Don’t give up on Chesapeake’s oysters

Maryland established its Oyster Advisory Commission in the latter half of 2007 to engage a wide range of interested people to consider strategies for bringing back a robust native oyster population in the Chesapeake Bay.

The commission was established at a time when hope for native oysters had all but vanished, not unlike the oysters population itself — which was, and still is, estimated to be about 1 percent of what it was centuries ago.

Many in the region were advocating for the introduction of disease-resistant Asian oysters, while others were calling for an all-out moratorium.

The OAC was the latest in a nearly century-long series of commissions and studies that examined the plight of native oysters in the Chesapeake Bay. Harvests in the late 1800s were reputed to have been well in excess of 15 million bushels, but by the latter part of the 20th century had fallen to around 50,000 bushels annually – a steep and prolonged decline.

Meanwhile, the recommendations of most of those reviews and studies were ignored or had proved inadequate.

Enter the 20-member OAC, comprised of watermen, other representatives of the oyster industry, academia, elected and other government officials, and the conservation community. I served as chair through 2011, having been a vice president of the World Wildlife Fund, and before that, during the 1980s, a senior official responsible for Maryland’s earliest integrated environmental protection programs.

In its first report, issued early in 2008, the OAC set forth the basic strands of the strategy for oysters in Maryland’s portion of the Chesapeake Bay, which it would develop in greater detail over the next two years, culminating in major recommendations made in early 2011. The strategy had three elements:

•Re-establish a healthy wild population of native oysters through the creation of extensive permanent sanctuaries.

•Energize the development of a robust oyster aquaculture industry by streamlining laws, and providing technical and other assistance.

•Establish procedures for the wild fishery so it would be biologically and economically self-sufficient.

It is important to note great relief in many quarters that the OAC had not recommended a moratorium on all oyster harvesting.

Now, in 2017, the second and third of these three elements are not the subject of significant controversy. But the first bullet point – building strong populations of native oysters by establishing sanctuaries – has proved difficult to keep in place, in the face of continued opposition from many watermen.

After its initial reports, the OAC eventually recommended 25 percent of the most productive oyster habitat be set aside as sanctuaries – permanently closed to harvesting. It also said these sanctuaries should be large and spread across the full range of potentially productive oyster bottom in the entire Bay. This became the basis for an oyster management plan for the whole bay, adopted through the Chesapeake Bay Program.

In Maryland, initial areas designated as sanctuaries included the Little Choptank River and, just to the north, two tributaries of the Choptank River: Harris Creek and Tred Avon River. Work was completed in 2015 in Harris Creek and resulted in 350 acres of newly improved bottom structure for the establishment of oyster communities.

Work has slowed in the Tred Avon and Little Choptank as the Hogan administration has weakened its support for sanctuaries.

While there is a pretty clear sense in the scientific community regarding the reasons for the decline in oysters, these are not well understood by the public. So let’s review some history and think logically about this animal, as the OAC did in developing its rationale for the sanctuaries.

It is indisputable the oyster has been the victim of a wide range of abuses. The first has to do with its preferred habitat – layer upon layer upon layer of shells left behind by countless previous generations. When Europeans first explored the Bay, they encountered these huge reefs everywhere, most of them no doubt thousands of years old and some reaching above the water level at low tide. Given their permanence and complexity, they provided habitat to many other species, much as coral reefs do in tropical waters.

But during the following centuries, oyster harvesting and dredging for navigation combined to destroy those reefs, and the unique master habitat builder of the bay is now forced to live a lowly life in the bottom sediments, far removed from the enriching flows of the currents carrying nutrients in all of the bay’s waters.

But that did not put them out of the reach of oystermen, who for most of the 19th century were allowed to harvest as many oysters as their boats could carry to shore. The result was that by the late 1800s, oyster harvests in Maryland’s portion of the bay were estimated to be on the order of 15 million bushels a year.

Oysters could not withstand this onslaught; by the early 1900s harvests had declined to 3 million or 4 million bushels a year.

