Sustainable fisheries management relies on maintaining healthy fish stocks. However, fish populations cannot be managed in isolation as they interact with multiple specific ecosystem components and processes throughout their lifecycle. Thus, understanding how fish populations use habitat and perceive habitat quality are major objectives of the ecosystem approach to fisheries management. Furthermore, in spite of current research showing the higher contribution of larger individuals to population replenishment compared to smaller individuals, traditional management practices commonly focus on protecting early life stages. Moreover, large adult individuals are commonly the main target of fishing operations and often display distinct spatio-temporal patterns in habitat use, involving association to specific habitats and site fidelity. Failing to incorporate spatial structure and behaviour in management plans might compromise the sustainability of fishing practices and lead to stock depletion.
In this context, gaining information about the spatial and temporal differences in habitat use of large adult individuals can help to understand what key features or processes are important for them and identify Essential Fish Habitats to improve and update management plans. Cod (Gadus morhua) is an important marine resource that exhibits a complex population structure at a fine spatial scale. In addition, previous cod management plans that failed to incorporate spatio-temporal information had limited outcomes and failed to recover overfished populations to its original biomass.
This research uses multiple data sources (samples from commercial fisheries, data from vessel monitoring systems and logbooks, scientific monitoring) from fishing activities targeting cod aggregations in the western Baltic Sea to determine the distribution profile of larger adults during two recurring aggregation periods: in winter/spring (spawning season) and peak summer (“quiescence”). The data will be superimposed and related to sediment and depth contour maps. The results will be used as a tool for better understanding the habitat requirements of adult cod in the shallow western Baltic Sea during important seasonal aggregation phenomena and therefore for potentially mapping Essential Fish Habitats in this estuarine environment on the southern edge of distribution of this species.
