6 3 



Fishery Bulletin 92(1). 1994 



160° 150° 140° 



. i 



-60 N 



156° 



154° 



152 c 



156° 



154° 



Figure 1 



Top panel shows location of the study area and a 

 generalized scheme of the surface circulation. 

 Middle and bottom panels show Shelikof Strait and 

 the sampling transect. Stations are numbered con- 

 secutively beginning with 55 near the Kodiak Island 

 shore; only the end and middle stations are labeled. 



are found primarily in the upper 50 m (Kendall et 

 al., 1993 1 ) and have been shown to prey heavily on 

 copepod nauplii during the first several weeks of 

 development (Dagg et al., 1984; Kendall et al., 1987; 

 Canino et al., 1991). 



The upper water column of Shelikof Strait con- 

 sists of at least three distinct water types (Reed and 



1 A. W. Kendall Jr., L. S. Incze, P. B. Ortner. S. R. Cummings, 

 and P. K. Brown. 1993. The vertical distribution of eggs and 

 larvae of walleye pollock in Shelikof Strait, Gulf of Alaska. Sub- 

 mitted to Fish. Bull. 



Schumacher, 1989). A cold, slightly freshened, tur- 

 bid coastal water band of narrow width (<10 km) 

 remains near the Alaska Peninsula (northern) side 

 of the Strait. This water receives its signature from 

 glacial melt-waters draining into Cook Inlet at the 

 northern end of the Strait and thus varies season- 

 ally in volume. A second water type is encompassed 

 in the Alaska Coastal Current (ACC), part of a 

 baroclinic current running more or less continuously 

 along 1000 km of the Alaskan south coast. The ACC 

 flows from northeast to southwest in a band approxi- 

 mately 20 km wide through the middle portion of 

 the Strait, but it has a highly variable current struc- 

 ture marked by numerous baroclinic instabilities 

 (Mysak et al., 1981; Vastano et al., 1992). In the 

 vertical, the southward flow of the ACC induces an 

 opposite bottom flow of more saline, nutrient rich 

 water that enters the sea valley at the shelf edge 

 south of the study area (Fig. 1; see Reed et al., 1987). 

 A third water type is made up of waters from a 

 mixture of sources, including outer shelf and oceanic 

 intrusions. Most of this water enters from the north 

 and flows the length of the Strait along Kodiak Is- 

 land, but current meter measurements and satellite 

 imagery show that water sometimes enters from the 

 south (Schumacher, 199 1 2 ). 



The work reported here was undertaken as part 

 of a multi-disciplinary program (Fisheries Oceanog- 

 raphy Coordinated Investigations: FOCI) aimed at 

 understanding the influence of environmental fac- 

 tors on the early life history of walleye pollock 

 spawned in the Strait (Schumacher and Kendall, 

 1991). An extensive grid of sampling stations occu- 

 pied in early May 1985, the first year of the pro- 

 gram, showed that the spring bloom of large diatoms 

 did not occur homogeneously throughout the Strait. 

 Rather, in that year, large diatoms bloomed first in 

 a band which occupied the longitudinal mid-portion 

 of the Strait (Incze, unpubl. observ.). Hydrographic 

 data show that this feature was in the ACC, which 

 had at that time a shallower upper mixed layer than 

 elsewhere in the Strait. It seemed likely, therefore, 

 that conditions affecting the feeding and growth of 

 larval walleye pollock would be subject to dynam- 

 ics of the ACC and would differ across the Strait as 

 well as through time. As part of the research pro- 

 gram, a standard across-strait transect was estab- 

 lished near the southern end of the Strait proper 

 (about halfway up the sea valley: Fig. 1). This 

 transect has been sampled with a CTD (Conductiv- 

 ity, Temperature, Depth) as often as ship and re- 

 search schedules have permitted. Biological sam- 



2 J. Schumacher. 1991. Pacific Marine Environmental Labora- 

 tory, Seattle, WA, unpubl. data. 



