Is Natural Oyster Drought Finally Over?

Chinook Observer | Aug. 29, 2012 8:20 a.m.

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NAHCOTTA — An eight-year “drought” in natural reproduction of Willapa Bay oysters is on the verge of ending.

“The next few days will be crucial. We are putting shell out as fast as we can. Alan Trimble and Jennifer Ruesink’s samples show there are oyster larvae in Willapa Bay and they are growing fast. Their numbers don’t look like it will be a boom year, but with the demand up worldwide for oysters, we may make some money,” Eric Hall, manager at Taylor Shellfish Company in Nahcotta, said Aug. 21.

It has been eight long and costly years for oystermen on Willapa Bay as conditions have not been right for a natural commercial oyster set, but this year may be different. “The number of larvae is up in Willapa Bay, the survival rate is up, and the growth rate of the larvae has been very good,” University of Washington research biologist Alan Trimble said.

“On Aug. 4 it was a very hot day. Willapa Bay warmed considerably, and the oysters began spawning. Several oyster growers began seeing spawned out oysters. By Aug. 10 we found enough early signs of oyster larvae in the water to begin keeping track. The weather stayed warm enough that the tidal flats helped raise the water temperature so that the larvae saw good growth,” fellow UW research biologist Jennifer Ruesink explained.

“The larvae usually take 21 days to grow from 60 microns at birth to 270 microns, or about 10 microns in size each day. The larvae this year have reached that size in two and a half weeks. The sunny weekend and three hot days has everyone pretty positive there will be a commercial set. There is also a mix of smaller larvae, which may add to the number of spat,” Ruesink said.

Will the spat make themselves at home?

Spat are oyster larvae that have landed on a surface and attached. The ideal surface is an old oyster shell, called a clutch. To have a “natural set,” between two and three spat must attach per shell to be commercially viable and at least five attached spat is the makings of a productive year.

“Last year we had about the same number of larvae in the water, but only one or two spat could be found per dozen shells. The jury is still out as to how many spat there will be this year, but it looks like something is happening out there (in Willapa Bay). It probably won’t be a big year, but according to Alan and Jennifer’s numbers, there is a good survival rate for the oyster larvae. The oyster growers are putting shell out in anticipation of a good set. Their thinking is that you don’t catch fish with a bare hook. We won’t know about the set until the Fat Lady sings in a couple of weeks,” Bruce Kauffman, of Washington Fish and Wildlife’s Willapa Bay Shellfish Laboratory, said.

“Oyster larvae usually have a 99.9 percent mortality rate during the three weeks it takes for them to grow enough to attach as spat. Last year there were one or two spat per dozen shells and this year we are expecting two to five times that many, which averages out to less than one spat per shell. Last year there were hundreds of larvae, but they survived very well. In 2010 there were tens of thousands of larvae, but they did not survive due to tough conditions after spawning. This year there are thousands of larvae, but they are again surviving well and growing rapidly,” Ruesink related.

“We have 500 shells at various places in the bay and in two weeks we will check them to see how many spat have attached and began growing. To find out how many larvae there are we pump 20 gallons of water into containers from various places on Willapa Bay and then use a sieve to count them. Our counting methods are the same as they used in the 1940s, but they work. I spent six hours today (Aug. 22) counting oyster larvae, which makes for a pretty exciting day. But that’s science. It has been fun to find nice big fat larvae and I hope this will pay off for the oyster industry,” Ruesink said, exhausted but with a smile.

“The largest concentration of larvae seems to be in the southeast part of the bay, near the Naselle Bridge and Cougar Point. That is also where we have found the highest concentration of carbonic acid and anything above the atmospheric concentration of 390 parts per million is bad for shellfish. That area is also the warmest part of the bay. We have had some big tides so the flats have been able to warm and heat the water. What the weather is like the next few days could be tricky and even after the larvae become spat, there still could be some post-settlement mortality,” Ruesink stated.

Earlier would have been better

“It would have been a whole lot better if the larvae had been here on the Fourth of July. This is late in the season to have a set, but the larvae grew very well and it looks like there is a decent survival rate. On my oyster bed east of the Nahcotta Post Office there are shells with three to five spat so it’s looking pretty positive. Historically we have had cycles with good commercial sets and then poor sets or one side of Willapa Bay has a set and then the other, but this looks good for the area by the Naselle River and over here, too,” oysterman Dennis Tufts related.

“The water temperature must be above 63.5 degrees (Fahrenheit) for the larvae to survive and right now the bay is between 65 and 66 degrees. If we get some steady winds from the northwest, that will cause the cold ocean water to come into the bay and could still kill off the larvae,” Hall said.

“It costs between $12 and $15 for a (40- pound) bag of shell with spats and it costs just pennies to haul a bag of shell out to the beds and have the larvae set naturally. We are taking the risk of putting out the shell and hoping to catch the larvae. One reason we decided to put out the shell is that the hatchery shell has been very poor. A banner year could have a hundred spat per shell and the last two years we had 20 to 30 spat per shell, but this year I struggled to find any spat on the hatchery shell,” Hall explained.

“If we get a good natural set we could get ahead. In the shellfish industry there isn’t a lot of margin. You have to be a good businessman as well as a good grower. A commercial set could really help the smaller scale oyster growers. We should know by the end of August how the set is doing. We all rely on the numbers Alan and Jennifer give us,” Hall said.

Hoping for sunny days on the bay

After frantically getting shell into Willapa Bay, oystermen will be checking the weather over the next couple of weeks and keeping their fingers crossed. Sun on the bay’s 17,000 acres of tidal flats and no large high pressure system moving away from Eastern Washington causing northwest winds at the coast could break the seven-year slump in commercial sets.

“The oyster growers go to a lot of effort and if the conditions are not near perfect, it can go unrewarded. At least we do know that it is possible for oyster larvae to survive and grow rapidly as they have this year,” Ruesink said. She and Trimble, when he returns from a conference in San Francisco, will continue to be the eyes and ears of the oyster industry that surely could use some good reports.

The oyster industry on Willapa Bay has employed up to 600 workers during boom years in the late 1990s and early 2000s when a natural set occurred every season and brought in as much as $20 million annually.

For excellent information and photographs on the life cycle of oysters, shellfish farming on Willapa Bay, and shellfish research projects, go to Ruesink’s website at

Keith Cox has made a series of informative videos at



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