In addition to depleting the population, this unchecked harvest pressure also had a genetic impact. Because virtually all of the oysters were taken once they had reached market size, those remaining – the genetic pool – became smaller and smaller, and more homogeneous. The biologic diversity within the species was impoverished.

At the same time, another assault was about to be launched against a now enfeebled species: water pollution. Industrialization without effluent cleanup; large-scale agriculture without controls for fertilizers; pesticides or sediment runoff; urban and suburban development without controls for runoff; and the widespread use of household chemicals – all combined to further degrade the quality of the water that flowed through the organism.

It is hard to imagine a strategy more perfectly designed to exterminate a species.

First, destroy its natural habitat. Then, kill virtually all members of the population as they reach sexual maturity. Finally, introduce toxic chemicals and sediment into the very water that is “breathed” by every individual.

Those three things had, in fact, pushed the species to the brink by the 1970s, by which time its survival came to depend more and more on artificial breeding programs (hatcheries) and human maintenance of oyster beds.

Then came the deadliest blow: foreign diseases. Most likely imported in the ballast water of Asian cargo ships, two organisms – commonly known as Dermo and MSX – found their way to the Chesapeake in the mid-20th century. Both were highly efficient at killing the oysters. While a species of Asian oysters had through many generations presumably developed resistance to these diseases, the weakened native oyster had no such defense and rapidly succumbed.

By the mid-2000s, Maryland’s oyster harvest had plunged to less than 30,000 bushels a year.

As noted at the start of this piece, this decline gave rise to a number of thoughtful efforts to develop strategies to rescue the native oyster, but none yielded results at any significant scale. The industry was ready to give up on the native oyster and shift to building a new fishery on Asian species which could, presumably, withstand the impacts of disease.

The creation of the OAC was a last-ditch effort to save the native oyster. In the commission’s early days there was much talk of a total harvest moratorium, which been very successful for rockfish (striped bass) in the 1980s. But the rockfish strategy was not a good model. The cause of the rockfish decline had been comparatively simple – overharvesting fish of reproductive age.

Oysters had a far more complex suite of problems and a longer period of destructive impacts. And the proximate problem was disease. To save oysters, we needed to help them develop a natural resistance to the disease, and large-scale sanctuaries were the key.

An animal is likely to have the maximum capability to develop genetically based resistance to disease if certain conditions are met. First, it must be given the most hospitable environment possible so individuals thrive physically. For the oyster, this means providing opportunities for re-establishment of the historic reef structures. This can only be done in the long-term absence of harvesting.

Second, the animals must be allowed to live out their full life expectancy, especially in the presence of disease. Animals that live long lives in the face of disease are likely to do so as a function of genetic and other factors disposing them to resistance. And they pass those traits on to future generations.

Sanctuaries need to be distributed throughout the bay. This will assure, as weather and other environmental conditions change from time to time and impose transient stress on particular sanctuaries, others not subject to that stress can help carry the whole system through such periods, especially in the reproductive processes. Also, the distribution of sanctuaries across the bay means larval dispersal from sanctuaries will benefit adjacent non-sanctuary oyster habitat.

Finally, sanctuaries need to be large, for enforcement purposes. Only large areas – an entire water body, such as Harris Creek or the Little Choptank – are on a scale that allows efficient law enforcement. In a 10-acre sanctuary, a scofflaw can easily slip across the line without being spotted. That’s impossible where an entire creek or river is the sanctuary.

The Maryland Oyster Sanctuary Plan envisages only covering 25 percent of good oyster habitat. That leaves 75 percent for traditional oyster practices. The sanctuaries are the only logical way to assure native oysters are eventually able to resist disease and again play an important role in the ecological life of the Chesapeake. They will also significantly improve the probable success of thriving oyster populations outside of sanctuaries.

To abandon this vision for the contribution of sanctuaries in Maryland is to abandon the native oyster.

William M. Eichbaum is a former chairman of the Oyster Advisory Commission.