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Fishery Bulletin 97(4), 1999 



tributed by each prey type was estimated visually 

 (Williams, 1981). Fullness was averaged for fish 

 grouped by date, gender, and stage of reproductive 

 development. Fish examined were 63-460 mm TL. 



Bottom water temperature, salinity, and dissolved 

 oxygen were measured weekly at each station with 

 YSI (Yellow Springs Instruments) oxygen and tem- 

 perature-conductivity meters. HydroLab DataSonde 

 II instruments were deployed near the bottom on 

 piers extending from the south shore of the Navesink 

 River near stations 1 and 6 to record temperature, 

 salinity, and dissolved oxygen each hour. 



Results 



Laboratory observations 



Behavior Two forms of simple courtship behavior 

 were observed in the research aquarium: "following" 

 and "avoidance." "Following" was defined as oriented 

 locomotion of one or more fish behind another, typi- 

 cally on the sediment surface. A following could be 

 relatively slow or fast (approx. 20-50 cm/sec), con- 

 tinued for 5-20 sec, and sometimes resembled chas- 

 ing. Turns by the lead fish were followed by the fish 

 behind, and, in most cases, the distance between fish 

 decreased but contact was never made. In all cases 

 where genders of the fish could be determined the 

 lead was female. One or more "followers" were al- 

 ways male. "Avoidance" was characterized by brief 

 contact (<1 s) between a "follower" and the female 

 being followed, then by rapid acceleration and eva- 

 sive turning by the female. Typically, the female 

 swam 1-2 m off the bottom. In at least 509^ of such 

 encounters additional males converged rapidly on the 

 female, eliciting strenuous evasive swimming by the 

 female. 



Our observations of spawning in winter fiounder 

 were relatively similar to those of Breder ( 1922), ex- 

 cept that females never initiated spawning. Spawn- 

 ing occurred after initial contact by a male as de- 

 scribed above. Instead of fleeing, the female remained 

 near the sediment surface (<1.0 m above it) and the 

 pair immediately made several very rapid circles with 

 diameters typically less than two body lengths. 

 Spawning events could be detected even in the far 

 reaches of the tank during darkness because the fe- 

 male nearly always rotated momentarily to the ver- 

 tical position so that the white underside of her body 

 was clearly visible on the outside of the circles. Par- 

 ticipation by multiple males in the spawning event 

 was common, and in approximately 107r of spawn- 

 ing events, one to several males converged on the 

 spawning location immediately after the female had 



departed, making rapid undulating motions on the 

 sediment surface. Despite convergence of males on 

 spawning females and spawning locations, agonistic 

 behavior among males was never observed. In less 

 than 29c of observed spawning events, a second 

 spawning by the same female occurred a short dis- 

 tance from the first encounter. In most cases the fe- 

 male avoided further contact. 



Spawning Spawning began on 8 February 1997, 

 about 2 weeks after the fish were introduced into 

 the research aquarium. One or more spawnings oc- 

 curred in camera view every day, except 14 Febru- 

 ary, until 1 April (Fig. 2A); maxima were evident in 

 mid-February and mid-March. The last spawnings 

 were observed on 8 April. In total, 211 spawning 

 events were recorded, 34% of which were definite. In 

 analyses that follow, we considered the "spawning 

 season" in the aquarium to be the period between 8 

 February and 8 April, 1997. The "postspawning sea- 

 son" was the remainder of the observational period, 

 9 April through 13 May 1997. 



Spawning began near or just before sunset ( 1700- 

 1800 h) and reached maximum frequency around 

 2100 h (Fig. 3A). Seventy-five percent of all observed 

 events occurred before midnight. Although some 

 spawning occurred as late as 0430 h, only 10% oc- 

 curred after 0200 h, when the fish became relatively 

 inactive. 



When the total number of spawning events dur- 

 ing the observation period was extrapolated to the 

 total dimensions of the aquarium and divided by the 

 ten females in the system, we estimated that the 

 average female fiounder spawned 40 times during 

 the reproductive season. It is unknown whether in- 

 dividual fish spawned over this extended observa- 

 tion period. However, given that the mean total num- 

 ber of spawns per night was just six, individuals prob- 

 ably spawned over a period of at least one week. Two 

 facts suggest that a subset of the females may have 

 been completely spent during the first three weeks 

 of the spawning period: the nightly spawning fre- 

 quency was bimodal, with a minimum on 2 March 

 (Fig. 2A), and female feeding increased rapidly after 

 approximately 3 March (Fig. 4). 



None of the observed spawning events involved 

 more than one female flounder, but multiple males 

 were engaged in the majority of spawnings. In 151 

 events with records for the number of males, only 

 22.5% were pair spawnings, 11.3% had two males, 

 3.3% had three males, and the majority involved four 

 to six males (62.9%). Given these numbers, a conser- 

 vative estimate for the total number of male spawnings 

 within camera view is 780. By extrapolating to total 

 tank dimensions and dividing among the ten males 



