The second and final fish releases were carried out at Durham Ferry on May 6 and Stockton on May 8, respectively. Release sizes were intended to be 285 fish at Durham Ferry and 190 fish at Stockton; however, sample sizes of both groups were reduced due to several factors including approximately 90 tags that could not be programmed or that stopped functioning during the post-surgery holding period, and approximately 5 fish that died or were pulled from the release groups because they exhibited strange behavior.
A tag life study is currently being conducted to estimate the probability of tag failure at a given date. Fifty of the 1000 tags purchased for this study were programmed but were not deployed. These tags will be continuously monitored in a closed system under simulated ambient San Joaquin River water conditions (e.g., similar water temperatures to those at Jersey Point). Test tags represent a random subset of similar tag codes and transmitter types to those that were implanted in released fish.
The principal objectives for the hydrophone layout are to: 1) estimate overall survival to Chipps Island and 2) to compare overall survival in the main stem San Joaquin River to survival in the central delta, which is potentially a function of San Joaquin River flows and export rates.
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Acoustic tagging of Chinook Smolts continued during the week of May 5th. Four surgical teams implanted sonic tags into the final two release groups of fish. Tags were implanted into Chinook Smolts weighing over 12.1 g to ensure a tag-to-body weight ratio of less than 6% and surgery was generally performed in less than three minutes. There were no mortalities during the 24 hour holding period between surgery and loading the fish into transport tanks.
