Sounds of Walleye Pollock: A Quantitative Description

Rapid changes in the global distribution of walleye pollock (Gadus chalcogrammus) due to climate change have raised concerns of potential negative interactions with other Arctic and North Pacific fishes, particularly with the Arctic cod (Boreogadus saida). Since both walleye pollock and Arctic cod are known to be soniferous, passive acoustic monitoring (PAM) surveys can be used to document changes in the temporal and spatial distributions of the two species. However, PAM requires a detailed knowledge of the sound characteristics of each species. Therefore, this chapter presents the first quantitative description of walleye pollock sounds to enable future PAM surveys. Over 6000 sounds attributed to walleye pollock were detected in 69 h of recordings in April 2018 at the Hatfield Marine Science Center (Oregon). Walleye pollock sounds averaged 95 ms in duration, with a peak frequency of 83 Hz (n = 635). Sounds were classified into four types of grunts, based on frequency structure: broadband, low-frequency, mid-frequency, and two-frequency. A comparison with published data for Arctic cod suggests that the two species can be distinguished by the sound duration, peak frequency, and pulse rate of their calls.