Federal Research Institute of Fisheries & Oceanography (VNIRO), Moscow

The maximum volume of cod fishing stock which was recorded in 1946 is 5.6 times larger than the minimum one (1983), while for haddock, the peak value of stock biomass (1972) may be as much as nine or twenty-one times larger than the minimum one (1984), depending on different estimations.

Such changes in the fish stock abundance primarily relate to large interannual changes in recruitment. For cod, the most strong year-class (1973) is sixteen times larger than the poorest one (1969). As for haddock, the strongest generation (1953) could be as much as 133 times larger than the weakest one (1984)! Such changes in these fish stocks are associated with habitat conditions for survival of new generations rather than with our efforts to sustain a certain level of the spawning stock biomass through decrease/increase of the respective TACs. In three or four years a strong/weak year-class of cod or haddock becomes the main component of the fishing stock and, consequently, it will determine increase or decline in the fishing stock biomass. Dealing with a biological species which annual production depends on natural factors rather than on our choice, we have to admit that strategies aimed at achieving a high long-term yield from stocks is Utopian.

Stability in catches is possible, however, only under condition that annual catches are minimized to the levels at which fisheries would not have negative effect on the stock even in years of its significant decline.

If we choose the strategy to obtain a biologically founded maximum yield which would not result in the fish stock collapse, fisheries should follow the stock dynamics. It is off the question to sustain the permanent level of catches because of the initial (natural) instability of fish stocks.

Retrospective analysis of the cod stock dynamics indicated that in adjacent years the stock could change by 20-30% or more. The cod TAC with the deviation of ± 10% established by the JRNC could mean risks of overfishing in years of the stock declining or under-fishing in years of the stock growth.
36 dots out of 60, analysed years, are outside of the ± 10% range. As for haddock, 33 dots (or 40 in according with different assessments of stock), out of 56 analysed years, i.e. 59 or 71% of the total variations are outside the 25% deviation from a relatively stable TAC. Recognizing inevitable great variations in the fish and spawning stock, the 33rd meeting of the JRNC adopted several amendments and limitations which actually leave no chance for the practical following to the Rule.

In case of the cod stock, and particularly in case of the haddock stock, the objective of setting a constant TAC could not be considered biologically sound because it disagrees with the natural population dynamics of these fish species.

It would be more reasonable TAC assessments in which included all major and traditionally surveyed characteristics of the stock status and the fisheries outcome. In this case it is especially important the objective to achieve correspondence between relative annual variations in catches and the stock. A TAC for the following year increases/decreases, compared to previous years, by a percent which corresponds to the predicted increase/decrease of the fish stock.

Forecasting the stock volume, we should give more attention to recruitment assessment and all those factors which determine survival of the generation at it's the first years of life. The necessity for prediction the spawning stock biomass assessments, however, is rather precarious. First of all, this is true for abundant and highly fecund species; success of their year-classes depends on survival condition at the early ontogenesis stage rather than on the initial quantity of egg, i.e. the spawning stock biomass (SSB).

In order to sustain a high level of the fish stock abundance it is much more important to implement all those measures which aimed at protection of cod and haddock at their first years of life. Among such measures the most significant are minimizing bycatch and discards of young fish; critical attitude to a particularly large increase in SSB which leads to increase in cannibalism; establishment of areas closed for trawling to protect dense concentrations of young fish.



Язык сайта:

English Danish Finnish Norwegian Russian Swedish

Популярное на сайте

Ваш IP адрес:

Последние комментарии

При использовании материалов - активная ссылка на сайт https://helion-ltd.ru/ обязательна
All Rights Reserved 2008 - 2019 https://helion-ltd.ru/

@Mail.ru .