Fisheries Habitat and Fish Populations 



Most of our box loss occurred during a Novem- 

 ber, 1989, precipitation event. We noted sub- 

 stantial movement of streambed material at this 

 time. We lost all W-V boxes planted in several 

 South Fork and Middle Fork Flathead tributar- 

 ies. Some box displacement and loss occurred 

 in the North Fork Flathead and Swan River 

 drainages as well. In all, we lost well over 100 

 W-V boxes during this event. 



Of the 182 boxes recovered, we analyzed 

 109 in the laboratory for fine sediment accumu- 

 lation and density. The overall linear regression 

 of submerged weight of a W-V box against the 

 percentage of material less than 4.75 in the 

 associated McNeil core sample showed a sig- 

 nificant positive relationship (p < 0.05), al- 

 though considerable scatter existed (r = 0.48). 

 When we compared the mean percentage less 

 than 4.75 mm in the W-V boxes (12 per site) 

 with the mean from McNeil coring (12 per site) 

 at each study area, we observed significant 

 differences (p < 0.05) in eight of the 12 com- 

 parisons. We expected the mean percentages 

 from the boxes to be in closer agreement with 

 the coring data. 



Based on these findings, we question 

 whether W-V boxes are suitable for monitoring 

 streambed conditions at this time. However, we 

 believe the potential advantages of this tech- 

 nique over presendy used methods warrant 

 greater effort at developing a W-V box program 

 for the Flathead Drainage. Questions relating to 

 box planting, box loss, timing of box planting, 

 and best marble size will require more evalu- 

 ation. A change in box design to use perfora- 

 tions 6.35 mm in diameter would yield more 

 usable results and might eliminate questions 

 about the maximum particle size which could 

 enter the boxes. 



Streambed Substrate Scoring 



Rearing fish, particularly juvenile bull trout, 

 often occupy open spaces between or under 

 streambed materials. Substrate score (Grouse 

 and others 1981) is an index indicating the 

 habitat's potential for rearing and overwinter- 

 ing fish. Silt-free streams with large rocks and 

 lots of hiding space would get a high substrate 

 score. As the streambed becomes more imbed- 

 ded with silt and sand, the substrate score would 

 become less. Scores above 1 1 .0 generally indi- 

 cate good rearing habitat quality. Other re- 

 searchers have specified 9.0 as the minimum 

 critical standard (Shepard and others 1984). 



Substrate scores ranged from 8.8 in Freeland 

 Creek to 13.2 in Piper Creek. Based on the 

 above values, Jim and Freeland creeks are at or 

 below the minimum recommended level. 

 Squeezer, Lion, and Coal Creeks scored be- 

 tween 9.0 and 10.0. Sixty-two percent of the 

 scores basin- wide were 1 1 .0 or higher. 



Linear regression of juvenile bull trout den- 

 sities (number of trout per 100 m^) against 

 substrate score showed a significant positive 

 relationship (r = 0.54, p = 0.05; n =15). (See 

 Figure D-4.) Densities of other trout species in 

 our study streams did not correlate with this 

 index. This is probably due to behavioral differ- 

 ences. These species are not strongly associated 

 with the streambed at the time our estimates 

 were made. 



During winter, long portions of stream chan- 

 nel are completely ice- and snow-covered. Field 

 crews have also observed extensive areas of 

 anchor ice. In other areas, upwelling ground 

 water keeps certain sections open, even during 

 extreme conditions. These open areas may sup- 

 port the majority of the winter rearing in the 

 streams where they occur. It is likely that if we 

 could obtain estimates of juvenile fish densities 

 during this winter period instead of late sum- 

 mer, a stronger relationship would result. 



Flathead Basin Cooperative Program Final Report 



Page 59 



