759 



Abstract— When monitoring endan- 

 gered species, natural resource manag- 

 ers require a recovery benchmark and a 

 statistical procedure to test whether the 

 benchmark has been met. We applied 

 statistical power analysis to devise such 

 a procedure for the endangered Sac- 

 ramento River winter chinook salmon 

 (.Oncorhyrichus tshauytscha). Winter 

 chinook salmon management currently 

 focuses on population growth rate, and 

 our procedure used a Students ?-test to 

 evaluate whether the average popula- 

 tion gi-owth rate is significantly lower 

 than the management goal of 0.57 per 

 generation. In the test, the null hypoth- 

 esis was that the growth rate was not 

 lower than the desired rate. In contrast 

 to the usual hypothesis-testing frame- 

 work, our procedure did not control for 

 the type-I error rate. Instead, it con- 

 trolled for the statistical power (the 

 complement of the type-II en-or rate) 

 and uses the resulting type-I error rate, 

 computed from the sample size and 

 other information, for the test. This pro- 

 cedure is conservative for winter chi- 

 nook salmon in that, if all assumptions 

 are met, it provides the specified level 

 of assurance of detecting dangerously 

 low population growth rates. 



Monitoring protocol for Sacramento River winter 

 chinook salmon, Oncorhynchus tshawytscha: 

 application of statistical power analysis to 

 recovery of an endangered species* 



Steven T. Lindley 



Michael S. Mohr 



Michael H. Prager 



Santa Cruz/Tiburon Laboratory 



Southwest Fisheries Science Center 



National Marine Fisheries Service, NOAA 



3150 Paradise Drive 



Tiburon, California 94920 



E mail address (for S T Lindley) Steve Lindleyiginoaa gov 



Manuscript accepted 14 March 2000. 

 Fish. Bull. 98:759-766 (2000). 



The Sacramento River winter chinook 

 salmon is listed as an endangered spe- 

 cies under the U.S. Endangered Spe- 

 cies Act (ESA). The historical spawning 

 grounds of the winter chinook salmon 

 were in upper tributaries of the Sacra- 

 mento River, including the Upper Sacra- 

 mento, Pit, and McCloud Rivers ( Fig. 1 ). 

 The completion of Shasta and Keswick 

 Dams in the 1940s blocked access to 

 these spawning grounds, although pop- 

 ulations had already declined from his- 

 toric levels owing to habitat destruction 

 in the upper tributaries (Fisher, 1994). 

 Quantitative winter chinook salmon 

 population size estimates began in 1967 

 when the Red Bluff Diversion Dam 

 (RBDD), a flashboard dam with three 

 fish ladders, was completed. Since the 

 completion of RBDD. winter chinook 

 salmon spawning runs have declined 

 from over 100,000 adults to a few hun- 

 dred adults in the 1980s (Fig. 2; Wil- 

 liams and Williams, 1991). 



The winter chinook salmon popula- 

 tion remains extremely depleted. The 

 California Fish and Game Commission 

 listed the population as a "candidate" 

 species under California's Endangered 

 Species Act in 1988 and declared it 

 endangered under that Act in 1989. 

 The National Marine Fisheries Service 

 (NMFS) declared the species "threat- 

 ened" under the federal ESA in the same 

 year, and it was declared "endangered" in 

 1994. NMFS has taken numerous regu- 

 latory actions under the ESA to improve 

 winter chinook salmon survival, includ- 

 ing changes in the regulations govern- 

 ing California's ocean salmon fisheries.^ 



In 1997, NMFS required that future 

 ocean fishery harvest regulations be 

 designed to achieve at least a 31% 

 increase in the winter chinook salmon 

 average cohort replacement rate over 

 that observed in 1989-93.2 Because 

 winter chinook salmon females spawn 

 predominantly at age 3 (Fisher, 1994), 

 the cohort replacement rate in year i is, 

 for simplicity, defined as /?, = NJNj_^, 

 where A^, is the number of adult spawn- 

 ers passing RBDD in year i. For statisti- 

 cal modeling purposes, it is convenient 

 to express this cohort replacement rate 

 on the log scale, r, = log(7J,), and refer 



* Contribution 103 of the Santa Cruz/Tib- 

 uron laboratory. Southwest Fisheries Sci- 

 ence Center, National Marine Fisheries 

 Service, NOAA, 3150 Paradise Drive, Tibu- 

 ron, CA 94920. 



' Pacific Fishery Management Council. 1998. 

 Review of 1997 ocean salmon fisheries. 

 (Available from Pacific Fishery Manage- 

 ment Council, 2130 SW Fifth Avenue, Suite 

 224, Portland, OR 97201.] 



- NMFS, 1996. Endangered Species Act-Sec- 

 tion 7; Consultation. Biological opinion. 

 The fishery management plan for commer- 

 cial and recreational salmon fisheries off 

 the coasts of Washington, Oregon, and Cal- 

 ifornia of the Pacific Fishery Management 

 Council. National Marine Fisheries Ser- 

 vice, Northwest and Southwest Regional 

 Fishery Management Divisions. NMFS, 

 1997. Reinitiated Section 7: Consultation 

 on the fishery management plan for com- 

 mercial and recreational salmon fisheries 

 off the coasts of Washington, Oregon, and 

 California as it affects the Sacramento 

 River winter chinook salmon. National 

 Marine Fisheries Service, Northwest and 

 Southwest Regional Fishery Management 

 Divisions. 



