Month: August 2016
Mid-Summer Bay Dead Zone Data Released
Earlier this summer, I reported on estimates that the Bay hypoxic zone would be smaller than average this year. The Maryland Department of Natural Resources (DNR) has just released their data for dissolved oxygen levels for July and early August in the main stem of the Bay (see this report). While the hypoxic area in August was about average, July measurements exceeded estimates.
To refresh, hypoxic zones are areas where dissolved oxygen levels fall below 2 milligrams per liter. Anoxic zones, which have not occurred this year, are areas where oxygen levels fall below 0.2 milligrams per liter. Hypoxic and anoxic zones are commonly referred to as dead zones, as low oxygen levels make it difficult for marine species to live in these areas.
Earlier estimates, made by a team of scientists from UMCES, the University of Michigan, NOAA and USGS, were calculated from spring rainfall and nutrient loading data from major Bay tributaries, such as the Susquehanna and Potomac Rivers. Spring rainfall, which carries nutrient runoff into the main stem of the Bay, is a major indicator of how big or small dead zones may be later in the year.
Measurements of dissolved oxygen are then taken throughout the summer months. Data is collected by the DNR, and compared to long-term averages (1985-2015).
July dissolved oxygen levels, and the subsequent hypoxic zone area, were higher than average. The hypoxic zone grew to 1.65 cubic miles last month, which was the seventh largest hypoxic zone on record in the Bay. (The July long-term average is 1.29 cubic miles). Early August levels were closer to estimates; the August 2016 (Aug 8-10) hypoxic zone measured 1.15 cubic miles, compared to the 1.13 cubic mile average.
Dissolved oxygen is measured with various other water quality indicators, which can give scientists a better idea of what causes average or above average dead zones. This year, scientists measured higher salinity in the Bay in June through early August. Higher salinity is indicative of less rainfall and less nutrient runoff. In wetter years, more nutrient runoff usually results in larger hypoxic zones. The results for early August confirm spring estimates. With the drier spring we had this year, we would expect to see average or lower than average dissolved oxygen levels, hypoxic zone areas, and salinity measurements.
But what about July? Why was the hypoxic zone so much larger than average? Other environmental factors, such as temperature, were likely to blame. July temperatures were especially high last month. Warmer air and water temperatures result in stagnant waters; oxygen on the Bay surface is unable to mix with bottom waters, where species such blue crabs, oysters, and finfish can be found.
Monitoring of the Bay hypoxic zone concludes in September. Check back for an update in a few weeks when the late August/ early September data is released.
More on Oyster Production: Aquaculture vs. Traditional Means of Harvest
Last week I posted a review of Kate Livie’s book, Chesapeake Oysters: The Bay’s Foundation and Future. The final portion of Livie’s book is dedicated to the rise of aquaculture in the Bay watershed over the past 15- 20 years.
Aquaculture is reliant on the production of disease-resistant, sterile triploid oysters. (To read more about the production of these triploids please see this former post on a Chesapeake Bay hatchery; and this former post on a nearby oyster farm). Raised in floating cages, or in cages suspended on the Bay floor, triploids are being raised in the millions in Virginia and Maryland, revitalizing the local oyster industry. The Chesapeake oyster can once again be found in restaurants and markets across the Eastern seaboard (and sometimes even across the country).
Aquaculture represents the future of the Chesapeake oyster in this region. However, traditional forms of harvest are still taking place in the Chesapeake and its tributaries. Despite the fact that traditional harvesting methods produce a minute fraction of historic records, harvesting of reefs, both natural and manmade, is an ongoing practice in Maryland and Virginia. Some question whether harvesting of reefs should be allowed at all, when the wild oyster population remains so low. As stated previously, the current population is estimated to be at or below 1% of historic levels.
Virginia and Maryland have both attempted to increase these population levels, with limited success. State-owned sanctuaries, where harvesting is limited or forbidden all together, are a way to protect and revive the wild oyster population. A recent report from the Maryland Department of Natural Resources unsurprisingly documents a population boom among oysters in Maryland sanctuaries over the past five years, while the oyster population outside of protected areas fell. Livie’s telling of the decline of the wild Chesapeake oyster, and this recent DNR report leave us with the questions: Should harvesting be allowed in these sanctuaries? Should harvesting continue at all while population numbers remain so low? If Maryland was more open to aquaculture, would this present a solution to displaced watermen, or those seeking alternate means of employment within the industry?
