Fisheries Habitat and Fish Populations 



By Thomas Weaver^ and John Fraley^ 



Introduction 



The fisheries study module focused on fish- 

 eries habitat and fish populations. Westslope 

 cutthroat trout and bull trout are native to the 

 Flathead system. Montana recognizes these fish 

 as "Species of Special Concern," and affords 

 them special protection. Sediment originating 

 from road building and other land management 

 activities can reduce embryo survival and emer- 

 gence of both species and decrease the available 

 space in the stream bed used for rearing by bull 

 trout. Spawning/incubation by both species and 

 rearing by bull trout are the life stages most 

 sensitive to sediment effects. Sediment deposi- 

 tion can also affect rainbow and brook trout, as 

 well as other fish species, by covering spawning 

 gravel, filling in pools, and altering food habits. 

 However, these other fish species are not good 

 indicators of sediment effects on rearing due to 

 specific behavioral differences. 



The objectives of this study were to 

 ( 1 ) evaluate the relationship between sediments 

 and westslope cutthroat and bull trout emer- 

 gence success, (2) determine capabilities of 

 several methods of measuring fish habitat qual- 

 ity, (3) examine cause and effects relationships 

 between forest practices and fish habitat and 

 populations, and (4) recommend methods for a 

 monitoring program for fish habitat and popu- 

 lations in the basin, relative to forest manage- 

 ment. 



In this study module, we concentrated on 29 

 tributaries. (See Table D-1 and Figure D-1.) 

 These tributaries were located in the following 

 drainages: Swan, Stillwater/Whitefish, North 



Fork, Middle Fork, and South Fork of the Flat- 

 head River. These tributaries were chosen by 

 the study team to be representative of the vari- 

 ety of geography, habitat, land ownership and 

 fisheries conditions in the basin. We selected 

 specific variables to indicate quality of spawn- 

 ing habitat (McNeil coring and Whitlock- Vibert 

 box sampling), rearing habitat (substrate scor- 

 ing), juvenile population levels (electrofishing 

 estimates) and spawner use (redd counts). A 

 complete description of the study design, meth- 

 ods, and findings is available in the Final Mod- 

 ule Report. 



Results and Discussion 



Embryo Incubation Studies 



Researchers examined emergence success 

 and quality (length and weight) of westslope 

 cutthroat trout fry in relation to varying levels of 

 fine substrate materials in a natural stream en- 

 vironment. We simulated natural incubation 

 conditions in a stream (Chapman 1988) by 

 constructing cells with particle sizes, egg pock- 

 ets, and egg planting depths characteristic of 

 natural westslope cutthroat trout redds. A sig- 

 nificant negative relationship (p < 0.005) ex- 



'Thomas Weaver is a Research Specialist with 

 the Montana Department of Fish, Wildife and Parks 

 in Kalispell, Montana. 



*John Fraley was a Fish and Wildlife Program 

 Officer with the Montana Department of Fish, 

 Widlife and Parks in Kalispell, Montana. 



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Flathead Basin Cooperative Program Final Report 



Page 53 



