Abundance of Northeast Arctic haddock year classes and its governing factors

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In 1950-1997, on the basis of analysis of both biotic and abiotic factors it was ascertain that mean annual water temperature at the first and second years of life of Northeast Arctic haddock cohorts exerts maximal influence on their abundance. Abundant year classes were registered only in normal and warm years. In periods of evident cooling of the Barents Sea all year classes were poor independently on the spawning stock condition, food supply and other factors. Year-to-year variations of water temperature profoundly affect the abundance of year classes as well. Abundance of year classes very largely depends on a size and structure of the spawning stock. In years, when biomass of mature individuals was at a high level and based on fish of older age classes, even unfavourable environmental conditions not always led to appearance of poor year classes. In the period of drastic decrease of a size of spawning stock and its rejuvenation, the abundant and middle in number year classes appeared only in warm and anomaly warm years or in periods of abrupt warming up of the sea. Mature individuals at the age of 6-8 spawning two and more times made maximal impact on the abundance of haddock year classes. Abundance of year classes was determined to a great extent by a size of immature part of the stock. At a high density of the population the abundant classes were observed much more seldom than at the low abundance of immature individuals. A link between abundance of year classes and density of population was especially pronounced in favourable for survival warm years, when a role of abiotic conditions decreased. The revealed complex influence of the thermal condition of the sea, spawning stock biomass and structure and density of haddock population on the abundance of its year classes permit to use these parameters at prediction of year class strength and stock management.