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Fishery Bulletin 93(2), 1995 



bongo net samples perhaps also reflecting a faculta- 

 tive association with the neuston (i.e. concentrated 

 at the surface only during certain hours). However, 

 the high (54-73%) fraction occurring in the neuston 

 suggests a strong association by these species with 

 the surface zone. 



The remaining dominant taxa of larvae in the neus- 

 ton were absent or scarce in the bongo samples and 

 all except Hemilepidotus spp. had a value of >85% 

 (Table 4). It seems that their association with the 

 neuston was obligative (i.e. permanent presence in 

 the surface zone). These obligative taxa included the 

 hexagrammids and cottids as well as Crypta- 

 canthodes aleutensis and Anoplopoma fimbria. They 

 formed a unique community of fish larvae in the 

 neustonic realm. 



Most of the dominant taxa of fish larvae that in- 

 habit the subsurface zone of the western Gulf of 

 Alaska were absent or rare in the neuston, includ- 

 ing Gadus macrocephalus and Sebastes spp., and 

 species of Bathylagidae, Myctophidae, Cyclopteridae, 



Agonidae, and Pleuronectidae (Kendall and Dunn, 

 1985; Rugen 3 ). 



Diel variation in catches of larvae 



To examine diel variation in catches of larvae for both 

 the neuston and bongo samplers, stations were 

 grouped by hour of the day, and mean densities of 

 larvae for each of the 24 hours were calculated. Be- 

 cause of the substantial variability in day length over 

 the 3-month sampling period, it was not possible to 

 assign a specific sunrise and sunset time that could 

 be used for all cruises. For the purposes of this analy- 

 sis, we assumed that the daytime period lasted from 

 0700 to 1900 hr and the nighttime from 2200 to 0400 

 hr. The intervening periods of 0400 to 0700 h and 

 1900 to 2200 h were presumed to have been twilight, 

 including dawn and dusk, respectively. 



For all neuston catches combined, both the total 

 mean density and the number of hauls in which lar- 

 vae were caught were higher at night than during 



