The Influence of Twenty-Five Years of Catch and Release Fishing Regulations on Hook Scarring, Size, and Abundance of Rainbow Trout in the Yakima River, Washington

Catch and release fishing regulations were implemented on the Yakima River in 1990 with the expectations of increasing the abundance and size of rainbow trout Oncorhynchus mykiss.  The overall population abundance trend has been significantly positive since 1990 which was consistent with the management objective.  In contrast, the annual average size of rainbow trout has steadily decreased during this period which is not generally a result desired from implementing catch and release regulations.  Comparisons of the length-to-weight relationship of fish caught and released in the fishery indicated that hook-scarred rainbow trout exhibited a significantly reduced body mass for fish of average length relative to the general population that did not exhibit visible hook-scarring.  Although the difference was small, average sized trout in river reaches that received the highest angling pressure had lower body mass than trout in river reaches that appeared less utilized.  We also observed that the bank orientation of trout was associated with hook-scar placement on the jaw for fish with visible scarring.  This study provides a unique look at the abundance, size structure, and hook-scarring of rainbow trout in the Yakima River for a 25 year period following the implementation of catch and release fishing regulations.