Lissodelphis borealis experienced very high levels of fishery-induced mortality in international high-seas, large-scale driftnet fisheries, from about 38°N to 46°N and 171°E to 151°W. Assessing the impact of this mortality is complicated by the possible existence of a coastal population off California and the Pacific Northwest that is separate from offshore populations that were subject to high levels of bycatch (Dizon et al. 1994). Total numbers killed by the North Pacific squid driftnet fleets of Japan, Taiwan, and South Korea in the late 1980s were estimated at about 15,000-24,000 per year, and this mortality is considered to have depleted the oceanic population by an unknown amount. Using a variety of assumptions about population estimates, growth rates, and bycatch levels, Mangel (1993) presented a range of analyses that indicate declines of less than 30% were most likely, although more severe declines of up to 45-75% could not entirely be ruled out under certain scenarios, including a few biologically unrealistic ones. The UN moratorium on large-scale high-seas driftnets that came into effect in 1993 relieved this pressure to a considerable extent, but the continued use of driftnets to catch billfish, sharks, squid, and tuna inside the exclusive economic zones (EEZ) of North Pacific countries and some continued illegal fishing on the high-seas results in the killing of unknown numbers of northern right whale dolphins each year.

Incidental catches have also occurred in Japanese and Russian purse seines, Japanese salmon driftnets, and U.S. shark and swordfish driftnets. Small numbers have been killed in commercial and experimental salmon drift-net operations in the western and central Pacific (Jefferson et al. 1994). An estimated 386 northern right whale dolphins were killed between 1990 and 2002 in U.S. driftnets targeting sharks and swordfish off the California, Oregon and Washington (Julian and Beeson 1998, Carretta et al. 2005). A short-lived Canadian experimental driftnet fishery for flying squid killed a total of 13 in 1986 and 1987 (Jefferson et al. 1994). Northern right whale dolphins have also been observed entangled in net debris in the western Pacific. The total reported take of northern right whale dolphins by Japan in 1987 was 261 individuals, of which 254 were discarded as bycatch (Government of Japan 1989).

Northern right whale dolphins have never been subject to extensive directed hunt, although they have sometimes been taken in Japan’s small-cetacean fisheries. In the western Pacific, coastal fisheries off Japan have taken them for many years, with 465 reported killed in the harpoon fishery in 1949. Although this fishery mainly targets other small cetaceans, northern right whale dolphins continue to be taken (Jefferson et al. 1994).