Monitoring protocol for Sacramento River winter chinook salmon, Oncorhynchus tshawytscha: application of statistical power analysis to recovery of anendangered species

when monitoring endangered species, natural resource managers require a rec overy benchmark and a statistical procedure to test whether the benchmark h as been met. We applied statistical power analysis to devise such a procedu re for the endangered Sacramento River winter chinook salmon (Oncorhynchus tshawytscha). Winter chinook salmon management currently focuses on populat ion growth rate, and our procedure used a Student's t-test to evaluate whet her the average population growth rate is significantly lower than the mana gement goal of 0.57 per generation. In the test, the null hypothesis was th at the growth rate was not lower than the desired rate. In contrast to the usual hypothesis-testing framework, our procedure did not control for the t ype-I error rate. Instead, it controlled for the statistical power (the com plement of the type-II error rate) and uses the resulting type-I error rate , computed from the sample size and other information, for the test. This p rocedure is conservative for winter chinook salmon in that, if all assumpti ons are met, it provides the specified level of assurance of detecting dang erously low population growth rates.