Ranging Year-Class Strength And Survival Rates During Early Life History Of The Barents Sea Food Fishes To Establish Biological Reference Points And Evaluate Environmental Effects

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Survival index (SI) of a year class in early life history is defined as the ratio of abundance of fish at age 3 to population fecundity (PF), or to the spawning stock biomass (SSB). SI is considered here to be an integrated indicator of survival conditions during early life, i.e. periods of egg, larval and fry development. Ranking of SI by means of cluster analysis revealed three types of survival conditions – favourable, moderate and unfavourable. The corresponding values of SI (*10-6) to these three types of conditions were estimated in spring spawning Norwegian herring as 152.49, 28.27, 4.97; in Northeast Arctic cod – 16.94, 6.40, 3.05; in Northeast Arctic haddock – 24.18, 8.55, 2.00; and in Greenland halibut of the Barents Sea – 219.29, 101.24, 45.60. Regression equations were obtained describing dependence of reqruitmtent on spawning stock size in three types of survival condtitions for each of the stocks considered. Three levels of PF and SSB - safe, minimal required acceptable and critical were calculated correspondingly to the types of survival conditions in the food fish populations studied. An attempt was made to collate long term changes in survival conditions (logorithm of SI) with the same of some indicators (three main components) of ambient conditions in the ocean (IO). There is a good correspondence between shifts in the state of ckimatic characteristics and SI of most North Anlantic fish stocks on decadal and inerdecadal time scales. However, the significant relationships between SI of spring spawning Norwegian herring, Northeast Arctic cod and haddock ranged into three groups of years corresponding to favourable, moderate and unfavouable survival condtitions and basin-scale and regional climatic indices were not found. The local oceanographic conditions (wind mixing, local eddy structure, vertical fluxes, etc.) should be also taken into account.