Effects of Spatial Variability, Associated with a Frontal Structure, on Predictions of Age-0 Walleye Pollock (Theragra chalcogramma) Growth around the Pribilof Islands, Bering Sea

Age-0 walleye pollock growth along a frontal transect around the Pribilof Islands, Bering Sea, was estimated by using a spatially-explicit bioenergetics model. Predicted growth patterns along the transect were tested against the spatial resolution of the model, to examine the extent to which informative results were affected by the input spatial resolution. Results of model implementation to the Pribilof Islands scenario showed that on average fish residing in the offshore region of the transect were exposed to areas in which growth potential was two to three times higher than in the inshore region. Modelling results corroborated well with independent indicators of age-0 pollock growth, such as age-specific length and Fulton condition index from fish collected at the same location examined with the model. In spite of the better feeding and growth potential of the offshore region, age-0 pollock were found mainly in the inshore portion of the transect. Evidently, other factors, besides habitat energetics, needed to be considered to explain the distribution of age-0 pollock around the islands. Predictions of age-0 pollock growth along the transect were highly sensitive to the input spatial resolution of the model, but only at a spatial scale larger than a threshold of about 1000–2500 m. It is proposed that such threshold represents the limit beyond which important physical and biological boundaries are crossed and consequently model predictions derived from average conditions become biased.