Simulating Future Escapements for the Late-Run Kenai River Chinook Salmon

The late-run Kenai River chinook salmon Oncorhynchus tshawytscha, which are managed under
the principle of maximum sustained yield (MSY) have experienced declines in run size in recent
years. Several runs in the past ten years have not met the lower end of escapement goals. Alaska
Department of Fish and Game sets escapement goals that use the Ricker stock-recruitment model
as their basis. The historical vital rate parameters deduced from records form the basis for these
calculations. In this paper, I create a model that uses historical variation in vital rates to simulate
late-run chinook runs for 20-year periods in the future using recorded average harvest rates, and
a theoretical lower harvest scenario. From the simulations, the median number of lower
escapement failures is 2 per 20 year period for both a normal and reduced harvest scenario. No
significant differences were found between the mean escapements of both harvest scenarios. The
results of this model suggest that manipulating harvest levels alone will not significantly improve
escapement, and that other factors in chinook life history will need to be improved to achieve
that goal.