Mitchell Tarnowski
Shellfish Program

Table of Contents


History of Oyster Population Surveys in Maryland

Present Day Fall Survey

Summary of the 2002 Survey Results

Additional Reading

The Author


"How are the oysters doing?" As a shellfish biologist for the Maryland Department of Natural Resources, this is probably the most common question asked of me, particularly at the start of the oyster season in October. The topic is a great icebreaker at social gatherings (providing the subject is changed before the listenerís eyes glaze over). Oysters have a mystique all their own, and not just for the watermen who depend on the bivalve for their livelihood. The general populace around the Chesapeake never seems to tire of news about oysters, as evidenced by the myriad of newspaper articles that crop up about the same time that the leaves start turning colors. Television news crews endure rough conditions on the bay for a few minutes of footage aboard the survey boat, all for the consumption of the expectant public. This fascination with oysters goes well beyond the merely gustatory, however, or their ecological role as reef builders and filter feeders; even beyond the history and tradition of oystering and the romance of earning a living on the water. At best resembling a mud-covered rock, an oyster is not warm or cuddly such as some Pooh-like creature, or aesthetically appealing like many of its molluscan relatives with their beautiful shells. Yet there is something inherently charismatic about the oyster itself that defies explanation. Perhaps this is a topic better left for poets and philosophers rather than biologists.

History of Oyster Population Surveys in Maryland

The opening question is an age old one. Aside from metaphysical inquiry or casual curiosity, however, the need for obtaining the answer has been driven by economic and (more recently) ecological considerations, stemming from the oysterís importance in commerce and in nature. Thus, the basic objective of an oyster population survey is to provide information for the conservation and enhancement of this valuable natural resource. In Maryland, the approximately 200,000 acres of natural oyster bars belong to the public domain. Because stewardship of these oyster grounds is the responsibility of the state, these surveys are inevitably undertaken with government sponsorship.

Scientific inquiry into the status of Maryland oyster populations has a rich history dating back 125 years, when Lt. Francis Winslow of the United States Navy braved the notoriously violent oyster dredgers of Somerset County to survey the oyster bars in Tangier Sound. This was a period when oysters were a principle source of inexpensive protein for the urban masses of the east coast, before the railroads brought in cheap western beef. In 1880, the Maryland oyster industry, valued at nearly $4 million per year (when a penny could buy a loaf of bread), supported some 24,000 workers. The tremendous demand for oysters during the mid-1870's increased harvesting pressure to the point where landings began to slip and people became concerned. Commissioned by the Maryland General Assembly, the Winslow survey was conducted in 1878-79 without incident, the Tangier Sound dredgers being merely curious and amused about the strange activities entailed in survey work. This was followed up by a Maryland-wide survey in 1882 at the behest of the newly formed Oyster Commission. Both surveys found the bars to be in a deteriorated state, mirroring the decline in harvests that prompted the surveys in the first place. Unfortunately, the release of the Commissionís report two years afterwards coincided with the all time high harvest of 15 million bushels. The survey findings, along with the warnings and recommendations that resulted from them (including instituting an annual survey), went largely ignored. The principle exception was the establishment of a minimum size limit for keeping oysters, legislated in 1890. In hindsight, 1884 was the high water mark for landings after which they began a steady decline that wasnít stanched until some 40 years later, when harvests leveled out at about 20% of the record total.

During the early 1900's, the Progressive Era of American politics developed as a response to the excesses of the previous century, a sentiment which even carried down to oyster management in Maryland. The Haman Oyster Culture Law was intended to increase oyster production by encouraging private aquaculture and providing for a Shell Fish Commission to oversee the process, including a survey of the oyster bars. The primary objective of the survey was to delineate the legal boundaries of the oyster bars so as to facilitate leasing grounds outside of the bars for oyster farming. The resulting Yates survey of 1906-1912 was possibly the apotheosis of oyster assessments in terms of thoroughness and sheer magnitude of the undertaking. Great care and objectivity were required since this was a such high profile, politically charged issue, given the fierce opposition to leasing in the state. Using primitive equipment, the survey painstakingly examined 350,000 acres of bay bottom and mapped 780 bars covering 216,000 acres over a six year period. The results were presented in a series of 43 charts showing the precise locations of all of the legally defined oyster bars in Maryland and the often whimsical names for them (eg. Old Womanís Leg, Butterpot, Blue Sow, Helsinki, and Pagan), along with several accompanying reports. Unfortunately, the biological underpinnings for these boundaries have been lost to time, although abbreviated tabular summaries of the results are still available in the old reports.

