Results of the multi-purpose expedition held in April–June of this year onboard the “Professor Kaganovsky” research vessel were presented at the meeting of TINRO-Center Academic Council. By words of Evgeny Ovsyannikov who led the expedition, their objectives included studies on the current condition of pollock, herring and capelin stocks in the Sea of Okhotsk (Stage 1); count survey of Pacific salmons and their nekton surrounding, background condition of the environment during their anadromous migrations (Stage 2); assessment of pollock stock and other species in South Kuril area (Stage 3). The works encompassed a water basin with a square area of 1.6 million km2. Expeditionary activities included 382 trawling stations, 481 oceanographic stations, 393 ichthyoplankton stations and 317 aquatic biology stations.
Key results of the expedition are stock assessments for major commercial species of the Far East - pollock, herring, capelin and Pacific salmons as well as potential commercial species such as mackerel and sardine.108 fish species belonging to 40 families, 9 species of cephalopod mollusks from 4 families, 8 species of scyphoid jellyfish and 3 species of hydroid jellyfish were observed in the surveyed area. Oceanographic observations showed that weather conditions in all study areas were cooler in this year than in previous years; still, environmental conditions remained at the normal climatic level.
Studies at Stage 1 of the expedition resulted in a conclusion that the Sea of Okhotsk pollock stock condition can be characterized as good and its size-age structure is favorable for stock retention in the coming years at a level higher than medium. Pollock abundance by results of trawling surveys was estimated at 46.2 billion individuals, its stock biomass at 11.0 million tons and fishable stock biomass at 6.4 million tons. The nearest recruitment for its fishable stock is represented by two strong year classes born in 2011 and 2013 and two medium-strength year classes of 2014 and 2015. This gives hope that the pollock fishery in the Sea of Okhotsk will remain stable in the coming period (through 2020) provided that scientists’ recommendations are observed. Pollock stock is currently stabilized at a level higher than medium and no reduction is foreseen in the nearest prospect.
Herring stock in the Sea of Okhotsk was evaluated at 2.4 billion individuals and 238,000 tons and capelin stock at 124 billion individuals and 13,900 tons. In both cases, the greater portion of large mature individuals had already migrated to the coastal zone for spawning which means that the above results are underestimated and cover largely the nearest stock recruitment.
All materials collected at this stage of the expedition will be used for preparation of short-term and long-terms forecasting of fishing conditions for pollock, herring and capelin, for justification of TAC for 2018 and recommendations on sustainable exploitation of these species.
At the second stage of studies performed near Kuril Islands and in the Northwest Pacific, pre-anadromous pink salmon abundance and biomass in the summer period was evaluated at 310.3 million individuals and 290,000 tons respectively. Based on collected materials, researchers analyzed spatial distribution of catches and frequency distribution of mean values of female and male gonad maturity for this species and divided this pink salmon stock into groups of later “autumnal” spawning period and earlier “summer” spawning period. Early-spawning pink salmon migrates for spawning to rivers on the western coast of Kamchatka, in northern part of the Sea of Okhotsk and, partly, to Amur River and Northeast Sakhalin. The later-spawning salmon form breeds primarily in Southeast Sakhalin and southern Kuril Islands. According to relevant calculations, the proportion of these two groups was roughly equal at the time of expeditionary works in that area.
Based on study results, fishing companies were advised that potential total catch of pink salmon in the Sea of Okhotsk basin may be around 140-160,000 tons which is twice higher than the preliminary forecast. Scientists had timely warned about potential migration of large pink salmon groups to West Kamchatka rivers (at least 40,000 tons) and have turned out to be right (catch exceeded 45,000 tons as of August 5 and fishery still goes on), and the rest pink salmon yield will come mostly from Sakhalin–Kuril area and northwestern part of the Sea of Okhotsk.
As for other salmon species, chum abundance and biomass in 2016 was 114.5 million individuals and 138,000 tons which is one of the highest estimates for this area in recent years. This gives hope that chum forecasts will come true and autumnal chum catches will be noticeably higher in some locations than was expected.
Furthermore, dense aggregations of mackerel and sardine were registered in the southern part of the surveyed water basin. Mackerel stock and biomass was evaluated at 3.8 million individuals and 959,000 tons, and respective figure for sardine were 7.8 billion individuals and 663,000 tons. These estimates show that an effective fishery for these species can be organized here. Another important finding of the studies is that, according to observations, zooplankton resources in the Northwest Pacific surpass nekton resources by several scores of times; therefore, feeding conditions are assessed as favorable for feeding of salmons and other commercial species.
The studies at the third stage in South Kuril area addressed feeding pollock stock. No surveys had been performed in that area in the summer season during several scores of years, and this study was of great scientific importance for understanding of the biology of this species. Pollock count surveys based on trawling method yielded the following results: on the Pacific side of southern Kuril Islands – 2.7 billion individuals and 432,000 tons, on the Sea of Okhotsk side – 46.8 million individuals and 29,700 tons. Its size-age structure was dominated by juveniles distributed largely on the Pacific side of Iturup Island. Mature pollock gathered into fishable aggregations only south of Shikotan Island and farther to the Japanese border. Adult pollock aggregations were also observed along the Sea of Okhotsk side of Kunashir and Iturup islands and in Kunashir Strait, although their density was low and they had no commercial importance. In general, the pollock stock in this area is at a medium level and may potentially decline in the coming years.
Source: TINRO webpage