RUGGERONE and ROGERS: ARCTIC CHAR PREDATION ON SOCKEYE SALMON SMOLTS 



have been lower, thereby reducing their success 

 rate when attacking the larger smolts in the mi- 

 gration. 



The larger smolts in less full char as compared 

 with average smolt length in the migration may be 

 due to the relationship between light intensity, 

 migrating smolt size, and decreased feeding activ- 

 ity by char during the darkest portion of the night. 

 Smolts migrating at night were significantly 

 shorter than those migrating during the day 

 (Ruggerone 1981; Burgner 1962; Aspinwall 1963). 

 Feeding activity of char was observed to decrease 

 substantially during the darkest 1-2 h of the night 

 (often char would leap from the water while feed- 

 ing). Also, hook and line fishing with lures was 

 notably less effective during darkness. Therefore, 

 the difference in average length of smolts consumed 

 by less full char and those in the migration re- 

 sulted from a decrease in smolt consumption when 

 smolts in the migration were smaller. These re- 

 sults indicate that predation may be reduced by 

 releasing hatchery salmon during the night. 



The difference between smolt length in all char 

 and length in the migration was relatively small. 

 In part, this was due to the large proportion of 

 smolts observed in full char, which was related to 

 high smolt abundance. Because fewer char will 

 reach stomach fullness during years of fewer 

 smolts, the difference between length of smolts con- 

 sumed and length in the migration is likely to be 

 greater. 



ACKNOWLEDGMENTS 



We would like to thank Robert Burgner, Bruce 

 Miller, and Joan Hardy for their constructive 

 comments on the manuscript and Daryl Pregibon 

 for his assistance with the nonlinear modeling. 

 John Barr, Kathryn Chumbley, Susan Eakin, and 

 Cari Rawlinson provided invaluable assistance 

 with the data collection at Wood River. This re- 

 search was funded by the National Marine 

 Fisheries Service and the Alaska Department of 

 Fish and Game. 



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