Independent Evaluation of Wild Coho Marine Survival Rates in the Strait of Georgia (Black Creek)

Black Creek (fence) is DFO’s only wild coho indicator system for the Strait of Georgia (SOG). Since 1984 an uninterrupted data set has been compiled under the present program and is considered one of the longest time series of coho smolt and adult returns in the Pacific Region. Marine survivals are currently being evaluated using coded wire tags (CWT) on wild, non-adipose marked coho (~20% of smolts). Based on the lower than expected ratio of CWT fish returning with the current program, DFO would like to use PIT tags as an alternate method to evaluate marine survival, and investigate if there would be a difference in survivals based on CWT or PIT tag methodologies. The advantage of using PIT tags is that every returning fish to Black Creek would be automatically scanned at the enumeration fence for the presence of a PIT tag, while the CWT component relies on handling each fish and scanning by hand. Also, a PIT array will scan all adults, even if the fence is topped, while the current CWT program is unable to scan fish when the fence is topped, and fish bypass the trap box. As an end result, this project would improve our ability to evaluate wild coho marine survival rates in the SOG.

Since the early 2000’s DFO in partnership with the A-Tlegay Fisheries Society have continued to deliver the downstream and adult Black Creek program. The application of PIT tags on juveniles and monitoring of adults in the following year(s) at the fence would only be a slight augmentation to the current program, without any major labour or infrastructure costs, just tags, antenna arrays, application and reporting.