PEARCY: DISTRIBUTION AND ABUNDANCE OF SMALL FLATFISHES 



Pacific sanddab, 37 to 90 m; slender sole, 90 to 183 

 m; small (ssl80 mm TL) rex sole, 55 to 183 m; and 

 small («180 mm TL) Dover sole, 55 to 150 m. 

 Therefore the stations sampled in my study were 

 not shallow enough to include all of the major 

 depth range inhabited by Pacific sanddab, rex sole, 

 or Dover sole. Furthermore, large Dover and rex 

 soles are known to be distributed in deeper waters 

 of the upper continental slope off Oregon (Demory 

 1971; Hosie see footnote 5; Demory^), regions un- 

 sampled in this study. 



The ranks of the dominant species as well as the 

 presence of other species implies a shallow water 

 (74-102 m) and a deepwater (148-195 m) as- 

 semblage of fishes. Cymatogaster aggregata and 

 Parophrys vetulus ranked within the top 10 

 species at the shallowest Stations 22, 7, 23, and 15 

 but not at deep Stations 6, 2, and 8 where they 

 were usually absent. Xeneretmus latifrons and 

 Sebastes juveniles, on the other hand, were only 

 abundant at the deep stations. 



Similarity among the stations was calculated as 



Table 3. — Indices of similarity (SIMI) for the species compo.si- 

 tion of fishes among each of the seven stations. Stations are 

 arranged by depth. 



SIMI 



2 PuP2i 



1=1 



(Sd^){Sd2) 



where S is the number of species present at both 

 stations; P i, is the proportion of the /th species at 

 one station; P 2, is the proportion of the zth species 

 at a second station; and iSd ^ ) (Sc?2 ' is the product 

 of the square roots of estimators of Simpson's di- 

 versity index for Stations 1 and 2. This measure of 

 similarity was used because it is analogous to a 

 correlation coefficient, relates closely to Simpson's 

 measure of concentration, and has maximum and 

 minimum values of 1 and (Mclntire and Moore 

 1977). 



Two assemblages of fishes, a deep and a shallow 

 one, were evident based on high similarity in the 

 species composition among the three deepest sta- 

 tions (2, 6, 8) and among three of the four shallow 

 stations (15, 22, 7) (Table 3). Similarity between 

 stations of each of these two groups varied from 

 0.85 to 0.95. Station 23, another station at about 

 100 m (like Stations 7 and 15) also had a fairly 

 high similarity with the other shallow water sta- 

 tions. It was similar to Station 7 (0.92 m) but less 

 similar to Stations 15 and 22 (0.77 and 0.65 m). 

 The benthic environment of Station 23 differed 



•^Demory, R. L. 1975. The Dover sole. Oreg. Dep. Fish 

 Wildl. Inf. Rep. 75-4, 4 p. 



from the other three shallow stations in that it had 

 more than twice the percentage of clay and silt 

 found at Station 22, 7, or 15, where sand was the 

 major sediment component. 



Based on sediment composition two of the three 

 station pairs were very similar (Table 3): Stations 

 22 and 15 (SIMI = 0.94), and Stations 6 and 8 

 (SIMI = 0.91). Stations 7 and 2, another station 

 pair, at 100 and 190 m, had a similarity of only 

 0.26. This disparity may be explained by the thin 

 layer of silt overlying a predominantly sandy sed- 

 iment at Station 2. For epifaunal organisms the 

 sediment type at this station may have been more 

 similar to that at Stations 6 and 8 than any other 

 stations. This may explain why Station 2 is so 

 similar in species composition to Stations 6 and 8. 

 However Station 7 showed high similarity (0.92- 

 0.93) with Stations 15 and 23, stations with differ- 

 ent sediment types but both at the same depth. 

 Thus clear separation of the effects of depth and 

 sediment was not always possible. Nevertheless 

 the most consistent and obvious assemblages were 

 correlated with depth. Stations of different sedi- 

 ment types had high similarity within the shallow 

 water assemblage. 



These results agree with those of Day and 

 Pearcy (1968) who studied the distribution of de- 

 mersal fishes from 40 to 1,829 m along a transect 

 just north of Heceta Bank. They delineated a 

 species association at depths of 42-73 m on sandy 

 sediments with Pacific sanddab as the dominant 

 species and an association at 119-199 m on silty- 

 sand sediments where slender sole predominated. 

 Because the same species associations sometimes 

 were found on different sediment types, they felt 

 that factors other than sediment texture may gov- 

 ern the distribution of fish assemblages. 



Diversity 



The number of species of fishes collected was 



633 



