Variations in the abundance and distribution of mesopelagic fishes in the Slope Sea off Atlantic Canada.
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Date
Authors
Themelis, Daphne Elizabeth.
Journal Title
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Publisher
Dalhousie University
Abstract
Description
Seasonal variations in the composition, structure, and spatial and vertical distribution patterns of the mesopelagic fish fauna in the Slope Sea off Atlantic Canada were studied from data obtained during ten midwater trawl surveys sampling at depths 0-1000 m between October 1984 and August 1989 to determine if a distinct and persistent fauna was present. In total, 227 species in 40 families were captured. Few species were very abundant or occurred frequently; 143 were rare ($$300 m in the day to $$300 m. Ordination of species data from six seasonal surveys indicated a faunal gradient of decreasing species richness and evenness which was significantly correlated with decreasing temperature and salinity in the upper 200 m. Classification analysis resulted in two or three station groups corresponding to three water masses: Warm Core Rings (Gulf Stream), Warm Slope Water (WSW) and Labrador Slope Water. Faunal differences were due to changes in abundance across the water mass boundaries rather than disjunct distributions. Three interacting mechanisms are proposed to explain the seasonal variation in faunal structure: (1) continuous advection of water and fauna by the Labrador Current and Gulf Stream into the Slope Sea; (2) seasonal abundance cycles of subtropical species with one year lifespans; (3) seasonal cooling of the WSW which decreases the reproductive success of invading subtropical species, thus requiring them to recolonize the WSW most years. The WSW fauna is persistent and distinct in structure from those of the adjacent water masses.
Thesis (Ph.D.)--Dalhousie University (Canada), 1996.
Thesis (Ph.D.)--Dalhousie University (Canada), 1996.
Keywords
Biology, Ecology., Biology, Oceanography.