The Haman Oyster Culture Law ultimately failed to increase private oyster farming due to overwhelming political opposition, so the emphasis in improving oyster production had to be shifted back to the public fishery. The Maryland Conservation Commission was created in 1916 from four disparate natural resources organizations including the Shell Fish Commission and State Fisheries Force. Confronted with the daunting task of stemming a 30 year decline in oyster harvests, the Commission began looking into innovative techniques for rehabilitating depleted bars. Experimental methods included transplanting stunted "seed" oysters from overcrowded bars to growout areas and planting shell to provide clean substrate for baby oysters (spat) to attach onto and grow.

As an aside, although oyster harvests never returned to 19th century levels, they did stabilize for a period of about 60 years from the mid-1920's to the mid-1980's, after which diseases decimated the oyster populations. In effect, the efforts initiated by the Conservation Commission and that were expanded and refined through the years by its successor organizations helped to provide sustainable livelihoods for a couple of generations of watermen.

Without knowing the condition of the bars over time, there was no way of evaluating the effectiveness of the management efforts. The Winslow, Oyster Commission, and Yates surveys were essentially one time affairs; they gave a snapshot of the condition of the oyster population at a single point in time. As acknowledged in the Oyster Commissionís 1884 report, to get an idea of trends in the population for management purposes, the oyster bars needed to be looked at more frequently. So it came about that a Maryland-wide dredge survey of the oyster bars was initiated by the Conservation Commission in 1919. In principle, this was the immediate precursor of todayís Fall Survey.

The scientist in charge was a young biologist for the U.S. Bureau of Fisheries named Reginald Truitt. He was a native of Boxiron, Maryland on the shores of Chincoteague Bay, where his family planted oysters. Truitt attended the University of Maryland (where he played lacrosse against the legendary Jim Thorpe) and flew rickety biplanes in World War I before succumbing to the siren call of the oyster. To further his investigations on oysters, in the mid-1920's he established what became the Chesapeake Biological Laboratory (CBL) in Solomons, an institution which he headed for nearly 30 years. Truitt was to become the most respected and influential scientist of his era in the Bay region and a tireless advocate for scientific inquiry into the Chesapeake. As CBL grew, its investigations diversified to encompass a wide range of scientific topics, but Truitt maintained a passion for oysters. His research had a strong practical bent and he constantly urged the application of scientific management to the oyster resource.

The 1919 survey visited most of the Maryland oyster growing waters, including Chincoteague Bay. Towing a dredge from various Oyster Police (as the State Fishery Force was called) boats provided by the Conservation Commission, a number of oyster bar characteristics were looked at, including the abundance of market (harvestable) oysters, the condition and reproductive state of the oysters, the presence of spat, and descriptions of the bottom. In addition, water was sieved through a very fine mesh net to capture the microscopic oyster larvae and diatom abundance was noted. The results were presented in largely descriptive form with little in the way of hard numbers. A number of management recommendations emerged from the findings, the most important of which was to plant shell to revitalize depleted bars. In addition, with modifications the survey served as a template for those that followed.

The next 20 years was a period of increased conservation efforts (not only of oysters but other living resources such as finfish and blue crabs) and innovative methods for increasing oyster production, fueled in part by the synergy of a progressive Conservation Commissioner (Swepson Earle, 1924-35, who had served on the Yates survey), an energetic scientific advisor (Reginald Truitt), and a supportive governor (Albert Ritchie, 1923-35). Although the oyster surveys were sporadic in scope and remained descriptive in nature, they provided valuable information for management actions. After some initial experimental shell plantings, the practice became institutionalized through legislation in 1922, with dedicated funding provided by the state legislature in 1927 through a shell tax and work boat gasoline tax. By the mid-1930's almost one million bushels of shell per year were being planted on oyster bars.

These shell planting efforts were not always successful. Because the program was relatively new, the best locations for spatfall potential took time to work out. This was hampered by the absence of quantitative historical records from the survey work. Another hindrance was the insertion of politics into the process, resulting in planting sites being selected on hearsay which could neither be confirmed or refuted because of the lack of records. Lastly, shell planting was done when watermen were available for labor, often months before the oyster spawning season. Consequently, the planted shells sat on the bottom getting fouled, leaving them in less than optimal condition for attachment of the baby oysters.

As these shortcomings became more apparent, in 1939 a new Conservation Commission began keeping records of the shell planting surveys, with the results recorded as spat per bushel of dredged material. This landmark action, which seems so basic to us now, precipitated a fundamental shift in oyster management in Maryland. It also marks the beginning of an unbroken record of annual oyster surveys extending 63 years to the present-day Fall Survey.

