Spatial and temporal distributions of larval sealworm (Pseudoterranova decipiens, Nematoda : Anisakinae), in Hippoglossoides platessoides (Pleuronectidae) in eastern Canada from 1980 to 1990

Larval sealworm (Pseudoterranova decipiens) infections were surveyed in the fillets and napes of 28 065 Canadian plaice (Hippoglossoides platessoides) , 31-40 cm in length, collected throughout Atlantic Canada between February 1980 and August 1990. Samples were taken from 11 locations in a 1980-1982 survey, and from 38 to 55 locations in 1983-1984, 1985-1986, 1987-1988, and 1989-1990 surveys. Prevalence (P) and abundance (A) of P. decipiens were g reatest (P=96-100%, A=12.47-22.32) in 1989-1990 samples from the central Sc otian Shelf near Sable Island, while plaice from northeastern Newfoundland and the Grand Banks were seldom infected (P<1%). Temporal trend analyses re vealed that between 1980 and 1990, sealworm infection levels increased sign ificantly in plaice in 33 of 41 locations in the Gulf of St Lawrence, on th e Breton and Scotian shelves, and in the Gulf of Maine. Spatial and tempora l distributions of larval P. decipiens in plaice seemed to reflect the dist ribution and growing abundance of grey seals (Halichoerus grypus), importan t definitive hosts of the parasite, but increases in levels of infection ov er the course of the decade may also have been promoted by a period of rela tively high near-bottom temperatures in Atlantic Canadian waters in the lat e 1970s and early 1980s. A more recent cooling trend in near-bottom tempera ture or other negative influences, such as sealworm density limiting mechan isms in fish and seal hosts, may have resulted in the stabilization or decl ine of sealworm levels in some plaice populations in the late 1980s and ear ly 1990s. (C) 2000 International Council for the Exploration of the Sea.