Original Paper


, Volume 97, Issue 9, pp 797-808

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

An unintended experiment in fisheries science: a marine area protected by war results in Mexican waves in fish numbers-at-age

  • Doug BeareAffiliated withEuropean Commission, DG Joint Research Centre, Institute for the Protection and Security of the Citizen, Maritime AffairsWageningen-IMARES Email author 
  • , Franz HölkerAffiliated withEuropean Commission, DG Joint Research Centre, Institute for the Protection and Security of the Citizen, Maritime AffairsLeibniz-Institute of Freshwater Ecology and Inland Fisheries
  • , Georg H. EngelhardAffiliated withCentre for Environment, Fisheries and Aquaculture Science (Cefas)
  • , Eddie McKenzieAffiliated withDepartment of Statistics and Modelling Science, University of Strathclyde
  • , David G. ReidAffiliated withMarine Institute


Marine protected areas (MPAs) are attaining increasing importance in the management of marine ecosystems. They are effective for conservation in tropical and subtropical areas (mainly coral and rocky reefs), but it is debated whether they are useful in the management of migratory fish stocks in open temperate regions. World War II created a large marine area within which commercial fishing was prevented for 6 years. Here we analyse scientific trawl data for three important North Sea gadoids, collected between 1928 and 1958. Using statistical models to summarise the data, we demonstrate the potential of MPAs for expediting the recovery of over-exploited fisheries in open temperate regions. Our age-structured data and population models suggest that wild fish stocks will respond rapidly and positively to reductions in harvesting rates and that the numbers of older fish in a population will react before, and in much greater proportion, than their younger counterparts in a kind of Mexican wave. Our analyses demonstrate both the overall increase in survival due to the lack of harvesting in the War and the form of the age-dependent wave in numbers. We conclude that large closed areas can be very useful in the conservation of migratory species from temperate areas and that older fish benefit fastest and in greater proportion. Importantly, any rise in spawning stock biomass may also not immediately result in better recruitment, which can respond more slowly and hence take longer to contribute to higher future harvestable biomass levels.


Marine protected areas North Sea World War II Age-structured population Gadoids Exploitation Mortality