Raising Oysters
A day at the hatchery
By Eric Weissberger
With the arrival of balmy spring weather, Maryland’s public oyster hatcheries begin their operations: producing oysters for restoration, the wild fishery, aquaculture and the Marylanders Grow Oysters program.
Maryland has three oyster hatcheries: the Piney Point Aquaculture Center, operated by the Department of Natural Resources (DNR); the Horn Point Oyster Hatchery, operated by the University of Maryland; and the Morgan State University Hatchery. Although the hatcheries differ in levels of technology, the basic process of spawning and setting oysters or producing oyster seed from larvae is the same.
Controlled breeding
First, staff members collect large adult oysters from various parts of the Chesapeake Bay for breeding. Back at the hatcheries, the water temperature is raised to 23-28° C (72-82° F) to promote spawning. (In the wild, oysters spawn in early summer.)
Lab technicians determine the gender of the oysters as they release gametes, the cells involved in reproduction. Once determined, males are separated from females, and the sperm and eggs are collected separately.
Technicians then mix sperm and eggs together and collect the fertilized eggs. Sometimes sperm and eggs from oysters collected from different Chesapeake Bay locations are combined to increase genetic diversity. Other times, oysters from the same location are used to foster the characteristics of oysters from that particular area. With proper care, the fertilized eggs develop into free-swimming larvae in less than 24 hours.
A natural diet
At Piney Point, oyster larvae are kept in water from the adjacent St. George Creek, allowing them to eat the same types of algae upon which wild oyster larvae feed.
Morgan State and Horn Point both grow different species of algae to create specific diets. Technicians adjust these diets as the oysters grow and have different dietary needs. At Horn Point, a computer-controlled system automatically feeds the larvae the appropriate combination of algal species.
Settling in
The larval period lasts approximately three weeks. During this time larvae develop a foot, which is used to crawl and find a place on which to settle.
Toward the end of the larval period, technicians lower a shell into the larvae tank to see if they are ready to set: When larvae settle onto the test shell, the tank is drained and larvae are transferred to tanks containing aged and washed oyster shells — the preferred substrate for oyster larval settlement. The larvae secrete a liquid, cement-like substance to attach themselves to this surface. From 1.5 to 5 million larvae are placed in a single setting tank.
The oyster larvae remain in the tanks with the shells for two to three days. Now called spat, the baby oysters continue to grow on the shells for another week. Like larvae, the spat also eat algae.
Moving forward
Next, technicians load the spat on shell onto boats for transfer to oyster bars. Some of the baby oysters go to sanctuaries to replenish the population, while others are deposited in areas reserved for the public fishery. Some may also be purchased by aquaculture businesses and placed on bottom leased from the State. Since 2000 Maryland’s hatcheries have produced 42.5 billion oysters that have been planted in Maryland waters.
The Marylanders Grow Oysters program also uses spat produced by the State’s hatcheries. They distribute cages full of spat on shell to private citizens to suspend from their docks. When the baby oysters have grown for about nine months, they are collected and placed on bars in local sanctuaries. Participants receive a new batch of spat the following year and repeat the process.
Maryland’s hatcheries operate until the late fall, when it becomes too cold to transfer the spat. Over the winter, the hatchery teams perform maintenance and prepare for the next season to begin.
Oyster Survival Rate Climbs in 2011
Maryland’s 2011 Fall Oyster Survey showed the highest survival rate for oysters since 1985.
The 92 percent survival rate builds upon the previous year’s strong spatset (number of baby oysters), which was the highest since 1997. The annual survey tracks reproduction levels, disease levels and annual mortality rates, offering a window into future population levels.
Scientists at the Cooperative Oxford Laboratory report that the frequency and intensity of diseases are low. Of the two diseases that have devastated populations for decades, Dermo, although still common, now occurs at the lowest level on record and remains well below the long-term average for the eighth consecutive year.
MSX, a lethal pathogen that has long plagued oysters in the Mid-Atlantic, is also at its lowest level on record.
Although increased freshwater flows from last year’s heavy storms — Hurricane Irene and Tropical Storm Lee — impacted oysters above the Bay Bridge, this represented a relatively small proportion of the total oyster population. The lower salinities proved to be beneficial to the majority of oysters in Maryland by knocking back disease.
In his fiscal year 2013 budget, Governor Martin O’Malley proposed a $7.5 million capital investment in oyster bar restoration in Harris Creek in Talbot County and the Little Choptank River in Dorchester County, two of the State’s new sanctuaries where reproduction conditions are favorable.
The Governor has also proposed an additional $500,000 for aquaculture infrastructure improvements. Those will include low-cost loans through MARBIDCO — the Maryland Agricultural and Resource Based Industry Development Corporation — for entrepreneurial watermen and other citizens who want to grow oysters.
In 2009, Maryland adopted regulations to implement Governor O’Malley’s Oyster Restoration and Aquaculture Development Plan. This plan increased the State’s network of oyster sanctuaries from 9 percent to 24 percent of remaining quality habitat; increased areas open to leasing for oyster aquaculture and streamlined the permitting process; established a $2.2 million financial assistance program for aquaculture interests; and maintained 76 percent of the Bay’s remaining quality oyster habitat for a more targeted, sustainable and scientifically managed public oyster fishery.
Eric Weissberger is an environmental specialist with DNR’s Fisheries Service.
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