lies in a long deeply glaciated valley and has a 

 moderately high shoreline development, similar 

 to the average of Iliamna Lake. 



The Naknek system contains seven major in- 

 terconnected lakes or basins all formed by glacial 

 action. In general, the basins are elongate, deep, 

 and steep sided. Within these basins, however, 

 are representatives of most of the major physi- 

 cal and biological types of sockeye salmon lakes 

 in southwestern Alaska. One exception is the 

 lack of a basin as shallow and eutrophic as Black 

 Lake of the Chignik system. 



Three lakes of the Naknek system — Coville, 

 Grosvenor, and Naknek — form a chain that 

 drains through Naknek River into Bristol Bay. 

 Coville Lake has the shallowest basin — mean 

 depth, 19 m. It receives a great part of its water 

 from snowmelt and runoff via 80-km.-long Amer- 

 ican Creek. Coville Lake acts as a settling basin 

 for downstream Grosvenor Lake. Iliuk Arm of 

 Naknek Lake receives drainage from Grosvenor 

 Lake and from glacier fields via the Savonoski 

 River, and from areas of volcanic ash and pumice 

 in the Valley of Ten Thousand Smokes via the 

 Ukak River. The heavy load of rock flour and 

 volcanic materials from these drainages has a 

 profound effect on the water quality and trans- 

 parency of Iliuk Arm, and to a lesser extent on 

 other areas of Naknek Lake. The South Bay 

 basin of Naknek Lake receives water from Iliuk 

 Arm and North Arm directly, and from Brooks 

 Lake via 1.6-km.-long Brooks River. Brooks Lake 

 receives snowmelt and runoff drainage from low 

 mountains and extensive lowland wet tundra ; the 

 water is extremely clear. The North Arm basin of 

 Naknek Lake has a restricted connection to South 

 Bay because of a moraine that forms islands and 

 shallow water along their common border. 

 Drainage into North Arm is snowmelt and run- 

 off, predominantly from areas of wet tundra. 

 The west end of Naknek Lake leading to the 

 outlet is less than 15 m. deep. The comparatively 

 small and shallow northwest basin is separated 

 from North Arm by a moraine and connected 

 to the west end of Naknek Lake across a wide 

 shoal. 



Little is known about the morphometry of the 

 remaining lakes in the Bristol Bay area. For 

 lakes of the Alagnak, Egegik, and Ugashik sys- 

 tems we have only the information available 

 from U.S. Geological Survey topographic maps. 



The morphometry of the two major lakes of 



the Chignik system, Chignik and Black, is con- 

 trasting. Maximum and mean depths are only 6 

 and 3 m. for Black Lake, but they are 64 and 

 26 m. for Chignik Lake. Black Lake flows into 

 Chignik Lake through Black River. Meltwater 

 from an ice field on Mt. Veniaminoff enters 

 Black River and, subsequently, Chignik Lake. 

 The Karluk system drains via Karluk River 

 into Shelikof Strait on the northwest side of 

 Kodiak Island. The system contains two small 

 lakes and one large lake. The small lakes. Thumb 

 and O'Malley, drain into separate basins of the 

 large lake, Karluk. Karluk Lake is about 20 km. 

 long, has a mean depth of 49 m., and appears 

 to be of glacial origin. Drainage is snowmelt 

 and runoff from a watershed composed predom- 

 inantly of sedimentary rock. 



LIMNOLOGY OF THE LAKES 



The limnological studies were designed to 

 help explain why the various lakes and systems 

 produce salmon at different rates. In addition 

 to morphometry of the lakes, we measured fac- 

 tors that other investigators have related to the 

 biological productivity of lakes — chemical and 

 thermal characteristics of the water. We meas- 

 ured biological productivity in terms of primary 

 productivity and the standing crop of phyto- 

 plankton. The several measures of water chem- 

 istry and biological productivity are examined 

 in relation to production of salmon. 



WATER CHEMISTRY 



The euphotic zones of the major sockeye salm- 

 on nursery lakes were sampled between May 

 1961 and November 1962 to determine their 

 chemical characteristics. The number of deter- 

 minations varies among characteristics and 

 lakes, but sampling was concentrated in the more 

 important systems (table 2) . Standard methods 

 of collection and analysis were used. In general, 

 lakes of the Peninsula Systems contained higher 

 concentrations of dissolved minerals than those 

 of the Mainland Systems (table 3). 



Total Dissolved Solids, Alkalinity, and pH 



We have ranked the lakes according to total 

 dissolved solids, total alkalinity, and pH (table 

 4). As would be expected, the rankings of the 

 lakes by the three measurements tend to be 

 similar, i.e., the more alkaline lakes tended to 

 have higher total dissolved solids and generally 

 higher pH values. Lakes of the Naknek, Chignik, 



SOCKEYE SALMON IN MAJOR RIVER SYSTEMS IN SOUTHWESTERN ALASKA 



411 



