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



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MID-WATER TRAWL 



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 n= 30 48 19 17 15 68 204 36 35 13 39 46 



FIGURE 2.— The relative abundance of each stage of Dover sole 

 larvae in bongo transect and mid-water trawl collections during 

 all months. 



Dover sole are known to spawn off Oregon 

 primarily in winter, November through March 

 (Hagerman 1952; Harry 1959), when stage III and 

 IV larvae were present. It appears that Dover sole 

 larvae are pelagic for at least a year. The large 

 proportion of stage Ilia larvae during all months is 

 puzzling, since relatively few of this stage would 

 be expected during the winter and early spring if 

 the larval period lasts a year or less. 



Interpretation of growth and length of larval life 

 is facilitated by the length-frequency data in 

 Table 4. A trend for increasing average size of 

 larvae is evident from April of one year to March of 

 the next year for larvae <30 mm SL. This suggests 

 growth only to at least 20-30 mm during the first 

 year of life, and a pelagic life that lasts at least a 

 year. No growth trends are apparent for large 

 larvae, which were present all months of the year. 

 Our interpretation of these data is that larvae 

 begin to settle out at 30-50 mm and metamorphose 

 after about 1 yr. Juvenile Dover sole of 40 mm 

 have been captured in bottom trawls in February 

 off Oregon. Possibly few 30- to 40-mm larvae were 

 available to our gear because they were close to 

 the sea floor. Larger larvae (>50 mm) may then 

 represent a residual pelagic population that has 

 not had an opportunity to begin benthic life, 

 perhaps because they resided in water too deep 

 during the period of settlement of most larvae. 

 Information on the size and seasonal occurrence of 

 juvenile Dover sole on the bottom, discussed in a 

 later section, supports these contentions. Such an 

 extended period of pelagic life after 1 yr suggests 

 that Dover sole larvae may delay metamorphosis 

 and settlement to the bottom if favorable condi- 

 tions are not present, a phenomenon known for 

 some benthic invertebrate larvae (Wilson 1968) 

 but to our knowledge not for any fishes. 



Mearns and Gammon 8 also reported Dover sole 

 larvae year-around in waters off southern 

 California with peak numbers in July. They 

 showed a distinct growth trend from about 5-9 mm 

 SL in April to 35-50 mm in October, suggesting 

 that larvae may attain a size of 50 mm or larger 

 during the first year of life. Ahlstrom and Moser 

 (1975) collected Dover sole larvae chiefly during 

 April through July off California. 



The trends for rex sole are more readily in- 

 terpretable than those for Dover sole. Rex sole 

 were also captured in every month, but a progres- 

 sion of stages was obvious through the year (Fig- 

 ure 3). All larvae collected in March, April, and 

 May were stage I, and all were stage IV by the 

 following February. Since rex sole spawn off Ore- 

 gon from January to June (Hosie 1975), pelagic 

 life apparently lasts about a year. The presence of 

 stage IV larvae in November and December and 



8 Mearns, A. J., and R. Gammon. A preliminary note on multi- 

 ple recruitment of Dover sole populations {Microstomas pacif- 

 icus) off Southern California. Unpubl. manuscr., 7 p. Southern 

 California Coastal Water Research Project, 1500 East Imperial 

 Highway, El Segundo, CA 90245. 



177 



