Fine-Scale Movements of Atlantic Cod While Spawning

The mating behavior of Atlantic cod has previously been described from tank experiments or inferred from conventional telemetry studies and survey catches.   Earlier studies suggest cod undergo a complex mating ritual, known as a lek, wherein males form a dense aggregation and compete for positions of dominance.  Females are believed to enter the male dominated territory and select a mate from this established hierarchy.  Using recent advancements in acoustic telemetry, a Vemco VR2W Positioning System (VPS), we observed the fine-scale movements of spawning cod in situ over two consecutive spawning seasons.  Males and females exhibited strong fidelity to a discrete location, particularly during daylight hours.  Females spent far more time near the aggregation site than males, and made fewer movements in general.  Males often left the aggregation at dusk and returned at dawn, following a similar path each night.  Both sexes remained near the seabed for most of the spawning season, making occasional brief ascents only at night.  It appears that the behavior of Atlantic cod within a spawning aggregation is more complex than previously thought, and may contradict the lekking hypothesis.  Understanding cod reproductive behavior has helped guide management actions designed to protect spawning aggregations and prevent fishery-induced disruption.