Abstract
In their paper, ‘Migration behavior of maturing sockeye (Oncorhynchus nerka) and Chinook salmon (O. tshawytscha) in Cook Inlet, Alaska, and implications for management,’ Welch et al. (Anim. Biotelem. 2:18, 2014) report data on migratory behavior and relative swimming depths of Chinook and sockeye salmon near the Eastside Setnet (ESSN) fishery, Cook Inlet, Alaska, using acoustically tagged fish and an anchored array of acoustic receivers. Using this information, they provide a model to estimate changes in Chinook and sockeye salmon harvests associated with potential regulatory changes affecting surface gillnet depths in this fishery. We are concerned that the modeling exercise paints an unrealistic picture of how simply changing gillnet dimensions would translate into a viable management approach to preserve or increase sockeye salmon harvests while minimizing catch of Chinook salmon. Much of this fishery occurs in very shallow water, and Cook Inlet tides range about 10 m with tidal current speeds reaching about 9 km hr−1. Model assumptions that gillnets in this dynamic environment were hanging vertically and that gillnets did not reach the bottom are not valid. Gillnets in this fishery billow in strong currents causing the lead lines at the bottom of the nets to rise in the water column, and an unknown but high fraction of all gillnets reach the bottom for some portion of each tide cycle. We believe further information and a more sophisticated analysis is needed to realistically model changes in Chinook and sockeye salmon harvests in relation to gillnet depths, and we are concerned about unintended consequences that may arise from unrealistic solutions based on limited data proposed in the regulatory arena.
Highlights
Main text The Eastside Setnet (ESSN) fishery is conducted in a 90-km section along the eastern shore of Cook Inlet extending from the beach to approximately 2.4 km offshore [2]
The marine array of acoustic receivers used by Welch et al [1] consisted of 16 acoustic receivers located along the offshore boundary of the ESSN fishery and 54 acoustic receivers located along transects extending 15 km offshore of the seaward boundary of the ESSN fishery
In our view, analyses in Welch et al [1] oversimplify problems associated with estimating changes in Chinook and sockeye salmon harvests that may occur with changing gillnet depths, and actual harvest changes would likely differ substantially
Summary
In their paper, ‘Migration behavior of maturing sockeye (Oncorhynchus nerka) and Chinook salmon (O. tshawytscha) in Cook Inlet, Alaska, and implications for management,’ Welch et al [1] provide interesting insights on migratory behavior and relative swimming depths of Chinook and sockeye salmon near the Eastside Setnet (ESSN) fishery, Cook Inlet, Alaska, using acoustically tagged fish and an anchored array of acoustic receivers. Based on data from 11 Chinook and 25 sockeye salmon, a central finding of their paper is that Chinook were deeper swimmers than sockeye salmon in the study area, with median migration depths of 4.8 and 1.8 m, respectively. These differences in water column distributions offer a means to
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