These aren’t easy questions to answer. Harvesting of oyster reefs remains an economic and cultural cornerstone of several waterfront communities in the Chesapeake region. The studies that have been undertaken do not definitively prove that harvesting of oyster reefs is harming current populations. On the other hand, with population levels as low as they are, it would seem that stricter regulations could only help.
As with many environment and water quality issues in the Bay, there are no easy solutions. But it’s certainly interesting to examine all sides to the story.
A Review of Chesapeake Oysters: The Bay’s Foundation and Future
Did you know that oyster aquaculture has been practiced and debated in the Chesapeake region since the late 1800s? William K. Brooks, a researcher with the Chesapeake Zoological Laboratory, was the first to experiment with Chesapeake oyster production in a controlled environment. Brooks, funded by the state of Maryland in the 1880s, studied and promoted ways in which oysters could be farmed to prevent against overharvest of natural oyster reefs. While hugely unpopular among the public, and especially among those in the oyster industry in his time, Brooks’ findings are used today in the booming oyster aquaculture industry.
Kate Livie, the director of education at the Chesapeake Bay Maritime Museum at St. Michael’s, Maryland, shares stories such as Brooks‘ in her 2015 book, Chesapeake Oysters: The Bay’s Foundation and Future. Live gives a fascinating account of the rise and fall and current renaissance of the Chesapeake oyster industry.
Livie’s begins her book by introducing the Chesapeake oyster and its importance in this region, by using historical accounts and anthropological evidence to describe pre- and post-colonial reliance on the oyster as major source of food. Livie argues that oysters were the foundation for colonial settlement in the Chesapeake region, and continued to be a staple in the regional diet over the next century.
Livie goes on to detail the rise of oyster harvesting in the Chesapeake Bay, which became an economic and cultural cornerstone of the region. Cities and towns, like Baltimore and Crisfield, grew in size and prominence during the oyster boom of the mid- to late-1800s. Packinghouses employed thousands of workers, charged with shucking, packaging, and shipping oysters out from the Bay region to other parts of the country.
Industrialization and advances in technology allowed watermen and packinghouses to produce, package, and ship out oysters at an unprecedented rate. They were able to do so as national demand for oysters rose. Chicago, New York, and New England were major consumers of Chesapeake oysters, as many of these places had wiped out their own native oyster beds. As a great number of packinghouses sprang up in the Chesapeake watershed, Livie paints a vivid picture of the efforts these places used to stand out. Unique and colorful cans, trade cards and advertisements for Chesapeake oysters could be found in restaurants and markets along the Eastern seaboard.
With the massive scale of oyster production going on in the nineteenth and early twentieth centuries, watermen adopted new methods, such as dredging, to harvest oyster reefs. Dredging and overharvesting led to the depletion of natural reefs and major reductions of stock. Dredging caused vertical reefs to become horizontal in structure, and made oysters more susceptible to sedimentation, and disease. This susceptibility was no more apparent than in the second half of the twentieth century, when the diseases MSX and Dermo reached the Chesapeake Bay watershed. MSX and Dermo wiped out much of -what was already- a severely depleted oyster population. Populations remain low to this day; current reports estimate that the Chesapeake oyster population is just 1% of historic levels.
Due to disease and overharvest, oyster production was a dying industry in the Chesapeake region until the early 2000s, when scientific researchers discovered a way to harvest an oyster immune to MSX and Dermo, and released this oyster to the market. The discovery of a disease-resistant triploid oyster, unable to reproduce and create spat, has resuscitated the industry. However, this revival is a complete turnaround from natural methods of harvest. Unable to form natural reefs, the triploid oyster must be farmed. Traditional oyster harvesters have been reluctant to switch to aquaculture, especially in Maryland where an aversion and distrust of oyster farming goes back to the days of William K. Brooks.
Virginia on the other hand, has been much more open to oyster aquaculture, historically and with the recent emergence of the disease-resistant triploid. While farming has had a slow start in Maryland, dozens of private oyster farming businesses popped up over the past ten years in Virginia (54 farms registered as of 2013). Outside of farming, hundreds of individuals throughout Virginia raise not-for-profit oysters in floating cages. On this explosion of aquaculture in Virginia, Livie states that from the time VIMS began tracking aquaculture, “Hatchery-produced seed plantings grew from 6.2 million in 2005 to 138 million in 2014- an increase of over 2,125 percent in less than a decade.”
If you want to read more about the emergence of aquaculture in the Chesapeake Bay watershed, or learn more about the history of the oyster in this region, pick up Livie’s book. It’s a great read.
[Livie, Kate. Chesapeake Oysters: The Bay’s Foundation and Future. Charleston: American Palate, 2015.]