236 



Fishery Bulletin 104(2) 



and Mantua, 2000). Biodiversity indexes are a robust 

 measure for large ecosystem monitoring and possible 

 indicators of resulting regime shift phenomenon from 

 climatic change based on an assemblage's long-term 

 responses. Hare and Mantua (2000) summarized over 

 100 studies from the eastern North Pacific identifying 

 two distinct periods of change or "regime shifts" in 1977 

 and 1989. Recently. Stabeno et al. (2001) and Hunt 

 and Stabeno (2002) suggested the possibility of a third 

 period of significant climatic change in the late 1990s 

 for the northeastern Pacific. Although environmental 

 changes may be readily identified, the ecosystem fauna 

 may respond more slowly, or in ways not immediately 

 obvious; however the changes may be persistent and 

 far reaching. According to survey data, the last 20 

 years have proven to be a very hospitable environment 

 iFor many flatfish species in the EBS, where populations 

 such as northern rock sole and arrowtooth and Kam- 

 chatka flounder have rapidly expanded since the late 

 1970s. Biodiversity indexes are significantly higher than 

 they were 20 years ago for flatfish as a group and have 

 remained high and unchanged. The biodiversity indexes 

 for flatfish guild corroborate the timing of the strong 

 regime shift reported in the late 1980s. An inflection 

 around 1990 is the strongest evidence of a regime shift 

 from the biodiversity indexes. It would be expected that 

 a purely biological response to a climatic event may lag 

 by a time period, perhaps accounting for a later year 

 than previously reported. 



Survey data indicate that many roundfish species 

 have not fared as well as flatfish species and biodiversity 

 indexes are significantly lower now than 20 years ago. 

 The roundfish guild has undergone a significant reorga- 

 nization in which a large group of species have declined 

 and a single species has become dominant, causing bio- 

 diversity to be suppressed. The regime shift is reflected 

 in the roundfish biodiversity around 1988. which agrees 

 with the results of other reported studies. 



Although EBS productivity has increased through the 

 1970s and 1980s and remained high through the 1990s, 

 the trend in the ecosystem is towards fewer or single 

 dominant species. The decline of many nonexploited spe- 

 cies in the EBS is difficult to explain with the current 

 regime shift theories. Unfortunately, a lack of informa- 

 tion on the life history of the large number of species, 

 such as poachers, sculpins, eelpouts, and skates in the 

 EBS hinders a complete understanding of recruitment 

 success or failure. 



Acknowledgments 



I thank all the dedicated scientists, vessel skippers, and 

 crew for their hard work over the years collecting data 

 and G. Walters and M. Martin for assistance with data 

 analysis. Also I thank the reviewers for their contribu- 

 tions in improving this manuscript. The reviewers were 

 D. Somerton, G. Walters, J. Orr, S. Kotwicki, G. Stauffer, 

 A. Hollowed, and an unknown journal reviewer. Thank 

 you all. 



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