. La parte orientale del Mare di Bering ripiano : oceanografia e risorse / a cura di Donald W. cofano e John A. Calder . 10 20 30 40 50 60 Lunghezza forche (cm) Figura 33-21. Confronto della dimensione frequenza distribu- zioni del sondaggio e della pesca di popolazioni di Pollock. I risultati del sondaggio vengono dal 1978 NMFS Crab-Groundfish sondaggio di campionamento dell'area di indice mostrato in Fig. 33-8. Risultati della pesca sono da 1978 NMFS estera della pesca programma osservatore di campionamento delle catture commerciali di giapponese madre- navi, Giapponese di grandi navi per la pesca a strascico di poppa e il coreano di grandi navi per la pesca a strascico di poppa in area INPFC 1. di un sempre maggiore propo

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. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . 10 20 30 40 50 60 Fork Length (cm) Figure 33-21. Comparison of the size frequency distribu- tions of survey and fishery pollock populations. Survey results are from the 1978 NMFS Crab-Groundfish sampling survey of the index area shown in Fig. 33-8. Fishery results are from 1978 NMFS Foreign Fisheries Observer Program sampling of the commercial catches of Japanese mother- ships, Japanese large stern trawlers, and Korean large stern trawlers in INPFC area 1. of an increasingly larger proportion of small and young fish. The size distribution of the 1978 fishery catch shown in Fig. 33-21 represents an age composition of approximately 2 percent one-year- olds, 20 percent two-year-olds, 40 percent three- year-olds, 18 percent four-year-olds, and 20 percent five or more years of age. In the perspec- tive of the apparent growth and reproductive schedules for the population (see Tables 33-6 and 33-7), it would appear prudent to reduce fishing pressures upon age-classes 1 to 3 years. SEASONAL AND INTERANNUAL VARIABILITY Seasonal variations The eastern Bering Sea environment is character- ized by strong seasonality. Temperatures are seasonally cyclic and extremely cold during winter. Mixing and overturn of the water column occurs as a result of heat loss from surface layers during the winter, followed by increased water column stability during summer warming. Biological production processes follow a cycle of pulsed high activities during spring and summer, followed by a long winter period of low activity. Apart from these generalizations, distinctive biological domains (i.e., geographical subregions and water mass layers) are apparently formed in the eastern Bering Sea characterized by differ- ences in mean and extreme values of environmental conditions, relative variability, and timing of events. These different domains, or habitats, are presumably used by biological sp

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