Dressel and Norcross: Using poststrafication to improve abundance estimates from multispecies surveys 



475 



Q. 

 CD 



a 



Rock sole 



zero catch 

 A nonzero catch 



habitat area 



Q. 60 

 CD 



Q 



Percent sand in substrate 



VL^yzt&m 



• •- 



, I high fish-density 



Yellowfin sole 



zero catch 

 A nonzero catch 



Percent sand in substrate 



; habitat area 

 ! i high fish-density 



Pacific halibut 



zero catch 

 A nonzero catch 



I habitat area 



i | high fish-density 



Percent sand in substrate 





& 60 

 Q 



I- - -A-AI A 

 !*** A 



-•"I*" : i Flathead sole 



i 



A*A 



. A 



A* 



A . 



A*A i A 



A-*- - A -A_> 



A' 



' A \ 



zero catch 

 A nonzero catch 



[ I habitat area 

 J ' high fish-density 



Percent sand in substrate 



Figure 3 



Summary of 1991-96 tows, in relation to depth and percent sand. 

 Tows are divided into zero and nonzero catches for each species. The 

 dotted line separates the depth and percent sand characteristics of 

 habitat and nonhabitat areas. The dashed line separates the depth 

 and percent sand characteristics of high and low fish-density areas 

 within the habitat area. 



rock sole had a 10% negative disproportion of samples 

 in the HFD area, Pacific halibut had a 3% negative 

 disproportion of samples in the HFD area, and flathead 

 sole had a 28% negative disproportion of samples in the 

 HFD area. For yellowfin sole, the average distribution 

 of samples between the high and low fish-density areas 

 was in direct proportion to the size of the areas, i.e., 

 there was no disproportion of samples. 



Two measures were used to characterize the distribu- 

 tion of a species within their habitat: the proportion of 

 zero catches and the mean of nonzero catches in high 

 and low fish-density areas. As expected, for all species 

 the average proportion of zero catches over all sites 

 was greater than the proportion of zero catches in the 

 habitat or HFD areas (Table 3). For rock sole, yellowfin 

 sole, and flathead sole, the average proportion of zero 



