August 12, 2009
Global fisheries show potential for comeback
Five out of 10 global ecosystems once threatened by overfishing are on the mend, according to a new study. A collaboration of scientists from seven countries analyzed fish populations around the world and found that the mass of fish removed from the ocean every year has decreased in some fisheries.
"This improvement might well be a reflection of the call to arms that has gone out over the last five to 10 years about the state of the ocean and its needs. It shows that fishery restrictions can actually pay off and things can get better," said Stephen Palumbi, professor of biology, director of Stanford's Hopkins Marine Station and one of the 21 collaborating scientists.
Fishing rates have dropped to at least a healthy level called maximum sustainable yield, which is the greatest amount of fish that can be harvested without depleting the population in the long term. The five ecosystems include oceans surrounding New Zealand; northwestern Australia; Iceland; the California current system stretching from Baja California to Canada; and western Canada and Alaska, up to the Bering Strait.
Scientists have presented numerous reports over the years cataloging the decline of marine ecosystems and the ominous collapse of global fisheries. A species collapse means the total mass of fish has fallen below 10 percent of original levels.
The new study, published in the July 31 edition of Science, was initiated by a disagreement between two groups of scientists. University of Washington fisheries scientist Ray Hilborn questioned methods used by a different group led by Boris Worm of Dalhousie University in Canada, which predicted in 2006 that most harvested fish species would collapse by 2048. Because the debate opened areas of common ground, the two began meeting to discuss their findings and eventually launch the new study.
The group used ecosystem models to analyze records of global catches, small-scale fishery data, trawl surveys and stock assessments, which show the status of exploited fish populations. Not all of their findings were good news; out of 166 fish stocks, 63 percent had collapsed, a figure similar to the one in the 2006 paper, Palumbi said. Five of 10 well-managed ecosystems are still in decline, including oceans surrounding southeastern Australia, the Gulf of Thailand, northern Europe, the northeastern United States and eastern Canada.
The scientists still seem hopeful for their recovery if a lower rate of harvesting is enforced. They suggest catch restrictions, area closings and economic incentives such as sustainable fishery certification.
The authors of the paper point to a successful case in Kenya where fish populations living in coral reefs recovered after local communities closed areas and restricted fishing gear such as beach seines, which catch unwanted marine animals along with the target fish. Fish size and weight improved, leading to steep increases in fishers' incomes.
Unfortunately, a promising global average based on the 10 studied ecosystems may hide regional variation. "These 10 ecosystems really are the elite fisheries of the world – the ones with the most funding, the most research and the most enforcement," Palumbi said. Recovery of fish stocks in a developing country, on the other hand, is challenging when locals lack alternative sources of food, income and employment.
The scientists also suggested joining forces with conservation through marine protection acts. "The two together – well-managed fisheries and marine protected areas – are likely to be great partners in rebuilding marine ecosystems. They're different strategies but they're quite complementary," Palumbi said.