Coldfish: potential benefits and risks of borealisation for fish stocks and ecosystems in a changing Arctic Ocean

The Arctic Ocean is exhibiting exceptional levels of warming and ice loss, which are expected to profoundly change the types of animal communities that coexist and the nature of interactions between animals and between animals and humans. In particular, the extent of ice cover in regions that are not permanently ice covered has been declining. The loss of summer sea ice has led to an increase in plankton in open ice free waters, while under-ice algae which are also important food-sources to Arctic species have declined with the retreating ice cover. The underlying marine warming is also making it possible for species from warmer waters to move northward. While these incomers have been flourishing, some native Arctic species have declined in abundance. Several of these species including resident Arctic cod and the incoming Atlantic cod are important in fisheries, which constitute the most direct benefit that society derives from these high-latitude waters. The Arctic species have adaptations to cold that may help protect them from the incoming species to some extent, but to date we have very few ideas of what the long-term ecological outcomes of these recent changes will be.

The Coldfish project will focus on the fish of these waters, exploring how their behaviour, specifically the types of food they eat, changes across a wide range of sites which vary in ice cover, the extent to which the incoming species are present and in other environmental respects. We will track fish diets by measuring the ratio of different stable isotopes of carbon, nitrogen and sulfur in their tissues. By comparing the range of different isotopic compositions found in populations of fishes living in different communities and under different physical conditions, we can answer a series of important questions about the current and future states of Arctic ecosystems.

For instance, the sensitivity of an ecosystem to change depends on how many different species perform similar ecological roles and are therefore able to compensate if some species are lost. We will determine the extent of this so-called 'redundancy' in terms of fish diets by measuring the degree of overlap in isotopic compositions between populations. We will measure how effectively carbon is transferred from surface waters to the seabed, and how this varies in regions of contrasting ice cover and differing fish communities.
We will also study how the incoming species are responding as they move northwards into colder waters, whether their feeding habits and metabolism are changing as a result, and whether the incoming species are likely to compete directly with those native to the Arctic.

Coldfish investigators bring a mix of expertise in arctic biogeochemistry, polar fish biology, marine ecology and stable isotope ecology, and this blend of methods and approaches will help deliver new insights. Our project builds on ecological study in the Barents Sea sector of the Arctic Ocean, and benefits from close integration with extensive ecological surveys co-ordinated by our project partners in Norway.

The main non-academic impact of Coldfish will be provision of information to assist fishery management. This will be achieved through close collaboration with partner organisation the Norwegian Institute of Marine Research, particularly through the TIBIA (Trophic Interactions in Barents Ecosystems) programme. TIBIA is a joint Norwegian-Russian initiative, and through close integration with TIBIA we will ensure that results are shared through Norwegian and Russian fisheries scientists.

Fisheries provide the main ecosystem service arising from the Arctic: the Barents Sea Atlantic cod quota is 0.8-1.0 Mt/yr with an estimated catch value of Euro 2 billion/yr. Scientific advice assisting sustainable management of cod and other commercial fisheries in the Barents Sea is of prime importance to Norwegian and Russian managers. This will be fostered through our strong links with ICES (S Jennings).

Traceability is a key emerging issue in global fisheries, with consumer demand driving retailers and suppliers to ensure products are derived from named sustainable fisheries. Fraud is relatively common in fisheries retail networks, however; genetic testing reveals levels of species mislabelling in excess of 20% (Heyer, etc). Geographic origin is an increasing important component of traceability, particularly in capture fisheries where geographic origin and sustainable management are inexorably linked. Stable isotopes are commonly used to establish geographic origin in terrestrial food products (Chesson, 2017) but a lack of reference isotopic data has limited their use in marine retail chains.

Development of the isoscape has great potential for traceability of fishery products. Coldfish will benefit from ongoing collaboration with Young's, MMO and Seafish (sea fisheries industry body) and by enhancing these links will build impact on the industry and planning agency. Together with an extensive database on stable isotope spatial variation, the isoscape will provide reference values for identifying Barents origin fish and fishery products. CoI Trueman is already working with Young's Ltd and Seafish to develop forensic tests for fishery products, and Coldfish will support this development extending to Norwegian and Russian fishery managers who help sustain much of the world's cod production.