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November 30, 2010, Vol. 15, No. 24
Turtle banner image: Claire Fackler, NOAA National Marine Sanctuaries

In This Issue

Science in the News

Bluefin Tuna Granted Minimal Catch Reductions

Bluefin tunaTuna fishing nations have set a 2011 quota for eastern Atlantic and Mediterranean bluefin tuna that is slightly lower than 2010 levels, a reduction that conservationists and scientists are saying isn't enough given sharp declines in Atlantic bluefin numbers. NOAA/Marine Photobank

At their annual meeting in Paris this November, the International Commission for the Conservation of Atlantic Tunas (ICCAT) agreed to decrease by only 600 metric tons the 2011 quota for bluefin tuna catch in the eastern Atlantic Ocean and Mediterranean Sea. This small decrease from the 2010 quota of 13,500 metric tons brings the new total to 12,900, only a fraction of what tuna conservation groups hoped for.

ICCAT also agreed to ban the fishing and sale of oceanic whitetip sharks and six types of hammerhead sharks. Tuna fishing fleets frequently catch sharks as bycatch and intentionally. They are then either discarded as waste or their fins are cut off for use in shark-fin soup. Populations of oceanic whitetip shark have declined 99 percent in the Gulf of Mexico and the Mediterranean Sea, while hammerhead numbers also have dropped 99 percent in the Mediterranean.

Representatives from conservation organizations pushing for significantly larger reductions say the limited decrease in the tuna quota is not enough. “Despite sound science to show how threatened these species are, … Atlantic bluefin tuna once again were denied the protection they desperately need,” said Sue Lieberman, director of international policy for the Pew Environment Group.

“This measly quota reduction is insufficient to ensure the recovery of bluefin tuna in the Mediterranean Sea,” added Sergi Tudela, head of WWF’s Mediterranean fisheries program. Greenpeace ocean campaigner Oliver Knowles called the outcome “a monumental failure of the way governments are supposed to protect our oceans.”

Researchers have concluded that during the past 40 years, bluefin tuna numbers have declined by 72 percent in the eastern Atlantic Ocean and Mediterranean Sea, and 82 percent in the western Atlantic. In 2006, ICCAT scientists recommended a total catch for the eastern Atlantic and Mediterranean of no more than 15,000 metric tons annually, a recommendation that was overruled when the commission adopted a European Union proposal for a limit of 29,500 metric tons, to be reduced to 25,500 metric tons by 2010. Two years later, ICCAT's scientific committee estimated that the 2007 catch had in fact been 61,000 metric tons, more than twice as high as the maximum permitted level and four times higher than the recommended quota. A large part of the reason for this discrepancy was the presence of a sizable illegal catch. A 2010 report by the International Committee of Investigative Journalists found that “rampant fraud, massive overfishing and virtually non-existent government oversight have resulted in the decimation of eastern Atlantic bluefin tuna and the creation of a black market in bluefin that was worth at least $4 billion between 1998 and 2007.” According to the report, this black market included more than one of every three bluefin tuna caught.

In the face of continued scientific evidence of the bluefin's decline and in response to continued political pressure for action, ICCAT in 2008 reduced quotas for the eastern Atlantic and Mediterranean, but not to levels recommended by scientists. Quotas were set at 22,000 metric tons for 2009, 19.950 metric tons for 2010, and 18,500 metric tons for 2011. Those figures were, in turn, reduced to 13,500 metric tons the following year. But with ICCAT scientists now saying that the continued decline of the population was such that quotas needed to be reduced to between zero and 8,500 metric tons, some governments looked elsewhere for help.

In late 2009, Monaco formally proposed that the Convention on International Trade in Endangered Species (CITES) ban international trade in Atlantic bluefin. However, under intense lobbying from Mediterranean tuna fishing nations and from Japan, the primary bluefin market, the proposal failed at the CITES meeting in Qatar.

Source: WWF has published an online timeline of bluefin tuna fisheries and conservation at http://assets.panda.org/downloads/tunatimelinenov2010.pdf.

For more information: The results of the International Commission for the Conservation of Atlantic Tunas Annual meeting can be found on its website at http://www.iccat.int/en/; ICIJ. 2010. Looting the Seas: A Global Investigation. The Center for Public Integrity, Washington, D.C.

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Science Briefs

“Fishing Down Food Chain” Theory Doesn't Hold Water, Claims New Study

Fishing vessel off the Solomon Islands
A new study says that although fishing vessels around the world (such as this one off the Solomon Islands) are combining to catch ever greater numbers of fish, the fishing industry as a whole is not "fishing down the food web." Wolcott Henry/Marine Photobank

The most widely adopted measure for assessing the state of the world's oceans and fisheries led to inaccurate conclusions in nearly half the ecosystems where it was applied, according to a new study in the journal Nature.

In 1998, a team led by Daniel Pauly of the University of British Columbia published a landmark paper in the journal Science that argued commercial fisheries were “fishing down the food web,” exhausting stocks of top predators such as cod before switching attention to smaller marine animals. That study established an indicator—the Marine Trophic Level, or MTL—to illustrate that trend. A fishery that exclusively targeted top predators such as pollock could have an MTL of around four, whereas one targeting only seaweed would have a trophic level of one.

