eat eggs (Hobson and Chess, 1978). Most egg-eating fishes cease foraging as 

 light levels diminish, since low light levels make visual orientation difficult 

 and also predation by piscine predators generally increases at this time 

 (Hobson, 1972, 1974: Hobson and Chess, 1978). Additionally, any planktivores 

 still actively feeding through dusk may be quickly satiated by the simultaneous 

 spawning of many fishes. 



Spawning during dusk may reduce mortality of fish eggs by predation, but 

 it also may increase the potential risk of predation for adult fishes. Hobson 

 (1968, 1972, 1974, 1978; Hobson, et aU , 1981) has documented extensive 

 evidence suggesting increased predation by fish predators on tropical reef 

 fishes exposed or otherwise vulnerable during the crepuscular periods. Fishes 

 also are thought to be more vulnerable to predation when preoccupied with 

 mating (Johannes, 1978, 1981; Robertson, 1983). Furthermore, it must be 

 noted that there are many fishes, particularly labrids and scarids, which 

 spawn throughout the day, appearing more in phase with tidal currents than 

 crepuscular periods (Barlow, 1981; Kuwamura, 1981; Robertson, 1983). 



In this study, we wanted to evaluate how a fish would alter its mating 

 pattern when disturbed or attacked. The results might then provide some insight 

 into the selective pressures molding the reproductive tactics of coastal marine 

 species in the tropics. At the time, the best arrangement we could devise to 

 test the possible effect of predation was by simulating predator behavior using 

 scuba divers. Other studies also have considered a fish's response to a human 

 diver as indicative of reaction to a piscine predator (e.g., Coates, 1980). 

 Nevertheless, results of this manipulation should be related only tenuously to 

 how the hamlet might respond to a fish predator. A fish predator probably 

 would not continue to attack the same prey throughout dusk. 



The hamlet, Hypoplectrus guttavarius , altered its normal mating behavior 

 when harassed by 1) attempting more clasps longer into the night and 2) spawning 

 progressively nearer to the bottom in and among shelter. In no case was spawning 

 terminated early; in fact, the opposite occurred, and fish prolonged spawning 

 attempts. This result simply may indicate that once ovulation has begun, the 

 fish must spawn. The spawning sites were all reef structures (gorgonian and 

 coral) taller than the surrounding terrain. Only after a pair had shifted 

 sites repeatedly did they commence spawning nearer the bottom or in shelter. 

 Difference in survivorship of the free-floating zygotes when released high 

 above the reef vs. near the bottom was not determinable. Fish which were 

 attacked and harassed one day showed no indication of lasting behavioral affects 

 the next day. 



The importance attributed to spawning above a tall reef structure is that 

 it provides a degree of safety for the adults. It allows the fish to mate 

 relatively high in the water column while remaining as close as possible to 

 shelter. Spawning high in the water places the free-floating eggs beyond the 

 grasp of benthic planktivores and in a position most favorable to advection by 

 currents. 



Hobson (1972, 1974) has suggested that the well defined twilight activities 

 of tropical reef fishes have been shaped by the threat of crepuscular predators 

 (Hobson, et al . , 1981). If this hypothesis is correct, then it would seem that 



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