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



565 



100 200 300 400 500 

 Depth (m) 



140 180 220 260 

 Julian day 



2^ 



4*10' SMO' 12*10' 

 Area swept (m2) 



1000 2000 

 Alongshore distance (km) 



■84 '87 '90 '93 '96 

 Year 



160 172 



Gear type 





Figure 2 



Estimated trends in number of species per haul by depth, alongshore 

 distance, Julian day, year, area swept, and gear type. Alongshore dis- 

 tance was measured along the 200-m depth contour from east to west. 

 Major geographic regions from east to west are Southeast (SE), Yaku- 

 tat (Yak), Kodiak (Kod), Chirikof (Chi), and Shumagin (Shu). Dashed 

 lines indicate approximate 95% confidence limits of the regression 

 lines. Horizontal lines in lower right plots indicate mean response 

 with 95% pointwise confidence intervals. Width of bars is proportional 

 to number of observations. Fitted lines in each panel are adjusted for 

 the effects of all other variables. Standardized effects in each plot 

 {y-£ixes, no units) are on the same scale for comparison. Effects are 

 standardized because the estimated CPUE at a given value of a vari- 

 able is dependent upon the levels of all other variables. 



to decrease during the last month of the survey season 

 and showed some variation across years (Fig. 2). There 

 was no consistent trend in species richness with tempera- 

 ture (not shown). One of the Japanese trawls (gear type 

 717, Fig. 2) tended to have a much smaller number of 

 species per haul on average, suggesting a low catchability 

 for at least some species. Residuals from the best model 

 were close to normally distributed (Fig. 3, A and B) and 

 showed no apparent trends with any of the covariates or 

 over time. 



Only a very small portion of the variability in species 

 diversity (Shannon-Wiener index) was accounted for by 

 the best regression (Pseudo-7-2=0.17). Depth had the stron- 

 gest effect on species diversity with highest diversities ob- 

 served at intermediate depths (Fig. 4). Diversity generally 

 increased with the number of species, which showed a very 

 similar trend with depth (Fig. 2). Diversity was higher in 

 the eastern Gulf and decreased west of Prince William 

 Sound (Figs. 4 and 5). It showed little variation over time, 

 both within the survey period and across years. However, 



