Editor's note: This is the first of a series of articles on the coasts and estuaries of the Mid Atlantic region of the USA. These articles will appear leading up to the ERF 2005 biennial conference in Norfolk, Virginia.

Human Influences on Chesapeake Bay's Aquatic Resources

Vic Kennedy
ERF 2005 Organizing Committee
kennedy@hpl.umces.edu

Pre-colonial bounty 

American Indians are thought to have arrived in what is now the Chesapeake Bay watershed about 4,000 years ago, after the last glaciation but before the bay had formed. The bay's formation subsequently increased their use of coastal resources. They captured fish with woven nets, fishing poles, wooden harpoons, and arrows attached to a line, as well as in woven pots and large, multi-compartmented traps made from reeds. Their shell middens, such as one 26' thick by the Potomac River, contain soft clams, ribbed mussels, and oysters (the name, Chesepiook, is thought to mean "Great Shellfish Bay" in an Algonquin dialect), as well as remains of fish, blue crabs, and diamondback terrapins. Prehistoric camps on the upstream banks of bay tributaries contain remains of anadromous fish.

It appears that Indians had a modest to negligible influence on the bay's aquatic resources, except perhaps near their encampments. Thus, the first European colonists led by John Smith encountered a bounty of resources, terrestrial and aquatic, in the early 1600s. However, as the numbers of settlers increased, they influenced the movement of materials into the bay and depleted aquatic resources.

Material and land use changes 

In relation to movement of materials, Indians used fire to drive game, cleared land for agriculture, and removed understory for firewood, thus affecting local runoff of sediment and nutrients. As European settlement increased, land clearing accelerated so that soil erosion in the central portion of the bay doubled after about 1760 when intensive agriculture began. Increased deposition of sediment led to infilling of tributaries so that some colonial ports like Port Tobacco are now landlocked. Declines in soil fertility led to use of natural fertilizers such as South American guano imported around 1820, and then to the use of manufactured fertilizers. Today, fertilizers, sewage effluents, and animal manure add thousands of metric tons of nutrients to the ecosystem. Light reduction as a result of these nutrient additions and suspended sediment is thought to be one reason for the decline in bay grasses in the 20th century. Inputs of nitrogen are estimated to have increased about 4 to 8 times and of phosphorous, about 10 to 30 times, since the pre-colonial period. As well as fertilizers, toxins from mining, petroleum refining, agriculture, and manufacturing pollute portions of the bay. In 1975 a notorious example of toxic contamination involved the release of large quantities of Kepone® into the James River at Hopewell, Virginia. Kepone® is a potent pesticide and suspected carcinogen if contaminated fish tissue is ingested in large quantities. As a result, commercial fishing from Richmond to the Hampton Roads Bridge Tunnel near Norfolk was banned until 1989.

Fisheries yields decline 

The bay has also been affected by over-harvesting of its biological resources. During the late 1800s, exploitation of these resources accelerated as human populations grew, distant markets expanded, and capture technologies improved. Initially, the fisheries were modestly important commercially, with most harvests occurring in spring and fall by means of gill nets and haul seines. The pound net, which is somewhat like the Indians' compartmented fish traps except that it is made of netting suspended on poles, was introduced in 1858 and helped make Chesapeake Bay a major center for U.S. fisheries in the late 19th Century. For example, the shad fishery in 1896 yielded about 40 to 50% of the total shad landings in the U.S., making it the most extensive and valuable fishery on the U.S. East Coast. Over 9000 people, and an estimated 4000 boats, 2100 pound nets, 13,000 stake gill nets, 4000 drift nets, and 132 haul seines were involved. These kinds of fishing gear were also used to capture alewife and blueback herring, with about 900 people and about 500 boats involved in 1896 when Maryland harvested 13% and Virginia harvested 9% of the total U.S. catch. Eventually, harvests of anadromous fish declined as a result of the rapid growth in the number and size of fishing nets that caught migrating adults, as well as the presence of dams and other river obstructions that prevented the adults from reaching their spawning grounds. Sawdust from sawmills; chemicals from tanneries, paper mills, and factories; and sediment compromised the spawning habitat of shad and river herring or the water in which the larvae swam.

