Volume 079 Article 05 FEDERAL AID IN FISH RESTORATION STATUS AND ANALYSIS OF SALMONID FISHERIES Westslope Cutthroat Trout Synopsis and Analysis of Fishery Information Project F-73-R-11, Subproject No. II, Job No. 1 Period Covered: March 1, 1988 to February 28, 1989 by Bruce E. Rieman, Principal Fishery Research Biologist And Kimberly A. Apperson, Fishery Research Biologist October 1989 TABLE OF CONTENTS Page ABSTRACT ................................................................1 INTRODUCTION ............................................................3 RECOMMENDATIONS .........................................................5 OVERVIEW ................................................................7 History and Characteristics ........................................7 Current Status ....................................................11 Range .........................................................11 Abundance .....................................................12 Abundance Factors .............................................16 Genetic Integrity .............................................16 Current Regulations ...........................................17 Other Management ..............................................17 Potential to Restore .........................................17 Summary ............................................................18 HABITAT ................................................................19 Characteristics of Habitat ........................................19 Degradation of Habitat ............................................22 Habitat Manipulation ..............................................25 Summary ............................................................26 INTERACTION WITH OTHER FISHES .........................................28 Competition .......................................................28 Predation .........................................................31 Genetic Introgression .............................................32 Summary ............................................................33 POPULATION DYNAMICS ....................................................35 Growth .............................................................35 Mortality .........................................................38 Natural Mortality .............................................38 Fishing Mortality ............................................40 Recruitment .......................................................41 Population Simulations ............................................47 Methods .......................................................47 Simulation Results ...........................................48 Discussion ....................................................51 Summary ............................................................57 R9FS078TC i TABLE OF CONTENTS Page HATCHERY SUPPLEMENTATION ...............................................58 History ............................................................58 Evaluations ........................................................58 Alternatives for the Future ........................................62 Broodstock and Genetic Considerations ..............................64 Summary ............................................................66 MANAGEMENT - HARVEST REGULATIONS .......................................67 Biological Results .................................................67 Sociological Results ...............................................71 Management Alternatives ............................................72 Methods of Evaluating Regulations ..................................73 Management Experiments .............................................75 Summary ............................................................77 DISCUSSION AND CONCLUSIONS .............................................78 ACKNOWLEDGEMENTS .......................................................83 LITERATURE CITATIONS ...................................................84 APPENDIX A ................... ........................................113 LIST OF TABLES Table 1. Summary of River's Data Base variables (stream miles classified) for westslope cutthroat trout in Idaho by total (statewide) ranges and by Idaho Fish and Game Management Region. Classifications are described in the text ..................................................13 Table 2. Estimated mean length-at-age for fluvial and adfluvial westslope cutthroat trout. Data was summarized by Lukens (1978) and Pratt (1985) ...............................37 Table 3. Total mortality, natural mortality, and exploitation estimated for westslope cutthroat trout in Idaho . 39 Table 4. Maturity rates (proportion mature at age) of westslope cutthroat trout. Data for Hungry Horse Creek, St. Joe River, and Wolf Lodge Creek were summarized by Lukens (1978) and are predicted rates from age composition of spawners. Data for the Coeur d'Alene River (Lewensky 1986; Apperson et al. 1988) and Middle Fork Salmon River (Mallet 1963) are actual proportions of maturing fish in population samples ...................................42 ii R9FS078TC LIST OF TABLES (Continued) Page Table 5. Parameter estimates used in westslope cutthroat trout population simulations ...................................... 49 Table 6. Numbers and total pounds of hatchery-reared westslope cutthroat trout planted in Idaho waters, from 1977 to 1987. Hatchery data base is complete only after 1981, but virtually all previous production went to Hayden Lake ........................................................ 59 Table 7. Summary of westslope cutthroat population and fishery responses to special regulations that have been evaluated ................................................... 68 Table 8. Densities of westslope cutthroat trout in Idaho streams and rivers estimated from snorkeling or approximated from snorkel trend counts ................................... 76 LIST OF FIGURES Figure 1. Historic and current range of westslope cutthroat trout in Idaho. "A" represents the historic range. "B" represents the current range of "strong" populations. \"C" represents strong populations and the locations of "wilderness" areas. "D" represents the range of "viable" (strong or depressed) and suspected genetically pure populations ................................................ 15 Figure 2. Growth of westslope cutthroat trout. Dark lines represent adfluvial populations; light lines represent fluvial populations. Growth of Wood River rainbow trout is shown for comparison with a productive trout stream outside the westslope cutthroat trout range. Wood River data are from Thurow (1989). Other data are summarized in Table 2 ................................................. 36 Figure 3. Relationship of catch rate (cutthroat/angler hour) and snorkel density (fish/transect) in the Lochsa River. The line was fit by inspection. Data are from Lindland (1982) ............................................ 43 Figure 4. Hypothetical stock-recruitment relationships for westslope cutthroat trout. The different curves are discussed in the text. "A" represents a population under heavy density-independent mortality, and "C" represents a population where carrying capacity has been reduced ............................................... 45 R9FS078TC iii LISTOFFIGURES (Continued) Page Figure 5. Simulations of westslope cutthroat trout number (proportion of unexploited population number) with varied growth, natural mortality, spawning frequency, and resilience in the stock-recruitment relationship under different levels of exploitation. The dark line shows a population with initial parameter estimates; the light lines show deflection of results with changes in single parameters described in the text ....................50 Figure 6. Simulations of westslope cutthroat trout number (absolute number) with varied growth, natural mortality, spawning frequency, and resilience in the stock-recruitment relationship under different levels of exploitation. The dark line shows a population with initial parameter estimates; the light lines show deflection of results with changes in single parameters described in the text ...........................52 Figure 7. Simulations of westslope cutthroat trout population structure (proportion of recruited population that was larger than 300 mm) with varied growth, natural mortality, spawning frequency, and resilience in the stock-recruitment relationship under different levels of exploitation. The dark line shows a population with initial parameter estimates; the light lines show deflection of results with changes in single parameters described in the text .......................................53 Figure 8. Simulated time (years) for westslope cutthroat trout populations to recover from overexploitation with varied growth, natural mortality, spawning frequency, and resilience in the stock-recruitment relationship. Populations were exploited to 10% of the unexploited population size. Recovery was to 90% of the unexploited population size ................................54 Figure 9. Simulations of westslope cutthroat trout population number (proportion of unexploited population) with varied growth, natural mortality, spawning frequency, and resilience in the stock-recruitment relationship under different minimum size limits in the fishery. The dark line shows a population with initial parameter estimates; the light lines show deflection of results with changes in single parameters described in the text. Exploitation was at