I I I I I I — I I I I I I I — I \ \ \ \ \ I \ I 

 Chukchi Sea 



Fig. I. Abundance and distribution of ichlhyoplanl^ton during August 1988. 



Fig. 3. Concentration ot chlorophyll (mg/nr ) integrated throughout the water 

 column (from Robie et al.. Subchapter 5.1.2, this volume). Larvae of 

 T. chalcogramma occur where chlorophyll concentrations are 

 <I00 mg/m-. 



The major spawning grounds in the Bering Sea for walleye 

 pollock are the Korfa-Karaginskiy Shelf on the western side of 

 the Bering Sea basin, where peak spawning times are in April 

 and May; the southeastern shelf near Unimak Island, where 

 peak spawning is in March and April; and the Pribilof Islands 

 area, where the peak spawning is in April and May but extends 

 into August; the shelf around St. Matthew Island, where peak 

 spawning is in May and June; and the Aleutian Trough, where 



Fig. 2. Abundance and distribution of walleye pollock (7". cluilcogramma) 

 larvae in the northern Bering and Chukchi Seas. Abundance peaks in 

 the northern Bering Sea. Spawning grounds are marked along the 

 shelfbreak (200 m line). 



peak spawning is January through March (Stepanenko, 1989). 

 It is thought that these populations represent discrete spawning 

 stocks (Hinckley, 1987). 



Is passive transport of eggs and larvae from the known 

 spawning grounds in Bering Slope Current a possible 

 mechanism for the occurrence of pollock larvae in the northern 

 Bering and Chukchi Seas? Pollock eggs have been collected 

 from theGulf of Anadyrbetween June and September, indicating 

 advection from spawning grounds near Cape Navarin (Haryu, 

 1980). Low levels of larval and juvenile pollock were sampled 

 in the Gulf of Anadyr with the highest concentrations (>10) in 

 the area of our highest concentrations (Fig. 2) (Sobolebskiy 

 el al., 1989). Concentrations of pollock larvae in the Gulf of 

 Anadyr can be explained by advection of eggs and larvae from 

 known spawning areas. 



Pollock larvae in the Chukchi Sea occurred in ASW 

 suggesting advection from the south. However, spawning 

 grounds that support the advection of larvae into the Gulf of 

 Anadyr are too far south to be a source of larvae in the Chukchi 

 Sea. The speed ofthe Bering Slope Current is lOcm/s (Kinder 

 et al., 1975; Khen, 1989). Using daily growth rates for larval 

 pollock from the Gulf of Alaska (Yoklavich & Bailey, 1989), 

 5-7 mm SL larvae are approximately 4-5 days old. Adding the 

 developmental rates for the pelagic eggs of 14 days, these 

 larvae could be in the current for approximately 20 days. At 

 average transport rates of 8.64 km/day, the larvae could cover 

 173 km. They would not reach the farthest stations where 

 larvae were caught (Stations 47, 50, 69, 89, and 94; .see 

 Frontispiece), located from 300-600 km from grounds where 

 spawning is reported to occur in July and August (Hinckley, 

 1987). 



196 



