RICHARDSON ET AL.: EGGS AND LARVAE OF BUTTER SOLE 



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LENGTH CLASS (mm) 



Figure 9. — Length-frequency histograms of Isopsetta isolepis 

 larvae collected in 70 cm bongo nets off Oregon in 1971 (un- 

 shaded) and 1972 (shaded). X = median length of larvae in 

 1971; = median length of larvae in 1972. 



The habitat separation of newly transformed 

 benthic juveniles of /. isolepis and P. vetulus is 

 interesting since spawning times overlap for the 

 two species and the larvae are codominants in 

 coastal waters off Oregon (Richardson and Pearcy 

 1977). Habitat separation also has been noted in 

 large OlO mm) larvae; P. vetulus is more abun- 

 dant in neuston samples relative to plankton sam- 

 ples than /. isopsetta (Laroche and Richardson 

 1979). Ratios of relative abundance of P. vetulus to 

 /. isolepis in plankton samples was 2:1 compared 

 with 36:1 in neuston samples. Thus the two cooc- 

 curring species appear to be utilizing different 

 parts of the water column. Smaller larvae might 

 be segregated similarly by depth, but we have no 

 data on vertical distribution to substantiate this 

 idea. Feeding studies, which may help verify these 

 habitat differences and provide evidence for re- 

 source partitioning between these morphologi- 

 cally similar larvae, remain to be conducted. 



ACKNOWLEDGMENTS 



We thank Michael D. Richardson (Department 

 of Navy, NORDA; formerly OSU) for providing 

 juvenile specimens from beam trawl collections off 

 the mouth of the Columbia River. Betsy 

 Washington (OSU) illustrated the larvae and 

 juvenile; Beverly Vinter (NWAFC) illustrated the 

 caudal fin and skeleton; Kenneth Waldron 

 (NWAFC) reared the /. isolepis eggs. Elbert H. 

 Ahlstrom (Southwest Fisheries Center, Nation- 

 al Marine Fisheries Service, NOAA, La Jolla, 

 Calif.) provided unpublished meristic data on /. 

 isolepis; he also provided stimulating discussions 

 on osteology of pleuronectids. Earl Krygier (OSU) 

 provided information on juvenile flatfishes col- 

 lected in Yaquina Bay and Oregon coastal waters. 

 Gail Gibbard (formerly OSU) compiled the mor- 

 phometric data. We thank Beverly Vinter, Ann 

 Matarese, and Kenneth Waldron for technical as- 

 sistance. 



This work is a result, in part, of research spon- 

 sored by the Oregon State University Sea Grant 

 College Program, supported by NOAA Office of 

 Sea Grant, Department of Commerce, under 

 Grant No. 04-6-158-44094. 



LITERATURE CITED 



AHLSTROM, E. H., AND R. C. COUNTS. 



1955. Eggs and larvae of the Pacific hake, Merluccius pro- 

 ductus. U.S. Fish. Wildl. Serv., Fish. Bull. 56:295-329. 



415 



