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Data from six years, September 1994–1999, of bio-acoustic surveys near the Pribilof Islands, Alaska, (AK), from which age-0 walleye pollock school and zooplankton patch locations have been extracted, were analysed using image-processing methods. Multiple passes along four transects in this major pollock nursery area were examined. The data showed high year-to-year variability in overall abundance of both fish and plankton, but consistent abundance differences between the transects. Juvenile pollock abundance was generally highest in the shallow shelf region to the north of the Pribilof Islands and lowest in the mouth of the Pribilof Canyon to the south. Plankton biomass patterns tended to be the reverse. We identified fronts and regions within the transects based on changes in hydrograpy (e.g. vertical stratification) and bathymetry. Diel migration patterns of pollock and zooplankton within these regions appear to depend on the degree of stratification, the depth, the size of the pollock and the relative abundance of the pollock and zooplankton. Several hypotheses are also discussed concerning the relationship of pollock recruitment year-class strength to large year classes including differences in the environmental conditions, the pervasiveness of the pollock, the size of juvenile pollock and the density of predators. Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]

Discusses the concept and the use of modeling in scientific research. Need for uniformity of language in modeling; Importance of transparent explanations; Phases involved in the act of modeling; Protocol for model disclosures.

We developed a simulation model based on energetics, habitat selection, feeding selectivity, and population dynamics to examine the effect of introductions of rainbow trout Oncorhynchus mykiss on parr of sockeye salmon O. nerka and longfin smelt Spirinchus thaleichthys resident in Lake Washington (Washington State). We modeled growth and population dynamics of rainbow trout cohorts introduced between 1981 and 1984, and compared results with length-at-age data obtained from marked released fish and with data on diets. Graphical comparisons indicated a reasonable fit to the growth data over the 150-400-mm size range. The model gave a close prediction of the size at which rainbow trout begin to eat fish, these results being sensitive to a size-selective feeding function. Diet data showed that model predictions for the major prey fish (longfin smelt and sockeye salmon) were reasonable. However, prey vulnerability had to be set lower for sockeye salmon than for longfin smelt to produce reasonable rainbow trout diets. Simulation experiments examined the effect ofaltered rainbow trout enhancement, fishing pressure, prey vulnerability, and prey abundance and species composition on prey fish survival. These experiments indicated that the effect of rainbow trout predation on prey fish strongly depended both on the magnitude of rainbow trout introductions and on the prey fish abundance and species composition, which varied from year to year. [ABSTRACT FROM AUTHOR]