Impact of Climate-driven habitat LOss in Norwegian fjords on ecosystem STructure and functional ecology of cartilaginous fishes (LOST)

Norwegian fjords are sites of cultural heritage and economic importance where tourism, recreational fishing, and aquaculture all coexist. The Norwegian red-listed spiny dogfish is a controversial but charismatic shark in Norwegian fjords; the species is protected but often in conflict with aquaculture and as bycatch in fisheries. Simultaneously, the fjord habitat used by these sharks is rapidly changing at the surface - which is getting warmer - and at depths, where oxygen levels are declining. In this project, we investigate the fjord ecology of the spiny dogfish to understand how this shark is responding to the rapid changes. Population surveys will be conducted and compared to historical baselines in the Osterfjord system of western Norway and genetic samples will help unravel the population structure and answer whether there are specific dogfish stock complexes within fjord systems. Dogfish have now been captured and tagged in the Bergen Telemetry Network, an array of acoustic listening stations covering the fjord, estuary, and coastal areas from the Osterfjord and outwards towards the city of Bergen to track the daily and seasonal movements of the sharks. Tags have special depth sensors to communicate when the sharks are in the deeper, hypoxic layers and temperature sensors to help us determine when they are exposed to thermal stress. This tracking project will reveal how changes to the environment may be increasing conflicts with fisheries and aquaculture by pushing them towards the surface. Activity sensors in the tags will also help reveal how activity budgets are spent and how different zones around the coast are used by the sharks. The project will have a role in training the next generation of ecologists in Norway, having engaged a PhD student at the University of Bergen who will be studying the vertical and horizontal movements of the sharks over the next two years. The project will deliver urgently needed data to Norwegian management agencies tasked with protecting these species and managing user conflicts. In addition to scientific publications, the project will produce a film about the Norwegian fjord sharks to submit to the Bergen International Film Festival (BIFF).

The LOST project aims to establish new knowledge about the urgent challenge of habitat compression caused by urbanization of the fjord environment and climate change. Coastal fjords in Norway are vulnerable to hypoxia because of prolonged residence times of water in the fjords and discharge of rivers that are increasingly productive due to climate change and eutrophication. In several fjords of western Norway, we have recorded increasing hypoxia and a progressively shallower oxygen minimum layer, with unknown consequences for at-risk shark species that are important predators of the deep water ecosystems. Indeed, the deep water habitat of this fjord complex is relatively unique given that the ocean shelf extending off Norway to Shetland is relatively shallow (mostly ~150 m deep). The fjord habitat is therefore an important topic for research given the relatively rare habitat that it provides. This is particularly urgent given that Nordhordland was recently declared a UNESCO Biosphere Reserve Area. Our project will build on historical sampling in the Hordaland fjords from the 1990s that sampled the shark community by longline fishing. Repeating this sampling in WP1 will provide novel insights into the changes the shark populations demography have undergone with increasing hypoxia in the decades since, and simultaneously allow us to sample sharks to resolve their genetic population structure by comparing it to baseline samples available from outside the fjords. Novel research on the behaviour of deep water species will capitalize on the Bergen Telemetry Network, a network of acoustic receivers in the Hordaland fjords in place for tracking fish that can be used for observing the vertical behavior of sharks in response to the changing oxygen minimum layer of the fjord. Finally, WP3 will utilize state-of-the art activity sensors to describe the energy landscape of sharks outside and inside the oxygen minimum layers.