Puyallups Track Baby Geoducks To Improve Resource Management

David Winfrey, shellfish biologist with the Puyallup Tribe, examines a plankton sample taken in Quartermaster Harbor near Tacoma. Photo: E. O'Connell

The image of a typical stuck-in-the-mud adult geoduck clam belies the bivalve’s more free-flowing young life.

“For the first few weeks, clams and other shellfish float in the current,” said David Winfrey, shellfish biologist with the Puyallup Tribe of Indians. Winfrey is tracking the earliest stage in the geoduck life cycle, when the usually settled bivalve is as free floating as any fish. “Their only limitation is how far the tide and ocean currents will take them.”

For the past six months, Winfrey has been collecting shellfish larvae at various locations around the Puyallup Tribe’s treaty reserved fishing area.

“To really understand the dynamics of the geoduck populations, we need to look at their entire lifecycle,” said Winfrey.

The project is a pilot study of a more thorough examination planned for next spring.

In addition to being the foundation for future generations of geoducks and other clams, larvae also support many other populations higher up on the food chain, including juvenile fish and other marine crustaceans which are an important food source for juvenile salmon and baitfish.

Winfrey is out on the water once or twice a week collecting samples. Using a small net with extremely fine mesh, he makes several tows in every location. “Mainly, we’re looking for geoduck larvae, because they are an important tribal fishery,” he said.

A clam larvae as seen under a microscope. Photo: D. Winfrey

The geoduck clam is the largest bivalve in Puget Sound and the largest burrowing clam in the world. About 109 million adult geoducks live in Puget Sound, the greatest concentration of any marine animal. Puget Sound bays and estuaries harbor the highest density of geoducks in the continuous United States, with the most abundant area being southern Puget Sound.

Clams will usually start spawning in early spring, when plankton, their main food source, is more plentiful and “the clams are hit by a slug of food,” said Winfrey. After the clams release their sperm and eggs, a small percentage find each other in the water and become larvae. After feeding in the water column for up to several months, the larval clams gain enough weight to settle onto the sea floor and continue growing.

“We want to find out how successful clams are at reproducing each year,” said Winfrey. “Do conditions have to be just right, and how often do these conditions occur?” Just because there is a lot of larvae in the water doesn’t mean a lot of clams will start growing in the mud, he pointed out. The larvae also need to have a successful settling and recruitment into the population, and Winfrey isn’t sure what causes that to happen.

Getting that basic information on the early life cycle of clams is important to their management, said Winfrey. “If we know more about how and when clams breed, and can track other characteristics of their early life cycle, then the tribe and state can be more responsible co-managers.” – E. O'Connell