Distribution and abundance of sealworm (<i>Pseudoterranova decipiens</i>) and other anisakid nematodes in fish and seals in the Gulf of St. Lawrence: potential importance of climatic conditions

Abstract

Prevalence and abundance of sealworm (Pseudoterranova decipiens) and other anisakid nematodes were determined in a variety of fishes from the Gulf of St. Lawrence in 1990 and. Sealworm abundance and prevalence were also determined in three species of seals in the Gulf between 1988 and 1992. Atlantic cod (Gadus morhua) and shorthorn (Myoxocephalus scorpius) and longhorn sculpin (M. octodecemspinosus) were the fishes most heavily infected with sealworm. Grey seals (Halichoerus grypus) proved to be the most important definitive hosts for sealworm in the Gulf. Abundance of sealworm increased, whereas that of Anisakis simplex and contracaecine nematodes decreased, from north to south in the Gulf. Abundance of sealworm increased compared to earlier surveys in most areas of the Gulf, but decreased in both cod and grey seals during the course of this study. In contrast, abundance of Contracaecum osculatum and Phocascaris spp. in grey seals and cod continued to increase during the study period. Observed increases of nematodes are attributed to growing populations of grey seals (for sealworm) and harp seals (for Contracaecinea). Levels of A. simplex remained relatively constant between 1988 and 1992 in both grey seals and cod. There is no evidence suggesting that observed patterns in nematode abundance were due to changes in grey seal diet. Nor was there any evidence of competition between P. decipiens and C. osculatum in grey seals affecting either sealworm abundance or fecundity. The trends detected herein are attributed to climatic events in the Gulf of St. Lawrence, where water temperatures in the cold intermediate layer consistently decreased between 1986 and 1994. It is suggested that low temperatures inhibited development and hatching of sealworm eggs, but not those of C. osculatum. 113NAMMCO Scientific Publications, Volume 3 D Di is st tr ri ib bu ut ti io on n a an nd d a ab bu un nd da an nc ce e o of f s se ea al lw wo or rm m ( (P Ps se eu ud do ot te er rr ra an no ov va a d de ec ci ip pi ie en ns s) ) a an nd d o ot th he er r a an ni is sa ak ki id d n ne em ma at to od de es s i in n f fi is sh h a an nd d s se ea al ls s i in n t th he e G Gu ul lf f o of f S St t. . L La aw wr re en nc ce e: : p po ot te en nt ti ia al l i im mp po or rt ta an nc ce e o of f c cl li im ma at ti ic c c co on nd di it ti io on ns s

Scientific Opinion on risk assessment of parasites in fishery products

“…Moreover, data on long-term variation of Anisakid abundance in seals are often inconclusive or insufficient. Both Marcogliese (2001) and McClelland (2002b) estimate that the relationship between definitive host population size and Anisakid abundance in fish is complex and may be mitigated by other factors such as water temperature and oceanic currents. Table 5 shows examples of prevalence and intensity data of Anisakis in various fish host species from different geographical areas and illustrates that, despite the lack of data on, systematic monitoring, the size of fish, and anatomical sites of infection, together with the dynamic nature of host populations and infections, there are no areas where fishery products are consistently free of Anisakis larvae.…”

Spatial and temporal distributions of larval sealworm, <i>Pseudoterranova decipiens</i> (Nematoda: Anisakinae), in <i>Hippoglossoides platessoides</i> (Pleuronectidae) in the Canadian Maritime Region from 1993 to 1999

“…The spatial and temporal distributions of larval Pseudoterranova decipiens in eastern Canadian groundfish seem to be related, primarily, to the geographical distribution and growth of Northwest Atlantic grey seal populations. Sealworm infection parameters recorded in Canadian plaice and other groundfish species over the past two decades (McClelland et al 1983a, 1983b, 1987, 2000, Boily and Marcogliese 1995, Marcogliese 1996, Marcogliese 2001, McClelland and Martell 2001 were greatest in fish from southern Newfoundland (3P), the Gulf of St. Lawrence (4RST), the Breton and Scotian Shelves (4VWX), and the northeastern Gulf of Maine 83 NAMMCO Scientific Publications, Volume 3 (4X-5ZE) (Fig. 1).…”

“…While grey seals are the most important definitive hosts of P. decipiens in Atlantic Canada (Marcogliese et al 1996, Marcogliese 2001), other seal species may also have a significant impact on larval sealworm levels in groundfish. Pseudoterranova decipiens B (sensu stricto) commonly occurs in harbour seals (Brattey and Stenson 1993), and, as there is no evidence of reproductive isolation, cross infection between harbour and grey seals and interbreeding between progeny of nematodes from the two host species may occur.…”

“…3) , McClelland 1995, McClelland et al2000. The parasite's distribution may also be influenced by abiotic factors such as ocean currents (dispersal of ova passed in seal feces) (McConnell et al 1997) and environmental temperatures , Marcogliese et al 1996, Marcogliese 2001, Measures 1996 Maine, from 1980Maine, from to 1999 val of the free-living ensheathed larvae, efficiency of transmission of larvae to and between poikilothermic intermediate hosts, and developmental rates of larvae in the these hosts (McClelland 1982(McClelland , 1990. Temperature may also affect sealworm transmission and survival indirectly by influencing growth rates, abundance and distribution (hence, availability) of important intermediate hosts (Swain and Kramer 1993, Campana et al 1995, Swain 1996, 1997.…”

“…Temperature may also affect sealworm transmission and survival indirectly by influencing growth rates, abundance and distribution (hence, availability) of important intermediate hosts (Swain and Kramer 1993, Campana et al 1995, Swain 1996, 1997. Marcogliese (2001) (Swain 1993), and an area varying from 12,000 to 25,000 km 2 between 1990 and 1996 (Gilbert et al 1996; D.P. Swain, Department of Fisheries and Oceans, Gulf Fisheries Centre, Moncton, N.B., personal communication).…”