Sakuma and Larson: Distribution of Citharichthys sordidus and C stigmaeus 



525 



ossification of bony structures (Ahlstrom et al., 1984). 

 The large increase in otolith size observed in later 

 metamorphic stages of both sanddab species may be 

 attributable to the transition from a planktonic form 

 to a benthic form. Jenkins (1987) observed acceler- 

 ated otolith growth in relation 

 to growth in length at the be- 

 ginning of metamorphosis for 

 the flatfish Rhombosolea tap- 

 irina, which resulted in signifi- 

 cant alterations in otolith incre- 

 ment morphology. One alter- 

 ation in otolith morphology ob- 

 served in pelagic stage Pacific 

 sanddabs was the formation of 

 accessory growth primordia. 

 Accessory growth primordia 

 first occurred in stage-3 indi- 

 viduals and completely enclosed 

 the otolith by stage 5 (Broth- 

 ers 1 ). Toole et al. (1993) found 

 that the initiation of accessory 

 primordia formation was coin- 

 cident with the onset of eye mi- 

 gration in Dover sole, Micro- 

 stomas paciftcus, and that the 

 completion of accessory primor- 

 dia formation occurred either 

 during the final stages of eye 

 migration in pelagic individuals 

 or shortly after settlement. 



Metamorphosis in some flat- 

 fish can take place in as little 

 as five hours, as in Cynoglossus 

 macrostomus (Ahlstrom et al., 

 1984), or up to nine months, as 

 in Microstomas pacificus (Markle 

 et al., 1992). The small increase 

 in length seen in metamorphos- 

 ing sanddabs (Figs. 3 and 5) 

 suggests a relatively rapid meta- 

 morphosis relative to growth. 

 However, if metamorphosis oc- 

 curred very rapidly, then the 

 probability of collecting meta- 

 morphosing specimens would be 

 small (Laroche et al., 1982; 

 Ahlstrom et al., 1984). The large 

 numbers of later stages col- 

 lected in 1991 and the large 

 otolith sizes in later stages sug- 

 gest that metamorphosis in 

 both sanddab species occurs 

 over a more prolonged period of 

 time (Figs. 5, 8, and 9). Prelimi- 



nary results from Pacific sanddab otoliths indicate 

 that the transition from stage 3 to stage 5 takes ap- 

 proximately three weeks (Brothers 1 ). Kendall's (1992) 

 data on otolith radius at age indicate that the tran- 

 sition from individuals with otolith radii correspond- 



Pacific Sanddabs 



1991 



Sweep 1 



Speckled Sanddabs 



Sweep 2 



Sweep 3 



123 122 123 



Longitude (°W) 

 Figure 9 



Salinity contours at the surface during the May-June survey of 1991 with overlaid 

 abundances of stages 2 (represented by squares) and 5 (represented by asterisks) of 

 Pacific and speckled sanddabs, Citharichthys sordidus and C. stigmaeus. Size of 

 each symbol is proportional to the abundance. 



