Use of parasite tags in delineating stocks of white hake (Urophycis tenuis) from the southern Gulf of St. Lawrence and Cape Breton Shelf

Protozoan and metazoan parasites were inventoried in 396 white hake (Urophycis tenuis), 40-60 cm in length, collected from the southern Gulf of St. Lawrence (NAFO division 4T) and Cape Breton Shelf (NAFO subdivision 4Vn) between August 2001 and May 2003. Discriminant function analysis (DFA) of parasite abundances revealed that cysts of unknown etiology (“CUE”) in the gill filaments, and three species of parasitic helminth, the monogenean, Diclidophoroides maccallumi, and the nematodes, Capillaria gracilis and Hysterothylacium aduncum, were useful as markers for discriminating 4T hake found at depths of >100 m along the southern slope of the Laurentian Channel and in the Cape Breton Trough from those found in the shallower (<50 m) waters of St. Georges Bay in the southeastern Gulf. DFA of the southern Gulf samples yielded an overall correct classification rate of 78%, thereby supporting earlier tagging, meristic and morphometric studies which indicated that 4T hake are comprised of distinct deep-water (Channel) and shallow-water (Strait) stock components. DFA of all 4TVn samples, with the inclusion of a fifth marker, the acanthocephalan Echinorhynchus gadi, yielded correct classification rates of 66 and 76% for “channel” and “strait” hake, respectively, and 76% for 4Vn hake from Laurentian slope waters of the Cape Breton Shelf. Hence, parasite tags could be applied, together with other biological and/or genetic markers, in studies of migration and possible mixing of 4TVn stock components over-wintering in Laurentian slope waters.