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Cultivating Shellfish Augments Local Harvest

In the late 1990s, Marion, Massachusetts, harbormaster Charles Bradley witnessed a sharp decline in the town’s recreational shellfish stocks. He had seen the harbor water quality decline and shellfish beds disappear in recent years from fertilizers, pesticides, and boat disturbances. To sustain the town’s shellfish, Bradley decided to take action.

With his own two hands, $800, and magazine article know-how, Bradley built Marion’s first shellfish nursery. The long wooden tank on four legs stands on the dock in front of his office holding six five-gallon buckets with screens for bottoms. Bradley’s design is known by aquaculturists as upwellers because their design allows nutrient-laden seawater to circulate through the system, providing food for the stocked shellfish. As water flows through, the screens provide a place for baby shellfish to settle and grow. Once in place, Bradley stocks the upwellers with half a million locally-bought quahog, oyster, and soft-shell clam “seed” — animals the size of sand grains.

The most costly part of the setup is the pump required to keep the seawater flowing from the harbor through the upweller on the dock. Power costs run about $300 a year for the pup. The system requires daily monitoring.

To assist with the monitoring, Bradley enlisted the help of high school students from neighboring Rochester High School and Tabor Academy. “The students were very dedicated,” says Bradley. “Everyday they measure the shellfish, clean the tank, and record air and water temperature.”

The shellfish remain in the upwellers all summer and once they reach pea size, around August, they’ve outgrown their stay in the nursery, signaling their readiness for the “grow-out” phase. This phase involves moving the animals to floating trays, or cages, with nets on top. The grow-out cages are placed in carefully selected, nutrient-rich areas.

In Marion, Bradley’s cages sit in the harbor just east of his dock. The shellfish remain in floating cages until late October when the flotation is removed and the trays sink to the bottom for the winter.

The following spring, Bradley retrieves the shellfish, now the size of ping-pong balls, and scatters them over natural shellfish beds. It will be another two years until the shellfish are harvest size. While Bradley has had success with quahogs and oysters, he has not fared as well with soft-shell clams.

Today, Marion is one of over 20 coastal Massachusetts towns using upwellers, including nearly every town on Cape Cod. For these communities, shellfish nurseries are a simple and inexpensive way to supplement public shellfishing beds in a range of coastal settings.