A Range of Estimates of Natural Mortality Rate for Chub Mackerel in the North Pacific Ocean

This paper provides a range of estimates of natural mortality rate (M) for north Pacific chub mackerels as a basis for discussion of M values to be used for models in stock assessment and for operating models (OMs) which will be developed by the Technical Working Group on Chub Mackerel Stock Assessment of the North Pacific Fisheries Commission. M estimates were obtained using a subset of estimators selected from all M estimators available and input parameters values based on the best available data at this stage. As a whole, M estimates across all the estimators considered range between 0.30 and 0.59. Most of the estimates fall in values between around 0.3 and 0.5. The median of this range is 0.41. Considering the range of the M estimates, we suggest that the median M value of 0.41 is used for a reference (base) case, the values of 0.3 and 0.5 are used for sensitivity analysis/robustness test in future stock assessments and for OMs.