9781934874097-ch19

Pacific Salmon Environmental and Life History Models: Advancing Science for Sustainable Salmon in the Future

Using a Salmon Life-History Simulation Model to Evaluate Escapement Goals Derived from a Spawner-Recruit Model

Toshihide Hamazaki

doi: https://doi.org/10.47886/9781934874097.ch19

Abstract.—This study demonstrates an application of a life history simulation model to evaluate robustness of a spawner-recruit model and fishery management practices. A Chinook salmon Oncorhynchus tshawytscha life history simulation model was constructed with inclusion of various density-dependent conditions, marine environmental changes, and marine derived nutrients (MDN). The simulation model was run for 200 years. At the 101st year, a fishery was introduced at harvest rates of 25, 50, or 75%. The Ricker spawner-recruit model was fit to data from pre-fishery (1–100th) and post-fishery (181–200th) years. The Ricker model parameters (α, β), equilibrium spawner size (Sk), and spawner population size that provides the maximum sustainable yield (Smsy) were estimated, and compared between pre-fishery and post-fishery. In addition, “true” Sk and Smsy were calculated directly from the life history model and were compared with those estimated by the Ricker-model. Results showed that: 1) the pre-fishery Ricker model Smsy estimates tended to be about the same or higher than the “true” Smsy, but lower than those with MDN effects, 2) the post-fishery Ricker model Smsy estimates tended to be lower than the pre-fishery ones and “true” Smsy, especially at the 50% and 75% harvest rates, and 3) the above results did not differ largely with inclusion of marine environmental variability in the model. These results suggest that the Ricker model is sufficiently robust to fit and estimate Smsy for various populations except for those with MDN effects, and only when it was fit to pre-fishery (unexploited) and/or low harvest rate data. However, for populations with high harvest rates, the Ricker model tends to underestimate Sk and Smsy.