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Seasonal dynamics of the cestode fauna in spiny dogfish, Squalus acanthias (Squaliformes: Squalidae)

SUMMARY This study furthers understanding of cestode infections in a marine environment through time and space by following seasonal fluctuations in infection parameters of three cestode species (Gilquinia squali, Trilocularia gracilis and Phyllobothrium squali) parasitizing spiny dogfish (Squalus acanthias) in the northwest Atlantic and comparing them to work previously published from the northeast Atlantic on T. gracilis. For each cestode species, host size, season and presence of the other cestode species were analysed using generalized linear models to determine if they were good predictors of prevalence and intensity. Infection parameters differed across season for the three cestode species. However, within T. gracilis seasonal trends were found to be remarkably similar on both sides of the Atlantic, differing only in a somewhat delayed decline in prevalence in the northwest Atlantic. The differences seen in infection measures across cestode species likely reflect the unique life history strategies of different parasite species. While general trends appear to be maintained across disparate localities, variation seen is likely due to differences in accessibility to intermediate hosts and host diet across sites. The knowledge gained from understanding cestode infections in the vast ocean environment allows us to speculate about the factors driving fluctuations in parasite infections in elasmobranchs.