The effects of environmental conditions and spawning stock size on yearclass strength of Northeast Arctic haddock in the period from 1950 to 2006

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Northeast Arctic haddock is characterized by wide-range fluctuations in the year-class strength. The effect of spawning stock size on the year-class strength for the entire period did not exceed 4.6%. Mortality-survival ratio during early life of this population proved to be much more dependent on the ambient conditions than on the parental stock abundance. To describe the quality of environment during early ontogeny of the population the year-class survival index was established as the ratio of abundance of 3-year olds to the spawning stock biomass in the year of the generation birth. The analysis of multi-year variability in survival factors allowed for establishing three recurrent types of conditions, namely, favorable, moderate and unfavorable. The influence of the spawning stock size within each type of conditions constituted 83.4, 53.8, and 28.9%, respectively, and it was described by the regression equations with the correspondent determination coefficients of 0.73, 0.63, and 0.41. The survival of NEA haddock depends to a great extent on water temperature conditions, which, in turn, are determined by the large-scale atmospheric patterns over the North Atlantic. There is a strong positive relationship of survival indices of haddock with duration of warm season and dates of its beginning and end in the year of spawning. This allows forecasting the three year olds abundance at the known SSB three years in advance.