Thursday, December 16, 2010

Measuring Tag Retention and Fin Clip Quality

Each year, our office coded-wire tags (CWT) and mass marks (adipose fin clip) over 2 million juvenile fish from the federal hatcheries on the Olympic Peninsula. The CWT is a tool that is used to assess overall success of hatchery practices. The tags are also used to estimate survival and assess run size and timing. Mass marks allow us to distinguish hatchery fish from wild populations. This is a key component in allowing fishing to occur for hatchery-raised fish in areas where they coexist with wild stocks.

Before these fish are released, a quality check must be performed to ensure successful retention of tags and proper clipping of fins. This is accomplished by examining groups of fish 1 month after being marked and tagged. The fish are individually passed over a detector to determine if a tag is present and then fish that received a clip are visually examined for the quality of the clip. This data is then recorded and used to calculate the success of our tagging and marking. Once examination is complete, the fish are returned to the raceways where they are cared for by the hatchery staff.

Following are three short videos demonstrating this process: