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 coexist. The spiny dogfish, a red-listed species in Norway, is a charismatic but often controversial shark in these waters. Despite being protected, it frequently comes into conflict with aquaculture and is caught as bycatch in fisheries. At the same time, the habitat that these sharks rely on is undergoing rapid changes—warming at the surface and declining oxygen levels in deeper waters. This project aims to investigate the fjord ecology of the spiny dogfish to better understand how this shark species is responding to these environmental shifts. Since the project's initiation, population surveys have been carried out and are being compared to historical baselines in the Osterfjord system in western Norway. Additionally, genetic samples have been collected, which will help clarify the population structure and determine whether there are distinct dogfish stock complexes within different fjord systems. The tagging component of the study is well underway, with spiny dogfish being successfully captured and tagged within the Bergen Telemetry Network. This network includes an array of acoustic listening stations that cover the fjord, estuary, and coastal areas from Osterfjord to the city of Bergen. These tags will track the sharks' daily and seasonal movements. Each tag is equipped with depth sensors to monitor when the sharks enter the deeper, hypoxic layers, and temperature sensors to detect when they are exposed to thermal stress. The collected data will provide critical insights into whether environmental changes are driving sharks towards the surface, potentially increasing conflicts with fisheries and aquaculture. The activity sensors in the tags are also operational and will provide valuable data on how the sharks allocate their activity budgets and how they use different coastal zones throughout the year. This information is essential to understanding the sharks' behavior and developing strategies for their conservation. In terms of educational impact, the project has recruited a PhD student from the University of Bergen who is focusing on the vertical and horizontal movements of the spiny dogfish over the next two years. This aspect of the project is vital for training the next generation of Norwegian ecologists. The project remains on schedule to deliver essential data to Norwegian management agencies tasked with protecting the species and resolving conflicts between human activities and wildlife. In addition to scientific publications, the team is working on a film about Norwegian fjord sharks, which will be submitted to the Bergen International Film Festival (BIFF) to raise awareness and engage a broader audience.

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.