(Published May 2002)
Oysters and crabs are two marine resources for which Chesapeake Bay is famous. Both organisms have been, and continue to be, economic engines and important parts of our heritage. Aside from “gardening” oysters and contributing financially toward restoring oyster reefs, most citizens are not in a position to help restore our oyster industry. But each and every one of us can help restore blue crab populations in the Bay.
The first step is to recognize that we do have a problem. Crab harvests have declined from between about 80 and 100 million pounds throughout the 1980’s to just less than 50 million pounds last year (2001). Some people claim that harvests have always been cyclic, and that the fishery is not in jeopardy. But breeding stocks have declined and, as any boater knows, the density of crab-pot floats can be quite amazing. Fishing pressure is undeniably intense, and each year seems to result in new and more stringent regulations. If not being over-harvested at present, we are certainly very near that slippery slope. So what can we all do?
Juvenile crabs are always under intense pressure from natural predators such as birds, otters and fish. Underwater grass beds (SAV or submerged aquatic vegetation) once provided one of the most important sanctuaries for juvenile crabs. Unfortunately, beds of SAV now occupy only about one-tenth the area of the Bay bottom than was true in the past. The reason for the decline in the abundance of underwater grasses is that the water has become progressively cloudier over time, reducing the amount of sunlight that can penetrate, and shading out the grass. One of the causes of cloudy water is sediment, which enters the water as the result of runoff from the land and from shoreline erosion. But the most important reason for the cloudy water is the presence of large populations of tiny suspended algae. The tiny algae (phytoplankton) grow rapidly because we continually fertilize them by allowing too much nitrate and phosphate to enter the water. Every septic system adds nitrate and phosphate to the groundwater. Moreover, when we over-fertilize plants, lawns or fields, the excess fertilizer is dissolved by the rain, and infiltrates down to the water table. The nitrate-bearing groundwater then discharges into the nearest waterway.
Waterfront property owners must be especially careful to minimize the addition of nitrate and phosphate to our waterways. A flourishing stand of deep-rooted plants and trees between homes and the water will tap into the nutrient-rich groundwater, using some of the nutrients before the groundwater can discharge into the waterway. Such a “riparian buffer” is far friendlier to our waterways than is a manicured lawn maintained by fertilizer and other chemicals. Each and every one of us (farmers included) can help the Bay’s SAV, and the crab population, by minimizing the load on our septic systems and fertilizing as little as possible, and never tossing any kind of organic material into the water.