August 6, 2009
Scientists compile most comprehensive look ever at fish stocks
In Kenya, scientists, managers and local communities have teamed up to close some key areas to fishing and restrict certain types of fishing gear. This has led to an increase in the size and amount of fish available. Josh Cinner
Twenty-one fisheries management researchers and marine ecologists — many of whom have been at odds with each other in the past over the state of the world’s fisheries — have collaborated on a groundbreaking paper that puts forth a common way to look at fish abundance and exploitation as well as identifying management tools that have worked for rebuilding depleted fish stocks.
UW’s Ray Hilborn, professor of aquatic and fishery sciences, and Dalhousie University’s Boris Worm, a marine ecologist, convened 21 scientists — with some 300 years of fisheries and ecological experience between them, Hilborn estimates — to hammer out common ground during the past two years. The results are published in the July 31 issue of Science with Hilborn and Worm as lead authors.
This is a far cry from 2006 when Worm published findings in Science that predicted the collapse of all seafood fisheries by 2048, to which Hilborn responded, “That’s alarmist and unfounded.”
In this week’s Science the authors write, “In light of this debate, we strive here to join previously diverging perspectives and to provide an integrated assessment of the status, trends, and solutions in marine fisheries.”
The group combined such things as exploitation rates, catch data, stock assessments, scientific trawl surveys, small-scale fishery data and ecosystem models.
“These data were all out there but it required a massive effort to obtain permission to access the data, to compile them and to put them all in a standard format database for analysis,” says Trevor Branch, a UW research scientist in aquatic and fishery sciences and co-author on the paper. The other UW co-author is Olaf Jensen, a postdoctoral scientist.
“I think the most important contribution was compiling stock assessments and trawl surveys, because these both directly measure the biomass, or abundance, of fish stocks,” Branch says. “Previously, people such as Worm and coauthors in 2006 tried to measure the status of world fisheries based only on catches.
“Although catch data have a global reach and are available back to 1950, they are not a very accurate measure of trends in fish abundance. For example, when catches decline dramatically, this could be because the stock has collapsed or because managers have cut the quotas to allow for rebuilding. In the latter case, a decline in catches should actually result in increases in abundance.”
The resulting analysis in Science showed that in five of 10 well-studied ecosystems, the average exploitation rate has declined and, for seven of the systems, is at or below the rate needed to achieve maximum sustainable yield.
It’s good news for Iceland and New Zealand and several regions in the United States.
“These highly managed ecosystems are improving,” Hilborn says. “Yet there is still a long way to go: Of all fish stocks that we examined, 63 percent remained below target and still needed to be rebuilt.”
Tools that appear to work include catch quotas, fishing closures, ocean zoning, selective fishing gear and economic incentives.
Some of these come with short-term costs to fishers.
“Some places have chosen to end overfishing,” Branch says. “That choice can be painful for fishermen in the short term, but in the long term it benefits fish, fishermen and our ocean ecosystems as a whole.”
