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Fishery Bulletin 97(4), 1999 



The location of spawning in an estuary may also 

 be related to temperature and salinity requirements 

 of the demersal eggs. Scarlett and Allen ( 1992 ) col- 

 lected eggs at salinities of 14-32 ppt and tempera- 

 tures of 0.9-10°C in the Manasquan estuary, about 

 30 km south of our study site. Rogers (1976) found 

 that the highest proportion of viable hatches occurred 

 at 3°C over a salinity range of 15-35 ppt. At tem- 

 peratures over 3°C, the optimal range was 15-25 ppt, 

 which closely matches temperature and salinity 

 ranges in the middle reach of the Navesink River 



Other factors that may influence the choice of 

 spawning habitat by winter flounder are hydrody- 

 namic properties and associated sediment character- 

 istics. Strong flood tidal currents that characterize 

 the lower Navesink River attenuate rapidly in the 

 middle reach (Chant'^). This attenuation is associ- 

 ated with deepening of the estuary and general re- 

 duction of sand bars, decrease in the mean grain size 

 of sediments, and increase in sediment organic con- 

 tent (Stoner, unpubl. data). It is unknown whether 

 spawning winter flounder respond to any of these 

 habitat characteristics; however, the depositional 

 qualities of the upper estuary and flood-dominated 

 circulation may aid in the retention of winter floun- 

 der eggs and the evolution of habitat choice in spawn- 

 ers. Crawford and Carey (1985) noted that winter 

 flounder spawned in two sites in an estuarine lagoon 

 in Rhode Island where hydrodynamic features re- 

 tained larvae. It is plausible that habitat choice, cued 

 by either fine-grained sediments or low cuiTent veloci- 

 ties, could be associated with such retention features. 



Seasonal variation in feeding activity 



The general conclusion has been that winter floun- 

 der are opportunistic feeders, consuming polychaetes, 

 small crustaceans, molluscs, and other prey accord- 

 ing to their abundance (Pearcy, 1962; Richards, 1963 

 Klein-MacPhee, 1978; Franz and Tancredi, 1992 

 Martell and McClelland, 1994; Steimle et al., 1994 

 Carlson et al., 1997 ). Winter flounder collected in the 

 Navesink River during this investigation consumed 

 a mixture of invertebrate prey, but the vast majority 

 ofthe diet was siphonsof the soft clam Mya arenaria. 

 The abundance of spent and feeding flounder in the 

 lower estuary may. in fact, be associated with the 

 observed abundance of this preferred prey in that 

 location. 



Cessation of feeding by adult winter flounder dur- 

 ing the winter has been noted previously ( Tyler, 1972; 



^ Chant, R.J. 1998. Instituteof Marine and Coastal Sciences, 

 Rutgers University, P.O. Box 231, New Brunswick, New Jersey 

 0890.3. Unpubl data. 



Martell and McClelland, 1994), but we found that 

 feeding was influenced strongly by gender and re- 

 productive state. Both in the field and in the 

 aquarium, female flounder appeared to resume feed- 

 ing immediately after they completed spawning for 

 the season. Early feeding probably provides an ad- 

 vantage for female fish because ovarian development 

 for the next spawning season begins immediately 

 after spawning (Burton and Idler, 1984). In the field, 

 males did not begin feeding until the end of March, 

 and feeding in the aquarium was light until after 

 the last spawning events. We conclude that male 

 behavior is dedicated to fertilizing the maximum 

 number of eggs, at the expense of feeding and late 

 winter growth. 



There is now substantial evidence for seasonal 

 variation in daily activity and feeding rhythms in 

 winter flounder During the summer, winter flounder 

 are primarily diurnal in general activity (011a et al., 

 1969) and feeding (MacDonald and Waiwood, 1987). 

 Bharadwaj (1988) found that adults fed throughout 

 the day and night in November, speculating that this 

 was related to maturation of gonads for the winter 

 spawning season. In our aquarium observations, 

 adult winter flounder were almost entirely noctur- 

 nal throughout the spawning season, remaining bur- 

 ied during the day. Daytime activity began again 

 when spawning was completed and increased 

 throughout the remainder ofthe postspawning period. 

 Primarily daytime activity during the nonspawning 

 season could be associated with visual predation modes 

 (Olla et al., 1969), but it remains to be determined 

 how mates are located in darkness and why spawn- 

 ing occurs at night. 



Conclusions 



This study provides the first detailed observations 

 on winter flounder spawning since Breder's (1922) 

 original description over 75 years ago, and the com- 

 bination of laboratory and field work provides new 

 insight into the biology and ecology of spawners. The 

 behavior of male winter flounder appears adapted 

 to maximize encounters with reproductive females 

 and numbers of eggs fertilized. From our field collec- 

 tions, it is apparent that one-year-old male winter 

 flounder ( 10 cm TL) are capable of spawning, whereas 

 female spawners all appeared to be at least two years 

 old. Males also became reproductively ripe earlier in 

 the season than did females and remained ripe to a 

 later date than most females. Males were more ac- 

 tive than females, had higher swimming speeds, and 

 initiated all spawning events. The males fed very 

 little during the reproductive season and appeared 



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