Current Patterns and Distribution of 

 River Waters in Inner Bristol Bay, Alaska 1 



RICHARD R. STRATY- 



ABSTRACT 



Hydrographic studies to determine the distribution of the waters of the major sockeye-salmon- 

 producing river systems in inner Bristol Bay show the net seaward flow of river water is along the 

 northwest (right) side of inner Bristol Bay. The net motion of seawater toward the head of Bristol Bay 

 transports with it the waters of Ugashik and Egegik rivers, which enter the bay on the southeast side. 

 Near Egegik Bay to Middle Bluff, the mixed sea and river waters join the seaward flow of Kvichak 

 and Naknek river waters, which enter at the head of Bristol Bay. Waters of these four rivers, along 

 with the large volume of water from the rivers entering Nushagak Bay, are eventually transported to, 

 and move seaward on, the northwest side of Bristol Bay. Waters of Naknek, Egegik, and Ugashik 

 rivers are similar to each other in the courses followed during ebb and flood tides. Flood tide currents, 

 along with the nontidal current, transport water from Egegik and Ugashik rivers above or north of the 

 entrance to Egegik and Ugashik bays. 



INTRODUCTION 



The distribution and migratory behavior of juvenile 

 and adult sockeye salmon, Oncorhynchus nerka, while in 

 Bristol Bay are influenced by physical and chemical 

 properties of the bay. The literature on salmon behavior 

 indicates that certain features of a bay or estuary, such 

 as salinity gradients (Mclnerney 1964), or phy- 

 sicochemical properties of home-river waters (Hasler and 

 Wisby 1951; Wisby and Hasler 1954; Donaldson and 

 Allen 1958; Hara et al. 1965; Hasler 1966), may provide 

 directive cues to salmon during their seaward and hom- 

 ing migrations. In Bristol Bay, the distribution of home- 

 river waters and the physicochemical properties they 

 contain are the result of ocean currents. 



In conjunction with investigations by the National 

 Marine Fisheries Service of the early marine life of 

 sockeye salmon (Straty 1974) and their later dis- 

 tribution during spawning migration (Straty 1975), data 

 were collected to describe the current patterns and dis- 

 tribution of waters from the major sockeye-salmon- 

 producing river systems in Bristol Bay. Such infor- 

 mation was expected to provide a better understanding 

 of the relationship between environmental factors and 

 behavior of salmon while in Bristol Bay and to provide 

 knowledge for predicting the distribution of pollutants 

 which might be introduced into the bay or rivers during 

 the critical period when salmon are present. 



In this paper I describe the distribution of water from 

 each major river system as it flows out of the bay and 



Based in part on a thesis submitted to the graduate school of Oregon 

 State University, Corvallis, in partial fulfillment of the requirements for 

 the degree of Doctor of Philosophy, June 1969. 



-Northwest and Alaska Fisheries Center Auke Bay Laboratory, Na- 

 tional Marine Fisheries Service. NOAA, P.O. Box 155, Auke Bav, AK 

 99821. 



describe current patterns of the mixed sea and river 

 waters within the bay. 



BACKGROUND 



Bristol Bay, the southeastern terminus of the shallow 

 continental shelf of the Bering Sea, is considered to be 

 the area east of a line drawn from Cape Sarichef on 

 Unimak Island to the Kuskokwim River (Fig. 1). Unimak 

 Island and the Alaska Peninsula bound Bristol Bay on 

 the south and east and separate it from the North Pacific 

 Ocean. The studies reported here were conducted in the 

 inner bay between Kvichak and Cinder rivers (Fig. 1). 



Most of the precipitation in Bristol Bay occurs from 

 July through September. Total rainfall varies from 76.2 

 to 101.6 cm annually, August being the rainiest month 

 (U.S. Coast and Geodetic Survey 1964). Mean air tem- 

 perature is about 1.7° C. Fog occurs in every month of the 

 year at most localities. Ice begins to form along shores of 

 the bay in October or November and expands seaward 

 until March. Although the ice pack usually begins to 

 break up and melt in April, compact fields of drift ice 

 may remain offshore until late May. Over much of Bris- 

 tol Bay, winds are from the northeast from October to 

 March and from the southeast in spring, summer, and 

 early fall. Average wind velocity is 15 knots at Port 

 Heiden in outer Bristol Bay and about 10 knots at Nak- 

 nek at the head of the bay. 



Movement of water in Bristol Bay is affected by ice, 

 runoff, winds, tidal currents, density gradients, and 

 movement of oceanic water off the continental shelf. The 

 funnel-shaped configurations of the bay and of the river 

 entrances create tidal currents with velocities up to 6 

 knots. Tides and currents in the bay are the mixed type 

 in which two highs and two lows occur during a tidal day, 

 generally with a significant diurnal inequality. The diur- 

 nal range of tide averages about 5.5 m at river entrances. 