Following up on the improved survey record keeping, an evaluation of shell planting practices by the recently created Board of Natural Resources led to a complete overhaul of the program in 1941. In an effort to optimize shell use, oyster bars were categorized as either: 1. seed production bars in high spat set areas, 2. seed growout bars in areas of good growth but poor spat set, and 3. self-sustaining bars of moderate spat set. The plan was to plant shell for seed production, which would then be moved to growout areas or sold to private growers. Some shell was to be planted to improve the self-sustaining bars when required. In effect, this was the initiation of a large scale aquaculture operation which continues to the present day as the MDNR Oyster Repletion Program. Obviously essential to the success of seed production was to plant shell in high spat setting areas. Spat surveys and quantitative record keeping were paramount in determining these areas and evaluating the plantings.

Through the years the Fall Survey has been refined, expanded, and otherwise modified to reflect changing objectives, although its core purpose to evaluate the seed grounds remains, keeping it intimately linked to the Oyster Repletion Program. The survey variously has been conducted in the fall, winter, and spring before returning to the fall again over the past two decades.

In order to allow more meaningful comparisons of spatfall among years, a spat index was developed in 1974. Fifty-three "Key" bars distributed throughout the Bay and major tributaries and sampled annually were designated to represent the measure for spatset in Maryland. Although spat are counted on all of the Fall Survey bars, only the "Key" bars are used to derive the spat index, which is simply the arithmetic mean of the spat counts on them.

When the oyster parasite diseases MSX and Dermo first appeared in Maryland waters during the 1960's, the Survey was expanded to include the collection of oysters for disease analyses, presently conducted at the Sarbanes Cooperative Oxford Laboratory in Oxford, Maryland. Since 1990, sampling locations have been standardized into 43 "Disease" bars. Most of these are also "Key" spat index bars. With oyster disease ratcheting up in Maryland over the past 15 years, this component of the Fall Survey has been crucial to understanding the impact of the parasites on oyster populations. This is particularly important in light of the numerous oyster restoration efforts now taking place or being planned.

Present-Day Fall Survey

Oyster bars are sampled on the Fall Survey much the same way as in the days of Lt. Winslow, by dragging a dredge along the bottom. The standard oyster dredge consists of a metal rod frame with a chain mesh bag at the end of it. A three feet wide bar equipped with short teeth is attached to the lower leading edge of the frame for digging into the bottom and scooping up the oysters and shell. The main concession to modernity is the use of a hydraulic winder to haul up the dredge, which when full weighs about three hundred pounds, from the bottom. In the old days four-man hand winders were used; backbreaking work that on the more unscrupulously captained dredgeboats was often relegated to shanghaied crew members.

In contrast to the sampling gear, the navigation equipment is state of the art, which translates to accurate positioning and efficient operation. A differential geographic positioning system(dgps) unit is hooked up to a laptop computer displaying a detailed nautical chart with the boatís position superimposed on it. All of the station locations are entered into the computer, so it is an easy matter to steer toward the next bar and take a sample. Before the advent of electronic navigation, positions were fixed using a horizontally-held sextant, a very time consuming process.

A color fishfinder shows a profile of the bottom and the location of shell deposits, allowing the dredge to be dropped precisely onto the oyster bed. As is often the case, however, old habits die hard. Despite the electronic wizardry, the traditionalist of the crew still uses a hollow metal sounding pole to probe the bottom. When the pole resonates with the impact on oyster shell, he loudly proclaims in his Eastern Shore drawl, "Thar they arrr!!". So enthusiastically does he call out, in fact, that one day he startled a romantic couple, who apparently oblivious to the "Miss Kay" and her crew, were strolling hand-in-hand along the shoreline near St. Maryís College. Thinking that he was referring to them, the flustered couple took flight back to campus, much as a brace of quail being flushed out by a bird dog.

After the dredge is hauled back and its contents dumped on a table, a half-bushel sample is taken and transferred to the culling table. Here the oysters are separated from the shell and other material. During this process a rapid-fire patois ensues as the cullers call out their findings to the recorder: "Market, small box recent, market gaper, SPAT". Spat are usually called out the loudest, perhaps because they represent hope for the future, in contrast to the empty rattle of the boxes (dead oysters with the shells still attached but no meat inside). After sorting, the size range and estimated average for each size/age category (spat - under one year old, smalls - older than one year but less than 3 inches, markets - 3 inches or greater) are recorded and a few oysters are opened to examine their condition. In addition, at each station fouling and other associated organisms are noted and temperature and salinity readings are taken. All of this information is duly recorded on standardized sheets that havenít changed in years.

