Modelling Of Age-Dependent Instantaneous Coefficients Of Natural Mortality For Northeast Arctic Cod

No abstracts are to be cited without prior reference to the author.

Natural mortality coefficients used to assess the commercial cod stock are presently taken to be identical (M=0.20) for almost all age groups of this stock. The paper describes a model suggesting that instantaneous coefficients of natural mortality change with age increasing from 3 years and further. The model explicitly reflects a conceptual relationship between natural mortality of cod, maturity age and theoretical maximum possible lifetime, and implicitly between natural mortality, linear and weight growth. Theoretical premises of the model are formulated and a method of estimating its parameters is suggested. Natural mortality coefficients are calculated for cod from 1946-1991 yearclasses at the age of 3 years and older. To calculate terminal values of coefficients mean weight of one fish at a particular age and the mean of average yearly water temperature in the main branch of the Murman Current in the O-200 m layer in the first three years of generation life was used. The coefficients can be applied for assessment of the total and spawning stocks, setting up of biological reference points and total allowable catch.