natural predation on spawning fishes or their eggs is not rare (Randall and 

 Randall, 1963; Hobson, 1965; Moyer, 1974, 1975; Meyer, 1977; Colin, 1976, 

 1978; Robertson and Hoffman, 1977; Jones, 1981; Robertson, 1983). Some 

 species gather in spawning aggregations and apparently are oblivious to human 

 or natural piscivore predators even when disturbed or attacked (Johannes, 

 1978, 1981; Robertson, 1983). In contrast, the mere presence of a diver- 

 observer will interrupt the mating of some smaller species unless the fish 

 are approached and observed with stealth (Johannes, 1978; Lobel , 1978). 



To date, studies on the reproductive behavior of tropical coastal marine 

 fishes in the field have been primarily observational. The emphasis has been 

 on documenting where, when, and how various species spawn. Herein we report 

 the spawning behavior, diel timing, and a manipulation that attempted to 

 disturb the behavior of a fish during reproduction. Our goal was to see 

 whether and how the spawning behavior of the Caribbean hamlet, Hypoplectrus 

 guttavarius , might be altered. Because hamlets and many other fishes spawn 

 during the evening crepuscular period when predation by piscivores is most 

 likely, we wanted to determine whether fish that were disturbed by scuba 

 divers during the spawning act would cease all activity, move sites, depart 

 and seek other mates, or merely continue despite the disturbance. 



The Caribbean hamlet, Hypoplectrus guttavarius (fig. 1) was selected for 

 study because it maintained stable, identifiable pairs which spawned almost 

 every evening at specific sites during February 1980, at St. Croix. It was 

 common, easily observed, and the spawning act was unmistakable and easily 

 quantified. The diel timing of spawning is compared with that of H. chlorurus , 

 H. nigricans , H. puel la , and hU_ unicolor . 



The reproductive ecology of hamlets is somewhat enigmatic. It has been 

 suggested that Hypoplectrus nigricans and other hamlets are simultaneous 

 hermaphrodites, and that individuals alternate sexual roles between spawning 

 clasps (Barlow, 1975; Fischer, 198Cta, 1980b, 1981). It is also controversial 

 whether different morphological variants oT hamlets represent aggressive- 

 mimetic morphs of the single species, Hypoplectrus unicolor , or are reproductively 

 isolated incipient species (Thresher, 1978; Graves and Rosenblatt, 1980; 

 Fischer, 1980b). Hamlets usually mate assortati vely by color patterns, 

 although mixed pairs have been observed, and individuals which exhibit color 

 markings characteristic of two or more color forms are known (Barlow, 1975; 

 Thresher, 1978; Graves and Rosenblatt, 1980; Fischer, 1980a_). Thus, the 

 reproductive behavior of hamlets is interesting from several perspectives. 

 To maintain simplicity and clarity, we refer to the various hamlets by their 

 established species names (cf. Randall, 1968). 



STUDY SITES 



Fish were examined at two locations on St. Croix, U.S. Virgin Islands 

 (64°35'W, 17°45'N). The first site was the east slope of Salt River canyon 

 within the excursion limits of the N0AA National Undersea Laboratory System 

 habitat (HYDR0LAB). Since we were saturated, we spent approximately 53 hours 

 per person observing fish at 20-30 m depths from February 11 to 15, 1980. 

 The second site was located on several patch reefs at about 10 m depths in 



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