Broodstock: The Unsung Heroes of an Oyster Hatchery

February 26, 2020

At Horn Point Laboratory’s oyster hatchery, winter is synonymous with one thing: broodstock. If the oyster hatchery process were broken down into phases, broodstock would be the first, beginning in January of every year and lasting through August.

What exactly is broodstock, you ask?

Broodstock is defined as a group of mature individuals used in aquaculture for breeding purposes. At the HPL oyster hatchery it means mature adult male and female oysters, which have been placed in floats and plunked into the cool waters of the laboratory’s tidal basin every fall. And there they sleep, until they are brought up to the hatchery beginning in January to begin the new season.

“We get them from all over the Bay,” explains HPL Oyster Hatchery Manager Stephanie Tobash Alexander. Some of the broodstock are reused year after year, but we are always looking for new sources of broodstock to keep the gene pool fresh. We attempt to spawn oysters from the river systems we are restoring, so if the spat are going to be deployed in the St. Mary’s River, we try to make sure the spat are from a St. Mary’s broodstock spawn – but this doesn’t always happen, but we make the best effort we can.”

Harris Creek, Little Choptank, and Tred Avon are other local hot spots where Alexander and her team have come to depend on finding their ‘talent’. This year they are expanding to include oysters from the Manokin, Nanticoke, and St. Mary’s Rivers since restoration work will begin in those tributaries in the 2020 season.

But what happens once the broodstock are brought in from the cold, winter water? This is where the real work begins.

The oysters are transported back to the hatchery, where they are separated by who is alive and who is dead (approx. 10% of every batch are DOA). Staff scrape the mud and fouling organisms off the shells, line them neatly in trays, and then place them into warmer confines of the conditioning lab, where they will sit under water for weeks, gradually being brought up to a temperature where they will awake and be ready to spawn.

“Broodstock are the unsung heroes of the hatchery,” says Alexander. “Without them, we can’t make the babies. And without the babies, we can’t do the restoration work. In order to get that spat you hear about, there’s probably three months of work involved in getting to that point.”

The broodstock can condition in as little as 8 weeks – or as long as 20+ weeks, like in 2019 when all of the rain caused a lack of salinity. (Things are looking better this year…keep your fingers crossed!) Once the oysters demonstrate they’re ready to spawn, staff remove them from the conditioning lab and move them to another part of the hatchery. More broodstock are brought in from the cold and prepped for the conditioning lab, setting up a rotation that will keep the hatchery constantly working. 

“We can’t have too many ripe animals at the same time, as we’re limited by space,” explains Alexander. “We time it so we consistently have ripe animals that we can work with. Once we free up a table, we replace it with something else. We are always planning ahead.”

The next chapter in the evolution of an oyster: spawning. More on that in the coming weeks. But for now, remember that nothing would happen without the work and cooperation of our unsung heroes, the broodstock.