Hoff Biodiversity as an index of regime shift in tfie eastern Bering Sea 



235 



Roundfish 



Inner domain 



'" °°o"oo°""°''»°"°°"°°' 



1 



o.s 



06 



4- 

 0? 



1974 1979 1984 1989 1994 1999 2004 



1974 1979 1984 1989 1994 1999 2004 



1-, 



0.8- 

 0.6- 

 0.4. 

 0.2. 



1974 1979 1984 1989 1994 1999 2004 



1974 1979 1984 1989 1994 1999 2004 



Outer domain 



10 

 9-\ 

 8 

 7 

 6 

 5- 

 4 

 3 

 2 

 1 

 1974 1979 1984 1989 1994 1999 2004 1974 1979 1984 1989 1994 1999 2004 



0.8- 

 0.6-1 X 



0.4. 

 0.2. 



All domains combined 



1- 

 0.8- 

 0.6- 

 0.4- 

 2- 



0- 



o^~a -e-r, — n P o .-■ f7< o 



P '  '  ' '■ ' u o 



1974 1979 1984 1989 1994 1999 2004 19'" 1979 1984 1989 1994 1999 2004 



Year Year 



Figure 4 



Biomass estimates of roundfish guild (left panel), and relative proportion of each species (right 

 panel) for the inner, middle, outer, and all domains combined, respectively. 



then a slight increase through 2002. A decrease in the 

 number of dominant species, such as sablefish, wattled 

 and shortfin eelpouts from 1979 to 1986, and a large 

 increase of skate biomass from 20% in 1975 to approxi- 

 mately 75% of the total biomass by 1986, explain the 

 index decline during this same period as the skate 

 biomass dominated. After 1986 the skate populations 

 stabilized somewhat to a slight decline which accounts 

 for the slight increase in evenness and richness as 

 other species gained a larger percentage of the total 

 biomass. 



All indexes for the roundfish guild, except for inner 

 domain richness, indicated two distinct linear periods. 

 Inflection points ranged from 1986 to 1990 and 1988 

 was an average inflection year for the roundfish 

 guild. 



Discussion 



Periods of climatic change have been shown to instill 

 long-term changes in the North Pacific ecosystem (Hare 



