DRAFT: Development of escapement goals for Grays Harbor fall Chinook using spawner-recruit models

Grays Harbor fall Chinook are currently managed for a system-total escapement goal of 14,600 naturally spawning adults (Chehalis: 12,364, Humptulips: 2,236), a goal established in 1979 based on estimates of total accessible spawning habitat and spawning habitat capacity for individual streams in the Grays Harbor Basin. Grays Harbor escapement goals have received additional attention since this capacity-based goal was developed, most recently by QDNR and WDFW in 2007 (a joint effort) and between 1999 and 2003 by the Chinook Technical Committee (CTC) of the Pacific Salmon Commission (PSC) and its Washington members. To develop an escapement goal for common use in the CTC’s review of indicator stock performance and by the Grays Harbor co-managers (QDNR and WDFW) in management, QDNR and WDFW recently conducted stock-recruitment analyses for Grays Harbor fall Chinook using updated escapement, terminal run reconstruction, and ocean abundance datasets. Goals were developed separately for each main tributary (Chehalis, Humptulips) and summed to generate an aggregate goal for the CTC Grays Harbor fall Chinook escapement indicator stock. Of three spawner-recruit functions considered (Shepherd, Beverton-Holt, Ricker), the Ricker model was identified as being the most appropriate form for both the Chehalis and Humptulips datasets. Parameter estimates indicate that the adult spawning escapement needed to produce maximum sustained yield (mean S_msy) for the Grays Harbor fall Chinook indicator stock aggregate is 13,326 (age 3+ individuals); S_msy is 9,753 for the Chehalis River and 3,573 for the Humptulips River. Although there are uncertainties and limitations associated with these updated escapement goals (e.g., narrow range of parent-generation spawning escapement levels), they constitute the best estimates of sustainable management parameters available for Grays Harbor fall Chinook at this time.