The mesopelagic fish and invertebrate macrozooplankton faunas of two Newfoundland fjords with differing physical oceanography

Richard, Jocelyn Marie (1987) The mesopelagic fish and invertebrate macrozooplankton faunas of two Newfoundland fjords with differing physical oceanography. Masters thesis, Memorial University of Newfoundland.

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Abstract

Mesopelagic fish and macrozooplankton assemblages were compared between two Newfoundland fjords which contain predominantly different deep-water masses and which differ in the nature and frequency of deep water exchange. Samples were collected using a 3 m Isaacs-Kidd Midwater Trawl in May 1982 and June 1983. The species composition of mesopelagic fishes was found to be dissimilar while the macrozooplankton fauna was largely the same. Melanostigma atlanticum and Benthosema glaciale were the most abundant fishes in Bay d'Espoir while Mallotus villosus was the most abundant fish collected from Fortune Bay. The macrozooplankton fauna in both fjords consisted largely of Thysanoëssa raschii, T. inermis, Meganyctiphanes norvegica and Sagitta elegans. Differences in species composition and relative abundances were partly attributed to the difference in deep water properties. -- The structure and persistence of the mesopelagic fish assemblage were related to environmental stability. In Bay d'Espoir six of thirteen (46 %) species were collected in both years compared to two of eleven (18 %) species in Fortune Bay. Percentage similarity between years was high in Bay d'Espoir (91.5) and low in Fortune Bay (43.6). Species composition and rank over abundances within and between years were less variable in Bay d'Espoir than in Fortune Bay, as were catch rates for the dominant species. These results suggest that the faunal assemblage in Bay d'Espoir was regulated primarily by in situ biological processes while advective processes were more important in Fortune Bay. Similar results were not obtained for the macrozooplankton assemblage which was thought to respond primarily to short-term or seasonal changes in environmental conditions. -- Species diversity and evenness, and average species richness of mesopelagic fishes was greater in Bay d'Espoir than in Fortune Bay. Similar results were not obtained for the macrozooplankton faunas and species diversity and evenness were higher in Fortune Bay than in Bay d'Espoir while average species richness was comparable between the fjords. These indices were not found to be useful in identifying the underlying processes structuring the fjord faunal assemblages. A comparison of biomass size spectra between the fjords showed no major differences. -- The fish fauna in Bay d'Espoir was probably derived in part from the Laurentian and Hermitage Channels while that of Fortune Bay was probably derived from the St. Pierre and Hermitage Channels. A small fraction of the fish and macrozooplankton faunas in both fjords was derived from the offshore continental slope region.

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