Survival of the fittest: Explanations for gadoid imbalance in heavily fished seas

Abstract

1. Anthropogenic activities have caused the degradation of the world's ecosystems, accelerating the 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 (south-west 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 the summers of 2013 and 2014, whiting and haddock arrived at coastal areas earlier than cod, and grew more quickly. 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 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 to restore fish population and assemblage structure.

Evaluating the effectiveness of management measures on skates in a changing world

“…Furthermore, at present we are unsure of skate mortality within their nursery habitats. For R. undulata this is particularly important, given juveniles inhabit coastal and estuarian areas which are subject to a range of anthropogenic pressures (Elliott et al, 2018).…”

Marine Conservation Begins at Home: How a Local Community and Protection of a Small Bay Sent Waves of Change Around the UK and Beyond

“…Evidence suggests that high fishing pressure, including bycatch in the current Nephrops fishery, has induced maturation to occur earlier and at smaller sizes in cod, haddock and whiting (Hunter et al, 2015). Baited Underwater Remote Video (BRUV) surveys around the Isle of Arran have also found that whiting recruited earlier, grew faster and were behaviorally dominant over other gadoid species, providing them with a competitive advantage (Elliott et al, 2018). Such evidence at least partly explains the present domination of small whiting in Arran's waters, and suggests that radical management interventions will be needed to restore the Firth of Clyde marine ecosystem to its more diverse and resilient former state.…”

“…These benefit from the mosaic of different seabed types within the MPA and the reduced disturbance in later years once trawling and dredging had been restricted (David Bailey, personal communication). These studies have revealed differences in nursery habitat use and other behaviors in the three main commercial gadoid fish species (cod, haddock, and whiting) (Elliott et al, 2017b(Elliott et al, , 2018 with evidence that cod in particular responds positively to higher benthic biodiversity and landscape heterogeneity (Elliott et al, 2017a,b). This work, which has involved over 600 camera drops at the time of this publication, provides a dataset covering the designation and protection of the wider MPA, which will allow changes to its protected features, biodiversity and ecosystem functions to be determined.…”