226 



Abstract — Data collected from an 

 annual groundfish survey of the 

 eastern Bering Sea shelf from 1975 

 to 2002 were used to estimate bio- 

 mass and biodiversity indexes for two 

 fish guilds: flatfish and roundfish. 

 Biomass estimates indicated that 

 several species of flatfish (particu- 

 larly rock sole, arrowtooth flounder, 

 and flathead sole), several large 

 sculpins {Myoxocephalus spp.), big- 

 mouth [Hemitripterus bolini), and 

 skates iBathyraja spp.) had increased. 

 Declining species included several 

 flatfish species and many smaller 

 roundfish species of sculpins, eel- 

 pouts (Lycodes spp.), and sablefish 

 (Anoplopoma fimbria). Biodiversity 

 indexes were calculated by using bio- 

 mass estimates for both guilds from 

 1975 through 2002 within three physi- 

 cal domains on the eastern Bering 

 Sea shelf. Biodiversity trends were 

 found to be generally declining within 

 the roundfish guild and generally 

 increasing within the flatfish guild 

 and varied between inner, middle, and 

 outer shelf domains. The trends in 

 biodiversity indexes from this study 

 correlated strongly with the regime 

 shift reported for the late 1970s and 

 1980s. 



Biodiversity as an index of regime shift 

 in the eastern Bering Sea 



Gerald R. Hoff 



Alaska Fisheries Science Center 

 National Marine Fisheries Service 

 7600 Sand Point Way N E 

 Seattle, Washington 98115 

 Email address; jerry.hofftSnoaagov 



Manuscript submitted 25 March 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 

 13 August 2005 by the Scientific Editor. 



Fish. Bull. 104:226-237 (2006). 



Environmental and biological events in 

 the North Pacific can indicate regime 

 shifts or reorganizations of the eco- 

 system at the environmental and bio- 

 logical level (Hare and Mantua, 2000). 

 Measurable climatic events were iden- 

 tified in the mid-1970s, late 1980s 

 (Anderson and Piatt, 1999; Anderson, 

 2000; Hare and Mantua, 2000; Zhang 

 et al., 2000; Minobe, 2002) and the 

 late 1990s (Hunt and Stabeno, 2002; 

 Minobe, 2002). Regime shifts in the 

 eastern Bering Sea (EBS) have been 

 correlated with several climatic events, 

 including the Pacific Decadal Oscilla- 

 tion, the El Niiio Southern Oscilla- 

 tion (Hollowed et al., 2001), sea ice 

 coverage (Stabeno et al., 2001; Hunt 

 et al., 2002; Hunt and Stabeno, 2002), 

 and summer sea surface temperatures 

 (Bond and Adams, 2002; Hunt et al., 

 2002; Minobe, 2002). The far reach- 

 ing effects that climate change has 

 on an ecosystem are not well defined, 

 but many studies have shown strong 

 correlations between climate change, 

 fish recruitment, and plankton pro- 

 duction in the North Pacific (Brodeur 

 and Ware, 1992; Anderson et al., 1997; 

 Anderson and Piatt, 1999; Brodeur 

 et al., 1999; Clark et. al., 1999; Hare 

 and Mantua, 2000; Zhang et al., 2000; 

 Hollowed et al., 2001; Sugimoto et al., 

 2001; Conners et al., 2002; Hunt et 

 al., 2002; Wilderbuer et al., 2002). 

 During periods of climatic change, 

 some fishes may not be well adapted 

 to dramatic changes over a short time 

 scale (1-10 years), whereas others 

 may proliferate in a more hospitable 

 environment. Key triggers of regime 

 shifts and the extent to which species 

 will respond remain unclear; however, 

 evidence may indicate that species 



diversity is correlated with primary 

 production in many systems, and the 

 two may be interdependent (Rosenz- 

 weig and Abramsky, 1993; Waide et 

 al., 1999). A biodiversity index can 

 be useful for monitoring the stability, 

 health, and productivity of an ecosys- 

 tem, as well as for aiding manage- 

 ment, by tracking exogenous changes 

 and their far reaching effects on spe- 

 cies. In the present study, I used bio- 

 diversity indexes, reflecting richness 

 and evenness, as indicators of species 

 composition changes and related these 

 changes to regime shift events for the 

 eastern Bering Sea (EBS) shelf. 



Methods 



Data were synthesized from a con- 

 tinuous 24-year period of standard- 

 ized groundfish surveys conducted by 

 the Alaska Fisheries Science Center 

 (AFSC) on the EBS shelf from 1979 

 through 2002; additional estimates 

 from 1975 were included. Biodiversity 

 indexes (species richness and even- 

 ness) were calculated from biomass 

 estimates for two fish guilds, flatfish 

 and roundfish, in each of the inner, 

 middle, and outer domains of the EBS 

 shelf. Biodiversity indexes were plot- 

 ted for each fish group and domains 

 and examined for changes over the 

 study period. The observed changes 

 were correlated with regime shift and 

 ocean climatic change events for the 

 EBS. 



Data collection 



Gear, station location, sampling pro- 

 cedures, and time of year of the AFSC 



