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



575 



60 N 

 58 N 

 56N 

 54°N 

 52-N 



1 70 W 



160W 



150W 



140'W 



170W 



160'W 



ISO'W 



140°W 



''tS, 



%^ 



:t?«" 



». •. 



1996 



170"W 



160'W 



150"W 



MO'W 



Figure 11 



All sampling locations l • ) where CPUE of skates (Rajidae) exceeded 300 

 kg/km2 in 1984, 1990, and 1996. 



recent SeaWifs data (Falkowski et al., 1998, see web site: 

 http://seawifs.gsfc.nasa.gov/SEAWIFS.html). Third, the 

 east-west gradient in productivity and biomass is consis- 

 tent with differences in upwelling, which is generally more 

 pronounced and more frequent in the western GOA ( Reed 

 and Schumacher, 1986). Fourth, the presence of strong 

 tidal currents in the vicinity of Kodiak Island (Kowalik*) 

 (see also Isaji and Spaulding, 1987) may further enhance 

 demersal productivity (Mann and Lazier, 1991). Fifth, 

 strong alongshore currents, advection, and nutrient input 

 from major rivers may contribute to a higher productivity 

 in the western GOA and around Kodiak Island. Finally, 

 lower productivity in the eastern GOA may be related 

 to the limited shelf area in this part of the Gulf Broader 

 shelf areas such as that in the central Gulf of Alaska 

 around Kodiak Island are generally believed to be more 

 productive because of increased nutrient enrichment. 



•^ Kowalik, Z. 2000. Personal commun. Institute of Marine 

 Sciences, University of Alaska Fairbanks, Fairbanks, Alaska 

 99775. 



There is evidence from many areas around the world 

 that high productivity is associated with a high biomass 

 of demersal fishes and vice versa. For example, Farina et 

 al. (1997) showed that on the continental shelf and upper 

 slope in the Mediterranean Sea upwelling areas with high 

 primary productivity correlate with a high biomass in the 

 upper trophic levels, including demersal species, and with 

 low species diversity. In contrast, low productivity areas 

 have the greatest species richness and a smaller biomass 

 of demersal fish. Our study suggests that the same gen- 

 eral patterns observed by Farina et al. (1997) may hold 

 for the continental shelf and upper slope of the GOA. The 

 productive western GOA is characterized by a high demer- 

 sal biomass and relatively low species diversity, which is 

 attributable to the presence of a few highly abundant spe- 

 cies of flatfish and gadids (including arrowtooth flounder. 

 Pacific cod, walleye pollock). In contrast, the eastern GOA 

 appears to be less productive and is characterized by a low 

 biomass of demersal fishes and high species diversity, due 

 to the presence of a large number of rockfish species with 

 relatively low abundances. 



