Can You Tell the Age of a Clam by Counting the Rings?

Pismo clam

Pismo clam (Photo by Michael Wilson)

Question: Although the population of Pismo clams is seriously depleted in the Ventura/Oxnard area, I was blessed to dig this guy during the recent low tides. He is bulky and has many (growth) rings. Most are dark in color, but there are lighter ones as well. To determine the age of the clam do you only count the dark rings or do you count all of the rings? The rings indicate this guy is between 25 and 50 years old. (Michael)

Answer: California Department of Fish and Wildlife (CDFW) marine biologist Christy Juhasz tells us that CDFW staff who conduct fisheries-independent Pismo clam surveys count and measure clams encountered and do not utilize an aging method. That said, Christy was able to find references to aging Pismo clams using their annual rings in CDFW’s 2006 Status of the Fisheries report, as well as in an article in the California Fish Bulletin No. 7. The article, entitledThe Life-History and Growth of the Pismo Clam,” was published in 1923 and examines this method in detail.

Pismo clam

Pismo clam (Photo by Michael Wilson)

According to these reports, the age of Pismo clams can be determined by the darker rings that are laid during the fall/winter, perhaps due to prolonged periods of exposure to colder water, reduced food abundance or spawning. These would be the annual rings that can be counted to age individual clams. The yearly rate of shell growth varies from individual to individual and considerably slows down as the clam ages. You can observe this rate of growth when you compare the greater distance found between adjacent annual rings toward the older part of shell (closer to the hinge) than the closer rings nearer to the newer section of the shell, near the growing margin.

More information concerning the growth rate can be found in the Status of the Fisheries report:

“The Pismo clam grows continuously throughout its life. As it grows the shell not only becomes thicker but increases in diameter. Growth varies considerably from month to month, with the greatest increase taking place in the spring, summer, and early fall months. The Pismo clam is about 0.009-inches (0.23-millimeters) at metamorphosis, and grows at an average rate of 0.84-inches (21.4-millimeters) for the first three years. Growth slows considerably as the clam ages, with the increase in shell length not more than 0.2-inches (5-millimeters) per year at age 10. Growth rates are dependent on water temperature and vary among beaches. A 4.5-inch (11.4-centimeter) clam could be from 5 to 9 years old. Along the central coast of California, clams are estimated to reach 4.5-inches (11.4-centimeters) between ages 7 and 8.”

As for unofficial records, the oldest Pismo clam was collected from Zuma Beach and was estimated to be 53 years old, measuring only 5.25 inches (13.3 centimeters) across. The largest Pismo clam in California came from Pismo Beach and was 7.37 inches across and estimated to be 26 years old.

CDFW’s official sport caught records don’t reflect sizes quite this large. It appears that 6.75 inches is the current record.

What’s new in turkey hunting?

Question: It has been a few years since I have been hunting but I hunted turkeys this past weekend with a friend and I’m glad he was with me because he told me there were new regulation changes for turkey hunting. Most important one was the need to use nonlead ammunition. Am I missing anything else? (Anonymous)

Answer: First of all, we’re happy you’re back! It is incumbent upon all hunters to review the laws and regulations any time before they return to the field, but especially if it is after a few years’ absence. Consulting with a friend can help, but going to the source is the best way to bring yourself up to date. The 2017-2018 Waterfowl and Upland Game Hunting regulations book is the place to start (see page 20) or go online.

There have been two significant changes over the past few years that should be highlighted: First, shooting hours for spring turkeys are now from one-half hour before sunrise to 5 p.m. Second, nonlead shot is required when taking wild turkeys with a shotgun anywhere in the state except when hunting on licensed game bird clubs. These regulations apply to both public and private land, including all national forests, Bureau of Land Management properties and CDFW properties. For more information on nonlead ammunition regulations, please visit wildlife.ca.gov/Hunting/Nonlead-Ammunition.

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After April 12, 2018, the California Outdoors Q&A column will be published
biweekly on Thursdays.