COOPER: VERTICAL DISTRIBUTION OF GOLDEYE 



fishery goldeye nets have No. 139 nylon twine. 

 This lV2-inch mesh was selected because it 

 gilled more goldeye than 1-inch, lV4-inch, 

 1%-inch, or 2-inch mesh (unpublished data). 

 Eight-foot sections represented the width of 

 gill nets used for goldeye on the Reservoir. 

 Usually the net was set for overnight and 

 then lifted. It was observed that daylight sets 

 rarely caught many goldeye in clear water. 

 The exact time of setting and lifting the net 

 usually had little influence on the catch as 

 long as the net was set well before dusk and 

 lifted after sunrise. Because so few goldeye 

 were caught in overnight sets during the ice- 

 cover period in 1968, the net was set for several 

 days before lifting during the 1969 ice-cover 

 period. 



RESULTS 



The vertical distribution pattern can be fol- 

 lowed in Table 1. 



During the summer and early fall, the 

 goldeye exhibited maximum stratification with- 

 in 8 ft of the surface, and they were easily 

 captured by floating gill nets. The summer and 

 early fall pattern began in 1968 and 1969 

 once the surface temperature reached 7.2 °C 

 and remained above 13.3 °C. 



The late fall pattern in 1967, 1968, and 

 1969 eventually exhibited the reverse of the 

 summer pattern; i.e., the greatest concentra- 

 tion in the top 40 ft was between the 32- and 

 40-ft level. However, the goldeye did not move 

 quickly from the surface to deeper depths. 

 There was a transitional period during which 

 the goldeye were scattered throughout all 

 depths sampled (0-40 ft). The late fall pattern 

 began as the surface temperature approached 

 6.1°C in 1967 and 8.9°C in 1968 and 1969. 



During the ice-cover period, the goldeye 

 appeared to concentrate between the 8- and 

 32-ft level; however, few goldeye were taken 

 per night set. In 1968, the catch per night 

 set was 22 goldeye; in 1969, the equivalent 

 catch per night set was 3.5 goldeye. In con- 

 trast, the ice-free period usually had catches 

 of 60 or more goldeye per night set. The water 

 temperature was 1.1 °C both winters. 



The goldeye vertical distribution pattern in 



the spring was not as predictable as in other 

 periods. The goldeye were caught at all depths, 

 near the surface, or near the 40-ft depth. No 

 clear relationship between the distribution 

 pattern and temperature was evident. Appar- 

 ently quick shifts in wind direction affected 

 surface temperatures more in spring than in 

 summer and fall. Since the warm surface- 

 water column in summer and fall penetrated 

 to deeper levels than the spring warm surface 

 column, maybe upward convection currents 

 more easily displaced surface water in the 

 spring. 



DISCUSSION 



The following discussion concerns mostly 

 the open-water area; i.e., little reference is 

 made to the goldeye that may habitually seek 

 shallow, turbid conditions such as would be 

 found in small bays and near river mouths. 



It is evident that the goldeye in the sampling 

 area do exhibit consistent seasonal vertical 

 distribution patterns and that the patterns 

 can usually be predicted from the surface- 

 water temperature. The cause of the patterns 

 is not clear, but it is suspected that the gold- 

 eye is following the food source, which in Foil 

 Peck Reservoir consists of zooplankton, ter- 

 restrial insects, aquatic insects, and small 

 fishes. It is believed from observations (re- 

 gurgitation of stomach contents when goldeye 

 were forced through the mesh), daytime versus 

 night-time sets, and cursory stomach examina- 

 tions that the goldeye do most of their feeding 

 at night during the summer and early fall 

 when zooplankton and terrestrial and emergent 

 aquatic insects are available on or near the 

 surface. Work by Bajkov (1930) and Grosslein 

 and Smith (1959) support the above contention 

 as does work by Sprules (1947). 



It is not known whether the goldeye move 

 to deeper water during the day. Surface sets 

 over clear, deep water during the day have 

 caught few goldeye although sets in turbid, 

 shallow areas often produce substantial catches. 

 Possibly the fish gilled in the shallow, turbid 

 water could not see the net. 



Obviously, terrestrial insects do not con- 

 tribute significantly to the diet during the 



475 



