Brodeur and Rugen: Vertical distribution of ichthyoplankton in the northern Gulf of Alaska 



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UDay □ Night 



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Length (mm) 



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Figure 6 



Day versus night proportional length distribu- 

 tions of Hippoglossoides elassodon larvae. 



larvae or their prey at certain depths or inhibit them 

 from migrating to different depths. 



The fact that walleye pollock larvae, which are the 

 dominant fish larvae in this area representing 70- 

 80% of the larvae present in Shelikof Strait in the 

 spring (Rugen 7 ; this study), show a normal migra- 

 tion pattern (Kendall et al., 1987) suggests one po- 

 tential explanation for reverse migration patterns 

 of other larvae. If other larvae feed on the same 

 microzooplankton prey as larval walleye pollock and 

 these prey resources were limiting, then the pres- 

 ence of these other larvae in surface waters at dif- 

 ferent times of the day than those of walleye pol- 

 lock would reduce competition with the numerically 

 dominant taxon. Copepod nauplii, an important 



7 Rugen, W. C. 1990. Spatial and temporal distribution of lar- 

 val fish in the Western Gulf of Alaska, with emphasis on the 

 period of peak abundance of walleye pollock tTheragra 

 chalcogramma) larvae. NWAFC Processed Rep. 90-01, 162 p. 



