Sakuma and Larson: Distribution of Cithanchthys sordidus and C. stigmaeus 



519 



Results 



Overall abundances and seasonal abundance pat- 

 terns of the two sanddab species were variable (Fig. 

 2). In 1991, the abundance of both species increased 

 monotonically during the May-June sampling period, 

 whereas in 1987 and 1988, catches were relatively 

 high in April but showed a marked decrease by the 

 end of May-June, suggesting that pelagic sanddab 

 abundance frequently declines during the April-June 

 period (Fig. 2). However, catches of Pacific sanddabs 

 in April of 1990 were low relative to May-June, and 

 the May-June catches in 1988 and 1989 did not 

 change monotonically, suggesting interannual varia- 

 tion in seasonal patterns (Fig. 2). Although April- 

 June abundances were variable (Fig. 2), the inter- 

 annual variation in year-class strength of pelagic 

 sanddabs could not be determined without complete 

 seasonal data. 



In both species, SL increased asymptotically with 

 metamorphic stage (Fig. 3). In addition, the range of 

 lengths within each stage was quite large (Fig. 3). 

 Pacific sanddabs were generally larger than speck- 

 led sanddabs at each metamorphic stage (Fig. 3). 

 Although stage-2 individuals were significantly 

 smaller than individuals of subsequent stages, the 

 mean SL's did not differ significantly among the three 

 later stages (oc=0.05, df=76 for Pacific sanddabs and 

 df=75 for speckled sanddabs). Whereas SL increased 

 asymptotically with metamor- 

 phic development in both 

 sanddabs, otolith diameter 

 showed a linear increase (Fig. 

 4). In addition, otolith diam- 

 eter increased dramatically 

 with SL (Fig. 5), and mean 

 otolith diameter increased sig- 

 nificantly with each successive 

 stage (a=0.05, df=76 for Pacific 

 sanddabs and df=75 for speck- 

 led sanddabs). It appears that 

 metamorphosis in sanddabs is 

 possible at a range of sizes (30 

 mm to >50 mm SL in Pacific 

 sanddabs and 25 to 40 mm SL 

 in speckled sanddabs) and that 

 once initiated, there is little 

 growth in length but continued 

 otolith growth (Figs. 3-5). 



In general, Pacific sanddabs 

 were relatively evenly distrib- 

 uted throughout the water col- 

 umn; there was a slight de- 

 crease in abundance with in- 

 creasing depth (Table 1). Sepa- 



rate analyses of the April and May-June surveys 

 showed similar results (Table 1). 



In contrast to Pacific sanddabs, speckled sanddabs 

 were significantly more abundant in shallow and 

 mid-depth trawls than in deep trawls (Table 2). Ana- 

 lyzed separately, the May-June surveys showed a 

 similar pattern to the overall analysis, but the April 

 surveys showed less distinct differences in depth dis- 

 tribution (Table 2). The April surveys showed a trend 

 of decreased abundance in deep trawls relative to 

 shallow and mid-depth trawls, but the differences 

 were not significant (Table 2). 



Depth distributions differed among the metamor- 

 phic stages of both sanddab species. Stage-2 individu- 

 als of Pacific sanddabs were significantly more abun- 

 dant in mid-depth trawls than in deep trawls, with a 

 trend for increased abundance in shallow trawls ver- 

 sus deep trawls (Table 3; Fig. 6). Although both stage- 

 3 and stage-4 sanddabs showed a relatively even dis- 

 tribution throughout the water column (with no sig- 

 nificant differences among depths), stage-3 individu- 

 als tended to be less abundant with increased depth, 

 whereas stage-4 individuals tended to be more abun- 

 dant with increased depth (Table 3; Fig. 6). Stage-5 

 individuals were generally less abundant in shallow 

 trawls and showed a tendency toward increased 

 abundance with increased depth (Table 3; Fig. 6). 



In speckled sanddabs, stage-2 individuals were 

 significantly more abundant in mid-depth trawls 



Pacific Sanddabs 



April 

 May-June - 



Speckled Sanddabs 



i 5 



S 3 



i 



■a i 



(1 5 



t 



\K 



1987 



1988 



1989 



1990 



1991 



1987 



1988 



1989 



1990 



1991 



Year 



Figure 2 



Means and standard errors of the log-transformed abundances of Pacific and speck- 

 led sanddabs, Citharichthys sordidus and C. stigmaeus, collected at standard sta- 

 tions during April and May-June 1987-91 (means of the three sweeps for the May- 

 June surveys are connected by a line). 



