Baltic cod recruitment – the impact of climate variability on key processes

Large-scale climatic conditions prevailing over the central Baltic Sea resulted in declining salinity and oxygen concentrations in spawning areas of the eastern Baltic cod stock. These changes in hydrography reduced the reproductive success and, combined with high fishing pressure, caused a decline of the stock to the lowest level on record in the early 1990s. The present study aims at disentangling the interactions between reproductive effort and hydrographic forcing leading to variable recruitment. Based on identified key processes, stock dynamics is explained using updated environmental and life stage-specific abundance and production time-series. Declining salinities and oxygen concentrations caused high egg mortalities and indirectly increased egg predation by clupeid fish. Low recruitment, despite enhanced hydrographic conditions for egg survival in the mid-1990s, was due to food limitation for larvae, caused by the decline in the abundance of the copepod Pseudocalanus sp. The case of the eastern Baltic cod stock exemplifies the multitude effects climatic variability may have on a fish stock and underscores the importance of knowledge of these processes for understanding stock dynamics

Young cod ecology and abundance survey in the Eastern Baltic

The peculiarities in young cod distribution and feeding were considered. On the basis of the investigations on young cod ecology and the analysis of quantitative characteristics of abundance by regions and seasons the most representative areas and the time for young cod abundance survey in the Eastern Baltic were determined. A rather high correlation (r = 0.88) between the results of young cod survey in Ventspils and other the Eastern Baltic areas, and in Gdansk region as well, and between the relative and absolute young cod abundance (r = 0.78 - 0.83) were revealed.Рассматриваются особенности распределения и питания молоди трески. На основании проведенных исследований экологии молоди и анализа количественных характеристик численности по районам и сезонам определены наиболее репрезентативные районы и время для учета численности молоди в восточной Балтике. Выявлена достаточно высокая корреляция между результатами учета молоди в Вентспилском, а также других районах восточной Балтики, и в Гданьском районе (r=0.88) и между относительной и абсолютной численностью молоди (r=0.78-0.83).7. ausgabe des sonderheftes über fischereiliche untersuchungen der DDR und der UDSSR in der Ostsee. 7. выпуск совместного сборника научных статей по вопросам рыбохозяйственных исследований ГДР и СССР в Балтийском море.Publishe

The influence of some stock and environmental parameters on the abundance of cod population in the Eastern Baltic

The relations of absolute and relative abundance of 13 year-classes (1966—1978) of the Eastern Baltic cod population with salinity and oxygen content in the Gotland Deep during spawning period and with spawning stock size (in all with 20 parameters of environment and stock) were considered using multiple regression analysis. In addition to the standard statistical parameters the influence of some terms in re-gression equation on the total sum of squares was estimated. The analysis of variants with the highest values of Fisher's criterion (P > 0.999) and the smallest values of standard error of regression showed, that year-class abundance is determined by a complex of environment and stock parameters, the influence of environmental factors and spawning stock size being approximately equal. All equations contain factors, related to abundance of parents, and their influence fluctuates from 36 to 74 %, the average is about 40 %. The dependence of year-class abundance on parents stock abundance suggests an explanation of relatively high level of cod stock recruitment in the Eastern Baltic during last years despite of rather unfavorable environmental conditions.Рассматривались связи урожайности 13 поколений (1966 – 1978 гг.) восточно-балтийской популяции трески с соленостью и содержанием кислорода в Готландской котловине в период нереста и величиной нерестового запаса. Выявлено, что численность поколений определяется комплексом параметров среды и запаса, причем сила влияния факторов среды во время нереста и величины нерестового стада примерно одинаковая. Проявляется также влияние родительского стада на урожайность дочернего поколения.8. ausgabe des sonderheftes über fischereiliche untersuchungen der DDR und der UDSSR in der Ostsee. 8. выпуск совместного сборника научных статей по вопросам рыбохозяйственных исследований ГДР и СССР в Балтийском море.Publishe

Некоторые закономерности в динамике вод Балтийского моря

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State, structure and exploitation of Baltic cod and its significance in the food chain

On the basis of investigations on the dynamics of the productivity of year classes within the yields and of growth, mortality, distribution of cod in the eastern Baltic and the dynamics of total cod catches and catches per unit effort, the structure and state of the cod stocks have been estimated and natural and the fishing mortality (M = 0,3-0,4; F = 0,5-0,7) and growth constants Lg = 99-120 cm, K = 0,11-0,146) have been determined. The estimation of the level of exploitation shows that fishing intensity lies within or near the limits of the optimum range. It is shown that regulation of the minimum, length and regulation of the percentage of young fish as by-catch can be of considerable practical use. The absolute cod resources in the eastern Baltic as well as the amount of food taken in are determined and it is shown that cod form a significant factor in the natural mortality of herring and sprat.Исследования по рыбному хозяйству СССР и ГДР в Балтийском море. Fischerelliche Untersuchungen der UdSSR und der DDR in der Ostsee. Первый совместный сборник научных статей, выработанных в ГДР и в СССР, посвященный проблемам рыболовства на Балтике.Publishe

Zivju krajumu stavokla novertejums Latvijas Republikas udenos Baltijas jura, nozvejas prognoze un priekslikumi krajumu racionalai ekspluatacijai

Available from Latvian Academic Library / LAL - Latvian Academic LibrarySIGLEMinistry of Transport of the Republic of Latvia, Riga (Latvia)LVLatvi