shocker was used with paddle -type electrodes; 

 downstream an electric seine was used. A five- 

 man crew shocked through each sampling sta- 

 tion (200 yards of stream) twice . On the first 

 trip all fish were measured to the nearest inch, 

 marked by clipping a small portion of the caudal 

 fin, and released in the water in close proximity 

 to where they were collected. On the second 

 trip, which was made within one -half hour of the 

 first, data were collected on the number of 

 marked and unmarked fish by inch groups . The 

 total population was calculated from the assump- 

 tion that marked and unmarked trout were cap- 

 tured in the second run in direct proportion to 

 their numbers in the stream . Since large trout 

 were collected more easily than small ones, it 

 was necessary to make separate estimates for 

 different size groups. There were no signifi- 

 cant differences in recovery rates between rain- 

 bow and brown trout of the same size range; 

 therefore, the average recovery rates of both 

 species were used to compute the population 

 estimates when too few trout could be collected 

 within a size group . The recovery rates of both 

 brown and rainbow trout by size groups were as 

 follows: 2.0 to 4.9 inches, 10.6 percent; 5.0 to 

 8.9 inches, 15.0 percent; and 12.0 to 21 inches, 

 30.7 percent. No block seines were used to 

 restrict the movement of fish out of the sample 

 area although the fact that the second trip was 

 made within one -half hour of the first would 

 minimize such a cause for error. 



The lower part of the Firehole (below 

 Station B) and the entire Madison River were 

 too large for the equipment and the sampling 

 method described above . Each sample area 

 was shocked once and a 60 -foot electric seine 

 with a pulsating D.C.-A.C. current was used 

 to collect fish. The information collected was 

 limited to gaining a general knowledge of the 

 size and structure of the fish population. The 

 electric seine was effective in stunning fish of 

 all size groups, although the crew could collect 

 only a small percentage of the fish actually 

 observed. Most fish collected were measured 

 to the nearest inch and then released. Rainbow 

 and brown trout were the two most common 

 species collected, and it is believed that this 

 sampling method collected both species at about 

 the same rate. Whitefish were more difficult 

 to collect than brown or rainbow trout because 

 they were located in deep holes . 



The age class composition of the brown 

 trout population was determined from aging 

 studies of fish caught by anglers during the 1957 

 fishing season and from 36 fish below 8.0 inches 

 captured by shocking. The 36 small trout were 

 all collected from the Madison, and the data 

 were applied to both the Madison and Firehole 

 Rivers. This method was considered reliable 

 since growth rate studies showed that small 

 brown trout grow at about the same rates in both 

 the Firehole and the Madison. When several age 

 groups were represented within a single inch 

 group, the percentage of each age group was 

 determined. For example, within the 8.0 to 8.9 

 inch group on the Firehole River, 76.9 percent 

 were Age Class I and 23 . 1 percent were Age 

 Class II. With this information it was possible 

 to convert all population data by one -inch groups 

 into the age class composition of the population. 

 All trout and whitefish above 8.0 inches were 

 considered to be catchable -size to the angler . 



FISHING PRESSURE AND CATCH 



Fishing pressure 



The number of fishermen on the Madison 

 River system from 1953 to 1957 was: 1953, 

 19,504; 1954, 27,233; 1955, 23,477; 1956, 24,293; 

 and 1957, 25,599 (not including Gibbon) (table 2). 

 The average annual number of trips per mile of 

 stream from 1953 to 1957 was: Madison, 425; 

 Firehole, 382; and Gibbon, 199 (not including 

 1957). The Madison and Firehole have been 

 attracting more fishermen in recent years, 

 while the Gibbon has been attracting fewer. The 

 fishing pressure, as measured by the total hours 

 of fishing effort, increased in the Madison from 

 1953 to 1955 and decreased in 1956 and 1957 

 (figure 3). This decrease apparently was due to 

 decreased planting of adult rainbow trout. Fish- 

 ing pressure on the Firehole increased from 

 13,904 hours in 1953 to 34,460 hours in 1956 and 

 decreased to 22,974 hours in 1957. The Gibbon 

 retained a relatively constant effort from 1953 

 to 1956, with a range of 8,401 to 10,861 hours. 

 The fishing pressure during each season on all 

 streams showed a peak in early July; subsequently, 

 fishing pressure showed a gradual decline to the 

 end of the fishing season. The peak in July was 

 probably related to the heavy influx of tourists 

 into the park during the July 4 weekend and from 

 the fact that stream fish become more difficult 



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