There’s one place where a population boom would be welcome—at the bottom of our local rivers.
And by all indications that is what’s happening, as hundreds of millions of oysters are taking up residence each year. Since 2000 several billion baby oysters, or “spat-on-shell,” have been planted on various reefs in the Chesapeake Bay by the Oyster Recovery Partnership (ORP), Chesapeake Bay Foundation (CBF) and other partner organizations and agencies.
Locally, about 178 million spat have been planted on reefs in the Severn River. Check here for total oysters planted by ORP at various middle Chesapeake Bay rivers over those years, including the South River and the Magothy River.
This past week CBF was back on the Severn, putting about four million additional spat on four reefs between the Naval Academy Bridge and Saltworks Creek. CBF’s custom-built oyster boat, the Patricia Campbell, could be seen in the river on several mornings spraying oysters like a tractor seeding a field.
It’s difficult to determine exactly how many of the billions of oysters planted over 12 years have survived. Scientists are researching the question. It’s tough growing up an oyster in the Chesapeake, where disease, low oxygen levels from pollution, and other factors make life literally difficult.
But a team of divers from The Paynter Labs at the University of Maryland this past fall checked several reefs in the Severn and found encouraging results. CBF first built those reefs in 2005, and has added oysters over the years. A Paynter Lab report to CBF had this to say:
“More oysters were observed that (sic) originally expected and most oysters were very large. The oyster densities at these sites have remained high over the past seven years and disease intensity has remained very low. Considering the low densities of oysters often observed on restored bars in Maryland, the perpetuation of relatively high densities of large, healthy oysters at this site is an example of successful oyster restoration in Maryland. “
Karl Willey, the manager of CBF’s oyster restoration work in Maryland, said it a little differently: “There’s some huge clusters of oysters down there, and some huge oysters. “
Those findings in November were especially welcome because record spring river flows this past year together with Tropical Storm Lee dumped so much fresh water in the Chesapeake Bay that salinity levels plunged, and many oysters in the upper Bay died as a result. The Severn oysters apparently weathered those storms, as did oysters in the large majority of restored reefs south of the Chesapeake Bay Bridge.
The Severn success is great news for the Greater Annapolis area. Oysters are what we call a “keystone species” in the Bay, meaning their survival is critical to the estuary’s ecology. A single adult oyster can filter up to 50 gallons of water a day. Millions of them concentrated in a river such as the Severn can act as filtering factories. And with all the pollution pouring into the Severn from sewage spills, urban and suburban runoff, septics and other sources, we need all the help we can get.
Oyster reefs also provide ideal habitat for tiny aquatic life and the fish that feed on them. A healthy oyster reef is one of the most diverse “communities” in the Chesapeake ecosystem. This concentration of life makes them favored fishing sites for watermen and anglers.
The Holy Grail of all oyster restoration work is to eventually get the oysters to reproduce sufficiently themselves, so humans don’t have to continually mother the mollusks. Every fall scientists survey oyster reefs to measure the “spatset” or the numbers of baby oysters (spat) that have settled onto the reefs after being spawned during the summer.
Bill Goldsborough, CBF’s senior fisheries scientist, cautioned that oyster reproduction is tricky to predict, especially in a river such as the Severn with relatively low salinity (oysters like a certain amount of salt in their watery home). Also, successful river-wide spatset typically involves concentrations of oysters spread widely over an area, not just on one or two reefs. Still, Goldsborough was optimistic that this might be the year:
“With salinities up this year and with the growing concentrations of adult oysters on these and other sites in the river, I would say the chances are better this year than they’ve been in a long time that we’ll have a spatset in the Severn in 2012. “