Salish Sea Marine Survival Project

46 COWICHAN PIT TAG PROGRAM THE IMPORTANCE OF PIT (PASSIVE INTEGRATED TRANSPONDER) TAGS PIT tags are tiny (rice-grain size) electronic tags that are cost-effective, easily applied and have a unique code. These very small glass tags (no battery, 2.1 mm x 12 mm) are applied world-wide for wildlife and fisheries research. They are injected into the animal but then require an antenna to instantaneously charge and read the unique code within each PIT tag. Antennas may be hand-held wands or large antennae arrays that animals must move past. The tag can be automatically detected and decoded as a fish crosses an antenna, which eliminates the need to kill or handle the fish during data retrieval. The tag code can be linked to information gathered at the time of tagging (i.e., tagging location, source (hatchery or wild) and size at tagging). During SSMSP, we installed such an array across the bottom of the lower Cowichan River and used smaller portable antennas in other locations. In the Salish Sea Marine Survival Project, these tags were essential for identifying individual juvenile Chinook and Coho Salmon (including hatchery or wild), monitoring downstream migration rates and survival, separating fresh- water survival from marine, qualifying predation, assessing critical size/time hypotheses, tracking growth and survival of individuals, and estimating survival between life-stages including as mature fish returning to the Cowichan River. HOW WERE PIT TAGS USED? Over 56,000 PIT tags were applied to juvenile Chinook in Cowichan River, Cowichan Bay (beach seining, purse seining) and Sansum Narrows (by microtrolling) between 2014 -2017 (Figure 1). Both wild (32,915) and hatchery (23,270) fish were tagged. More hatchery fish were tagged in-river, while more wild fish were marked in the marine environment. Since 2014, Chinook returning to the Cowichan River have been scanned for PIT tags using automated antennas ("arrays") installed at the counting fence at the Skutz Falls fishway, and since 2016, at a full stream Biomark array placed at the bottom of the river. Hatchery broodstock have also been scanned for tags using hand-held scanners since 2016. Monitoring has resulted in the detection of 582 unique tags between 2014 and 2018. Data were expanded based on antenna detection efficiency, and survival esti- mates created based on tag returns from all years, pooled by location. These data allow us to compare survival among the four different cohorts, and to compare survival between wild and hatchery fish, as well as the relationship between size, time of ocean entry, growth, residency and survival. PIT tags have also been used in SSMSP predation stud- ies, both to examine levels of in-river predation in the Cowichan River, as well as to determine predation by seals on Big Qualicum Coho. QUESTIONS ADDRESSED DATA CONCLUSIONS When is the bottleneck to survival in juvenile Chinook Salmon? What is the difference between hatchery and wild survival? Over 56,000 PIT tags applied to juvenile Chinook in Cowichan River, Cowichan Bay (beach seining, purse seining) and Sansum Narrows (by microtrolling). Compare returns from each tagged cohort returning to the Cowichan River using an antenna in the river. There appear to be two key mortality periods: downstream migration of smolts to the ocean and then during the first winter. Hatchery fish survival is about 35-40% of that of wild fish across all stages. The mechanism controlling this difference likely occurs after their first summer at sea. Figure 1. PIT tags applied to hatchery and wild Cowichan Chinook 2014-2017. Graph provided by Kevin Pellett, DFO. 0 2000 4000 6000 8000 10000 12000 River Beach Purse Microtroll TAGS DEPLOYED 2014 2015 2016 2017 Photo by Jeremy Koreski Chinook fry in Cowichan River

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