Oyster management study released
Special from the Star Democrat
— It may be too early to tell whether Maryland’s oyster sanctuaries are working as theorized, according to a study released by the state Department of Natural Resources on Sunday.
However, indicators like abundance, survival, biomass and size structure have shown stable or increasing trends in sanctuaries, according to the study. But, the study also indicates that biomass, or the total mass of oysters in a given area, in public fishery areas began to decline in 2014 and 2015.
The long-awaited study is a comprehensive five-year look at the state’s oyster population management, including how the sanctuaries are doing since the state overhauled efforts in 2010 to increase the Chesapeake Bay’s oyster population. It also looks at public fishery grounds and the state’s aquaculture movement. DNR plans to release a new study on the state’s oyster population management every five years.
It is a widely accepted belief that the Bay’s oysters have declined to 1 percent of their historic levels due to various factors, including disease and overfishing. Oysters are important to the Bay’s ecosystem and provide water filtration and habitat and are valuable to Maryland’s economy and culture.
The state’s sanctuary program’s scale was expanded in 2010. It sought to facilitate development of natural disease resistance in oysters, provide ecological benefits that can’t be obtained on a harvest oyster bar and serve as a reservoir for reproduction.
The study states that oyster populations in Maryland, both sanctuaries and public fishery grounds, have benefitted from low disease mortality and from two good years of reproduction in 2010 and 2012. While oyster biomass in Maryland has generally increased in the last decade, it started to decline in public fishery areas in 2014 and 2015 as the oysters from the 2010 and 2012 year classes reached market size and were harvested.
The study indicates that older, larger oysters that are not harvested in sanctuaries see increased biomass each year, and since they produce the most eggs, reproductive potential in sanctuary areas also continues to rise.
But, the study still states that it might be too early to tell how oyster populations reacted to being in sanctuaries.
“Given the complexity of the Chesapeake Bay ecosystem, five years has not been long enough to show how oyster populations respond to the absence of harvest,” the study states. “Many sanctuaries show positive signs such as increased biomass and reproductive capacity, while others have not shown any changes.”
The study states that the long-term behavior of sanctuaries will depend on a variety of factors, like changes in weather, water movement patterns, disease and predator abundance.
Sanctuary oysters developing resistance to diseases remains a conceptual expectation for Maryland’s sanctuaries and would require long periods of study over a broad geographical area, the study states. Oyster resistance to both MSX and dermo diseases are heritable, genetic characteristics that can be strengthened by planned selective breeding, according to the study.
“At this time, it is impractical to directly and objectively evaluate whether oysters within sanctuaries develop resistance faster than oysters in harvested populations,” the study states.
The study also states that it’s too early to conclude if sanctuary oyster bars are providing more ecological services than harvest bars, and that quantifying it would take decades and must account for climate, spat settlement, disease, mortality, salinity, shell accumulation and sediment.
“Oyster reefs present in Chesapeake Bay grew over centuries so that by the late 1880s the Chesapeake Bay was the greatest oyster-producing region in the world,” the study states. “The degradation of the oyster resource occurred over at least 150 years. Hence it is unrealistic to expect a reversal within a decade.”
The study recommends looking at adjusting the boundaries of some sanctuaries and opening some areas to harvest, but stressed the importance of maintaining the scale of the sanctuary effort within the range of 20 to 30 percent of the remaining productive oyster bottom.
“If the ultimate goal is to have more oysters in the water, then some areas that are currently sanctuaries could contribute to this goal and provide economic and cultural benefits to fishing communities,” the study states. “... particularly if these areas are managed in a way that balances harvest with continuous investment to maintain oyster populations in the area.”