“…The gray whale lineage has a geological and historical presence in much of the North Atlantic, and it is reasonable to expect that C. rhachianecti also once ranged throughout the North Atlantic as well (Bisconti and Varola, 2006;Noakes et al, 2013;Alter et al, 2015;Bosselaers and Collareta, 2016;Hufthammer et al, 2018;Rodrigues et al, 2018). Overharvesting led to the final collapse of this population by sometime in the 18 th century, however, and today C. rhachianecti is found only in the North Pacific, where it is a host-specific symbiont of the gray whale (Newman and Ross, 1976;Newman and Abbott, 1980;Scarff, 1986;Bradford et al, 2011;Hayashi, 2012). Modern gray whales live in two distinct populations in the western and eastern North Pacific, although some interchange between these populations does occur (LeDuc et al, 2002;Cooke et al, 2007;IWC, 2011).…”