Mueter and Norcross: Spatial and temporal patterns in ttie demersal fish community off Alaska 



577 



Hemithptcrus holini 

 Depth (m) Slnim.igii Chirikof Kodi.ik Yakutat SouthtMst 



0-100 CPUE 



FO 



Myoxocephalus spp. 



SInimagin Chirikof Kodiak Yakiil:il Southeast 



St-^ 



100-200 CPUE 

 FO 



200-300 CPUl 

 FO 



300-500 CPUl 

 FO 



Lcpidupselta spp. 



Figure 13 



Changes in CPUE-where-present and frequency of occur- 

 rence (FO) by depth stratum and area for three species that 

 decreased significantly over time. Significant changes at the 

 59c level are indicated by '+' or '-'. Changes that were signifi- 

 cant at the IVc level are indicated by '-i-i-' or '-'. Areas-depth 

 strata where a species was not caught in any of the five 

 survey years are shaded. Significance was tested by using 

 generalized linear models including gear effects (see text). 



dor shelf from 1978 to 1991 and dramatic changes in the 

 spatial distribution of groundfish assemblages after 1987. 

 They attributed the changes primarily to intense exploita- 

 tion, although environmental effects were likely at work 

 as well. Similarly, on the continental shelf off Northwest 

 Spain, significant decreases in commercial groundfish spe- 

 cies, and a concurrent increase of several noncommercial 

 species, can be attributed to a combination of fishing and 

 environmental changes (Farina et al., 1997). 



The recent period of stability in the GOA can be con- 

 trasted with a period of dramatic changes in the late 

 1970s and early 1980s that affected many parts of the 

 North Pacific ecosystem including groundfish communi- 

 ties (e.g. Beamish, 1995). There is strong evidence of a 

 shift in species composition of at least the nearshore 



demersal communities during this time period (Piatt and 

 Anderson, 1996; Anderson and Piatt, 1999; Mueter and 

 Norcross, 2000). Whether similarly dramatic changes oc- 

 curred in offshore demersal communities is not known due 

 to the lack of long time series for most species. 



Estimated biomass trends for important commercial 

 species based on recent stock assessment data (NPFMC^) 

 and historical surveys (Ronholt et al.'') suggest that the 



Ronholt, L. L., H. H. Shippen, and E. S. Brown. 1978. Demer- 

 sal fish and shellfish resources of the Gulf of Alaska from Cape 

 Spencer to Unimak Pass 1948-1976: a historical review. Proc. 

 rep., vols. 1-3, 872 p. Northwest and Alaska Fisheries Center, 

 National Marine Fisheries Service, NOAA, 7600 Sand Point 

 Way N.E., Seattle, WA. 