During the course of a six-week odyssey around the Maryland portion of the Chesapeake, including the Potomac River and other major tributaries, nearly 300 bars are examined and close to 400 samples are taken. In addition to natural oyster bars, shell plantings for seed production and seed plantings are checked, as well as special management areas such as sanctuaries, power dredge zones, and experimental sites.

Primarily due to improvements in navigation, the survey has been reduced to about 18 sampling days in October and November, not including travel days and bad weather days. Although the survey has been conducted in all manner of inclement weather, small-craft advisories usually mean a day in port. Even a 48 ft. boat gets to pitching and rolling pretty good in 20 knot winds, and hundreds of pounds of a fully loaded dredge swinging around in rough seas is more hazardous than a hard hat can deal with. During the 2002 survey there seemed to be more than the usual share of rough days - physically demanding trips requiring constant attention to balance, shifting obstacles, and the dredge, trying not to trip when transferring the 50 pound sample to the culling table. Those were the nights one slept the best.

So How Are The Oysters Doing?

There has been one overriding environmental factor affecting the findings of the 2002 Fall Survey: RAINFALL, or lack thereof. The Chesapeake watershed has been in the grip of a drought for four years. Consequently, Susquehanna River flows, the primary source of fresh water into the Maryland portion of the Chesapeake, have been well below the 50 year average. As a result, bay salinities have climbed. For example, in September the salinity at the Bay Bridge averaged 17 parts per thousand (ppt), which is normally found much further down bay. (Coincidentally, the skies finally opened up during the Fall Survey, requiring more than normal use of the foul weather hoods).

Elevated salinities can be both a blessing and a curse for oysters. On the one hand, reproductive effort is often benefited, particularly in marginal salinity areas. This past year, although the spat index was slightly below average, the spatfall was considered respectable or even greatly improved in several areas. Good spat counts, in the hundreds of spat per bushel, were found in Tangier Sound and the St. Maryís River. One seed production area had counts as high as 1500-1800 spat per bushel. Perhaps even more remarkable was the presence of spat in the Head of the Bay above the Bay Bridge, a region which does not usually receive a set because the normal salinity regime is too low. Although many of the counts could be tallied on the fingers of one hand (despite the fact that one of the recorders is missing the tips of a couple of digits), just about every bar examined had spat on it. The Kent Island shore below the Bay Bridge also received a higher than normal spatfall.

Unfortunately, other usually productive regions such as Eastern Bay and the Choptank River and its tributaries had disappointing sets, while the Little Choptank River, which was once a source of seed for planting elsewhere, was almost devoid of spat.

Another benefit to higher salinities is improved growth. Ordinarily, oysters in the low salinity reaches of the tributaries exhibit stunted growth. A good example is the oyster population on Beacon, a bar in the Potomac River above the Rt. 301 bridge. This is the upriver-most bar sampled, with few oysters inhabiting the river further upstream. Because of the depressed salinity regime, oysters there can be six or seven years old and still be sublegals (less than 3 inches in size). In contrast, the rule of thumb for oyster growth in other parts of the Bay is 1 inch per year or three years to attain market size. As a result of higher salinities, this year the market oysters on Beacons averaged an astounding 4 inches, displaying fresh growth along the bill or leading growing edge of the shell.

For areas where the salinity is normally conducive for spatfall and growth, the picture during a drought is possibly more complex. The lack of runoff from rainfall reduces nutrient input into the bay, which might mean suboptimal phytoplankton (single cell plants) concentrations for oysters to feed on. As the theory goes, with less food available during a drought oyster growth and reproduction may be actually impaired. However, this drought induced effect has yet to be confirmed.

A more ominous and well documented down side to the present environmental conditions is that the two oyster parasites which cause MSX and Dermo diseases thrive in higher salinities. That same Beacon Bar was always considered to have a "naive" population of oysters, that is, oysters that had never been exposed to disease, due to the low salinity and isolated location of the bar. Having a source of naive oysters was of great value for experimental purposes. This fall, 43% of the oysters sampled from this bar were infected with the Dermo parasite. The significance of these findings is that there is no refuge from Dermo for oysters in the Potomac River, even on bars in areas normally not conducive to disease and remote from infective sources.

This is just the tip of the iceberg. Every one of the 42 Disease Bars (DB) examined had oyster populations infected with Dermo (the 43rd DB, Cook Point in the Choptank River, had its oyster population so decimated that not enough could be caught for a laboratory sample). The average infection rate or prevalence on these bars was 94%, that is, almost all of the oysters examined tested positive for the disease. The Disease Bar findings, along with the Beacon Bar results, indicate that Dermo is found on nearly every oyster bar (if not all) in the state of Maryland and most of the oysters are infected with the disease, a truly disheartening situation.

