Coastal fishery officials will use the resulting data to incorporate ocean climate variations in their management policies.
Approximately $100,000 of the grant will finance an HSU master’s candidate in fisheries biology, collaborating with Hankin, to analyze data recovered from coded wire tags attached to Chinook salmon released from regional river system hatcheries. Coded wire tags are very small lengths of labeled, magnetized wire inserted into the nasal cavity of juvenile salmon prior to their release.
A small vestigial fin, the adipose fin, is removed from each tagged specimen so that ocean and freshwater samplers can identify it later.
The sequence of recoveries from a large group of juvenile salmon, say 100,000, released with a specific tag code allows, among other things, estimates of survival between release and ocean age two years. Estimates primarily reflect variations in ocean survival conditions because typically only about two weeks of freshwater downstream migration elapse between hatchery release and ocean entry. Estimated survival rates can then be compared to and correlated with a suite of oceanographic indicators of survival conditions. That analysis allows identification of the key oceanographic factors that appear best to explain variations in rates of hatchery fish survival.
Based on Hankin’s previous work with Klamath-Trinity recovery data, the survival rates of Klamath-Trinity Chinook released as fingerlings range from less than 0.03% to about 4%, more than two orders of magnitude in variation. “Most of this variation is no doubt attributable to variation in ocean environmental conditions," Hankin said. “A recent analysis of the causes of the recent collapse of Sacramento River fall Chinook salmon clearly implicated extremely poor ocean conditions for salmon—and other organisms—as the key apparent explanation of the collapse.”
The three-year California Sea Grant project will be conducted in two phases. The first will assess the influence of ocean environmental conditions on fluctuations in Chinook abundance and the second will determine to what extent reductions in life history diversity contribute to the instability of stocks.
“In the long-term, this kind of project is designed to help fishery managers better incorporate variable ocean climate and future climate change in developing effective management policies for coastal salmon fisheries,” Hankin said.