FISHERY BULLETIN: VOL. 78, NO. 3 



15° C) during the course of their migration, and 

 Smith et al. concluded that yellowtail flounder 

 larvae were "physiologically adapted to wide 

 ranges in temperature." Even though larger 

 yellowtail flounder larvae are apparently rather 

 eurythermal, the fact that their zone of tolerance 

 can be exceeded in nature is demonstrated by the 

 observation of Colton (1959). Colton found many 

 dead yellowtail flounder larvae across a 16 km ( 10- 

 mi) transect in which the temperature rose from 8"' 

 to 20° C in <24 h. This observation does not, 

 however, refute eurythermality in this species 

 since the temperature changes were so extensive 

 and abrupt. 



These experimental results indicate that tem- 

 peratures between 8° and 12° C have little direct 

 effect on survival of yellowtail flounder larvae. 

 This, combined with the observations of Smith et 

 al. (1978) indicate that early stages of yellowtail 

 flounder are eurythermal. Because of this, it 

 seems doubtful if temperature causes the observed 

 fluctuations through direct physiological means. 

 Obviously abrupt thermal changes such as those 

 observed by Colton (1959) could cause mass mor- 

 tality and therefore poor recruitment of a year 

 class. Perhaps it is through such a mechanism that 

 temperature affects abundance. It is also possible 

 that temperatures tested in this study were not 

 high enough to demonstrate a clear relationship 

 between a high temperature and some physio- 

 logical response that would affect the larva's 

 ability to survive. 



ACKNOWLEDGMENTS 



I am grateful to Tom Dykstra and the crew of the 

 FV Freisland for their considerable help with col- 

 lection of specimens. Al Smigielski, Mike Johns, 

 and Gary Davis provided valuable discussions. I 

 am also indebted to Saul B. Saila, William H. 

 Krueger, H. Perry Jeffries, and the two anony- 

 mous reviewers who critically reviewed the manu- 

 script and offered many helpful suggestions. 



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