoena phocoena vomerina, in Cook Inlet, Alaska
The harbor porpoise, Phocoena phocoena, is among the smallest of the six porpoise species in the Family Phocoenidae, with an adult length of 1.4 m to 1.9 m (4.6–6.2 ft). They are rotund, have a stubby beak with small, spade-shaped teeth, and a triangular-shaped dorsal fi n (Fig. 1). In general, their dorsal surface is dark gray, becoming lighter gray on the sides, with a white under-belly. The sounds they make when breathing have earned them the nickname “puffi ng pig.” This species is rarely active at the surface but instead presents a low profi le when surfacing and often travels alone (Leatherwood et al., 1982). They generally forage on small, pelagic schooling fish in waters less than 200 m (656 ft) deep (Bjørge and Tolley, 2008).
The species is widespread in the Northern Hemisphere, inhabiting coastal and inland waters. There may be as many as four distinct subspecies, of which P. p. vomerina Gill, 1865 occurs in the eastern North Pacific (Rice, 1998; Perrin1). Alternately referred to as Phocoena vomerina in the literature2, this synonym is no longer accepted (Perrin3). In the eastern North Pacific, harbor porpoise range from California to Alaska, with at least 10 distinct stocks identified within this range (Carretta et al., 2009; Allen and Angliss, 2010). The regional differences between stocks, based on genetic analyses (Rosel et al., 1995; Chivers et al., 2002; Chivers et al.4), pollutant residues (Calambokidis and Barlow, 1991), and discontinuities in density, suggest that, unlike the North Atlantic porpoise, P. p. phocoena, eastern North Pacific porpoise are not panmictic or migratory. In Alaska waters, harbor porpoise stock structure is unclear, and three stocks are currently recognized for management purposes: Southeast Alaska, Gulf of Alaska (GOA), and Bering Sea (Allen and Angliss, 2010). Porpoises found in Cook Inlet are included in the GOA stock (Fig. 2).