180 



Abstract — Endoparasitic helminths 

 were inventoried in 483 American 

 plaice iHippoglossoidesjjlatessoides) 

 collected from the southern Gulf of 

 St. Lawrence, NAFO (North Atlantic 

 Fisheries Organization) division 4T, 

 and Cape Breton Shelf (NAFO sub- 

 division 4Vn) in September 2004 and 

 May 2003, respectively. Forward step- 

 wise discriminant function analysis 

 (DFA) of the 4T samples indicated that 

 abundances of the acanthocephalans 

 Echinorhynchus gadi and Corynosoma 

 strumosum were significant in the 

 classification of plaice to western or 

 eastern 4T. Cross validation yielded a 

 correct classification rate of 79% over- 

 all, thereby supporting the findings of 

 earlier mark-recapture studies which 

 have indicated that 4T plaice comprise 

 two discrete stocks: a western and 

 an eastern stock. Further analyses 

 including 4Vn samples, however, indi- 

 cated that endoparasitic helminths 

 may have little value as tags in the 

 classification of plaice overwinter- 

 ing in Laurentian Channel waters 

 of the Cabot Strait and Cape Breton 

 Shelf, where mixing of 4T and 4Vn 

 fish may occur. 



Use of endoparasitic helminths as tags 

 in delineating stocks of American plaice 

 iHippoglossoides platessoides) 

 from the southern Gulf of St. Lawrence 

 and Cape Breton Shelf 



Gary McClelland (contact author) 



Jason Melendy 



Fisheries and Oceans Canada 

 Gulf Fisheries Centre 

 343 University Avenue 

 Moncton, New Brunswick 

 E1C9B6 Canada 



Email address for G. McClelland: mcdeliandgcSdfo-mpo gc.ca 



Manuscript submitted 17 May 2006 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 25 August 2006 by the Scientific Editor. 



Fish. Bull. 105:180-188(2007). 



American plaice iHippoglossoides 

 platessoides) are found in Northwest 

 Atlantic waters along the continental 

 shelf and upper continental slope from 

 west Greenland to Rhode Island, favor- 

 ing intermediate depths (90-250 m), 

 cold waters (<0-1.5°C), and fine sand 

 or mud bottom (Scott and Scott, 1988). 

 Amercian plaice has ranked second 

 in importance to Atlantic cod (Gadiis 

 morhua) among groundfish landed 

 in the southern Gulf of St. Lawrence 

 (North Atlantic Fisheries Organiza- 

 tion [NAFO] division 4T) over the past 

 four decades, but commercial landings, 

 which had ranged from 4907 to 11,780 

 t between 1965 and 1992 (Morin et 

 al.i), fell to 401 t by 2004 (Fisheries 

 and Oceans Canada'-). Commercial 

 and research survey data show that 

 declines in abundance of southern Gulf 

 plaice since 1991 have occurred primar- 

 ily in western 4T between the Gaspe 

 Peninsula and the Magdalen Islands 

 (see Fig. 1), and abundances east of 

 the Magdalens have remained stable. 

 The eastern and western 4T stocks 

 monitored in recent assessments are 

 consistent with the meristically indis- 

 tinguishable "Miscou-Magdalen" and 

 "Cape Breton" groups which Powles 

 (1965) delineated through mark-recap- 

 ture experiments. Powles (1965) sug- 

 gested that the meristic uniformity 

 of these two groups may be a conse- 

 quence of larval drift because mature 

 fish from the respective groups seldom 



mix on their summer feeding grounds. 

 More recently, Stott et al. (1992) found 

 no evidence of population subdivision 

 of Southern Gulf plaice in respect to 

 allozyme variation and restriction 

 fragment length polymorphisms in 

 mitochondrial DNA. 



As evident from commercial catch 

 records and tag returns, 4T plaice, 

 with the exception of some immature 

 fish that remain in the shoals year 

 round, migrate from summer feeding 

 grounds on the Magdalen Shallows 

 to deeper waters of the Laurentian 

 Channel in winter (Powles, 1965). 

 The winter distribution of plaice in 

 the Laurentian Channel is continuous 

 from the Gaspe to the Cabot Strait 

 (Clay, 1991) and eastward along the 

 Cape Breton Shelf (NAFO subdivision 



' Morin, R., I. Forest, and G. Poirier. 

 2001. Status of NAFO Division 4T 

 American plaice, February 2001. Cana- 

 dian Science Advisory Secretariat 

 Research Document. 2001/023, 70 

 p. Fisheries and Oceans Canada, Sci- 

 ence Branch, Marine Fish Division, Gulf 

 Region, P.O. Box 5030, Moncton, New 

 Brunswick, Canada. 



- Fisheries and Oceans Canada. 2005. 

 American plaice in the southern Gulf of 

 St. Lawrence (Division 4T). Fisheries 

 and Oceans Canadian Science Advisory 

 Secretariat Science. Advisory Report. 

 2005/008, 5 p. Maritime Provinces, 

 Regional Advisory Process, Fisheries 

 and Oceans Canada, P.O. Box 1006, 

 Dartmouth, Nova Scotia, Canada. 



