1008 



Fishery Bulletin 97(4), 1999 



Spawning period 



Postspawning period 



Female 



Figure 7 



Locomotory activity in adult winter flounder in the research aquarium shown on an hourly basis for (A, B) females 

 and (C, D) males during the spawning and postspawning periods. See text for the method used in generating this 

 index of activity. 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. 



ness indices (59%-84%) occurred in immature fish, 

 most containing substantial amounts of food. Aver- 

 age fullness in females was also high throughout the 

 survey period (60'^-80%), but variation was large 

 and associated with reproductive state. Ripe females 

 had an average fullness of just 24*^, whereas spent 

 females had an average fullness of 72%. Variation 

 among males was even higher, with an obvious in- 

 crease in fullness from about 1% early in the survey 

 to a range of 70'/(-90'7r during the last three collec- 

 tion dates (Fig. 12). Ripe males had average stom- 

 ach fullness of only 17%, whereas average fullness 

 of spent males was 69%. Therefore, the rapid increase 

 in stomach fullness of males in late March was asso- 

 ciated with rapidly declining numbers of ripe males. 

 Stomach fullness was weakly correlated with GSI in 



both females (/•=-0.439) and males (r=-0.582) be- 

 cause fullness in fish with a low GSI spanned the 

 entire range from 0%-100%. 



Siphons of soft clam (Mya arenaria ) were the most 

 abundant prey items taken by winter fiounder, on 

 the basis of both percentage volume and frequency 

 of occurrence. Of the 257 flounders that contained 

 prey, 150 contained siphons with diameters of 3-13 

 mm. However, diet varied with collection site (Fig. 

 13). Siphons of M. arenaria were most abundant in 

 fish collected in the middle reach of the estuary (sta- 

 tions 3-6), whereas another clam, Macoma halthica, 

 was most abundant in fish from the upper reach (sta- 

 tion 1 ). Ampeliscid amphipods, mysids, shrimps, and 

 other crustaceans were the most important food 

 items in the lower estuary. 



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