Report on improved predictive models of recruitment under different habitat scenarios

SEAwise research

This study focused on several different environmental factors that can affect juvenile health and therefore stock recruitment. The main factors assessed across the SEAwise Case Study regions were: sea temperature, salinity, ocean currents and food availability. The ecological effects of these environmental variables were assessed against stock recruitment, with real-world observations feeding into models to predict how recruitment might change under different climate scenarios over space and time. 

Results from the four Case Study regions are summarised below. 

• In the Baltic Sea recruitment was shown to be affected by environmental factors, for example, with recruitment decreasing as temperatures increase for Western Baltic Cod and herring. However for the Gulf of Riga spring spawning herring, climatic conditions were less important than prey abundance (i.e. food). 
• In the Mediterranean Sea including environmental factors in stock recruitment models showed improved predictive performance over classic models. Projections under different climate change scenarios were species specific. For example, European hake and red mullet showed negative effects on recruitment while deep-water rose shrimp, giant red shrimp and blue and red shrimp could benefit from warming sea temperatures.
• In the North Sea the effect of different environmental factors was also shown to differ by species. For cod and saithe, temperature was a major driver for decreased recruitment, while currents and salinity were more important for spawning herring recruitment. 
• In Western Waters the inclusion of environmental factors in recruitment models improved predictive performance for Irish Sea cod, Bay of Biscay anchovy and sardine, Northern hake, sole, mackerel and blue whiting. In contrast, Irish Sea whiting and sole, seabass, southern hake and horse mackerel were less affected by environmental factors, although impacts for sole may occur in nursery areas. The environmental factors with the greatest influence on stock recruitment were sea surface temperatures, prey availability and ocean circulation. 

In terms of caveats, results of predictive models were affected by uncertainty in different climate change projections in the North Sea, particularly on the availability of forage fish. Some studies in the Mediterranean Sea used only one climate model, meaning results are limited to the scope of projections within that model.