Markle et al : Metamorphosis of Microstomus pacificus 



295 



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Standard Length (mm) 



Figure 12 



Relationship between the SINT/BDIA ratio and standard 

 length during development of Dover sole Microstomus pacifi- 

 cus. Symbols represent Stage 1 ( • ), Stage 2 (A), Stage 3(B), 

 Stage 4 (O). and Stage 5 (A). 



specimens after March (Fig. 13). Ail small larvae (< 10 

 mmSL) were collected on one day, 12 June 1971, be- 

 tween 50 and 67km offshore, whereas larger larvae 

 from June were collected considerably further offshore, 

 108-275km on various dates. There appears to be little 

 or no coherent size progression after the 24.5 mm mode 

 in March. Specimens >30mm are found in every 

 month, and weakly-defined modes can be visualized 

 around 50 mm in June, July, and September. Accel- 

 erated growth in April and May would seem to be re- 

 quired if the modal size were to double from about 

 25 mm in March to 50 mm in the second summer of life. 

 Paradoxically, April is a time when micronekton bio- 

 mass is normally low (Pearcy 1976). 



Stage-2 specimens were caught from June to Febru- 

 ary (Table 4). The coherent progression of metamor- 

 phic scores for Stage-2 larvae indicates that metamor- 

 phosis begins as early as June; Stage-3 larvae are 

 present as early as December and as late as March. 

 About 6 months seems to be required to progress 



4 5 6 7 8 9 10 11 12 1 2 3 



Month of Capture 



Figure 13 



Relationship between standard length and month of capture 

 for Dover sole Microstomus pacificus, Stages 1-4 collected 

 in midwater trawls. Stars indicate modes determined by modal 

 progression analysis in larvae <40mmSL. Stage-2 and -3 

 specimens are circumscribed by lines. 



Table 4 



Seasonal catch-per-effort for planktonic Stage-2 and Stage-3 

 Dover sole Microstomtis pacificus larvae off Oregon. N = 

 number of trawls. 



No. of Stage 2 based on 

 metamorphic score 



Month of No. of 



collection N 12345678 Stage 3 



January 128 ------2- 2 



February 167 -------2 4 



March 147 ________ 2 



April 201-------- 



May 106-------- 



June 278 1------- 



July 291 -----1-- 



August 303 1 1 ----- - 



September 217-1-421-- 



October 129 ----11-1 



November 217 — -----2 1 



December 126 ------26 2 



through Stage 2. 



The seasonal distribution of Stage-3 larvae in ben- 

 thic samples was consistent with their planktonic dis- 

 tribution (Table 5). During bimonthly sampling in 1989, 

 98.5% of Stage-3 specimens were caught in January 

 or March. Five Stage-3 specimens were caught in May, 

 and most new settlers appear to be in Stage 5 by July 



