Scenario analysis of the effects of the Great East Japan Earthquake on the chum salmon population-enhancement system

The Great East Japan Earthquake may have resulted in increased mortality of artificially propagated chum salmon fry (2010 year class) from Iwate Prefecture (CSI), both in the hatchery and after release. Individuals from the 2010 year class will return in 2014-2015. To evaluate the potential for future issues associated with the effects of the earthquake, we simulated CSI population dynamics using a model that incorporated stratified earthquake-influenced survival rates lambda (l) (l = 0.00-1.00 at intervals of 0.25) under various scenarios. Under laissez-faire scenarios (median exploitation rate E (Med)) under low post-release survival rate S (Low) and all lambda (l) , the median number of hatchery-released fry did not reach the target H (*) in 2014 and 2015. The probability P (j,t) of not meeting the targets was 0.56-1.00 (2014) and 0.79-1.00 (2015). Meanwhile, with simulation of a low exploitation rate, S (Low), and a higher lambda (l) (0.50), the P (j,t) in 2014 and 2015 was 0.00-0.17 and 0.21-0.72, respectively. Under S (Med) and S (High), reached H (*) at lambda (l) (> 0.50) regardless of E (l) , and the cumulative catch varied primarily with S (l) . Our results suggest that simulations can provide a method of predicting potential issues and can offer insight into strategies to minimize future problems.