Comparative characteristics of growth of the scales from pink salmon in returns to Sakhalin Island (southeast coast) and Iturup Island in 2017 and 2018

Iturup Island (in southern Kuril Islands) and southeastern Sakhalin Island are known by the highest catches of salmons within the Sakhalin-Kuril region. The timing of pink salmon mass return to Iturup is 5–10 days later than to Sakhalin, and the females returned to Iturup have higher relative individual fecundity, on average. In 2014, an unexpected increase of pink salmon catches occurred on southeastern Sakhalin Island, with a simultaneous sharp decrease of the catches on Iturup Island. Assumption on appearance of Kuril pink salmon in the Sakhalin waters was confirmed by analysis of the scale parameters (number of sclerites and intercirculi distance in the first-year scale zone), dynamics of catches, and individual fecundity of females. Sharp opposite changes of the pink salmon catch dynamics were noted again for these areas in 2017 and 2018. Such changes of pink salmon abundance could be reasoned by environmental conditions of reproduction in these areas or new redistribution between two areas. To clarify the issue, complex analysis (same as for 2014) was applied for pink salmon at southeastern Sakhalin and Iturup in 2017 and 2018 (187 and 215 fish samples from Sakhalin and 194 and 152 fish samples from Iturup in these two years, respectively). The results were interpreted following the hypothesis of fluctuating stocks. Taking into account the complex of traits, there is concluded that the assumption about redistribution of pink salmon between southeastern Sakhalin and Iturup Island in 2017 and 2018 is untenable.

Interannual variability of water temperature in coastal waters of Eastern Sakhalin in May-June and abnormal cold snap forecast

The analysis of water temperature interannual variability at weather stations of Roshydromet network in coastal areas of South-Eastern Sakhalin is carried out. The years of abnormal cold snaps in May and June were determined. The interval recognition method is used for their prediction. It is established, that the months preceding the anomalous ones have high recognition coefficients. To verify the results, baric maps for months with the highest recognition coefficients are constructed. General dynamics pattern of the prior pressure fields that determine extreme cold thermal regimes in the coastal waters of southeastern Sakhalin has been found. These years are distinguished by the presence of tropospheric depressions or tropospheric cyclonic vortex over the Sea of Okhotsk in winter season. Method for predicting of extreme cold events during the period of pink salmon growth in estuaries is developed for southeastern Sakhalin. Using this method, abnormal cooling of coastal waters could be predicted by dynamics of baric fields in advance of 1–5 months. This approach can be applied for other areas of pink salmon habitat at different stages of its life cycle. The method is based on relationships with strong correlation; results of forecasting could be verified by the baric fields plotting.

ESTIMATION OF ABUNDANCE FOR THE MIGRATING JUVENILE PINK SALMON IN THE RIVERS OF SAKHALIN AND ITURUP ISLANDS IN 2019

Number of the pink salmon fry migrating downstream from their spawning grounds in the control rivers in 2019 is assessed as 17546.2 . 103 and 14795.7 . 103 ind. for the Dagi and Bolshoi Khuzi Rivers (northeastern Sakhalin), as 89.1 . 103 and 2636.1 . 103 ind. for the Poronai River tributaries — the Kholodny and Orlovka, as 2759.8 . 103 and 21456.0 . 103 ind. for the Lazovaya and Pugachevka Rivers (western coast of the Patience/Terpeniya Bay), as 5803.8 . 103 and 19020.0 . 103 ind. for the Voznesenka and Ochepuha Rivers (southeastern Sakhalin), as 1822.4 . 103 and 2139.0 . 103 for the Taranai and Kura Rivers (Aniva Bay coast), and as 15834.1 . 103 and 7626.1 . 103 ind. for the Rybatskaya and Olya Rivers (Iturup Island), respectively. In all areas, the pink juveniles migrated from the spawning grounds earlier than usual, obviously because of accelerated development of the embryos in conditions of abnormally warm autumn. The number of juveniles migrated from all spawning grounds in the rivers of respective regions is estimated taking into account the escapement of pink salmon spawners and the downstream migration index determined for the control rivers (ratio of the spawners escapement and the number of subsequent downstream migrating juveniles): the total number for the natural spawning grounds is estimated as 1168.9 . 106 ind. for the rivers of the eastern coast of Sakhalin (including the Aniva Bay) and 471.1 . 106 ind. for the rivers of Iturup Island (Okhotsk Sea coast). Additional 141.3 . 106 ind. were released from artificial hatcheries of eastern Sakhalin and 122.0 . 106 ind. — from artificial hatcheries of Iturup Island. The downstream migration is considered as highly abundant for northeastern Sakhalin and Iturup Island, but is insufficiently abundant for the Patience/Terpeniya Bay and Aniva Bay where the landings of this generation should be limited. The pink salmon return to southeastern Sakhalin in 2020 is expected to be better than in 2018 due to satisfactory abundance of the juveniles from natural spawning grounds.