Annual Report For Interagency Agreement 14-16-0001-89508 EVALUATION OF INSTREAM FISH HABITAT RESTORATION STRUCTURES IN KLAMATH RIVER TRIBUTARIES 1988/1989 by A.D.Olson and J.R. West USDA-Forest Service, Klamath National Forest 1312 Fairlane Road, Yreka, CA 96097 ABSTRACT Ten instream fish habitat techniques were evaluated to determine which most effectively restored salmonid spawning and/or rearing conditions. Structure stability was estimated based on how intact each structure remained (by percent) and its age, we then projected useful life for each structure type. Cost in 1989 dollars was used to determine cost per unit habitat area provided. Observed use by spawners was used to estimate total number of redds per structure (over its life). Cost of providing spawning habitat (cost per redd) was calculated by dividing estimated total redds by structure cost. Habitats resulting from instream structures were classified using the modified Bisson method and we determined the influence zone of each structure using physical variables to define habitat area. Structures were biologically sampled using direct underwater observation techniques described by Hankin and Reeves1 (1989). Two person dive teams used a "two-pass" method to enumerate and classify salmonids by species and age-class (0+, 1+ or older juveniles, and adults), noting the presence of other species. Fish use of structure affected habitat (post-modification) was compared to use of habitats like those present prior to structure placement (pre-modification). Comparison of "pre-modification" and "post-modification" fish standing crops resulted in a "net fish difference" which was divided by structure cost, yielding "cost per fish reared11. Boulder weirs, the most expensive structures investigated, did not affect enough surface area to make cost per unit of affected habitat reasonable. Cabled cover logs and digger logs (lowest cost structures) were very cost effective at altering physical habitat condition. We believe cost of physically modifying habitat area is only one factor that is important enough to effect success or failure of a large scale habitat restoration program. Assuming all other factors are of equal weight, lowest cost structures can provide the "best value". Modification prescribed to restore stable spawning habitat needs close scrutiny. We believe it is essential to know how the existing habitat is used by spawners by conducting spawning area use surveys which identify redd location and quantify habitat available during each spawning period. Boulder deflectors were best utilized by Chinook salmon spawners, however chinook spawner use of "traditional" structures (weirs backfilled with gravel) was disappointing. Backfilling of instream structures with suitable gravel is a practice that should be discontinued. Steelhead spawner use of structures which result in "pocket water" type spawning areas were heavily used. This habitat configuration proved most desirable when woody object cover was readily available to the spawners. The highest steelhead spawner use was associated with boulder groups with wood and boulder/rootwad groups. We found rearing structures which provided high habitat and cover diversity received the best response from juvenile fish. We observed fish use over one summer and saw dramatic unpredictable use changes even through this short time period. Fish rearing needs during other seasons may differ substantially from summer needs, therefore, suitability of modified habitat probably also changes. Digger logs, one of the least costly and simplest structures, provided the best increase in fish standing crop (fish/m2) for the lowest cost. We believe digger logs were well used by rearing fish because they are one of the most natural restoration structures investigated. Other structures which were well used (small weirs, deflectors, and boulder groups with attached wood) also seem to closely duplicate naturally productive habitats. Higher velocity habitat types associated with boulder groups with wood, boulder rootwad groups, and boulder deflectors were selected by juvenile steelhead and chinook salmon. Providing overhead cover, especially if it extends into the water where it may also be used as object cover, seemed most valuable for juvenile steelhead and salmon if it was placed in a habitat type which would normally receive high fish use. Placement of object cover in slow velocity areas (pool and glide edges) had questionable value for summer rearing habitat restoration, however we do not know what value these structures may have during colder water high flow periods when fish seek slow velocity, densely-covered habitats. We defined the most cost effective method as one meeting restoration objectives, providing the greatest increase in fish use (per surface area or volume), over the longest time period, for the lowest cost. We rank structures evaluated in this study (from most cost-effective to least cost effective) as follows: Digger Logs, Boulder deflectors, Small Boulder Weirs, Boulder Groups with Woody Cover, Free Boulder Weirs, Large Boulder Weirs, Boulder Groups, Boulder/Rootwad Groups, Boulder/Rootwad Deflectors, Small Boulder Weirs, and Cabled Cover Logs.
Cover title. ; "89(4.25)"--Cover.; "Annual report for Interagency Agreement 14-16-0001-89508."; Shipping list no.: 92-1473-M.; Includes bibliographical references (p. 36).