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Shellfish Disappearing Off Pacific Coast


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Posted by on July 09, 2012 at 20:42:25:

From San Diego to Puget Sound, the future of some iconic West Coast shellfish species and fisheries is now in doubt. In late June, the National Marine Fisheries Service (NMFS) reported "a dramatic and continued decline" in the population of white abalone (Haliotis sorenseni) along the southern California coast, a trend that has worsened since the fishery on the succulent snail was halted in the 1990’s. Another report, from a UK science journal, found that Olympia oysters (Ostrea lurida), which once blanketed subtidal regions from Southern California to Southeastern Alaska, are now functionally extinct. And in Washington’s Willapa Bay, ocean acidification why destroys shellfish has forced a major aquaculture operation to relocate to Hawaii.

"White abalone were abundant in kelp forests and rocky reefs from Point Conception to Baja California until the 1970s, when commercial divers plucked some 350,000 of them from the ocean for food. The overharvesting caused landings to plunge near zero and the fishery was shut down in 1997. White abalone was listed as a federally endangered species in 2001," the Los Angeles Times reported in a 4 July story. Abalone populations along the southern California coast were also decimated in the 1990’s by an outbreak of withering foot syndrome (WS), spread by a pathogen from non-native mariculture abalone from South Africa that were out-planted along California’s south coast.

"In 2001, the white abalone became the first marine invertebrate to be listed as endangered under the Endangered Species Act (ESA). Low densities and recruitment failure due to Allee effects were identified as being the major threats to the species’ long-term viability""" The continuing decline 30 years after the last major commercial harvest demonstrates that the strategy of benign neglect, or allowing the population to recover without intervention, has clearly failed," said the authors of the report in the science journal Biological Conservation, "On the road to extinction? Population declines of the endangered white abalone." (www.sciencedirect.com/science/article/pii/S0006320712001565) The authors continued, "We recommend immediate proactive conservation through population enhancement by out-planting healthy, captive-bred white abalone in areas where populations have reached or are approaching local extinction."

"Underwater surveys found a 78 percent drop in the number of white abalone lodged between rocks off the coast of San Diego since 2002, with most of those remaining either so old or isolated from one another they can no longer reproduce. Researchers warned that, without the ability to spawn a new generation, these aging sea creatures, which can live up to 35 years, will not be able to recover on their own," said the Times article. "‘The study highlights a new sense of urgency about the importance of captive breeding,’ said Kevin Stierhoff, lead author of the study and research fisheries biologist at NMFS’ Southwest Fisheries Science Center in La Jolla." Unlike central California abalone populations, southern California abalone populations have not as yet been affected by sea otter predation.

A second report on West Coast shellfish, Proceedings of the Royal Society B, has found the Olympia oyster "functionally extinct." In a 6 July article, the San Francisco Chronicle reported a "disturbing nationwide decline in oysters and the life-giving reefs that they build is particularly dramatic in California, where the once-abundant native species has been virtually wiped out".. The problem is widespread throughout the country. The first-of-its-kind study".. found that the size of oyster reefs in the dozens of bays and estuaries across the U.S. where there is comparable data has shrunk 64 percent in 110 years. Worse, the number of living oysters dropped 88 percent nationwide, according to the study."

"Essentially, today, the number of oyster reefs is zero," Rob Brumbaugh, co-author of the study told the Chronicle. "It's the complete elimination of a key species and habitat on the West Coast." The loss of native oysters -- not to be confused with the farm-raised Japanese Pacific oysters -- is a serious issue, he said, because oysters clean the water by filter feeding. A single oyster can filter up to 30 gallons of water a day, removing nitrogen and other pollutants, Brumbaugh said. The oyster beds, or reefs, they create provide habitat for myriad fish, crabs and other creatures.

"In 1893," the Chronicle went on to report, "Olympia oyster beds covered a total of 8,033 acres in Newport Bay, Elkhorn Slough, San Francisco Bay and Humboldt Bay, according to the study by the early 1900s. The native oyster beds in Tomales, Humboldt and Newport bays in California and most of the beds in Washington were also virtually scoured clean. Although harvesting continued in some areas of California until the 1930s, wild oysters in the Bay Area were pretty much wiped out by 1911. The oysters people now eat along the West Coast are mainly Pacific oysters, which are native to Japan and cannot reproduce naturally in this climate.

"Local conservation groups have been sinking shell mounds in areas of San Francisco and Tomales bays in an attempt to attract the oysters. The West Coast aquaculture industry, which has recently been combating the effects of ocean acidification caused by climate change, has also been working to restore native oysters, which are smaller but more adaptable than their Japanese cousins".. Invasive predators, like the whelk snail, also known as the Atlantic Oyster Drill, are making it difficult -- killing as many as half the remaining Olympias on the Point Reyes National Seashore."

Finally, on Washington’s Willapa Bay ocean acidification, the direct result of the increased levels of carbon dioxide (a major greenhouse gas) in the atmosphere, threatens a more than century-old Washington State oyster mariculture industry. "Oysters were no longer reproducing naturally on the Washington Coast. Oyster larvae were even dying in nearby hatcheries, which use seawater to raise baby shellfish that get sold as starter seed to companies ".." reported Craig Welch in a 2 July Seattle Times article.

In 2009, oceanographers identified the culprit -- increasingly corrosive ocean water, a byproduct of the same greenhouse gases that contribute to global warming. "Scientists for years have warned that excess carbon dioxide from the burning of fossil fuels eventually would be taken up by marine waters and begin lowering the pH of the world's oceans," reported the Times. "In the past five years, oceanographers at the National Oceanic & Atmospheric Administration working along the U.S. West Coast repeatedly have documented that ocean chemistry is already changing, decades earlier than anyone predicted."

The Times reported further, "scientists are still learning just how those changes ultimately may upend marine food webs. Researchers have shown that less-alkaline seawater causes sea urchin larvae to change shape, makes squid more lethargic and prompts clown fish to race toward rather than away from predators.

"But the type of calcium carbonate used by juvenile oysters during the initial stage of forming their shells is particularly vulnerable to even slight increases in acidity. And the dark, frigid water that wells up from the deep along the Northwest coast during north winds already is naturally richer in carbon dioxide than most ocean surface water".. Those natural conditions combined with greenhouse-gas emissions, scientists reported earlier this year, have turned the tidal currents on Washington's once oyster-rich coast into a death trap for juvenile oysters".. Oysters now haven't reproduced on their own in Willapa Bay since 2005."

For more information, see the 4 July Los Angeles Times at: www.latimes.com/news/local/la-me-abalone-20120705,0,750588.story, the 6 July Peter Fimrite San Francisco Chronicle story at: www.sfgate.com/default/article/Once-abundant-West-Coast-oysters-near-extinction-3689709.php, and the Seattle Times article at: www.miamiherald.com/2012/07/02/2878225/pacific-northwests-acidifying.html.



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