Evaluating the Sounds Produced by Pacific Cod (Gadus macrocephalus, Gadidae) During the Spawning Season

Marine organisms produce sounds for various purposes, including spawning, avoidance, and migration, with each species exhibiting unique acoustic characteristics. This study observed the grunt sounds of Pacific cod (Gadus macrocephalus) during the spawning season for the first time using passive acoustic monitoring (PAM) techniques. Acoustic signals were recorded continuously for about one month at an aquaculture fish farm in Korea. From these recordings, 1208 grunt sounds of Pacific cod were extracted using an automatic grunt detector, and statistical time–frequency parameters were estimated. On average, the grunt sounds consisted of 29 pulses at 6.5 ms intervals within a duration of 205 ms, with a pulse rate of 122.6 per second. The periodic pulse-type signal creates multiple harmonic frequencies on the spectrogram, characterized by time-harmonic modulation with a slope of −240 Hz/s. The mth harmonic frequency distribution ranged from 162 to 822 Hz, with a median source level of 122.6 dB re 1 μPa at 1 m. These findings provide essential scientific data for understanding Pacific cod communication during the spawning season and can aid in identifying spawning sites, conserving habitats, and managing biological resources, contributing to marine ecosystem protection and sustainable management.