Like rings on a tree trunk, the rings on a geoduck shell reveal the age of the bivalve.
With some geoduck living to nearly 200 years, that’s a lot of rings to count.
The Suquamish Tribe is working with the state co-managers to do just that to better understand the geoduck population age structure in Puget Sound.
“Geoduck has become an important commercial opportunity for our people,” said Leonard Forsman, the tribal chairman. “It is a unique species of shellfish in our traditional diet, with a distinctive flavor and texture.”
Knowing the age range and natural mortality rates of geoduck in Puget Sound helps the treaty tribes and state co-manage the harvest, said Viviane Barry, the Suquamish Tribe’s shellfish program manager.
“Geoducks live almost 200 years, and the tribes have only co-managed them with the state since the mid-1990s, so it’s very difficult to have a complete picture on what’s going on,” she said. “Three decades is nothing for a geoduck. And scientists 200 years from now will have a much better handle on what’s going on and will hopefully benefit from the data that we’re collecting for them today.”
Using similar methods as the Washington Department of Fish and Wildlife’s (WDFW) geoduck aging studies from recent years, the tribe collected nearly 800 geoduck from an unharvested 2-acre tract in the Port Orchard shellfish growing area this spring, an area that has not been studied much for its geoduck population, Barry said.
After working with the Suquamish Seafoods’ dive team to collect the geoduck, individual animals from 32 sample sites were numbered, weighed and their shell length measured. The siphon and body were removed from the shells and set aside for the tribe’s elders meal program. The shells were dunked in boiling water to help remove remaining tissue and set aside to dry. The shells will be sent off to a state lab later this year to be processed, where they will be aged using a technique that includes shaving thin slices from the shell, then read like one reads tree rings to determine age.
The results from this work will add to the data previously collected in the WDFW studies, which has been used to design the model that sets the harvest rates by the tribes and the state since 2000.
“The more data we have to inform geoduck natural mortality values in different regions of Puget Sound, the more informed we’re going to be about setting harvest rates using this model,” Barry said. “In addition, tribes and state biologists are committed to improving recruitment rate information in various geoduck management regions by fine-tuning survey methods pre- and post-harvest.”
A geoduck sample is numbered for the aging study. Photo and story: Tiffany Royal