234 



Fishery Bulletin 104(2) 



Flatfish 



Inner domain 



1974 1979 1984 1989 



Middle domain 



1999 2004 



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« 1974 



1 984 1 989 



1999 2004 



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Outer domain 



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1974 1979 1984 1989 1994 1999 2004 



All domains combined 



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1974 1979 1984 1989 1994 



Year 



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Figure 3 



Biodiversity indexes (richness left, evenness right) for the flatfish guild determined with two 

 linear models (or a single model) separated at the inflection point derived from the piecewise 

 linear model. The graphs represent the inner, middle, outer, and all domains combined, respec- 

 tively. The X represents biodiversity index for survey year 1975 which was not included in linear 

 models or the piecewise model because of a gap in the time series. 



is plotted for each shelf domain and for all domains 

 combined. The inner domain richness index revealed 

 a steady level of approximately 2-3 dominant species 

 or species groups iMyoxocephalus sculpins, skates, and 

 Pacific herring) over the 24-year period. The gradual 

 increase in skates and slight decline in the plain sculpin 

 caused an increase in the evenness index to somewhat 

 even proportions of the three dominant species in the 



inner domain, from 7 to 2 dominant species over the 

 24-year period, and evenness declined by about one-half 

 (Fig. 4). The increase in skates and decline of many 

 inner domain species from 1975 through the early 1990s 

 resulted in an assemblage dominated by two species 

 groups, Myoxocephalus sculpins and skates (Fig. 2). 



The outer domain showed a dramatic decline in rich- 

 ness and evenness from 1975 to the mid-1980s and 



