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Acoustic markers of Atlantic cod (Gadus morhua) spawning in coastal Newfoundland

Knickle, D. Craig, Rose, George A.
Fisheries research 2012 v.129-130 pp. 8-16
Gadus morhua, acoustics, cod (fish), eggs, females, fisheries management, ichthyoplankton, spawning, spring, surveys
Knowledge of spawning location and timing is an essential component of ecosystem-based fisheries management. For Atlantic cod (Gadus morhua) in the northwest Atlantic, such knowledge is at best sparse. Acoustic and ichthyoplankton surveys of Smith Sound, coastal Newfoundland, from January to August in 2006 and 2007, indicated that the presence of vertically oriented pelagic behavior, or ‘spawning columns’, coincided with spawning times back-calculated from following early stage egg abundance peaks. Column numbers peaked in early April in both years and in mid-July in 2007 followed by peaks in egg densities. Maturity data from sampled fish confirmed that cod were not spawning in January, but between April and June between 5 and 40% of mature females were spawning at any one time. Column heights reached 30m at depths from 60 to 250m in the middle of the Sound in spring, moving to the outer part of the Sound as the spawning season progressed. Our results indicate that pelagic ‘column’ behavior, as observed on echosounders in this and other regions, comprises a simple, unobtrusive and non-lethal marker of the location and timing of cod spawning in coastal Newfoundland waters.