Long-term dynamics of biological indicators of navaga Eleginus nawaga (Walbaum, 1792) of the White Sea in relation to changes of the reservoir temperature regime

Systematic studies of navagа of the White Sea were initiated in the late 1960-ies. Data sets on dimensional indicators, age composition of populations of navaga of the Onega, Dvina, Mezen Bays and Voronka of the White Sea have been accumulated during 45 years of observations. The aim of this work is to identify the causes of the interannual and long-term changes of biological population parameters of navaga. As investigated interannual changes reflecting fish growth, the length and mass of 2 and 3 years old specimens have been chosen. It has been proved that interannual fluctuations in length and weight may depend on the length of the feeding season, as well as the number of populations. Climate warming has resulted that over the past 45 years since the beginning of observations the water temperature in the White Sea in April on average has increased by one degree, and some years - even more. Due to lengthening of the feeding period the seasonal growth of navaga has increased, respectively the annual rates of its length and weight have increased as well. The increase in the growth rate of navaga in the Onega and Dvina Bays has led to its mass mature and joining the fishing (commercial) herd at the age of two years. In the Mezen Bay and Voronka the trend on the increase in annual average length and weight navaga of only younger age groups has kept. Growth rate of large size navaga has decreased due to the almost complete cessation of fishing and the increase of older fish number. The revealed regularities in the change of the navaga population parameters of the White Sea should be used for preparing the forecast data on the state of its reserves.