Marine biologists at Plymouth University and the activist group WorldFish conducted analyses of catches over the past 90 years and found significant evidence of the practice of 'fishing down the food web' - removal of many top predators from the sea that has left fishermen 'scraping the barrel' for increasing amounts of shellfish.

Sharks, rays, cod, haddock and many other species at the head of the food chain are at historic lows with many removed from the area completely, they say.

The report used catch statistics from the International Council for the Exploration of the Seas to establish a 'mean trophic level' for catches – an average for how far up the food chain the fish are located.




Discards from a prawn trawl in the Irish Sea. Credit: Johnny Woodlock, Sea Fishery advisory Group, Irish Seal Sanctuary

Professor Jason Hall Spencer, of the School of Marine Science and Engineering, and the Marine Institute, said: "It is clear from our analyses that fishing pressure has caused significant changes to food webs of the English Channel over the past 90 years. The mean Trophic Level of English Channel landings has fallen by 0.1 unit per decade, one of the fastest rates reported among other heavily fished regions of the world, providing yet more evidence that 'fishing down food webs' is a worldwide phenomenon."

Today, the UK and France land around 150,000 tons of seabed fish and shellfish per year from the 75,000 km2 Channel – a huge increase from the 9,000 tonnes recorded in 1920 and the 51,000t in 1950. During that time, the composition of landings has altered dramatically, with sharks and rays declining from 34% of catch in 1920 to 6% in 2010. The contribution of 'cods, haddocks and hakes' similarly fell from 48% to just 4% over the same time frame.

Spurdogs, tope sharks, thornback rays, Atlantic cod, ling and European hake show the most remarkable decline, while flounders, halibut and soles have changed relatively little during the time-series.

The falling levels of finfish has been counterbalanced by increased landings of shellfish such as scallops, and of squid, octopus and cuttlefish. This has in turn raised concerns over long-term sustainability, and the potential damage done to the marine environment as a result of dredging and trawling for these invertebrates.

Plymouth researcher Carlotta Molfese said, "Fisheries typically remove top predators first and as a result their direct competitors and prey are able to prosper, affecting the overall productivity and ecological stability of the ecosystem. Severe declines in the populations of major predator species have now been reported around the world."

The researchers say that far from being a modern phenomenon, overfishing can be traced as far back as the 19th century, with declining stocks reported in 1863. But geographic expansion into new fishing grounds and improved technology combined to maintain increased landings.

Hall-Spencer added, "All around the UK we are scraping the barrel, destructively dredging the seabed for scallops and prawns as fish have disappeared. When destructive fishing practices are banned, marine life soon recovers. So we urgently need a network of recovery zones in the English Channel to allow marine life to bounce back."