Some Population Dynamics Issues of Pink Salmon Oncorhynchus gorbuscha Temporal Forms on Sakhalin and the Southern Kuril Islands

Journal of Ichthyology - Population dynamics of early and late temporal forms of pink salmon Oncorhynchus gorbuscha on the Iturup and Kunashir islands (southern Kuril Islands) and on the...     

Influence of Extreme Environmental Factors on the Dynamics of Abundance of the Pink Salmon <Emphasis Type="Italic">Oncorhynchus gorbuscha</Emphasis>

The correlation between the number of returned fish and the spawners of the parent generation recorded in the rivers (the reproduction index) has been analyzed in a series of generations of the five largest stocks of pink salmon Oncorhynchus gorbuscha in the Sakhalin-Kuril region. The hypothesis that the appearance of low-yielding generations of pink salmon was mainly due to the impact of typhoons as extreme environmental factors has been confirmed. Low values of the reproduction index of pink salmon generations that have been exposed to typhoons during embryonic development in the rivers (redds) or during the feeding period of juveniles in the coastal region of the sea (the next few days after downstream migration) allow for a conclusion on their significant importance for the formation of the abundance of this species. During some adjacent year groups, the frequency of typhoons attributable to the indicated periods of the pink salmon’s life cycle increases, this causes a number of low-yielding generations. At the same time, the strength of the typhoons and the limits of their impact are constantly changing, which explains the lack of synchronism in the sharp changes in the pink salmon population of all the stocks in the region.     

On Catching Humpback Salmon Oncorhynchus gorbuscha and Chum Salmon Oncorhynchus keta of Rare Age

Data on catching humpback salmon Oncorhynchus gorbuscha at the age of 0+ and chum salmon Oncorhynchus keta at the age of 1+ in the Ilyushina River (Kunashir Island) in the period of spawning migration are given. The sex of fish, the body length, the stage of gonad maturity, and the number and width of sclerites on scales are indicated.     

Population dynamics of pink salmon <Emphasis Type="Italic">Oncorhynchus gorbuscha</Emphasis> (Salmonidae) from the southeastern coast of Sakhalin island

The results of monitoring from 1971 to 2004 of pink salmon Oncorhynchus gorbuscha spawning in the rivers of the southeastern coast of Sakhalin are presented. It is shown that fluctuations in the value of its return more largely depend on the level of mortality of fish of the respective generations in the marine period of life than on the yield of downstream migrating juveniles, that, in turn, is weakly related to the numbers of parents, which is explained by the spawning conditions in small rivers at a dense aggregation of spawners on the spawning grounds. Stable long-term tendencies in the variation of numbers, biological indices of fish, and the dates of their return for spawning are established. It is suggested that they indicate a decisive role of globalcyclic, climatic-oceanological processes in the population dynamics of pink salmon     

Wild and hatchery reproduction of pink and chum salmon and their catches in the Sakhalin-Kuril region,Russia

In the Sakhalin-Kuril region hatchery culture of pink and chum salmon is of great importance compared to other regions of the Russian Far East. During the last 30 years the number of hatcheries increased two-fold, and significant advances were made in hatchery technologies. As a result, chum salmon capture in regions where hatcheries operate (southwestern and eastern Sakhalin coasts, and Iturup Island) was 9 times as high during 2006–2010 than during 1986–1990, whereas wild chum salmon harvest markedly declined. Recent dynamics in pink salmon catch appear to track trends in natural spawning in monitored index rivers, suggesting natural-origin pink salmon play a dominant role in supporting the commercial fishery. It remains uncertain as to whether hatcheries have substantially supplemented commercial catch of pink salmon in this region, and I recommend continued research (including implementing mass marking and recovery programs) before decisions are made regarding increasing pink salmon hatchery production. Location of hatcheries in spawning river basins poses problems for structuring a management system that treats hatchery and wild populations separately. Debate continues regarding the existence and importance of density-dependent processes operating in the ocean environment and the role hatcheries play in these processes. Loss of critical spawning habitat for chum salmon in the Sakhalin-Kuril region has lead to significant declines in their abundance. I conclude by recommending increases in releases of hatchery chum salmon numbers in the region to help recover depressed wild populations and provide greater commercial fishing benefits in the region.     