The news about MSX is equally grim. This parasite, which requires higher salinities than Dermo and therefore is normally confined to the lower bay, has been found as far upbay as Hackett Point, a bar off the mouth of the Severn River near Annapolis. Nearly 90% of the Disease Bars tested positive for MSX, the highest on record. The portion of the sampled oyster population infected with MSX was 28%.

What all this disease translates into is record high mortality levels. Of all the oysters caught on the Disease Bars, 58% of them were dead. In contrast, before Dermo became established in the mid-1980's, mortality averages ranged between 5% and 10%. The big boost this year from the 35% mortality average of the previous three years was probably due to the spread of MSX, which can be a particularly rapid proliferating and lethal disease once the oyster is infected.

Some areas fared worse than others, especially the higher salinity tribuaries. The St. Maryís River on the western shore had observed mortalities averaging 80%. Even more devastated was the Little Choptank River, a leading producer of oysters in Maryland during the late 1990's, which had an average observed mortality of 93%. The difference between the two tributaries was the good spatfall in the St. Maryís, whereas the Little Choptank has almost nothing to replace the oysters that have died, a truly worst case scenario.

Elevated salinities can also bring an increase in other pests and predators. For instance, during the spring of 2002 spat counts were taken at some experimental locations in Tangier Sound. Surprisingly, at one site 76% of the spat had recently died. A closer inspection of the still attached upper valves (shells) of the dead spat revealed that most of them had a small hole bored through them. They obviously had fallen victim to oyster drills, small snails that are notorious oyster predators. Sure enough, a few individuals of two drill species turned up in every sample, and egg cases abounded. The drills were thriving in the higher salinities of Tangier Sound with the ample supply of food provided by the previous yearís spat set.

With the increase in rainfall and snowfall that the region has experienced this fall and winter, there is hope that the drought is broken and salinities will decline. What is needed for a real impact is a buildup of the snowpack in central New York and Pennsylvania, so that come the spring thaw the freshwater rush will drive down salinities. It must be remembered, however, that too much freshwater (called a freshet) can also kill oysters, with the Head of the Bay and upper bars of the Potomac (including Beacon) particularly at risk. Letís hope thatís not next yearís story.

Hope your eyes havenít glazed over yet. If they havenít, some additional reading is suggested below.

Click here for Commercial Harvest and Historical Information

More historical facts about the oyster industry in Maryland during 20th century

Marylandís Oysters: Research and Management. Victor Kennedy and Linda Breisch. 1981. Maryland Sea Grant. A highly informative though somewhat dated and often opinionated summary of oyster biology and management along with an annotated bibliography.

The Oyster Wars of Chesapeake Bay. John Wennertsen. 1981. Tidewater Publishers. A colorful history of oystering in the old days.

Most of the historical information for this article was gleaned from old government reports, supplemented by the above publications. Many of these reports can be found in university libraries and the Maryland State Archives. They include:

- Ingersoll, E. 1881. The History and Present Condition of the Fishing Industries. The Oyster-Industry. U.S. Census Bureau, 10th Census. Dept. of Interior. Washington, D.C.

-Report of the Oyster Commission of the State of Maryland. 1884.

-Stevenson, C.H. 1894. The oyster industry in Maryland. Bull. U.S. Fish Commission for 1892. pp.205-297.

-Grave, C. 1912. Fourth report of the Shell Fish Commission. Summary of the biological findings of the Yates Survey.

-Maryland Conservation Commission, Conservation Department, Board of Natural Resource. 1916-1969. Annual reports of MDNRís predecessor organizations.

-Meritt, D. 1977. Oyster Spat Set on Natural Cultch in the Maryland Portion of the Chesapeake Bay (1939-1975). Univ. Md. CEES Spec.Rept. No.7.

-Krantz, G.E. 1996. Oyster Recruitment in the Chesapeake Bay, 1939 to 1993. MDNR Fish. Srv. Spec. Publ. Oxford, Md.

           The author has been a Shellfish Biologist with MDNR since 1993. His interest in the sea developed while growing up in New York City, where he was only a subway ride from the shore and got his sea legs on the Staten Island Ferry. He studied shellfish biology at the New Jersey Oyster Research Lab of Rutgers University, and had worked with molluscs on the MDNR Bay Bottom Survey, at the Smithsonian Institution, and at the Chesapeake Biological Laboratory before earning a graduate degree at Yale. He is presently responsible for shellfish monitoring working with oysters, hard clams, and soft clams, and has conducted a general molluscan inventory of the coastal bays. His favorite project was a scallop restoration effort in Chincoteague Bay, primarily because of their lively personality and lovely blue eyes (all 18 pairs).