618 



Fishery Bulletin 104(4) 



0.6 



0.4 - 



0.2 



-0.2 



-0.4 - 



-0.6 



Lower main 

 channel 



Lower side 

 channel 



Upper 

 estuary 



English sole 

 Starry flounder 



-.*--- Pacific sanddab 

 -■— - Sand sole 



Figure 2 



Average density anomaly (and standard error bars) for Eng- 

 lish sole {Pleuronectes vetulus). Pacific sanddab iCitharichthys 

 sordidus), sand sole (Psettichthys melanostictus), and starry 

 flounder iPlatichthys stellatus) by habitat type across all study 

 estuaries, months, and years. 



necessary to standardize the data within each estuary. 

 We used the normalized anomaly (Zar, 1974) of flatfish 

 densities as the dependent variable to compare use of 

 habitats within estuaries for each species, where 



sd„. 



In this equation the subscript i refers to an individual 

 density from a trawl survey site within an estuary- 

 month-year combination, emy refers to the estuary- 

 month-year combination where a trawl survey occurred, 

 and X and sd are the mean and standard deviation of 

 all trawl surveys occurring in that estuary-month-year 

 combination. By using the anomaly of the densities, we 

 reduced the variation in the data that was attributed to 

 estuarine, seasonal, and interannual sources in order to 

 concentrate solely on the within-estuary component of 

 variation. For example, if the average catch of Pacific 

 sanddab was 1000/ha for the Grays Harbor estuary in 

 June 2000, individual trawl hauls from Grays Harbor 

 in June 2000 with catches <1000/ha would have a nega- 

 tive density anomaly, whereas trawl hauls with Pacific 

 sanddab catches >1000/ha would have a positive density 

 anomaly. 



The density anomalies were analyzed by using analy- 

 sis of variance (Zar, 1974). The full model used to ana- 

 lyze spatial distributions of each species included the 

 main effects of habitat type, month of survey, year of 

 survey, and estuary, as well as estuary-habitat, month- 

 habitat, and year-habitat interaction terms. The inter- 

 action terms were specifically included to test the hy- 

 potheses that spatial distribution of each flatfish species 

 was consistent across estuaries, years, and months. All 

 significant (P<0.05) main effects and interactions were 

 compared for significant differences among effect levels 

 by using the least squares mean approach as a post hoc 

 test with a Tukey's adjustment for multiple comparisons 

 (Zar, 1974). 



Results 



Juvenile Pacific sanddab collected during the trawl 

 surveys ranged in length from 23 to 150 mm TL. The 

 analysis of Pacific sanddab density anomalies for habitat 

 types within estuaries resulted in significant differences 

 among habitats in the estuaries. There were signifi- 

 cantly higher density anomalies in lower main channel 

 habitats and significantly lower anomalies in upper 

 estuary sites (Fig. 2). Lower side channels usually had 



