A dynamic model for the life history of Maurolicus muelleri, a pelagic planktivorous fish |
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| Authors: | RUNE ROSLAND & JARL GISKE |
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| Institution: | Department of Fisheries and Marine Biology, University of Bergen, HIB, N–5020 Bergen, Norway |
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| Abstract: | 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. |
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