FISHERY BULLETIN: VOL. 71, NO. 2 



(1967) for a past history of the commercial 

 fishery in Canada and the United States. 



To better understand the problems associated 

 with harvesting goldeye from the clear waters 

 of Fort Peck Reservoir, the availability of 

 goldeye to gill net fishermen at different times 

 of the day and year was investigated. Emphasis 

 was placed on selective fishing; i.e., floating 

 gill nets, 8 ft deep, were set in open-water 

 areas away from shallow bays and shorelines 

 to avoid game fish. The results of selective 

 netting revealed that goldeye were present in 

 commercial quantity away from shallow, turbid 

 areas and that the catch consisted of almost 

 100% goldeye (unpublished data). 



However, during the winter, spring, and 

 late fall, the goldeye were not gilled in the 

 floating gill nets. Preliminary netting with 

 8-ft-deep, sinking gill nets (nets were set 

 obliquely and horizontally at different depths) 

 indicated that the goldeye were present during 

 the fall and spring periods, but usually at the 

 20- to 30-ft level. To better determine some 

 of the parameters associated with the vertical 

 distribution of goldeye, the following study 

 was begun in November 1967. 



DESCRIPTION OF FORT PECK 

 RESERVOIR AREA 

 AND SAMPLING SITE 



Fort Peck Reservoir is located in sparsely 

 populated northeastern Montana. At maximum 

 pool the reservoir has a surface area of 245,000 

 acres, a maximum depth of 225 ft near the 

 .dam, and an irregular shoreline over 1,500 

 miles long. Only the Missouri River and Mussel- 

 shell River continuously flow into the reservoir. 

 There are detailed descriptions of the area 

 (U.S. Fish and Wildlife Service, 1952). 



The water of the reservoir is clear except 

 for the shallow ends of large bays and upper 

 ends of the two main arms (Missouri Arm 

 formed by the Missouri River and the Big 

 Dry Arm formed by the intermittent Big Dry 

 Creek). Surface-water temperatures varied from 

 freezing in winter (the Reservoir is completely 

 ice-covered for almost 4 mo) to the low 20 °C 

 in summer. 



There was little indication of thermal strati- 



fication. During the ice-cover period, the water 

 temperature in the sampling area was 1.1 °C 

 from the surface to at least a depth of 50 ft. 

 Also, water tapped from approximately 140 

 to 160 ft below the surface for the turbines 

 at the dam was 1.1 °C during most of the above 

 period (records kept by U.S. Corps of Engineers 

 at Fort Peck). The continued withdrawal of 

 water for power production (10,000 cfs) prob- 

 ably discouraged formation of a winter in- 

 verse stratification. The almost ever present 

 prairie winds and withdrawal of water for 

 power production probably discouraged the 

 formation of a true summer thermocline. During 

 the warm months of July and August, the 

 temperature from the surface to depth of 

 50 ft varied only a few degrees Celsius in the 

 sampling area. Phenicie (1950) found little 

 evidence of a thermocline, and he recorded a 

 high temperature of 8.3 °C at a depth of 180 ft. 

 Temperature data kept by the U.S. Army 

 Corps of Engineers during July and August 

 were usually in the 9°-13°C range for water 

 taken from the 140- to 160-ft level. 



The area sampled was open water located 

 from V2 to 1 mile off a point of land near the 

 west end of Fort Peck Dam. The water was 

 clear, and depths ranged from 50 ft to over 

 100 ft. Netting efforts in other parts of the 

 lower reservoir area by the Montana State 

 Fish and Game Department and commercial 

 fishermen indicated that the sampling site was 

 representative of open, clear-water areas of 

 the lower reservoir. 



MATERIALS AND METHOD 



To determine the vertical distribution of 

 the goldeye, a floating nylon gill net was used. 

 The net measured 100 ft long and 40 ft deep. 

 The webbing, of No. 139 nylon twine, was 

 IVa-inch mesh, square measure. The net was 

 divided into five horizontal sections, each 8 ft 

 deep. The depth of 40 ft was chosen since 

 numerous (approximate number not known) 

 test-netting efforts during spring, summer, and 

 fall of 1966-69 gilled few goldeye below the 

 40-ft depth (oblique, horizontal, and bottom 

 sets were utilized). Most of the Montana State 

 Fish and Game Department and commercial 



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