PEARCY ET AL.: DISTRIBUTION AND DURATION OF PELAGIC LIFE OF LARVAE 



high off Brookings, Oreg. Mean abundance of rex 

 sole larvae was lowest off the Columbia River 

 (Table 7). 



Certainly the distribution of these larvae is 

 related to both alongshore and inshore-offshore 

 currents over the continental shelf and slope as 

 well as to spawning location of adults. The 

 predominant flow throughout the year off Oregon 

 is alongshore, yet current reversals occur ( south in 

 summer, north in winter) and subsurface counter- 

 currents are present (Huyer et al. 1975). There is 

 additional transport of surface waters offshore in 

 summer, and inshore in winter (Wyatt et al. 1972). 

 Perhaps these interacting current systems serve 

 to maintain the majority of these larvae within 

 areas favorable for settling, even though they 

 have extended pelagic lives and the continental 

 margin off Oregon is narrow. 



VERTICAL DISTRIBUTION 



Information was obtained on vertical distribu- 

 tion of Dover sole larvae from a series of opening- 

 closing mid-water trawl collections from the upper 

 1,000 m, 120 km off Newport. There, water depth 

 was about 2,800 m. All but two larvae were found 

 in the upper 600 m, revealing that this species 

 may occupy a broad depth range (Table 8), nearly 

 as extensive as the bathymetric range of adult 

 Dover sole (Alton 1972). Larvae were most 

 abundant (196 larvae/10 5 m 3 ) in the upper 50 rh. 

 Convincing evidence for diel vertical migration 

 was absent, although the vertical distribution of 

 larvae during the July 1971 cruise appeared to be 

 shallower by night than by day. Rae (1953) 

 concluded that Microstomas kitt larvae exhibited 

 diel vertical migration of 10-20 m into near- 



TABLE 8. — Average catches (number/10 5 m 3 water filtered) of 

 Microstomas pacificus larvae in an opening-closing mid-water 

 trawl during one cruise in July 1971 and five cruises July 1971- 

 September 1974, 120 km off the central Oregon coast; water 

 depth was 2,800 m. D = day, N = night. 



surface waters at night. Such a shallow migration 

 would not be detectable from our samples. 



BENTHIC JUVENILES 



The season and depth of occurrence of the 

 smallest benthic juveniles are important indi- 

 cators of the lengths of the pelagic phase of these 

 fishes. Hagerman (1952) reported that young 

 Dover sole become demersal between 50 and 55 

 mm total length (TL). Mearns and Gammon (see 

 footnote 8) caught juvenile Dover sole of 45-75 mm 

 SL during both mid-autumn and early spring off 

 southern California, suggesting two major periods 

 of recruitment. Demory (1971, see footnote 4, and 

 pers. commun.) caught the largest numbers of 

 small juvenile Dover sole (40-70 mm TL) in 

 February in bottom trawls between 130 and 183 m 

 depth off northern Oregon. According to Demory, 

 these fish, which were 1 yr of age, subsequently 

 move into shallow water in the summer. Though 

 not common, we have taken Dover sole of 40-50 

 mm SL in the winter in beam trawl collections on 

 the outer shelf off central Oregon. These results 

 indicate that Dover sole off Oregon usually 

 complete metamorphosis and take up a benthic 

 life on the outer continental shelf after about 1 yr, 

 when they are less than 50 mm long. Larger larvae 

 are probably older than a year and have delayed 

 complete transformation to the benthic juvenile 

 form. These large, "holdover" larvae may con- 

 tribute little to the juvenile and subsequent adult 

 age-groups, based on Demory's (1972b for 

 methods, pers. commun.) observation of two cir- 

 culi patterns in the scales of small juvenile Dover 

 sole. These were: a dominant pattern with 6-9 

 circuli, and another rarer pattern with 20 or more 

 circuli. Thus fish with the larger number of circuli 

 probably represent our large larvae, which be- 

 come benthic well after 1 yr. 



Juvenile rex sole, 40-60 mm SL, were common 

 in our beam trawl collections on the outer edge of 

 the continental shelf ( 150-200 m depth) during the 

 winter months off central Oregon. We also col- 

 lected 22 G. zachirus larvae of 46-60 mm TL (stage 

 III) in an otter trawl at 230-260 m depth off Coos 

 Bay, Oreg., in September. We do not know if these 

 rex sole larvae were benthonic before meta- 

 morphosis was completed or if they were living 

 pelagically when caught by the trawl. From these 

 data, we surmise that rex sole settle to the bottom 

 mainly on the outer continental shelf during the 

 winter when they are about 1 yr old. It is possible 



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