Report on improved predictive models of recruitment under different environmental scenarios

As a management approach designed to take into account potential benefits and impacts of fisheries management across both the marine environment and the societies that rely on them, a key element of Ecosystem Based Fisheries Management (EBFM) is understanding how changes in different environmental influences can impact fishing patterns.

Our Ecological Effects on Fisheries theme in this report investigates the influence of various key environmental factors, including temperature, ocean currents, surface circulation, and zooplankton availability, on the “recruitment process” of commercial fish stocks – that is, how young fish survive to become adults. Understanding which environmental factors significantly affect recruitment for different fish species is vital for us to be able to tailor and adapt management strategies according to changing environmental conditions, and to minimise the risk of overfishing stocks with poor recruitment.

SEAwise research

Unsurprisingly, the diversity of fish species across the SEAwise Case Study regions means that the same environmental conditions can have very different effects on recruitment depending on geography and species. For example:

  • In the Gulf of Riga (Baltic Sea): The individual weight of herrings at one year old was significantly influenced by prey abundance, the temperature of the previous year’s feeding period, and spawning stock biomass (the combined weight of individuals, usually females only, in a stock which are capable of reproducing). Meanwhile, recruitment in both Western Baltic cod and herring reduced in step with increasing temperature. 
  • North Sea: Variations in temperature, salinity, currents, chlorophyll and zooplankton were all found to influence recruitment of cod, haddock, herring, plaice, saithe, and sprat, but not sole and whiting, which were much more significantly affected by spawning stock biomass.
  • Western Waters: Irish Sea cod recruitment was found to fall as sea surface temperatures increased and the availability of key prey (in this case, copepods) decreased. Meanwhile in the Bay of Biscay, anchovy recruitment was impacted by turbulence, and the upwelling of nutrients from the depths due to the rising of cold water to the surface.
  • Mediterranean: For European hake, spawning stock biomass had a positive effect on recruitment but only up to a certain stock size, with recruitment decreasing at larger stock sizes (a phenomenon known as “density dependence”). 

An overarching theme revealed by this research is that the ability of our models to predict future recruitment in fish stocks is closely linked to the age at which a fish species can first begin to reproduce (known as “life history strategy” among scientists). Species which have a longer life cycle – and therefore take longer to begin reproducing – were found to be more difficult to make predictions about in comparison to species which prefer the “live fast, die young!” approach.

What happens next?

SEAwise’s work on this topic is still ongoing, with the results anticipated to support the development of more accurate predictions of how fish stocks will respond to environmental changes. This will ultimately help to inform the implementation of robust fisheries management in an EBFM context. 

Read the full report here.

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