Scientific Acoustic Data from Commercial Fishing Vessels: Eastern Bering Sea Walleye Pollock (Theragra chalcogramma)

Abstract

Although the International Council on the Exploration of the Sea Working Group on Fisheries Acoustics, Science and Technology provided guidance on using commercial fishing vessels for collecting opportunistic acoustic data (OAD), an approach for working with these non-traditional datasets has not been addressed. This dissertation demonstrates methods for processing and analyzing acoustic data collected from commercial fishing vessels to investigate current issues in fisheries management. Although the opportunistic acoustic data in this project were uncalibrated and therefore could not be used for biomass estimates, it was found to be suited to investigating fisheries issues where an index of abundance proportional to biomass could be substituted. This dissertation demonstrates the scientific application of

opportunistically collected acoustic data from commercial fishing vessels operating in the winter Eastern Bering Sea (EBS) walleye pollock (Theragra chalcogramma) fishery. The spatial and temporal attributes of winter EBS pollock aggregations are not well understood due to the inaccessibility of the area to research vessels during harsh winter months. With their high resolution and wide spatial and temporal range OAD provided an excellent data source for investigating spatial and temporal dynamics. Results from this study suggest that pollock aggregations exhibit diel contraction and expansion and pollock aggregations exhibit scale dependent spatial structure. Questions on the intensity of the EBS pollock fishery arising from declines in Steller sea lion populations have been a focus of many researches, but a lack of informative data on winter distribution has hindered these efforts. OAD provided an index of abundance that was used in a spatially explicit depletion model to examine the temporal and spatial intensity of the winter fishery and found that fishery exploitation rates inside Steller sea lion critical habitat was higher than outside. The lack of comprehensive survey data on pollock distribution in the EBS during the winter is problematic for predicting possible effects of climate change in the EBS. An OAD index of abundance was used to develop and evaluate a generalized additive model for predicting effects of environmental covariates on winter pollock distribution. Sea surface temperature and bottom depth were found to be significant predictors of pollock density.