The 1998 study claimed that the MTL of fish landed globally was declining by 0.1 per decade, leading the authors to warn that, “it is likely that continuation of present trends will lead to widespread fisheries collapses.”

However, the new paper argues that the MTL of a fishery does not necessarily reflect the MTL of the relevant ecosystem or that ecosystem's biodiversity. The paper's authors,Trevor Branch of the University of Washington and colleagues, conducted a series of ecosystem surveys using research trawls, examining the trophic level of the species they brought to the surface and comparing them with the MTL of fisheries in each region. They found inconsistencies between changes in the average trophic levels of fisheries and the trophic levels of what was caught in the research trawls in 13 of 29 trawl surveys in 14 ecosystems.

Furthermore, Branch and his co-authors argue that MTL only works as an accurate gauge of the development of a fishery when that fishery begins at higher trophic levels and works down through the food chain. In the Gulf of Thailand, for example, fisheries first targeted species low in the food chain, such as mussels or prawns, and are now “fishing up.” As a result, the MTL of the fishery is increasing, which according to the 1998 paper should indicate improved ecosystem health. In fact, fish at all levels in the Gulf have declined tenfold since the 1950s because of overfishing.

In contrast to the warnings of the 1998 paper, Branch and colleagues say their data reveal that, following declines during the 1970s in the average trophic levels of fish being caught, catches of fish at all trophic levels have generally gone up since the mid-1980s.

“Globally we're catching more of just about everything,” said Branch in a press release issued by the National Science Foundation to announce the study’s publication. “Therefore, relying on changes in the average trophic level of fish being caught won’t tell us when fishing is sustainable—or if it is leading to collapse.”

Pauly, the lead author of the 1998 paper, has criticized the new study. In a separate article in Nature, he says the paper fails to account for the huge expansion in the area of fisheries through time. As fishing boats range farther, they can catch more high-scoring predators in the open ocean, he points out. This would mask the fact that fisheries near to shore, for example, had indeed been fished down.

“The results are therefore completely invalid,” he says.

Sources: Branch, T., et al. 2010. The trophic fingerprint of marine fisheries. Nature 468: 431-435; Cressey, D. 2010. Fishing down food chain' fails crucial test. Nature doi:10.1038/news.2010.619; Pauly, D., et al. 1998. Fishing down marine food webs. Science 279: 860–863.

Contact: Trevor Branch, University of Washington. E-mail: tbranch@uw.edu


Stranded Dolphins Are Sometimes Deaf

DolphinsResearchers have found that some stranded dolphins and whales had damaged hearing that may have contributed to their coming to shore and also casts doubt on whether such animals can survive if returned to the ocean. John Rafferty Photography/Marine Photobank

Dolphins and small whales that strand themselves along the shore frequently have damaged hearing, sometimes to the point of being essentially deaf, say researchers. The finding could not only help explain the reason for at least some such stranding events, but also cast doubt on the usefulness of returning stranded cetaceans to the sea, either immediately or after rehabilitation in captivity, without first being able to test their hearing.

Writing in the open-access online journal PLoS One, David Mann of the University of South Florida and colleagues describe examining the hearing of 34 small whales and dolphins from eight species, 33 of which had stranded along the Florida coast and one that had been rescued from fishing gear. All of them, had been taken to facilities that specialize in rehabilitating stranded cetaceans. The researchers used suction cups to fix sensors to the animals’ heads and then played a series of sounds. If the whales and dolphins could hear the sounds, the sensors would record heightened activity in the relevant portions of their brains.

Indeed, Mann and colleagues found no evidence of hearing loss in seven Risso’s dolphins, two pygmy killer whales, a spinner dolphin, an Atlantic spotted dolphin and a Gervais’ beaked whale. However, five of 14 rough-toothed dolphins, four of seven bottlenose dolphins, and one short-finned pilot whale all exhibited hearing defects equivalent to severe or profound hearing loss in humans.

The researchers were unable to determine how the hearing loss occurred. While in some cases it may have been due to exposure to extremely high noise levels from, for example, shipping or sonar, they argue that it was just as likely that in some cases the hearing loss was congenital. In addition, one bottlenose dolphin had lost most of its teeth, suggesting that it may have lost its hearing naturally as a consequence of aging.

However, they do point to the extreme importance of hearing in cetaceans, and particularly in dolphins and toothed whales, which find prey and map their surroundings by using echolocation. Indeed, the stomachs of two young rough-toothed dolphins that had stranded and were examined in the study contained sponges, suggesting that perhaps those animals were unable to catch their normal prey, such as squid.

Furthermore, given the fact that toothed cetaceans use echolocation as a means of examining their immediate environment, it is possible that hearing loss is in fact a reason those cetaceans stranded themselves. It would also help explain why stranded cetaceans, when returned to the water, frequently swim right back on to the beach. For that reason, the authors suggest that, whenever possible, beached dolphins that are rescued and taken to a stranding facility should be tested for hearing loss before any attempt is made to return them to the ocean.

Source: Mann, D., et al. 2010. Hearing loss in stranded odontocete dolphins and whales. PloS One 5(11): e13824. doi:10.1371/journal.pone.0013824

Contact: David Mann, University of South Florida. E-mail: dmann@marine.usf.edu.

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Banner image credit: Claire Fackler, NOAA National Marine Sanctuaries