Commercial oyster set fails on bay for 6th straight year

WILLAPA BAY – An infusion of 48-degree ocean water into Willapa Bay from upwellings in the Pacific and the lack of July sunshine have all but killed the chance for a natural commercial oyster set for the sixth straight year in the estuary. The six-year dearth of natural commercial sets is the longest since Pacific oysters were introduced to the bay in 1929 and will severely curtail the oyster industry supply just when demand is at its all-time peak due to the BP oil spill in the Gulf.

University of Washington research biologist Alan Trimble says, “If water temperatures in the bay drop any more oyster larvae will stop developing and as it is we are not finding any in our samples. It would take 50 days for the larvae to set and become spat and normally it takes 21 days or less.” He adds, “In the 10 years I have done research on Willapa Bay this is the coldest the water has been in the summer, even colder than 2007.”

Another enemy of oysters is partial carbon dioxide (PCO2) present in Willapa Bay. The level of PCO2, or carbonic acid, is currently about 380 parts per million in the atmosphere and has steadily risen due to emissions from gasoline engines, coal-burning electric plants and many other factors worldwide.

The PCO2 levels in the bay have vacillated from 1,500 to 5,000 parts per million due in large part to clear-cutting of timber near rivers that enter the bay and the eradication of 10,000 acres of spartina. Experiments in Netarts Bay west of Tillamook, Ore., have shown that a level of PCO2 above 600 parts per million is correlated with difficulties raising oyster larvae. Trimble is using a prototype machine from Oregon State University to obtain data about the bay’s PCO2 levels thanks to a sea grant from National Oceanic and Atmospheric Administration.

Pacific oyster spawning has been “at a trickle” according to Trimble and the very slim possibility of two months of sunshine could lead to a late natural spawn on commercial beds in Willapa Bay. “The probability is slim at best,” Trimble concludes after experiencing yet another cloudy day last week.

In 1936 the Pacific oyster had an astronomical record set. Trimble said, “We have reports of oysters setting everywhere in the bay, even on people’s discarded rubber gloves and as far up the Willapa River as Raymond. Unfortunately the huge population of oysters depleted food sources and there has never been as large a set again.”

Manila clams in Willapa Bay have spawned successfully. Trimble said July 12, “The warm weather of the past week led to very extensive spawning of clams along the western and southern flats (of Willapa Bay). Extremely high numbers of larvae are present at many of our sampling stations.” Reports of 14,000 Manila clam larvae in a 20-gallon sample were not uncommon.

Trimble predicted of the Manila clams, “We expect high mortality rates of larvae as the numbers currently present are probably quite a bit above food-carrying capacity.” Manila clams have become a $5 million industry in Willapa Bay over the past decade, while the oyster industry has topped out at between $25 and $30 million annually.

Trimble said in mid-July, “We are now hoping for a trigger event to set off spawning in the adult Pacific oysters and are considering directly inducing spawning in a few tide pools over the next few days to see if this can help things along.” He related, “It did many years ago, as reported in oyster bulletins of the 1950s.”

That bulletin was released just before the influx of frigid Pacific Ocean upwellings and the July skies stayed slate gray, chilling Willapa Bay and putting a freeze on the possibility of a natural commercial oyster for a dubious sixth straight year.

Kevin Heimbigner, Chinook Observer, 3 August 2010. Full article.


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