Information Report Stock Assessment and Optimal Escapement of Coho Salmon in Three Oregon Coastal Lakes Shijie Zhou Fish Division Oregon Department of Fish and Wildlife 2501 SW First Avenue PO Box 59, Portland, Oregon 97207 December 2000 Contents Contents................................................................................................................................ i List of Tables.......................................................................................................................ii List of Figures ....................................................................................................................iii Acknowledgement............................................................................................................... v Abstract ............................................................................................................................... 1 Introduction ......................................................................................................................... 1 Methods............................................................................................................................... 2 Estimation of escapement ................................................................................................ 2 Estimation of recruitment ................................................................................................ 5 Freshwater harvest and terminal run................................................................................ 5 Ocean harvest and recruitment......................................................................................... 6 Stock-recruit relationship................................................................................................. 7 Estimation of management parameters............................................................................ 8 Uncertainty assessment: bootstrap and simulation .......................................................... 9 Results ............................................................................................................................... 10 Siltcoos Lake.................................................................................................................. 10 Tahkenitch Lake............................................................................................................. 12 Tenmile Lakes................................................................................................................ 14 Discussion ......................................................................................................................... 16 Reference........................................................................................................................... 19 i List of Tables Table 1. Escapements of coho salmon in Siltcoos Lake, 1960-1999............................................... 22 Table 2. Coho salmon freshwater harvests and terminal runs in Siltcoos Lake basin, 1960-1999.......................................................................................................................... 23 Table 3. Estimated adult and jack ocean harvest rates for Oregon coastal coho salmon, 1960-1999.......................................................................................................................... 24 Table 4. Spawners and recruitment of coho salmon in Siltcoos Lake, brood years 1960-1996. The ocean survival rates were estimated from coded-wire- tagged North Umpqua River hatchery coho. ..................................................................... 25 Table 5. Parameter estimates from selected models for Siltcoos Lake coho salmon....................... 26 Table 6. Escapements of coho salmon in Tahkenitch Lake, 1960-1999.......................................... 27 Table 7. Coho salmon freshwater harvests and terminal runs in Tahkenitch Lake basin, 1960-1999. .............................................................................................................. 28 Table 8. Spawners and recruitment of coho salmon in Tahkenitch Lake, brood years 1960-1996.......................................................................................................................... 29 Table 9. Parameter estimates from selected models for Tahkenitch Lake coho salmon. ................ 30 Table 10. Escapements of coho salmon and its standard error (SE) and coefficient of variance (cv) in Tenmile Lakes, 1960-1999. ..................................................................... 31 Table 11. Coho salmon freshwater harvests and terminal runs in Tenmile Lakes basin, 1960-1999.......................................................................................................................... 32 Table 12. Spawners and recruitment of coho salmon in Tenmile Lakes, brood years 1960-1996.......................................................................................................................... 33 Table 13. Parameter estimates from selected models for Tenmile Lakes coho salmon................... 34 ii List of Figures Figure 1. Location of Siltcoos, Tahkenitch, Tenmile Lakes and nearby major rivers on Oregon coast. ..................................................................................................................... 35 Figure 2. Estimated ocean recruitment and terminal run of coho salmon in Siltcoos Lake basin from 1960 to 1999........................................................................................... 36 Figure 3. Siltcoos Lake coho salmon spawner and recruitment relationship with regard to high, mean, and low ocean survival rates for Siltcoos Lake coho salmon................................................................................................................................ 36 Figure 4. Relationship between ln(R/S) and S with high (3.72%), mean (2.51%), and low (0.89%) ocean survival rates for Siltcoos Lake coho salmon. The equation was for the mean survival rate. ........................................................................... 37 Figure 5. Residuals from stock-recruitment model with weighted regression over brood years for Siltcoos Lake coho salmon....................................................................... 37 Figure 6. Residuals from stock-recruitment model with weighted regression by spawner abundance for Siltcoos Lake coho salmon.......................................................... 38 Figure 7. Residuals from stock-recruitment model by ocean survival rates for Siltcoos Lake coho salmon.............................................................................................................. 38 Figure 8. Autocorrelation among residuals from weighted regression for Siltcoos Lake coho salmon.............................................................................................................. 39 Figure 9. Distribution and 90% confidence intervals for Smsy and Smsp from Monte Carlo simulations for Siltcoos Lake coho salmon. ............................................................ 39 Figure 10. Distribution of Umsy and Umsp from stochastic simulations for Siltcoos Lake coho salmon.............................................................................................................. 40 Figure 11. Adult escapements of coho salmon in Siltcoos Lake from 1960 to 1999 with regard to escapement goals........................................................................................ 40 Figure 12. Estimated ocean recruitment and terminal run of coho salmon in Tahkenitch Lake basin from 1960 to 1999........................................................................ 41 Figure 13. Tahkenitch Lake coho salmon spawner and recruitment relationship with regard to high, mean, and low ocean survival rates........................................................... 41 Figure 14. Relationship between ln(R/S) and S under mean (2.51%) ocean survival rates for Tahkenitch Lake coho salmon............................................................................. 42 iii Figure 15. Residuals from stock-recruitment Model 2 (see text) over brood years for Tahkenitch Lake coho salmon........................................................................................... 42 Figure 16. Residuals from stock-recruitment model by spawner abundance for Tahkenitch Lake coho salmon........................................................................................... 43 Figure 17. Residuals from stock-recruitment model by ocean survival rates for Tahkenitch Lake coho salmon........................................................................................... 43 Figure 18. Autocorrelation among residuals from weighted regression for Tahkenitch Lake coho salmon.............................................................................................................. 44 Figure 19. Distribution and 90% confidence intervals for Smsy and Smsp from Monte Carlo simulations for Tahkenitch Lake coho salmon........................................................ 44 Figure 20. Distribution of Umsy and Umsp from stochastic simulations for Tahkenitch Lake coho salmon.............................................................................................................. 45 Figure 21. Adult escapement of coho salmon in Tahkenitch Lake from 1960 to 1999 with regard to escapement goals........................................................................................ 45 Figure 22. Estimated