The results of long-term (1948–2021) studies on the spatial and vertical distribution, dynamics of abundance, and size composition of the Aleutian skate Bathyraja aleutica in the North Pacific Ocean are presented. Maximum densities of this species were characteristic of the eastern Bering Sea slope, off the central Aleutian Islands, consisting of the Pacific waters off southeastern Kamchatka and the northern Kurils, and northeastern Sakhalin. This species was most abundant at depths of 100–600 m; in the cold months, B. aleutica migrates to greater depths for over-wintering, and in warm months it feeds at shallower depths. Bathyraja aleutica was most common at the bottom, at temperatures around 3 °C. The total length of individuals ranged from 9.6–170 cm, with a predominance of skates with a length of 50–100 cm. Males did not differ significantly from females in body weight and length. The maximum values of the condition factor were typical for the autumn–winter period. Across years, there was an increase in Aleutian skate catch rates from the western Bering Sea and the Sea of Okhotsk, and a decrease in the Pacific waters off the Kuril Islands and Kamchatka, as well as in Alaskan waters.

This study characterizes the spatiotemporal variability of chlorophyll-a in the Bering Sea and adjacent Pacific Ocean based on 2003–2019 MODIS data. Average long-term seasonal variations of the chlorophyll-a concentration are described, and the typical times of phytoplankton bloom in various parts of the given area are found. Interannual variability of spring bloom times is analyzed for three regions: the western part of the sea northeast of the Kamchatka Strait, the northern part of the sea near Cape Navarin, and the central part of the sea. The first two of these regions have similar average long-term characteristics. We have shown that the interannual variability of the onset of spring bloom times vary between these two regions with an amplitude of around 2 months. The western part of the sea is characterized by a shift in bloom to earlier periods (March–April), while the spring bloom in the northern region shifts to May–June. Unlike these two regions, the spring bloom is much less pronounced in the central part of the sea; it usually starts in May–June and may last for several weeks. In this case, the chlorophyll-a concentration can be relatively high in August–October as well. In some years, the fall bloom can be even more pronounced by intensity (with a peak of the chlorophyll-a concentration) than the spring bloom. This situation is more typical for the open Pacific Ocean, rather than for the Bering Sea. For the entire water area under consideration, we have compared the course of spring bloom in 2010 and 2015 to reveal that the spatial development of bloom in different years can also vary significantly. The interannual differences in its onset in different regions of the sea are most likely associated with the features of physical processes that control the formation of stable water stratification (spring ice melting and solar heating under weak wind impact) and can also be associated with the variability of currents.

The eastern Sea of Okhotsk is one of the most important areas of the World Ocean in terms of fisheries. The high productivity of this region is supported, in particular, by the inflow of waters from the Pacific Ocean. The process of inflow and propagation of these waters into the sea is poorly understood. In this paper, altimetry data on current velocities and the Lagrangian approach are used to track the events of the inflow of waters of Pacific origin into the Sea of Okhotsk and to characterize their evolution. Daily values of two types of indices describing propagation of Pacific waters in the Sea of Okhotsk were obtained based on the data on the location and shape of water intrusions. It is shown that in winter such waters are usually located closer to Kamchatka, and in summer, farther from the coast. In 1998, 2003, 2010, 2013, 2017, and 2019, Pacific waters penetrated the farthest distance to the north. Analysis of the morphometric characteristics of the intrusions showed that after reaching the maximum area of the intrusion, its shape quickly becomes more complex. The centroids of the largest intrusions are usually located in the band 152°–154° E. Based on the developed indices it is shown that the inflow of water from the ocean into the sea has increased since 2010.

Цель: описать сезонную и межгодовую изменчивость поступления и распространения вод тихоокеанского происхождения в восточной части Охотского моря на основе лагранжева похода и пространственного анализа. Материалы: использованы данные компонент скорости геострофического течения, полученные с помощью спутниковой альтиметрии; разрешение данных 0,25° × 0,25° × 1 сутки. Для каждых суток в интервале с 31 января 1997 г. по 17 апреля 2022 г. прослежены траектории движения ~100000 частиц воды на 400 суток назад во времени. Для каждой даты определены частицы, пересекшие условный разрез вдоль Курильских островов, а также срок и место пересечения разреза. На основе этих двух параметров для каждой даты выполнен кластерный анализ частиц методом DBSCAN и обнаружены интрузии вод тихоокеанского происхождения. Проанализированы особенности расположения, формы и размеров интрузий. Результаты: получены ежесуточные значения двух типов индексов распространения тихоокеанских вод в Охотском море. Изменчивость расположения центроида области, занятой водами тихоокеанского происхождения в выбранном районе, показала, что весной-летом эти воды распространяются максимально на север, а осенью-зимой они наблюдаются южнее. Зимой такие воды обычно располагаются ближе к Камчатке, а летом — дальше от побережья. В 1998, 2003, 2010, 2013, 2017 и 2019 гг. тихоокеанские воды проникали наиболее далеко на север. Второй тип индексов связан с анализом расположения и особенностей формы интрузии, сформированной водами тихоокеанского происхождения. Показано, что после достижения максимальной площади интрузии её форма быстро усложняется. Центроиды наиболее крупных интрузий обычно располагаются в полосе 152–154° в.д. На основе разработанных индексов показано, что заток вод из океана в море усилился с 2010 г. Практическое значение: разработанный подход и полученные индексы предложено использовать при описании изменений экосистем и промысловых запасов восточной части Охотского моря.

The Bering Sea and its surrounding waters are commercially and ecologically important ecosystems. Knowledge of phytoplankton phenology is crucial for understanding ecosystem dynamics. However, estimates of phenological parameters of spring phytoplankton bloom are sparse for this region. We used the Moderate Resolution Imaging Spectroradiometer (MODIS) daily data from 2003–2024 to assess the climatology of phenological parameters. A combination of data regriding, spatial interpolation, and temporal smoothing was applied. Three methods of spatial interpolation for missing data acquisition are compared: iterative first-order neighbor, inverse distance weighted interpolation, and data interpolating empirical orthogonal functions (DINEOF). We suggest that the first outcompetes the other two methods when compared to initial data. Date of the bloom initiation, bloom peak, chlorophyll-a maximum, and duration of the bloom before its peak are evaluated. The spatial distribution of mentioned phenological parameters is presented and discussed. We show that bloom starts early in Bristol Bay, in the narrow band along the eastern shelf, along the Kamchatka Peninsula, and south of the Aleutians and Alaska Peninsula. In the deep Bering Sea, bloom starts surprisingly later considering the latitude of the region. The main reason for this may be the wind mixing during the spring. The first phase of the bloom is generally longer in the deep southern areas (up to 60 days) and shorter in the northern shelf areas (less than 2 weeks in some cases).