Micah J.Dean, co-author
Atlantic cod is one of the most commercially sought-after and socio-economically important fish species in the world. Despite inordinate attention on stock assessment and fishery management, most cod populations have experienced steep declines in abundance with limited success at rebuilding. In each case, a suite of contributing factors can be pointed to, including overfishing, climate change, and predator-prey relationships; yet, there appears to be an element to the population dynamics of this species that is currently misunderstood to allow for such pervasive stock depletion and recovery failure to occur.
Recent research suggests that ignoring fine-scale population structure is a contributing, if not a leading cause. There is ample evidence that many cod stocks function as a metapopulation, containing multiple subunits comprised of semi-discrete spawning components. By managing stocks as a single homogeneous group, we ignore this fine-scale population structure and risk the serial depletion of unique sub-components, thereby lowering stock productivity.
Spawning behaviour is at the heart of a metapopulation; it provides not only the mechanism by which population structure is developed and maintained, it also influences whether lost or depleted components will recover. Understanding the 'where', 'when', and 'how' of spawning allows for the more effective management of cod stocks by providing the necessary information with which to design conservation measures that prevent the loss or depletion of spawning components.
Using an acoustic telemetry positioning system, Dean et al. describe the fine-scale movements of spawning cod in situ as they return to the same spawning location over multiple seasons. This unprecedented view of natural spawning behaviour challenges the conventional wisdom about cod's mating system and underscores their vulnerability to disturbance and depletion while spawning. Their findings are particularly relevant to the design of spawning closures and the influence of behaviour on stock assessments as well as general reproductive ecology.
Micah Dean and Bill Hoffman with a tagged cod prior to release; Photo: Brad Schondelmeier