Rapid expansion of an enhanced stock of chum salmon and its impacts on wild population components

A harvested stock of chum salmon homing to Kurilskiy Bay, Iturup Island, consists of two genetically distinct river populations that reproduce in two rivers that drain into the bay and are characterized by limited gene flow. One of these is small and can be regarded as wild, whereas the other is much larger and, until recently, was composed of naturally reproducing components spawning in the river??s mainstem and tributaries, with almost no hatchery reproduction during the past two decades. The only human impact on reproduction of the chum salmon stock was regulation of the escapement, with officially accepted limits to avoid ??over-escapement??. Recently the hatchery began to release a large amount of chum salmon juveniles. As confirmed by data on variation in both age composition and microsatellite DNA, first-generation hatchery-origin fish that returned from the first large releases occupied spawning grounds and presumably competed directly with, and potentially displaced wild fish. The most dramatic example is a genetically distinct beach-spawning form of chum salmon that was swamped by much more numerous hatchery-origin fish of the river-spawning form. In order to restore and support naturally reproduced population components, careful estimation of the carrying capacity of natural spawning grounds is necessary with efforts to increase escapement to these habitats. We also recommend concerted efforts to restore and conserve a unique beach-spawning population of chum salmon. We further recommend development of a marking program for direct estimation of straying and evaluation of ecological and genetic impacts of hatchery fish on neighboring wild and natural populations.     

Some Results of Studies on Pink Salmon Oncorhynchus gorbuscha’s Number Dynamics on the Northeastern Coasts of Sakhalin Island

Journal of Ichthyology - Data characterizing the number of individual generations of pink salmon Oncorhynchus gorbuscha (the volume of harvest, entry of spawners into the rivers, and subsequent...     

Morphobiological specific features of the river and lake forms of chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> (Salmonidae) on the southern Kuril Islands

Morphobiological differences between chum salmon Oncorhynchus keta dwelling in rivers and lakes on the Iturup and Kunishir islands are shown. The differences between chum salmon of different islands are reduced mainly to the interpopulation variation in growth determined mainly by the action of ecological factors. First of all, these are differences in the rate of growth and the number of sclerites in the first annual zone of the scales growth related to specific features of feeding in the area subjected to the action of different currents. The differences between the river and lake forms of chum salmon are, to a greater extent, determined by the action of selection according to body sizes and production of different amounts of eggs by females.     

Temporal structure and some features of stock dynamics of pink salmon <Emphasis Type="Italic">Oncorhynchus gorbuscha</Emphasis> (Salmonidae)

Characteristics of early and late migrants of pink salmon Oncorhynchus gorbuscha that spawned in the rivers of the coast of Aniva Bay (southern Sakhalin) and Iturup Island (southern Kuril Islands) are described. Upstream migration of the late form is characterized by the presence of large exemplars, especially males, and increasing proportion of these fishes in the catches. Absolute fecundity of the females of the early and late forms can be similar (Iturup Island) or different (Aniva Bay), but relative fecundity is lower in the females of the late form in both regions. Production of a larger number of eggs by the females of the early form is associated with a larger level of mortality: the abundance of the early form is comparatively low, and substantial annual variation of the abundance is registered. Relative abundance of pink salmon from the temporal groups depends mainly on reproductive conditions during the freshwater part of their life cycle. Analysis of size composition of the fish conducted over many years shows a trend in the ratio between the body lengths of males and females: unfavorable foraging conditions (and slower growth rate) lead to the appearance of females that are larger than males. To take into account a positive correlation between the body length and fecundity of females, this feature is regarded as a compensatory reaction of the population directed to more intensive reproduction at poor foraging conditions.     

On possible re-distribution of pink salmon <Emphasis Type="Italic">Onchorhynchus gorbuscha</Emphasis> between the reproduction areas of different stocks in the Sakhalin-Kuril region

The scale structure of pink salmon Oncorhynchus gorbuscha inhabiting southern Sakhalin and Iturup Island were studied in 2014. These locations are characterized by the unusual dynamics of catches and biological parameters of the fish that come to spawn in different areas in the Sakhalin-Kuril region. The pink salmon that has originated from Iturup Island appeared en masse in the waters of southern Sakhalin, according to the analysis of the scleritogram fragments that reflect the fish growth during the first months of life. This is the first confirmation of the hypothesis of the fluctuating stocks of pink salmon approved by the ichthyological methods. It is suggested that wide-scale straying of pink salmon takes place in the years of dominance shift between the generations of even and odd spawning years.