Do Adfluvial Female Spring Chinook Present a New Life History Strategy in High-Head Dam Reservoirs?

Spring Chinook salmon in the upper Willamette River, Oregon are listed as threatened under the endangered species act. In this system spring Chinook are being reintroduced above several high-head dams in an effort to contribute to their recovery. In the South Fork McKenzie River, a Willamette River tributary, we have genetically monitored the spring Chinook reintroduction since 2007 using molecular parentage methods. Genetic pedigrees have been constructed with adults (n=3738) and outmigrating fry sampled above the dam (n= 8644) from 2008-2011. We found the average proportion offspring missing at least one parent each year was 22%; despite sampling 99.8% of all anadromous adults reintroduced; our use of 11 highly polymorphic microsatellites (average number of alleles = 33.8) when determining parent-offspring relationships; and low genotyping error (2%). Interestingly, the average proportion of offspring missing mothers (13.2%) was nearly double that of those missing fathers (7%), which is counterintuitive given spring Chinook life history - we expect only unsampled precocial males to exist in this system. Our research will determine if adfluvial females contribute to juvenile production using newly developed grandparentage methods and cumulatively aid in our understanding of spring Chinook life history diversity.