Joint effects of climate and fishing on dynamics of exploited ecosystems

Marine ecosystems are important providers of food and other services. Many ecosystems worldwide are under heavy pressure from fisheries. While some areas have seen trends toward better sustainability, other areas need better management in order to secure their healthy state and continued ability to provide services. At the same time, warming of the oceans poses new challenges, most obviously manifested as species ranges that are shifting poleward. It is therefore necessary to better understand the dynamics of ecosystems under the simultaneous pressures from fisheries and climate change. In this project, we have approached this question from different angles. How temperature changes affect fish varies from case to case. Some fish populations might benefit from warming, but others might be negatively affected. When there is little ecological information available, we can still use species traits to give clues whether a fish population is likely to benefit or not. When more information is available, population-specific models can be used to make more detailed predictions. As an example, cod in the Barents Sea are predicted to benefit from temperature increases. This is not surprising for a population that lives at the northern limit of the species. Fishing affects fish populations by reducing their abundance. A more subtle effect is that fish left behind are not a random subset of all fish: they have particular traits that are partly heritable. Sustained fishing will over time change biological traits of fish populations, as we in this project have shown using both experiments with real fish and with models. Fishers are constantly adapting their operations to the changing conditions, some of these dictated by nature – e.g., fish abundance and weather – others by the society at large – e.g., markets and resource managers. Our research shows how Taiwanese fishers are quickly responding to changing prices of different fish species and how Norwegian fishers are responding to changing availability of different fish, for example taking advantage of the hake boom in the northern North Sea. This underscores the importance of treating fishers as adaptive agents in modelling and keeping resource management apace with changing resources. Managing fish is no easy task, especially when more than one country is involved. Managing these so-called transboundary stocks requires that the countries involved agree on quota shares, otherwise there is a high risk of overexploitation. Climate change makes this task more challenging: if fish are changing their distribution, the countries’ perception of their rightful shares will also change. This makes sharing agreements more fragile – as we have seen for mackerel in the Northeast Atlantic.

* Climate impacts can be predicted with a range of approaches. Some approaches can be used in data-poor situations, but stronger predictions require more detailed data on specific populations and their environment. Either way, our work highlights that climate impacts on fisheries can be both positive and negative. * Our work contributes to the growing recognition that the human component of a fishery system is equally important as its biological component and needs to be properly understood in order to sustainably manage living marine resources. * Our work highlights the vulnerability of transboundary fish stocks to climate-induced range shifts. Sustainable management requires collaboration between involved countries, but such sharing agreements become fragile when fish stocks shift poleward.

This project is set up to study the combined effects of changing climate and alternative fishing exploitation scenarios on the ecosystem state and the associated benefits to the society. We focus on two study areas, the Norwegian Sea-Barents Sea and the Yellow Sea-East China Sea ecosystems. The project is based on a combination of statistical data analyses and ecosystem modelling. The statistical analyses will tell us about the sensitivity of the systems to climatic and exploitation-related drivers in the past. These results also provide input to the two ecosystem models - one for the Norwegian ecosystem, based on the Atlantis framework, and one for the Chinese one, based on the OSMOSE framework - that are further developed in this project. The ecosystem models will then be used to study ecosystem responses under changing climate, represented by climate scenarios, and under a range of management regimes, including continuing the status quo. We are particularly interested in how fisheries productivity is expected to change, and how alternative management regimes could be used mitigate negative climate effects. The results from this project contribute to planning of sustainable utilization of future oceans.