Oysters 

In addition to fish, oysters also became a heavily exploited resource. Their size and abundances in the colonial period impressed early writers. A Swiss visitor wrote that the oysters were four times larger than English oysters, requiring that they be cut in two to be eaten. Colonists sailing on the bay sometimes ran aground on reef-like oyster beds that broke the bay's surface at low tide. Subsequent oyster harvesting depleted the stock of oysters and broke up the reefs and eliminated them as navigational hazards. Oysters were not just used for food. The shells were burned to provide agricultural lime, were used in road building and as landfill, and were ground up for chicken grit. Thus oysters were increasingly in demand as population growth continued. Westward expansion of the Baltimore and Ohio Railroad and national turnpikes helped increase demand inland, which was met by increased exploitation. By 1868 there were about 80 raw and steam packers and steam canners in Baltimore alone, with similarly intense exploitation occurring in Virginia. The average annual harvest of oysters in the bay between 1834 and 1890 was 7 million bushels. Oyster harvests in Maryland peaked in the 1884?1885 fishing season with a catch of about 15 million bushels; there was a later, smaller peak in Virginia. Thereafter there was a general decline bay-wide to a fairly constant harvest level of 2 to 4 million bushels from about the late 1920s to the 1950s. Since then, the presence in the bay of two virulent oyster diseases has depleted harvests to 50,000 bushels or less.

Impacts on food webs 

Depletion of filter-feeding oyster populations may have affected food webs. The decline in oyster abundance is thought to have resulted in a corresponding decline in the filtration of phytoplankton from the water by oysters and other filter-feeders like hooked mussels that attach to oyster shell, a decrease in the amount of nutrient material packaged in bivalve feces and deposited on the estuarine bottom, and a probable change in the amount and the size spectrum of phytoplankton present, especially in summer. This may have contributed to a shift from food webs dominated by benthic production in clear-water conditions to those dominated by pelagic phytoplankton in more turbid conditions. Such a shift may have resulted in an increased abundance of zooplankton and their predators, including sea nettles, whose numbers may be higher now (evidence is limited) than they were when oysters were abundant.

Crabs, striped bass, and shad 

Populations of other commercial species have also been declining. Blue crab harvests have been declining since 1994. Development of an escalator dredge to harvest soft clams produced an initial large harvest in the 1960s followed by a general decline to about 10% of levels when the fishery was new. Catches of striped bass were low and constant until after World War II when they tripled in quantity before declining rapidly in the late 1970s to the point that a fishing moratorium was imposed in the 1980s. This moratorium allowed the species to recover so that it again supports a fishery. A similar moratorium and habitat-restoration efforts on behalf of American shad have produced spawning fish in mostly increasing numbers every year, although in much smaller numbers than the stream-clogging runs of the last century. Efforts to restore the former three-dimensional structure of oyster reefs have been attempted, although with such limited success because of disease that there is pressure from the industry to introduce an Asian species of oyster.

Multi-species ecosystem-based management 

These declines, and controversy over the status of the menhaden fishery and its influence on non-target species, have stimulated movement towards initiating multi-species ecosystem-based management. Also, various multi-state agreements have been formed to help restore the bay. Although nutrient reduction, habitat restoration, and more sophisticated management will not return Chesapeake Bay to conditions that Europeans found in 1607-1608, if these efforts can mitigate or partially reverse the effects of predicted increases in the human population and increased development in the watershed, they may allow the bay once again to support large areas of bay grasses and a thriving seafood industry.

Further reading:

Curtin, P.D., G.S. Brush and G.W. Fisher. 2001. Discovering the Chesapeake. The History of an Ecosystem. The Johns Hopkins University Press, Baltimore MD. 385 p.

Michener, J.A. 1978. Chesapeake. Random House, New York. 865 p.