FISHERY BULLETIN: VOL 76, NO. 3 



Table 4. — Results of an analysis of variance (ANOVA) of the numbers and weights of fishes caught per square meter or 

 per tow'; * indicates P<0.05; ** P<0.01. R^ (coefficients of determination) values are given below. 



'An ANOVA using a square root transformation for the data on all species combined per tow and per square meter gave similar significance effects 

 The ANOVA was unbalanced because of unequal numbers of observations per station, season, depth, etc Effects were tested using the extra sum of 

 squares principle (Searle 1971) 



The biomass of Pacific sanddab. on the other 

 hand, showed opposite trends (P 0.05) and was 

 large on sandy sediments and small on silt or clay 

 sediments ( see also Day and Pearcy 1968; Barss et 

 al. see footnote 8). Since the effect of sediment was 

 not significant for total fish catch by numbers or 

 weight sandy stations with low percent organic 

 carbon, apparently did not support a markedly 

 lower abundance of demersal fishes (Table 2). Al- 

 though adult Dover sole show a strong preference 

 for mud or silt bottom (Barss et al. see footnote 8; 

 Demory see footnote 6), this trend was not appar- 

 ent for the small Dover sole caught inshore of 

 Heceta Bank in this study. 



A sediment-season effect was indicated for slen- 

 der sole. They were caught in larger numbers per 

 tow and weight per square meter (P<0.05) at the 

 stations with a low percentage of sand (6-8) in the 

 winter than the summer. 



Depth Effects 



The slope of the regression between depth and 

 number and weight per tow of Pacific sanddab was 

 significant (P<0.01) and negative. Catches per 

 square meter on a number and weight basis gave 

 the same trends (P<0.05). Sanddab were most 

 abundant in shallow water. Weight of rex sole per 

 square meter and per tow and total fish numbers 

 and weight per tow also tended to decrease 

 (P<0.05) with depth. 



Depth-season interactions were significant on a 

 square meter basis for all species combined 

 (number and weight) and for numbers of rex and 

 Dover soles. These effects were caused by appreci- 

 ably larger catches in deep water in winter than 

 summer. Seasonal differences were small in shal- 

 low water. This trend for lower catches on the 



outer edge of the continental shelf during summer 

 than winter was obvious for Pacific sanddab. They 

 were completely absent from the deep stations (2, 

 6, 8) during the summer but were present at all 

 stations during winter. Seasonal bathymetric 

 migrations, with spawning migrations into deep 

 water in the winter and return to relatively shal- 

 low depths in the summer, have been described for 

 Dover sole and rex sole by Hagerman (1952), 

 Harry (1956), Alverson (1960), and Demory 

 (1971). Such movements could explain these 

 depth-season effects. 



Seasons 



No significant seasonal differences were de- 

 tected, indicating little seasonal variation in 

 catches of these species when all stations are com- 

 bined. 



Year Effect 



On the basis of numbers and weight per square 

 meter and per tow, more fishes were captured in 

 1969 and 1968 than in 1970 at all stations (Figure 

 3). This trend was significant (P<0.01) for all 

 species combined and for rex sole, Dover sole, and 

 Pacific sanddab. Year effects were also indicated 

 for slender sole (P<0.05). I have no cogent expla- 

 nation for these large annual variations. They 

 could represent actual variations in abundance or 

 availability, due to natural events or increased 

 fishing activity, or to undetected changes in sam- 

 pling efficiency. Dominant year classes have been 

 reported for these flatfishes off Oregon (Demory 

 and Robinson see footnote 9), which may contri- 

 bute to these annual differences, though changes 

 in length-frequency distributions were not obvi- 

 ous over this 2-yr period. 



636 



