Survival of the fittest: explanations for gadoid imbalance in heavily fish seas

1.Anthropogenic activities have caused degradation of the world’s ecosystems, accelerating loss of biodiversity. In marine ecosystems, fishing has had strong impacts on fish populations and their habitats. However, not all species have responded equally to fishing pressure.
2. Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus) are of high commercial value throughout the North Atlantic. Despite having relatively similar life cycles, the state of stocks of these three species varies enormously, with whiting faring better than cod. Within the Firth of Clyde (southwest Scotland) this imbalance is especially accentuated, where small whiting now make up the greater proportion of the biomass.
3. In this study, cod, haddock and whiting recruitment to coastal areas, growth and bait attraction were explored within a marine protected area (MPA) in the Firth of Clyde. Over the course of summer 2013 and 2014, whiting and haddock arrived at coastal areas earlier than cod and grew faster. Cod were on average the smallest gadoid observed and whiting the largest. Whiting also had more predominant scavenging behaviour.
4. These results in combination with other life history and behaviour traits indicate that whiting may be at a competitive advantage over cod, and this
may partly explain the imbalance of gadoids in the Firth of Clyde. This study highlights the importance of considering life history differences in multi-
species fisheries management and how appropriately managed MPAs could help restore fish population and assemblage structure.