232 



Fishery Bulletin 93(2). 1995 



During the 1970's and 1980's, several investiga- 

 tions of ichthyoplankton in the neuston were con- 

 ducted in the northeast Pacific Ocean, primarily off 

 the coasts of Washington and Oregon but also ex- 

 tending to southern California waters ( Ahlstrom and 

 Stevens, 1976; Shenker, 1988; Brodeur, 1989; Doyle 

 1992). These studies established that larvae of many 

 fish are abundant at the surface as well as deeper in 

 the water column and that an additional group of 

 species is almost exclusively neustonic. Doyle (1992) 

 identified obligate and facultative members of the 

 neuston among the larvae and juveniles of fish col- 

 lected off Washington, Oregon, and northern Cali- 

 fornia and attributed their association with the neus- 

 ton primarily to the unique trophic conditions that 

 prevail in this environment. Clearly, the neustonic 

 realm is important in the early life history of many 

 fish species (Zaitsev, 1970; Hempel and Weikert, 

 1972; Moser, 1981; Tully and O'Ceidigh, 1989; Doyle 

 1992). The level of importance, however, varies with 

 geographical area and local conditions. 



Rogers et al. (1979), Kendall and Dunn (1985), 

 Kendall et al. 1 , and Rugen 3 identified a unique sur- 

 face component in the ichthyoplankton of the west- 

 ern Gulf of Alaska and concluded that the larvae of 

 several species, mainly hexagrammids and cottids, 

 are primarily neustonic. This finding merits further 

 investigation concerning the ecological significance 

 of a neustonic existence, particularly in this shelf area 

 where there is a dynamic surface zone with a vigor- 

 ous flow field (Reed et al., 1988; Reed and Schu- 

 macher, 1989). The present paper focuses on the 

 neustonic ichthyoplankton in the western Gulf of 

 Alaska. During seven of the spring cruises (1981- 

 86), neuston as well as subsurface bongo net sam- 

 pling was carried out. Data from these collections 

 were used 1 ) to examine species composition and rela- 

 tive abundance of ichthyoplankton taxa in the neus- 

 ton and to compare these with 

 subsurface ichthyoplankton col- 

 lected concurrently; 2) to iden- 

 tify obligate and facultative 

 members of the neustonic ich- 

 thyoplankton; 3) to investigate 

 diel variation in catches of lar- 

 vae in the neuston; 4) to com- 

 pare size distributions among 

 the neustonic and subsurface 

 larvae; and 5) to describe hori- 

 zontal distribution patterns of 

 the dominant neustonic ich- 

 thyoplankton species and to re- 

 late these to the oceanography 

 of the western Gulf of Alaska. 



Methods 



In 1981, the National Marine Fisheries Service 

 (NMFS) initiated studies on the early life history of 

 walleye pollock in the northwestern Gulf of Alaska. 

 These studies included cooperative cruises with the 

 Soviet Pacific Research Institute (TINRO, Vladi- 

 vostok). Although the primary purpose of these 

 cruises was to assess the spatial distribution and 

 abundance of walleye pollock and to understand the 

 dynamics of their planktonic stages, all taxa collected 

 were identified and measured. For the present study, 

 we used data from seven cruises during which both 

 neuston net and bongo net samples were collected at 

 each station. These cruises were conducted during 

 spring months of the years 1981 to 1986 (Table 1). 

 The survey area extended from the Kenai Peninsula 

 ( 145°W), southwest along the Alaska Peninsula and 

 Kodiak Island to Unimak Pass (165°W). The topog- 

 raphy of the study area in the western Gulf of Alaska 

 is characterized by numerous troughs and shallow 

 banks (Fig. 1). The shelf area, as defined by the 200- 

 m isobath, is generally wide (65-175 km) and drops 

 abruptly to depths of 5,000-6,000 m in the Aleutian 

 Trench, which parallels the shelf break (Fig. 1). A 

 detailed description of the physical oceanography of 

 the region is provided by Reed and Schumacher 

 (1986). 



The neuston was sampled at a total of 898 stations 

 (Table 1). Station locations varied for each cruise 

 because of specific objectives and are given in Dunn 

 and Rugen. 4 Neuston net samples were collected with 

 a Sameoto sampler ( Sameoto and Jaroszynski, 1969 ) 



Dunn, J. R., and W. C. Rugen. 1989. A catalog of Northwest and 

 Alaska Fisheries Center ichthyoplankton cruises, 1965-1988. 

 U.S. Dep. Commer., NOAA, Natl. Mar. Fish. Serv., Alaska Fish. 

 Sci. Cent, 7600 Sand Point Way NE, Seattle, WA, 98115. Proc. 

 Rep. 89-04, 197 p. 



