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Vol. 22 (2019 year), No. 2, DOI: 10.21443/1560-9278-2019-22-2

Dolotov S. I., Samokhvalov I. V.
Distribution and spawning area of Atlantic salmon Salmo salar L. in the River Ura (the Murmansk Region)

The development of measures to preserve the population of Atlantic salmon has been carried out on the basis of the results of studying the state of its habitat and the conditions of reproduction. During the survey of the habitat conditions of this species in the River Ura (the Murmansk region, Russia), the area of spawning and nursery fund has been determined, the qualitative and quantitative distribution of salmon in the river basin has been established, and the migration barrier (waterfall) and the bypass for this obstacle have been described. The data obtained during the calibration of spawning and nursery plots and juveniles fishing have indicated that Atlantic salmon Salmo salar L. is widely distributed in the River Ura and runs along the main watercourse, three tributaries of the 1st order and one inflow of the 2nd order. The waterfall located on the River Ura at the distance of 28 km from its mouth does not limit the distribution of salmon which has the ability to make spawning migration along the creek bending the waterfall. The total area of the spawning and nursery fund is 69.4 ha, 83 % of which are located in watercourses below the waterfall. Spawning and nursery habitat of the Atlantic salmon is represented by a variety of habitat conditions with various longitudinal relief of the lake - river system, and the fractional composition of the bottom substrate. During the studies it has been noted a relatively high content of gravel and cobble fractions forming the most important types of spawning and nursery grounds, most suitable for Atlantic salmon spawning. "Spawning-nursery" grounds (42 %), as well as "spawning-nursery grounds with spawning grounds predominance" (35 %) constitute the bulk of spawning and nursery fund of the Atlantic salmon in the River Ura basin. Nursery grounds play a smaller role in its formation. The role of the latter is more noticeable in the river reaches above the waterfall where their share reaches 50 %.

(in Russian, стр.5, fig. 4, tables. 0, ref 7, Adobe PDF, Adobe PDF 0 Kb)

Vol. 25 (2022 year), No. 2, DOI: 10.21443/1560-9278-2022-25-2

Dolotov S. I., Kuzmin D. O.
Changes in the smoltification age of Atlantic salmon (Salmo salar L.) of the Yokanga, Kharlovka and Vostochnaya Litsa Rivers (the Murmansk Region)

Throughout the world, in recent decades, there has been a decrease in the abundance of Atlantic salmon, the main reason for which is a decrease in its survival rate during life at sea. Its value has a direct dependence on the length and, accordingly, the age of the smolts. Foreign researchers have found that the nature of long-term changes in the age structure of smolts can vary significantly by region. At the same time, the age of Atlantic salmon in Russian rivers, which account for a significant part of the area of the range of this species, was not considered. In this regard, the analysis of long-term data characterizing the age composition of salmon smolts of some rivers of the Murmansk region has been carried out. It has found been that in the first years of the period 2000–2018, the age structure of Atlantic salmon smolts was transformed in the rivers Yokanga, Kharlovka and Vostochnaya Litsa. As a result, fish at the age of 6 ceased to occur among them, the abundance of fish at the age of 5+ significantly decreased and the abundance of fish in the age groups of 3+ or 4+ significantly increased. The most likely reason for this is the change in the temperature regime of rivers since the mid-1990s, as a result of which the life time in the rivers of juvenile salmon has been reduced. Rejuvenation of the smolt population may have ambiguous consequences for the abundance of adult salmon, which are determined by the cumulative effect of reducing natural mortality at the stage from eggs to smolts, increasing their abundance and reducing their length, and reducing the survival rate during salmon life in the sea.

(in Russian, стр.9, fig. 4, tables. 0, ref 32, AdobePDF, AdobePDF 0 Kb)