HASTINGS ET AL.: FISH FAUNA ASSOCIATED WITH OFFSHORE PLATFORMS 



were made during this study for E. umbrosus, 

 which was present during almost every observa- 

 tion at Station 1. 



The smaller demersal sea basses (family Ser- 

 ranidae) observed at the stages were relatively 

 inactive fishes which did not exhibit obvious 

 day-night changes in behavior. However, counts 

 of Centropristis ocyurus and S. subligarius de- 

 creased at night, possibly indicating that some 

 had taken shelter under objects or within shells 

 or crevices. Literature records indicate that these 

 and related sea basses are diurnal (Starck and 

 Davis 1966; Bortone 1971). 



Chaetodon ocellatus was usually seen swim- 

 ming about near the bottom during the day and 

 frequently in pairs. One individual observed at 

 night resting on the bottom next to a piling ex- 

 hibited the typical nocturnal color pattern de- 

 scribed by Starck and Davis (1966). 



Counts of Pomacentrus variabilis and H. 

 caudalis at Station 1 were considerably higher 

 during the daylight observations than at night. 

 Daylight counts for P. variabilis (10-14) were less 

 variable than those for H. caudalis (6-22). 

 Pomacentrus variabilis is territorial and probably 

 remains at the same general location throughout 

 the day while H. caudalis is less sedentary and 

 tends to move about more. Starck and Davis 

 (1966) stated that P. variabilis and other 

 pomacentrids are diurnal feeders which seek 

 shelter at night in sponges, rocks, coral, or other 

 close cover. Most of those at the stage may have 

 taken shelter in and among the many empty mol- 

 lusk shells which cover much of the bottom at the 

 base of the stage. Halichoeres caudalis has not 

 been studied previously, but several species of 

 labrids, including H. bivittatus which was also 

 present at times at Stage II, have been reported to 

 bury themselves in sand at night (Breder 1951; 

 Hobson 1965; Starck and Davis 1966), and this 

 may also be the case with H. caudalis. 



The numerous species of free-swimming fishes 

 occupying the various levels of the water column 

 under the platform apparently include several 

 distinct groups based upon activity patterns and 

 feeding habits. Mycteroperca microlepis is a large 

 predator which appeared to be continually mov- 

 ing about under or around the stage, usually near 

 the bottom, but a few inactive individuals were 

 observed at night on the bottom resting against 

 the pilings. Such species are normally described 

 as being opportunistic feeders with peaks of feed- 



ing activity during twilight periods when the 

 changeover of activity patterns in prey species 

 makes them more vulnerable (Starck and Davis 

 1966; Collette and Talbot 1972; Hobson 1972). 



Lutjanus griseus (Starck 1971), Haemulon au- 

 rolineatum, and Orthopristis chrysoptera are ap- 

 parently nocturnal feeders, which utilize the 

 stage only as a shelter during daylight hours, and 

 move out into surrounding areas at night to feed. 

 Lutjanus griseus was normally seen schooling 

 during the day in the lower-to-middle water col- 

 umn under the platform. Haemulon aurolineatum 

 and O. chrysoptera were two of the most numer- 

 ous fishes in Station 1 at Stage II (Figure 4), al- 

 though both were rare or absent during the 

 nighttime observations. There may be a differ- 

 ence in the time of major movement for these two 

 species. Haemulon aurolineatum apparently 

 began to disperse and move out of the area at or 

 shortly after sunset, and returned shortly after 

 sunrise. Orthopristis chrysoptera possibly leaves 

 the area under the stage earlier in the evening 

 (just before sunset) and also may return earlier in 

 the morning. Apparently these grunts feed at 

 night in the open areas surrounding the stage 

 and school under the stage as a defense against 

 diurnal predators (Hobson 1965; Starck and 

 Davis 1966). 



Other species (such as H. plumieri, Diplodus 

 holbrooki, Lagodon rhomboides, Kyphosus sectat- 

 rix, Chaetodipterus faber, Holacanthus ber- 

 mudensis, Acanthurus chirurgus, Balistes capris- 

 cus, and Monacanthus hispidus) seemed to feed 

 mostly on benthic organisms attached to the pil- 

 ings or other objects, and may move up and down 

 in the water column, grazing upon this material. 

 However, some of these were more numerous 

 near the surface (such as D. holbrooki, L. rhom- 

 boides, and K. sectatrix) while others normally 

 remained near the bottom (such as Haemulon 

 plumieri, C. faber, Holacanthus bermudensis , and 

 B. capriscus). Most of these species are appar- 

 ently diurnal and become inactive at night. A 

 few L. rhomboides, H. bermudensis, and B. cap- 

 riscus were observed near the bottom at night, 

 either resting on the bottom or in protected places 

 below cross-members or between pilings and ad- 

 jacent objects. Kyphosus sectatrix was inactive at 

 night, but remained in the upper water column. 

 In contrast, Haemulon plumieri is nocturnal but 

 seemed to remain in the same general area near 

 the bottom throughout the day and night. Such 



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