The effects of bottom temperature and fishing on the structure and composition of an exploited demersal fish assemblage in West Greenland

The distribution and abundance of marine fishes have been changing over the last decades due to climate change and overfishing. We evaluated the status of an important exploited marine ecosystem for one of the largest fisheries in Greenland, Greenland halibut Reinhardtius hippoglossoides, in the offshore slopes of West Greenland. We examined how five ecological indicators changed from 1997 to 2019 under the effect of climate and commercial fishery. The oscillatory tendency of the bottom temperature modified the structure and composition of the demersal fish community. In the shallower zone, the warming bottom temperature favoured high trophic level and warmer water species, and subsequently, an increase in halibut biomass, which reduced the biodiversity. In the middle depth zone, the high biomass of halibut masked increases of less common higher trophic level species. In the deep zone, the drastic reduction of halibut biomass coincided with an increase of high trophic level and colder-water species. Despite the increasing exploitation, especially the mid depth zone, the current fishery did not induce changes to community structure. With the present study, we demonstrate the value of using ecological indicators and estimating spatio-temporal trends to provide a further understanding of the ecosystem status.