1004 



Fishery Bulletin 97(4), 1999 



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Hour of day 



Figure 3 



Hourly frequency of (A) spawning, (B) following, and (C) avoidance behavior by 

 winter flounder during the spawning season in the research aquarium. Values rep- 

 resent mean numbers of observed events per hour ±1 standard error. The dashed 

 vertical lines show the times of artificial sunrise and sunset in the aquarium at the 

 midpoint of the spawning season. Photoperiod was maintained on a natural cycle 

 for the latitude of the laboratory. 



did not differ appreciably between spawning (90.3'^ ) 

 and postspawning (89.8%) periods. 



It is possible that feeding frequency was related to 

 water temperature. During the time when water tem- 

 perature was 4°C (until 25 March), average feeding 

 frequency was 14 bouts/day (SD=:17,n=45). During the 

 period when temperature was 9^C (26 March-8 April), 

 feeding frequency increased to 94 bouts/day (SD=47, 

 n = ll ), and when the temperature was 15°C ( 14 April- 

 13 May) there were 159 bouts/day (SD=107, « = 17). 



Diurnal feeding periodicity was similar in males 

 and females. During spawning season, most feeding 



occurred in the hours immediately following sunset 

 and ended before sunrise (Fig. 6, A and C). After 

 spawning ended, feeding (particularly by females) 

 was dispersed throughout day and night, and maxi- 

 mum feeding occurred from afternoon to early 

 evening, primarily 1300-1900 h (Fig. 6B). The least 

 feeding activity occurred from approximately mid- 

 night until 1100 h. Feeding by males during the 

 postspawning season continued to be much less fre- 

 quent than feeding by females; however, the diurnal 

 pattern shifted similarly to an earlier period of maxi- 

 mum activity (Fig. 6D). 



