War & Fish

War isn’t the answer — but it wasn’t so bad if you were a Scottish haddock. A 6-year pause in commercial fishing caused by World War II helped cod, haddock and whiting populations in Europe’s North Sea recover from years of pre-war exploitation, according to a new analysis. The “accidental” reserve suggests that cold-water fish stocks could benefit from modern marine protected areas.

Marine researchers tend to agree that protected areas can be great conservation tools in tropical and subtropical habitats such as coral reefs, because fish and other sealife tend to hang close to home. There’s more debate about their value in cooler seas, however, because creatures there tend to wander over bigger territories. A group of European researchers realized that the North Sea’s wartime closure offered an unusual opportunity to see just what a reserve might be able to do for wide-ranging and commercially important cold-water fish like cod and haddock.

In 1939, fishing captains essentially abandoned the North Sea after numerous vessels were sunk by mines, submarines and aircraft, and sailors were called to war. Fishing effort by Britian’s fleet of steam trawlers, for instance, dropped by 97% between 1938 and 1941. The war created “an extensive, ‘accidental’ marine protected area (MPA) or arguably a 6-year temporary closure to fisheries,” notes a team led by Doug Beare of the European Commission’s DG Joint Research Centre in Ispra, Italy in the current issue of Naturwissenschaften. The closed area covered 575,000 square kilometers. “In comparison, the world’s largest network of no-take marine reserves on Australia’s Great Barrier Reef covers a mere 115,000” square kilometers, they note.

To see how the closure affected North Sea fish stocks, the team compiled catch and other data collected between 1928 and 1958 off Scotland. Using statistical models, they then studied how the age structure and size of the stocks changed over time in one important fishing area. In general, they found that the closure, which lasted from 1939 to 1945, enabled more fish to live to older ages and start spawning. But that didn’t necessarily translate into immediate increases in the number of younger fish. Instead, the closure caused a kind of ripple effect in the years after the war, with a gradual aging of stocks followed by periodic increases in overall fish numbers, probably during years when ocean conditions were good for spawning.

The authors conclude that “large closed areas can be very useful in the conservation of migratory species from temperate areas,” although it may take time to see benefits. This time, however, marine conservationists hope it won’t take a war to put some waters off-limits to killing. – David Malakoff

Source: Doug Beare & Franz Hölker & Georg H. Engelhard &, & Eddie McKenzie & David G. Reid (2010). An unintended experiment in fisheries science: a marine
area protected by war results in Mexican waves in fish
numbers-at-age. Naturwissenschaften DOI: 10.1007/s00114-010-0696-5

Image © David Kay