FISHERY BULLETIN VOL 76, NO 3 



(<50 mm) and age-groups III- V (200-250 mm) rex 

 sole (see Hosie and Horton 1977 for age-length 

 data) preferentially inhabit deep waters on the 

 outer edge of the continental shelf while inter- 

 mediate sizes (75-150 mm) inhabit shallower wat- 

 ers of the inner shelf. The peak of young-of-the- 

 year rex sole at 200 m corroborates the conclusion 

 of Pearcy et al. (1977) about the depth of larval 

 settlement and the nursery ground for early 

 benthic life. They concluded that rex sole larvae 

 settle to the bottom mainly on the outer continen- 

 tal shelf during the winter when they are >50 mm 

 SL. Powles and Kohler (1970) and Markle (1975) 

 believed that the nursery grounds ofGlyptocepha- 

 lus cynoglossus are also in deep waters off the east 

 coast of the United States. 



Small Pacific sanddab (<70 mm) composed a 

 larger proportion of the catch at 102 m where sand 

 was 28'7f of the sediment (Station 23) than at 74 

 and 102 m where sand made up over 647f of the 

 sediment (Stations 22, 15) (Figure 5). Young 

 sanddab appear to inhabit deeper water with finer 

 sediments in early life and then aggregate on 

 sandy bottom areas in shallow water where they 

 often dominate the demersal fish fauna. Hence, 

 this trend of decreasing depth with increasing age 

 is similar to that found for rex sole. 



SUMMARY 



1. Demersal fishes were sampled at seven sta- 

 tions on Oregon's central continental shelf at vari- 



01 

 Q. 



100 150 200 



STANDARD LENGTH (mm) 



250 



Figure 5.— Length-frequency data for Pacific sanddab at .sta- 

 tions with 84-99'7f sand (above) and 28% sand (below). 



ous seasons of the year during a 2-yr period. A 

 fine-meshed, 3-m beam trawl was used in order to 

 quantitatively sample small flatfishes. The sta- 

 tions ranged from 74 to 195 m deep and had sedi- 

 ment types ranging from nearly lOO'/r sand to 

 clayey-silts with about 3''/< sand. 



2. Stations were selected in an attempt to sepa- 

 rate the effects of depth and sediment on the as- 

 semblages of fishes and abundances of common 

 species. Three station-pairs were recognized that 

 had similar sediment types but were located at 

 different depths. Separation of sediment and 

 depth effects was complicated however by differ- 

 ences in measured (and possibly unmeasured) fac- 

 tors between station pairs. 



3. Two general assemblages of fishes were re- 

 cognized on the basis of species composition of 

 fishes by numbers, biomass per square meter of 

 dominant species, and similarity indices among 

 the seven stations. These were a shallow water 

 (74-102 m) assemblage dominated numerically by 

 Pacific sanddab, and a deepwater ( 148-195 m) as- 

 semblage dominated by slender sole. 



4. Species diversity iH) varied between 1.6 and 

 2.5 except at the shallow, sand station where it 

 was only 0.7. Dominance was pronounced at this 

 station: 86''^^ of all the individual fishes captured 

 were Pacific sanddab. The largest number of spe- 

 cies (34 or 35) was recorded for the three deep 

 stations. These values of H are similar to others 

 for temperate, demersal fish communities. 



5. Similarity indices of the species composition 

 of fishes were high for two of the three station pairs 

 with similar sediments. However, indices were 

 also high among the four shallow stations of differ- 

 ing sediment types. Stations that were near each 

 other geographically were similar, indicating the 

 possibility of a proximity effect, but high similar- 

 ity was also found among deep stations, one of 

 which was over 65 km from the others. 



6. An analysis of variance of the number and 

 weight per square meter and per tow of Dover, rex, 

 and slender soles. Pacific sanddab, and all species 

 combined indicates some effects of sediments and 

 depth. Largest catches of slender sole were at the 

 clayey-silt station pair, and largest catches of 

 Pacific sanddab were on sandy sediments. Catches 

 of Pacific sanddab were significantly larger at the 

 shallow stations. Catches of rex sole and all 

 species combined also tended to decrease with in- 

 creasing depth. 



7. Differences in the length-frequency distribu- 

 tions of Pacific sanddab and rex sole were corre- 



638 



