Comments: The taxonomic status of the two morphologically distinct forms of Dall's porpoises, Phocoenoides dalli (dalli- and truei-type), has been uncertain. A neighbor-joining tree of mtDNA haplotypes presented by Escorza-Trevino et al. (2004) showed 2 distinctive clades, each containing individuals from both types. According to Escorza-Trevino et al., "This suggests that truei- and dalli-types are forms of the same species. However, at the population level, statistically significant genetic differentiation was found between truei-type and sympatric dalli-type populations. These results argue that differentiation between truei- and dalli-types is at the population level, much in the same way that dalli-type populations differ among each other."

Rice (1998) and Mead and Brownell (in Wilson and Reeder 2005) recognized dalli and truei as subspecies.

See Winans and Jones (1988) for information on genetic relationships among populations in the North Pacific and Bering Sea. Based on calving grounds, there may be at least six stocks of dalli-type and one stock of truei-type in the North Pacific (see IUCN 1991).