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The Barents Sea is the north‐eastern fringe of the distribution of blue whiting (Micromesistius poutassou). Fluctuations in distribution and abundance of blue whiting in the area have been marked. Two hypotheses are put forward to explain these fluctuations. First, rich year classes in the main Atlantic stock of blue whiting may contribute to increased abundance in the Barents Sea. Second, variations in hydrography, such as influx of warm Atlantic water, may be particularly important in this fringe area. We investigated these hypotheses using data from bottom trawl surveys conducted during the period 1981–2006. Variations in abundance (measured either as incidence or density) and distribution were correlated with recruitment in the Atlantic stock of blue whiting as well as hydrographic conditions. Regression analyses indicated that the abundance fluctuations are primarily determined by variations in recruitment of Atlantic blue whiting, a strong year class leading to high abundance in the Barents Sea the year after spawning. However, salinity anomaly in the Fugløya–Bear Island transect during the previous year, an indicator of high inflow of Atlantic water, had also a significant, positive effect. Thus, the data suggested a climatic modulation of dynamics that were primarily determined by recruitment of blue whiting in the main Atlantic stock. Analyses of size structure as well as earlier studies on population genetics supported this conclusion. 相似文献
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The life history and vertical distribution of a female cohort of the mesopelagic fish Maurolicus muelleri is simulated using stochastic dynamic programming. The environment is represented by vertical profiles of zooplankton biomass, light intensity and temperature, all variables changing with season. The fish physiology is modelled by dynamic state variables that represent structural fish weight, energetic state and the age of developing oocytes. The model is used to simulate optimal depth distribution (feeding vs. predation risk) and energy allocation (somatic growth or reproduction). The optimal strategies predicted by the model depend on structural fish weight, energetic state and seasonal factors in the environment. The different strategies predicted for different size groups of fish are consistent with field observations of M. muelleri . Small fish give higher priority to growth and tolerate higher levels of predation risk than large fish. The strategies of small fish seem to be little affected by changes in energetic state or seasonal factors in the environment. On the other hand, the predicted strategies of large fish are largely dependent on energetic state and seasonal changes in the environment. In the winter they do not reproduce and minimize visual predation risk by staying at depths with a low light intensity. The low light intensities also result in a low food intake and a negative energy budget in the winter months. In spring, summer and autumn, the predicted strategy of large fish is to stay at depths that provide feeding rates sufficient to rebuild energy reserves lost in the winter and to provide energy for reproduction and somatic growth. 相似文献
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An individual based model of fish school reactions: predicting antipredator behaviour as observed in nature 总被引：5，自引：0，他引：5
An object-orientated, two-dimensional, cellular automata (CA) model is developed to describe and predict the schooling behaviour of fish in general, with Norwegian spring-spawning herring, Clupea harengus L., being used as a case study. The CA model is applied to visualize internal school dynamics based on individual decision rules. Several antipredator strategies, such as split , join and vacuole, performed by schools during predator attack, are visualized in the model. The primary driving force of individual fish is based on simple attraction rules. The model includes stochastic elements which assume that individual herring do not have perfect information about their surroundings. Isolation of individual fish from a school during predator attack is also predicted by the model. The disruption of highly organized fish schools, followed by an attack on solitary herring individuals, may be an important tactic for predators feeding on schooling prey. The conceptual CA model identifies patterns and mechanisms both within and between schools that may be important in all schooling fish. Model simulations are compared with observed predator–prey interactions between killer whales, Orcinus orca L., and herring in northern Norway. 相似文献
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