Marine mammals in macro-ecosystems of the Far Eastern seas and adjacent waters of the North Pacific

This article considers the role of marine mammals in a sea or ocean ecosystem based on the example of the Far Eastern seas with adjacent waters of the North Pacific, which is one of the regions of the World Ocean that is distinguished by its high biological and fish capacity and by a high abundance of cetaceans and pinnipeds. Based on extensive data, which was published mostly by Russian experts, the authors have estimated the quantities of annual consumption of fish and invertebrates by marine mammals in three Far Eastern seas: 14.6–18.2 million tons in the early 20th century; 12.3–15.1 million tons in the late 1970s; 22.7–28.8 million tons in the pre-harvest period; and 24.0–24.7 million tons in the early 21st century (27.0–29.5 million tons, if 3–5 million tons in ocean waters off the Kuril Islands and Kamchatka are taken into account). More than half of this quantity is formed by zooplankton and zoobenthos; the second largest portion consists of fish and squid. At the same time, the values of food consumption by fish and large invertebrates are much higher than these estimates for the 0–1000 m layer: 516 million tons were consumed in the 1980s–1990s; 389 million tons in 1991–1995; and 461 million tons in 1996–2005. In the years of high abundance, large walleye pollock alone consumed nearly 40 million tons of small fish and squid. Based on the data of 35-year-long ecosystem studies that were conducted by the Pacific Research Fisheries Center (TINRO Center), the following biomass estimates have been obtained for the biota of the Far Eastern Economic Zone of Russia: mesoand macroplankton, 1000 million tons; zoobenthos, 500 million tons; nekton, 100 million tons; benthic fish, 5 million tons; and large benthic invertebrates that are not included in the benthos, 2.43 million tons. By using these estimates and by comparing the quantities of food consumption by marine mammals, the conclusion was made that the role of marine mammals in food webs of waters of the Russian Far East is remarkable, but it does not reach a level that is high enough to regulate such a large-scale ecosystem as the macro-ecosystem of a sea or ocean.     

On the Persistence of Stereotypes Concerning the Marine Ecology of Pacific Salmon (<Emphasis Type="Italic">Oncorhynchus</Emphasis> spp.)

Some of the views on the marine ecology of Pacific salmon (Oncorhynchus spp.) that were popular in the second half of the 20th century are discussed critically: the absolutization of the influence of sea surface temperature on distribution of salmon and strength of their year classes, as well as the conclusions on the shortage of food (particularly in winter) and the fierce competition for food, the “suppression” of other salmon species and own adjacent broodline by pink salmon, the limited carrying capacity of the pelagic zone of subarctic ocean waters for salmon, the distortion of the structure of epipelagic communities in ecosystems of the North Pacific due to the large-scale stock enhancement of chum salmon, etc. Most of these ideas have not been confirmed by the data of long-term monitoring conducted in the form of complex marine expeditions by the Pacific Research Fisheries Center (TINRO Center) in the Far-Eastern Seas and adjacent North Pacific waters since the 1980s. The data show that Pacific salmon are ecologically very flexible species with a wider temperature range of habitat than was previously believed. Salmon are able to make considerable vertical migrations, easily crossing zones of sharp temperature gradient and different water masses. Having the wide feeding spectra and being dispersed (as non-schooling fish) when feeding in the sea and ocean, they successfully satisfy their dietary needs in vast areas even with relatively low concentrations of prey organisms (macroplankton and small nekton). The total biomass of all the Pacific salmon species in the North Pacific is not greater than 4–5 million t (including 1.5–2.0 million t in Russian waters), whereas the biomass of other common species of nekton is a few hundreds of millions of tons. Salmon account for 1.0–5.0% of the total amount of food consumed by nekton in the epipelagic layer of the western Bering Sea, 0.5–1.0% in the Sea of Okhotsk, less than 1% in the ocean waters off the Kuril Islands, and 5.0–15.0% in the ocean waters off East Kamchatka. Thus, the role of Pacific salmon in the trophic webs of subarctic waters is rather moderate. Therefore, neither pink nor chum salmon can be considered as the species responsible for the large reorganization in ecosystems and the population fluctuations in other common nekton species.     

New Data About Seasonal Distribution and Migrations of Whales and Dolphins in the Sea of Okhotsk

This paper presents new data about the seasonal distribution of whales and dolphins in the Sea of Okhotsk including the ice period. Even under the most severe ice conditions, the migrating species of whales and dolphins may be encountered in the Sea of Okhotsk. In all seasons the density of cetaceans is higher in the eastern part of the sea, which is more abundant in fish.     

Illusions and realities of the ecosystem approach to the study and management of marine and oceanic biological resources

The scientific and applied problem of the ecosystem approach to the management of marine biological resources arose during the last quarter of the 20th century as a component of the Rational Nature Use Concept. This occurred mostly because the existing fishery rules and concepts of the optimum yield theory, which were introduced in the practice of fishery regulations, have proven to be insufficiently effective to conserve biological resources and provide stability of the fishery resource base. The ecosystem approach to biological-resource management implies a change of the autecological studies of commercial stock units (populations) and the managerial single-species models for the sustainable-sized management, taking the impacts of the fishery on marine ecosystems into account, as well as those of marine ecosystems on the fishery. At present, the ecosystem-based biological-resource management includes a complex of ecological topics and issues, such as biodiversity conservation, effect of climate changes, sustainability of stocks and communities, interspecies relationships, multi-species fishery, conservation of rare species, protection of especially important water bodies and landscapes, biotope degradation, anti-pollution measures, invasive species, ranching aquaculture, genetic diversity, etc. The main current problem, besides insufficient knowledge of many of these issues, is how to practically integrate such a large number of parameters into the management system. Thus, the complicated and long-term problem of ecosystem management of marine biological resources should be solved step-by-step, following the progress in the technical capabilities and concepts of natural processes. As well, certain better-studied elements of the ecosystem approach should be implemented first in the practice of management, while taking the regional specifics into account.     

“Unreliable Fish” or Unreliable Hypotheses: What Happens to Nekton in Ocean Waters off the Kuril Islands?

Russian Journal of Marine Biology - The phenomenon of population waves of nekton in the Kuroshio Current system is discussed using the example of the Japanese sardine Sardinops melanostictus, one...