GRAYLING OF GREBE LAKE 



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and were made of 2%-inch mesh. The remaining 

 equipment consisted of 2 trap nets (much as shown 

 by Crowe, 1950) having a pot, heart, and wings. 

 The pot was of 1-inch mesh and the heart and 

 wings were of 2%-inch mesh. When set, such 

 units tapered from the wings which were 20 feet 

 apart at their outermost end, to the pot which was 

 5 feet wide by 8 feet long by 3 feet deep. All the 

 net gear was soaked in dark -green, copper 

 naphthanate. 



In 1954, four trap nets and a seine were used to 

 capture the fish. Two trap nets were those used 

 during 1953. Two new units were identical with 

 the 1953 design except for a smaller mesh size (1%- 

 ins. rather than 2%-ins.) in the wings. Leaders 

 were not used. These new nets were preserved 

 with light-green copper napthanate. The tied 

 seine was 75 feet by 4 feet, with 1-inch mesh. 



In the population studies, both trout and gray- 

 ling were taken from depths up to 30 feet. The 

 first sets made in deep water (more than 20 feet) 

 killed all the fish that entered the impounding nets. 

 Subsequently only the shallow portions of the lake 

 (less than 20 feet deep) were fished. These shoal 

 areas were sampled randomly by dividing a map 

 of the lake into a grid pattern, numbering the 

 intersections, and drawing numbered slips of paper 

 to determine the sites. Nets were set, lifted each 

 morning, moved to the next predetermined 

 location, and reset. The few shallow areas where 

 seining was possible were fished 9 times at night 

 during the 21 -day sampling period in 1954. 



Captured fish were held in a floating live box 

 attached to a boat. The seined fish were towed to 

 the approximate center of the lake, fin-clipped, and 

 released. Fish from nets were distributed around 

 the lake as the boat moved from one net location 

 to the next. The left pectoral fin was removed 

 in 1953 and the right pelvic fin in 1954. Only 

 grayling in their third year of life (longer than 8.4 

 ins.) and older, and trout more than 5 inches in 

 length, were marked in 1954. The previous year 

 all fish captured were marked (minimum size 4.3 

 inches for grayling, 3.3 inches for trout). 



The period of netting extended from July 8 to 

 August 9 (33 days) in 1953, and from July 1 to 

 July 21 (21 days) in 1954. 



To determine the most effective direction to 

 face nets and capture grayling and hybrid trout, 

 30 sets were placed randomly. The results of the 

 collections (table 4) showed that traps facing the 



shore were two to five times as effective as those 

 directed toward the center of the lake or parallel 

 to shore. An analysis of variance between 

 numbers of fish captured during various facings 

 indicated significance at the 5-percent level. 



In the evening feeding period, the grayling and 

 hybrid trout were evenly distributed about the 

 lake, as judged from patterns of rises. For trout, 

 this conclusion was substantiated by net captures. 

 However, net locations along the outer border of the 

 lily pads and in the shallow eastern portion (fig. 5) 

 consistently resulted in more grayling captures 

 than those in any of the other areas (table 5). 



In 1953, the average daily catch in nets during 

 the 33-day period was 40 fish (table 6). The trap 

 nets were the most effective gear in this operation. 

 These two units accounted for 983 (74.5 percent) 

 of the 1,320 fish taken. By species, the trap nets 

 took 21.5 percent (284) of the hybrid trout and 78.5 

 percent (1,036) of the grayling. Angling added 

 209 grayling and 67 trout to the marked popula- 

 tion with 6 grayling and 4 trout recaptured by this 

 means. 



The greater effectiveness of trap nets over fyke 

 nets in total catch of fish (fig. 6), and the difference 

 in sizes of individuals captured in the two types of 



Table 4. — Numbers of fish captured by 30 net sets faced 

 randomly in Grebe Lake in 1954 



