Four new species of Ceratomyxa were found during parasitological studies of fish caught in shallow areas of Peter the Great Bay, Russia. Two of them (C. aspera n. sp. and C. durusa n. sp.) were found in the gall bladders of the flounders Limanda aspera and L. herzensteini. The third species (C. azonusi n. sp.) infected the gall bladder of the greenling Pleurogrammus azonus, and the fourth (C. lianoides n. sp.) was found in the gall bladder of Stichaeus grigorjewi. Ceratomyxa spp. have not been previously described from P. azonus or S. grigorjewi.
Recent changes of the main oceanographic, chemical, and biological parameters of the Okhotsk Sea ecosystem are considered briefly for the last decades (2000–2010s), mostly on the data obtained in marine expeditions conducted by Pacific Fish. Res. Center (TINRO) annually. Since the mid-2000s, anomalous oceanographic conditions were formed there with prevailing heightened temperature in all layers of the sea and lowered ice cover caused by changes in the atmosphere circulation with northward shift of cyclones tracks in winter and weakening of winter monsoon. The ice cover was below the normal value every year since 2004. In the warmer winter conditions, producing of the high-density water on the northern shelf decreased from 3.2–7.8 . 103 km3 in 1998–2002 to 1.2 . 103 km3 on average in 2004–2015, and the water with density sq > 26.8 was not formed at all in 2007–2009, 2011, and 2014–2015. As the result, winter convection, including the slope convection, became weaker and shallower and ventilated worse the water column, so dissolved oxygen content decreased in the lower portion of the intermediate layer, usually ventilated by slope convection. For the core of the intermediate layer (isopycnal surface 27.0 σθ), positive trend of temperature is estimated as +0.04…+0.16 o/decade, by areas, while the trend of dissolved oxygen content is negative: –0.07…–0.14 mL/L.decade, by areas. From the other hand, spring phytoplankton bloom became less intensive, presumably because of poorer upward flux of nutrients in conditions of weaker vertical mixing, and zooplankton biomass decreased, particularly for phytophages. However, these changes did not cause significant response in fluctuations of stocks for the main commercial fish and crab species. The largest stock of walleye pollock had cyclic fluctuations driven mostly by intra-population regulations, the stocks of pacific herring were rather stable, and the stocks of deep-water fish species, as flounders and halibuts had a slight tendency to growth, possibly because of better conditions for reproduction. Indeed, the densest aggregations of greenland halibut shifted from the depth of 600–700 m to 500–600 m that may be caused by de-oxygenizing of the lower portion of the intermediate layer. Crabs abundance also had positive dynamics obviously because of the effect of protective measures for red king crab in the 2009–2012, though its biomass continued to grow even after restoring the commercial landings. There is concluded that recent changes in the macroecosystem of the Okhotsk Sea correspond to the conception of the sub-polar ecosystems transformation under climate warming toward decreasing of their productivity and increasing of their functioning efficiency that was proposed earlier for the Japan Sea. Thus, from position of commercial exploitation of marine biological resources, the modern reconstruction of the Okhotsk Sea ecosystem under the climate change impact could be considered as a positive process.
State of the greenland halibut stock in the Sea of Okhotsk fishing zone is evaluated as overfished with a high probability of 97.5 % by the index of fishable biomass, and the overfishing continued in 2021. This conclusion is based on results of double filtering the posterior parameter estimates in the state-space generalized surplus production model JABBA (Just Another Bayesian Biomass Assessment), with additional tuning of the new model taking into account these results. The overfishing was not caused by significant changes of environmental parameters (average SST and EOF modes of SST were examined), but its main reason was the overestimated target harvest rate established for the Far East of Russia as 10 % of the total biomass or a half of natural annual mortality (20 %). This incorrect value of the rate was based on incorrect determination of age structure and terminal age for the halibut by the fish scale method. The new approach of the stock status evaluation with JABBA model is independent on the age data. It includes the additional filtering of the JABBA model result, its refinement with stringent tuning using the algorithm of No-U-Turn sampler, and checking additional parameters on hyperstability or hypersensitivity. The new reference point of the target harvest rate is between 2.5 and 5.4 % (95 % credible interval) of the total biomass, with a median of about 3.75 %. This new value is slightly higher than that one used by ICES for greenland halibut in the northeastern Atlantic (3.5 % for fishable biomass, its reduction to 2.5 % is discussed), but these values cannot be compared because of different habitat conditions and probably different growth rate of greenland halibut in the Okhotsk Sea and the Atlantic. Researches on the optimal level of greenland halibut exploitation should be continued; anyway, the new reference point of the target harvest rate has to be implemented immediately and to be used at least until correction of the age-length key for greenland halibut in the Okhotsk Sea. The input data and Stan code of the new model are presented in the annexes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.