Fisheries Centre Prof. Daniel Pauly has hard evidence to back up what many scientists have long suspected -- marine fisheries are in a global crisis.
In an article which appeared in the Feb. 6 issue of the journal Science, Pauly and four co-authors demonstrate a shift in global fisheries catches away from predators high in the food web, like snapper, halibut and tuna, towards plankton-eating species lower in the food web, like anchovies and shrimp.
Pouring over 50 years of United Nations catch data, the researchers show conclusively that as fishers decimate larger predators, they move systematically down the food web to smaller plankton eaters.
"When we remove big predators and go after their smaller prey, we are ripping the fabric of these webs, and endangering their ability to produce harvestable fish at any level," Pauly says.
He points to the east coast of Canada, where the shrimp fishery has expanded since the cod were fished out. Since cod feed on shrimp, Pauly warns that the increased fishing of shrimp may hinder the recovery of cod stocks.
In case after case around the world, targeting smaller and more abundant plankton eaters at first leads to increasingly large catches, but the resulting disruption of the ecosystem soon results in stagnating or declining catches.
This pattern of destruction, which Pauly calls "fishing down the food web," is worst in the northern hemisphere, with its highly efficient and technologically advanced fishing fleets.
Pauly says if present exploitation patterns continue the only fish in the seas in about 25 years will be lanternfish, jellyfish and krill.
Creating large `no-take' marine protected areas may be the only way to avoid the widespread collapse of fisheries and rebuild healthy food webs, he says.
The research is another nail in the coffin of traditional fisheries management, says Pauly.
"Current fisheries management only worries about the health of particular fisheries within the fishing industry," he says. "Instead, we should be focusing on the health of ecosystems, and the consequences of extracting single species stocks from the system."
Pauly conducted the research with Fisheries Centre graduate student Johanne Dalsgaard, and three researchers from the International Centre for Living Aquatic Resources Management in the Philippines.
The researchers analysed catch data for 1,300 different groups of marine species covered in the official statistics of the United Nations' Food and Agricultural Organization since 1950. These statistics were then compared against 60 published food web models for all major aquatic ecosystems.