Fisheries Habitat and Fish Populations 



Population Esttmatton 



Mean total fish density for the 28 elec- 

 trofishing areas was 13.1 trout greater than or 

 equal to 75 mm per 100 m^ of stream surface 

 area. Densities ranged from 2.1 in Jim Creek to 

 75.8 in Freeland Creek. (See Table D-5.) Tribu- 

 tary streams to large lakes which support rear- 

 ing populations of rainbow trout (Freeland and 

 Fish Creeks) and westslope cutthroat trout (Hun- 

 gry Horse, Tiger, Margaret, and Emery creeks) 

 had the highest densities. Eastern brook trout 

 populations in Sheppard and Hand Creek were 

 also present at high densities. (See Table D-5 .) 



Juvenile bull trout are much more substrate 

 oriented than these other trout species. Because 

 of their close association with the streambed, 

 bull trout are better indicators of the influence 

 of fine sediment. We compared juvenile bull 

 trout densities with substrate scores and found 

 a significant positive relationship (r = 0.54; p = 

 0.05; n = 15) existed. (See Figure D-3.) Previ- 

 ous work showed a similar but somewhat stron- 

 ger relationship for Swan River tributaries sup- 

 poning juvenile bull trout (Shepard and others 

 1984). 



We observed a mean juvenile bull trout 

 density of 3.8 fish greater than or equal to 75 

 mm per 100 m^. Densities ranged from 0.4 in 

 Jim Creek to 11.8 in Morrison Creek. (See 

 Table D-5.) Swan River tributaries supported 

 juvenile bull trout at an average density of 2.7 

 fish greater than or equal to 75 mm/100 m^ 

 while the North and Middle Forks averaged 4.6 

 fish/100 m^. Eastern brook trout arc present in 

 the Swan River tributaries but not in the North 

 and Middle Fork sections. 



Information on juvenile bull trout densities 

 and streambed conditions in winter rearing ar- 

 eas may show stronger relationships than we 

 obtained using late summer electrofishing. It is 

 possible that winter rearing habitat may control 

 juvenile bull trout densities in our study streams. 



Any ground-disturbing activities proposed 

 above these critical rearing areas should be 

 carefully planned and monitored. In general, 

 these findings support the use of bull trout as an 

 indicator species for future monitoring efforts. 



Linkage between Risk Assessment and 

 Fisheries 



To demonstrate the linkage between land 

 management activities and fisheries we used 

 simple linear regression analysis. We used arc- 

 sine transformations on the output from the 

 Sequoia index and H^OY model. This is a stan- 

 dard procedure used when data are percentages 

 and the values are limited in range and close to 

 zero. We evaluated the McNeil coring data and 

 the substrate scores as percent differences. 



X = observed value - minimum value (100) 

 minimum value 



This was necessary to expand the range of the 

 data. 



Results showed significant relationships (p 

 < 0.05) between McNeil coring results and 

 output from both Sequoia and H^OY models. 

 The correlation with the Sequoia index was 

 slightly stronger than with the H^OY model. 

 (See Figures D-7 and D-8.) Comparisons of 

 substrate scores with output from both the risk 

 assessment index and H^OY model also show 

 significant relationships (p < 0.05). In this case 

 the correlation with Sequoia was sUghtly weaker 

 than with H^OY results. (See Figures D-9 

 and D-10.) 



Although these relationships are signifi- 

 cant, considerable scatter exists. There are sev- 

 eral reasons which may explain a portion of this 

 scatter. First, to keep this analysis as simple as 

 possible we elected to use linear regression 

 techniques. By including more variables in a 

 multiple regression analysis it is likely we could 



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Flathead Basin Cooperative Program Final Report 



