Effects of climate change in the North Sea: more sole biomass, but smaller numbers

Published on
March 5, 2021

The North Sea is warming up and how will that affect fish species? Marine ecologist Karen van de Wolfshaar recently tested three climate change scenarios by combining a larval transport model for sole larvae with a DEB (Dynamic Energy Budget) model to determine the transition from spawn to young sole. Her publication in the ICES Journal of Marine Science shows that climate change has an effect on the growth and survival of juvenile sole (Solea solea) in several nurseries of the North Sea.

Three climate change scenarios, inspired by the Intergovernmental Panel on Climate Change (IPCC) projections for 2040, were tested by Van de Wolfshaar. The results were compared with a reference situation that is representative of current climate conditions and describes the climate based on temperature, current and wind in the North Sea for the period 2003-2011. The larval transport model describes how larvae disperse in the North Sea, from the spawning grounds towards the nursery grounds, based on currents. The locations of the spawning grounds and the amount and timing of the modelled larvae were based on field data documented in scientific literature.

Temperature determines metamorphosis moment and timing of transport to nurseries

The temperature of the North Sea determines the growth of the sole larvae and thus the moment of metamorphosis into flatfish. After metamorphosis, the young sole settles on the seabed and, if transported successfully by currents, arrives in a nursery. Sole that has not arrived here after the moment of metamorphosis is considered lost. The growth model was then used to model the growth of the small soles that reached the nursery areas, based on the temperature course in each nursery area. The temperature course in these areas is taken from the scenarios of the larval transport model. This model also provides the arrival dates and the quantity of young sole.

Future climate scenarios: higher biomass and reduced chance of survival in the first year

In climate change scenarios where changes in variables such as currents, wind, water temperature and spawning period were included, an equal amount of eggs results in more sole in the nursery areas. In addition, earlier arrival of sole results in larger juveniles at the end of the summer. However, earlier arrival leads to higher mortality in nurseries due to initially slow growth of juvenile sole in spring. Future climate scenarios ultimately lead to higher biomass and reduced survival, and thus lower numbers at the end of the first year of life.

Climate change impact assessment on fish populations requires understanding of life stages of fish and area use

How this research result translates into changes on the total sole population and fisheries management needs further investigation, says Van de Wolfshaar: "Nevertheless, this study shows that processes linking fish life stages and area use are crucial to understand and predict possible impacts of future climate conditions on population dynamics and management."