A PIT tag based method to investigate survival of Cowichan River Chinook throughout various stages in their first year of marine life

This project utilizes PIT-tagging of Cowichan Chinook juveniles with the objective of calculating the relative survival to adult return from several stages within the first year of life. The application of PIT tags to juvenile Cowichan River Chinook is a novel approach to studying in-river and marine survival. The program was piloted in 2014 with the deployment of approximately 7,000 tags and expanded in 2015 to 15,500 tags. Detection of tags in returning adults will provide new information on the relative survival rates from freshwater and marine tagging episodes (defined by location and timing). A new antennae array is planned for the Cowichan River in 2016 that will allow detection of returning PIT-tagged Chinook without handling these adults. These ‘matt’ like antennas have been tested previously in the United States. PIT-based estimates of marine survival are analogous to the more commonly used coded-wire tag-based programs used coastwide, but PIT tags are uniquely coded and can be interpreted without sacrificing the animal. Further, by developing novel techniques to catch under-yearling Chinook during their early marine residence, we can assess the survival of juvenile Chinook from various stages of their development until they return to the Cowichan River; thereby making it possible to directly test the critical-period hypothesis about early marine survival in juvenile salmon. Tag detections in-river and within the estuary have provided valuable insight into the behavior of rearing juveniles in-river, relevance of estuary habitats, as well as the survival of downstream migrants