Strong tidal currents in eastern Maine, USA, make that region attractive for tidal power development. Little is known about the effects of marine hydrokinetic (MHK) devices on fish, yet many fish species use tidal currents for movements. We used empirical data from stationary and mobile hydroacoustic surveys to examine the probability that fish would be at the depth of an MHK device and may therefore encounter it. The probability was estimated using three components: 1) probability of fish being at device-depth when the device was absent; 2) probability of fish behavior changing to avoid the device in the far-field; and 3) probability of fish being at device-depth in the near-field when the device was present. There were differences in probabilities of fish encountering the MHK device based on month, diel condition and tidal stage. The maximum probability of fish encountering the whole device was 0.432 (95% CI: [0.305, 0.553]), and the probability of fish encountering only device foils was 0.058 (95% CI: [0.043, 0.073]). Mobile hydroacoustics indicated that fish likely avoided the device with horizontal movement beginning 140 m away. We estimated the encounter probability for one device, but results can be applied to arrays, which may have bay-wide implications.

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Walleye pollock (Theragra chalcogramma) is the target of one of the world's largest sheries and is an important prey species in the eastern Bering Sea (EBS) ecosystem. Little is known about the potential e ects of shing on the school characteristics and spatial distribution of walleye pollock. Few dedicated research surveys have been conducted during pollock shing seasons, so analysis of shery data is the only feasible approach to study these potential e ects. We used acoustic data collected continuously by one shing vessel in January-February 2003, which operated north of Unimak Island. Results from comparisons between two shing periods showed signi cant changes of pollock distribution at di erent scales. The schools were smaller and denser during the second period. Furthermore, the spatial distribution of schools became sparser, as evidenced by the lower frequency of schools per elementary distance sampling unit and the increase in average next-neighbor distances (NNDs). However, the average NND between schools within a cluster and the average abundance of clusters did not change signi cantly. Variography was used to investigate the changes at scales larger than 1 nm. The increased range, nugget e ect, and sill in the second period indicated changes of pollock spatial distribution; however, it is unclear whether these changes are attributable to shing or ecological processes.

Shen, H., Dorn, M. W., Wespestad, V., and Quinn, T. J. 2009. Schooling pattern of eastern Bering Sea walleye pollock and its effect on fishing behaviour. – ICES Journal of Marine Science, 66: 1284–1288 Walleye pollock (Theragra chalcogramma) form persistent midwater and near-bottom schools in the daytime during the winter spawning season in the eastern Bering Sea (EBS). Two spawning areas in the EBS, north of Unimak Island and near the Pribilof Islands, are the main fishing grounds. To study the schooling pattern of pollock and its effect on fishing behaviour on these two fishing grounds, a principal component analysis with instrumental variables was carried out using acoustic and observer data from 2003 and 2005. Significant differences between the school descriptors distinguished the schooling patterns among areas and years. The harvester, that is to say, the fishing vessel and its crew taken together, searched for fish aggregations, which were caught in a different manner when the schooling pattern changed. School density had a greater effect than school size on fishing behaviour. Aggregations were less dense in 2003 than in 2005, and the harvester tended to fish with longer tows, at higher speeds, when it encountered less dense aggregations.