HASTINGS ET AL.; FISH FAUNA ASSOCIATED WITH OFFSHORE PLATFORMS 



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Figure 3. — Large school of Harengula pensacolae surrounding a piling of Stage 11 off Panama City, Fla. 



gathered in compact schools below the stage dur- 

 ing the day apparently as a defense against pre- 

 dation (Hobson 1965). Station counts at Stage II 

 for H. pensacolae and D. punctatus indicate that 

 they left the protection of the platform and moved 

 into the open areas surrounding the stage at 

 night. Several species of clupeids and schooling 

 carangids, including H. pensacolae, Sardinella 

 anchovia, D. punctatus, and Selar crumen- 

 ophthalmus, have been described as nocturnal 

 plankton feeders (Hobson 1965; Starck and 

 Davis 1966), although some diurnal feeding 

 activity by Decapterus and Sardinella was ob- 

 served by us and others (Klima and Wickham 

 1971). During daylight hours at Stage II, from 

 about 0500 to about 1800 CST, extensive schools 

 of if. pensacolae were present around and under 

 the platform, and, at times, were so dense that 

 they darkened the area below (Figure 3). Rela- 

 tively large numbers were present at the census 

 stations during most daylight dives, but none was 

 observed during any of the night censuses. Simi- 

 lar records were obtained for D. punctatus, al- 



though the numbers present were considerably 

 less than for H. pensacolae. In addition, D. 

 punctatus may have left the vicinity of the plat- 

 form earlier in the evening (about 1500 CST). 



The other pelagic species are, in most cases, 

 large predators and are continually on the move 

 in the upper water column surrounding the plat- 

 forms, occasionally darting into the schools of 

 smaller fishes to feed. Some, such as Seriola 

 dumerili, were often seen near the bottom as well. 

 Most of these pelagic predators probably feed to 

 some extent at night as well as during the day, 

 and may follow the bait species, as the bait 

 species disperse at night. However, studies indi- 

 cate that many such piscivorous fishes are 

 primarily crepuscular, with peaks of feeding ac- 

 tivity at dawn and dusk (Hobson 1965, 1968, 

 1972, 1974; Starck and Davis 1966). 



Only Caranx crysos was consistently present in 

 the station counts (but only in Station 2 near the 

 surface). These counts show a pattern similar to 

 that of//, pensacolae, with fairly large numbers 

 present during daylight hours and none present 



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