Structure and Dynamics of Northeastern Pacific Demersal Fish Assemblages Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2801pj510

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  • Regions of similar species composition and groups of demersal fish species with similar distribution patterns from Cape Flattery, Washington to Point Hueneme from 50-250 fm (93-460 rn) were defined based on results of an agglomerative cluster analysis of National Marine Fisheries Service Rockfish Survey data taken during the summer of 1977. Three major site groups appeared: 1) an upper slope region extended from Juan de Fuca Canyon to Point Hueneme at depths of 100-250 fm (183-467 m); 2) a northern mid-shelf break region extended from Cape Flattery to Cape Blanco at depths of 55-187 fm (100-340 m); 3) a southern mid-shelf break region began inshore at Cape Flattery and extended to the shelf break from Cape Blanco to Point Hueneme at depths of 50-146 fm (91-267 m). These major site groups were subdivided into subregions, often along depth contours. Eight species groups appeared: a deepwater group (in site region 1 and parts of site region 2), including some ubiquitous species; a shallow water group, concentrated in the south (site region 3) and a shallow water group, concentrated in the north (site region 2) included the most abundant species. Five other groups included rarer species with more localized distributions. Diversity trends and relationships between composition of species groups and environmental factors were investigated using AIDN analysis of information and diversity and principal component, canonical correlation and factor analyses. Diversity decreased with depth, and was highest at the northern and southern ranges of the sample areas. Local low diversity values within latitudes were usually due to dominance by splitnose rockfish (Sebastes diploproa) in the south or Pacific hake (Merluccius productus) inshore between 38°N and 46°N. Diversity was relatively low in some assemblage regions between Cape Blanco and Cape Mendocino, an area of strong upwelling and narrow shelf. The effect on species group composition of a 50 fm (92 m) change in depth within a particular degree of latitude appears larger than the effect of a 10 change in latitude in many regions. Multivariate analyses extracted and clarified local patterns of latitudinal change in species groups from cluster analysis, which appeared most strongly related to latitude itself and onshore Ekman transport. Several hypotheses relating assemblage structure to oceanographic features are presented. Assemblage characteristics may change with depth in response to changing forms of available food and distance from inshore upwelling fronts; and with latitude in response to environmental uncertainty. Replicate surveys and analyses are desirable to measure the repeatability of assemblage structure, and eventually assess the natural range of variability in composition and spatial and temporal extent of species groups. A model is hypothesized to consider the relative influences of environmental variability and density dependence (among and within functional groups) on structure and dynamics of demersal fish assemblages of the California Current.
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