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Study finds that declining biodiversity poses a global threat of fisheries collapse

by Eric Jackson, from other media

An article by 12 scientists from Panama, the United States, Canada and Sweden that was published in the November 3 issue of Science magazine finds that fisheries in all of the world's large marine ecosystems may collapse by mid-century if current losses of biodiversity continue. However, the researchers said that by establishing protecting reserves and closing threatened fisheries, such a collapse might be averted.

The general definition is that when catches of a species in an ecosystem decline to 10 percent or less of the recorded maximum, that fishery has collapsed. Currently 29 percent of the world's fisheries have collapsed, and most others are in serious decline.

The researchers looked at a half-century worth of studies, both experimental and the catch data collected by the UN's Food and Agricultural Organization from all of the world's major marine fisheries. They concluded that the problem is not so much the overfishing of a particular species, but a decline in a marine system's biodiversity that hampers the recovery of fish populations.

The study also noted that biodiversity loss apart from fished species carries with it the destruction of other valuable natural resources. For example, the decline in sea grasses and molluscs that filter out pollutants leads to a degradation of water quality that can affect tourism, recreation and real estate values.

Large marine ecosytems are complex webs of relationships that are difficult to study. But when many studies are reviewed together, the Science article's authors found, certain salient facts emerge. For example, the collapse of a related fished species that shares an ecosystem with another commercial species means that fishing industries can't readily switch from one species to another to give the more threatened one a chance to recover. For another example, commecially fished species typically eat a number of different things, but when the population of one one or more but not all items in their diets collapse, the health of the target species can be harmed. But the authors admitted that their study of studies established correlations between biodiversity and the collapse of fisheries, rather than specific cause and effect mechanisms.

The alarming note in the article was the finding of a worldwide trend that's advancing more quickly than most people realize. "[T]he elimination of locally adapted populations and species not only impairs the ability of marine ecosystems to feed a growing human population but also sabotages their stability and recovery potential in a rapidly changing marine environment," the study warned.

The ray of hope in the scientists' findings was that fisheries management can work. "We found that reserves and fisheries closures showed increased species diversity of target and nontarget species, averaging a 23% increase in species richness. These increases in biodiversity were associated with large increases in fisheries productivity...."

One of the article's authors was retired Smithsonian Tropical Research Institute biologist Jeremy Jackson, who lives in Panama.