FISHERY BULLETIN: VOL. 81, NO. 3 



In the present study, certain families were collected 

 more frequently in, or were restricted to, night trawl 

 tows (Table 8). Ophidiids (4 species), sciaenids (3 

 species), and gadids (2 species) occurred only in 

 night tows. Seven of the 15 most abundant species 

 were taken significantly more frequently in night 

 collections (Table 9). The explanation for these pat- 

 terns varies according to the species. 



The significantly greater frequency of occurrence in 

 night catches of black sea bass, Centropristis striata, 

 was caused by this species' increased vulnerability to 

 night trawl tows. Trap and handline collections, as 

 well as underwater television observations, have 

 shown C. striata to be much more abundant than was 

 indicated by our otter trawl tows. This supports the 

 findings of Powles and Barans (1980). 



Ophidioid fishes of the sponge-coral habitat are 

 nocturnal species that were unavailable to day trawl 

 tows. Starck and Davis (1966) indicated that 

 although cusk eels were abundant in rotenone collec- 

 tions, they were never visually observed moving 

 about reef systems during the day. These inves- 

 tigators found, however, that Ophidion holbrooki was 

 active over the sandy portion of a Florida reef at 

 night. When this species was disturbed with lights, it 



Table 8. — Families of fishes taken primarily in night otter trawl 

 tows in the sponge-coral habitat of the South Atlantic Bight. 



TABLE 9. — Comparison of frequency of occurrence of the 15 most 

 numerically abundant species in day and night trawl tows in the 

 sponge-coral habitat, South Atlantic Bight. * = significant at the 

 95% probability level. 



burrowed tail-first into the sand. Another species (O. 

 selenops) was seen by Starck and Davis (1966) swim- 

 ming near bottom in night dives at deeper water reef 

 sites. The four species (0. holbrooki, 0. beani, 0. 

 selenops, Otophidium omostigmum) collected during 

 the present study were taken only in night trawl tows 

 indicating that because of their daytime burrowing 

 behavior, cusk eels are unavailable to day col- 

 lections. 



Atlantic midshipman, Porichthys plectrodon, is 

 another nocturnal species that burrows into the sedi- 

 ment during daylight thus making itself unavailable 

 to day trawl tows (Lane 1967). In laboratory tests 

 (Lane 1967), P. plectrodon emerged from the sub- 

 strate 45 min after sunset and burrowed about 45 

 min to 1 h before sunrise. Nocturnal feeding on near- 

 bottom crustacean plankton was shown (Lane 

 1967). 



Sciaenids (Pareques umbrosus, Equetus lan- 

 ceolatus, P. acuminatus) were absent from all day 

 samples but occurred in 2 7 of 29 night tows. Their ab- 

 sence from day collections can more likely be at- 

 tributed to their unavailability rather than their 

 decreased vulnerability to day trawl tows. Unlike the 

 burrowing ophidioids and Porichthys plectrodon, 

 these secretive sciaenids (Parker et al. 1979) seem to 

 hide around or under available structures. Starck and 

 Davis (1966) reported that Pareques acuminatus 

 hides under rocks on the reef during the day and ven- 

 tures out to feed at night. Hobson (1965) indicated 

 that the closely related P. viola is a nocturnal foraging 

 fish that hides under ledges and rocks during the 

 day. 



The daytime residence of Apogon pseudomaculatus 

 in caves and crevices on the reef (Starck and Davis 

 1966) effectively excluded this species from the sam- 

 pling capability of the trawl. The emergence of A. 

 pseudomaculatus and other apogonids at night to 

 forage on midwater plankton over the reef (Collette 

 and Talbot 1972) explains the occurrence of this 

 species only in night tows. 



Triglids (Prionotus carolinus,P. ophryas,P. scitulus, 

 P. roseus,P. salmonicolor) were found in only a single 

 day tow but were in 23 of 29 night tows. The domi- 

 nant northern searobin, P. carolinus, is a nocturnal 

 species, however, which would seem to suggest that 

 its greater frequency of occurrence in night trawl 

 tows cannot readily be explained by a concomitant 

 increase in its vulnerability to the gear. Prionotus car- 

 olinus is a common member of the South Atlantic 

 Bight open-shelf ichthyofauna in depths from 9 to 55 

 m ( Wenner et al. 1979a). Analysis of stratified, ran- 

 dom % Yankee trawl collections from summer 1974 

 and 1975 and fall 1973 showed that although this 



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