Optimal Stratification and Cost Analysis to Estimate Steelhead Harvest Using Parentage Based Genetic Tagging in the Snake River Basin, Idaho

The Lower Snake River Compensation Plan (LSRCP) was created in 1976 to mitigate for anadromous fishery losses due to the construction of dams on the lower Snake River.  Much of this mitigation is in the form of hatchery production of steelhead Oncorhynchus mykiss from hatcheries that were constructed under the LSRCP.  The Idaho Department of Fish and Game (IDFG) applies an estimated proportion of fish harvested from each hatchery to a total estimate of harvest to estimate the contribution of LSRCP-produced fish to total harvest.  To estimate the proportion of fish from LSRCP hatcheries harvested in the fishery, IDFG has historically relied on recoveries of coded wire tags (CWT).  Because few fish that are tagged with CWT return as adults, surveys are not based on probability sampling but are instead conducted to maximize the observation of harvested fish.  Parentage based genetic tagging has been implemented to “mark” nearly 100% of all hatchery steelhead in Idaho.  The objective of our research was to determine optimal spatial and temporal stratum boundaries based on historic CWT data.  These methods will significantly reduce sampling costs and provide an unbiased estimate of LSRCP-hatchery produced steelhead in the sport fishery harvest.