Metazoan Parasites in deep-sea sharks Part I. A Review of the Parasite Fauna of sharks of the genus Etmopterus Part II. Metazoan gastrointestinal parasites of Etmopterus spinax (L., 1758) from southern Norwegian waters

Abstract

Parasites play an important role in ecology due to their potential influence on the biodiversity and dynamics of ecosystems. The complexity of interaction between parasites and their hosts is crucial to understanding the host’s populations dynamics, behaviour as well as interconnections between food chains in an ecosystem. Parasites have wide applications as bio-indicators for example to detect and monitor pollution and to provide additional information on the host’s population connectivity. With increasing fishing pressures globally, an understanding of affected ecosystems including the species and their dynamics therein is crucial in order to implement effective management strategies. The velvet belly lanternshark (Etmopterus spinax) is a small deep-sea shark which is a common bycatch species in North Sea fisheries. There have been only few studies on the parasites of E. spinax in Norwegian waters and none of them included mature individuals studying the entire parasite community. Therefore, this study investigated a total of 115 E. spinax specimens from box sexes in different sexual stages were sampled at eight stations with different depths in the North Sea in January 2016. In addition, this thesis aimed to review all available literature on metazoan parasites within the entire genus Etmopterus to lay the basis for the expectations of the empirical study and to identify potential knowledge gaps. The literature review indicated 21 existing parasite species on 9 host species belonging to the Etmopterus genus, on 13 different sites of the host’s body. The empirical data from eight stations in southern Norwegian waters revealed fairly low parasite prevalence and diversity on E. spinax. From a total of 115 studied shark specimen in this study only a total of four different parasite species (from four taxonomic groups) were recorded and only 18 host specimens were infected with at least one parasite species. The comparison of E. spinax individuals showed that larger sharks had a significantly higher prevalence of the parasite species A. simplex and A. squalicola, although the same could not be found for the other two parasite species. The generally lower values compared to the literature could be explained by e.g. parasite seasonality, diet shifts or methodological constraints, which are all discussed. The parasites species found here presented both strong and weak points for potential use as biological tags for host dynamics and food web interactions in the future.