ESTIMATING THE INFLUENCE OF TEMPERATURE ON THE SURVIVAL OF CHINOOK SALMON SMOLTS (ONCORHYNCHUS-TSHAWYTSCHA) MIGRATING THROUGH THE SACRAMENTO-SAN-JOAQUIN RIVER DELTA OF CALIFORNIA

Data from the U.S. Fish and Wildlife Service are used to investigate t he relationship between water temperature and survival of hatchery-rai sed fall-run chinook salmon (Oncorhynchus tshawytscha) smelts migratin g through the Sacramento - San Joaquin Delta of California. A formal s tatistical model is presented for the release of smelts marked with co ded-wire tags (CWTs) in the lower Sacramento River and the subsequent recovery of marked smelts in midwater trawls in the Delta. This model treats survival as a logistic function of water temperature, and the r elease and recovery of different CWT groups as independent mark-recapt ure experiments. Iteratively reweighted least squares is used to fit t he model to the data, and simulation is used to establish confidence i ntervals for the fitted parameters. A 95% confidence interval for the upper incipient lethal temperature, inferred from the trawl data by th is method, is 23.01 +/- 1.08 degrees C This is in good agreement with published experimental results obtained under controlled conditions (2 4.3 +/- 0.1 and 25.1 +/- 0.1 degrees C for chinook salmon acclimatized to 10 and 20 degrees C, respectively): this agreement has implication s for the applicability of laboratory findings to natural systems.