Red Fish, Blue Fish, One Fish, Two Fish: Using Calcein Dye to Test Assumptions Related to Juvenile Sockeye Abundance Estimates

Since 1992, the Washington Department of Fish and Wildlife has operated an inclined-plane trap on the Cedar River, a very urban and alter system near Seattle, WA. This trap provides juvenile sockeye salmon abundance estimates which are used to describe factors limiting sockeye populations, estimate survival of subsequent life stages, and inform harvest and hatchery management.

There are both naturally and hatchery produced sockeye salmon in the Cedar River. Accurate mark-recapture abundance estimates rely on high quality catch composition data on hatchery release nights but differentiating between hatchery and naturally produced sockeye is visually impossible because hatchery fish are not externally marked.  In this study, we used calcein dye to mark hatchery sockeye fry to test assumptions associated with a) catch composition, b) timing and movement of hatchery sockeye, and c) mark-recapture population abundance estimates. Results revealed previous sampling methods to assess catch composition on hatchery release night did not provide a representative sample. We noted a larger portion of hatchery fish migrate later than anticipated and capture rates of hatchery and natural-origin sockeye are similar, both important in forming confident abundance estimates of natural and hatchery produced sockeye.