Determining deep-sea fish community structure in the Arctic: Using species assemblages, stomach contents, parasite infracommunities and stable isotopes to evaluate trophic interactions

Little is known about deep-sea Arctic fish communities, especially relating to species distributions, basic biology and ecology. Surveys usually focus on commercially exploitable species such as Greenland halibut ( Reinhardtius hippoglossoides) and shrimp (Pandalus spp.). Most community studies on Arctic food web dynamics often overlook underlying patterns such as shifting trophic position with environmental change. This is the first study in which the fish/invertebrate food web of the deep-sea Arctic is described in terms of predator-prey and host-parasite relationships. The objectives of this thesis were to determine factors that affect community dynamics and trophic relationships within deep-sea fish communities of Davis Strait and Baffin Bay and involved 1) recognizing broad feeding patterns by combining fish groups, regardless of phylogenetic relationships, by size and/or age class as well as similar ecologies, 2) determining factors that affect community dynamics and trophic relationships in benthic Arctic marine communities and 3) assessing the trophic position of individual species based on stomach content analysis, parasite assemblages and stable isotope data. Four hypotheses were generated, involving fish community composition with changing environmental variables, the effectiveness of trophic guilds in the construction of deep-sea Arctic food webs, the value of using parasites and stable isotopes in combination with stomach content analysis, and the role of size and age class in determining trophic position.;I have provided Arctic science with the first insights into community dynamics within deep-sea Arctic habitats. Hopefully, better decisions will be possible regarding the health and structural integrity of marine Arctic communities in the face of environmental change. Marine resource managers can no longer consider single-species populations when assessing the health of marine communities as the data from this thesis clearly show a marine system in which the life histories of its species are inextricably intertwined. Clearly for the future, disturbances such as single or multiple species overfishing and/or global warming must be considered in the context of the National Marine Fisheries Policy of 'Ecosystem-Based Management'.;Species within this region are distributed along one or more environmental gradients such as latitude, longitude, temperature and depth, resulting in continually shifting species composition throughout the system. Traditional methods of trophic evaluation, namely guild determination and food web construction, were not appropriate for deep-sea Arctic communities due to the prevalence of generalist feeding throughout. These results are different from previous reports on tropical or temperate marine environments in which fish species can be separated into clear trophic levels. A multivariate approach combining stomach contents and endohelminths demonstrated that habitat utilization and diet best described trophic relationships within the region; fish species were divided into trophic 'groups' based on their ability to utilize benthic and pelagic zones. I provide, for the first time, an analysis of endohelminth communities of deep-sea species that supports dietary information. Data from parasite infracommunities revealed that, at best, they can be used to describe the preferred habitat zone of individual fish species without stomach content analysis and, at the very least, they give strong support to diet data. Due to the broad overlap of dietary preferences, tissue values of delta 13C and delta15N stable isotopes were not as useful to describe trophic position; these values could not be used to designate a species to a clearly defined trophic position. However, the use of differences in delta13C and delta15N values were used to reveal similar patterns of habitat utilization and feeding strategies to those seen for diet and parasite analyses. There was no significant relationship between fish size and stable isotope signature; diets of different fish size classes overlap and/or prey species contain similar isotopic signatures in the deep-sea.