Report on a survey of the hydrography of Great South Bay made during the summer of 1950 for the Town of Islip, N.Y.

Abstract

Between July 25 and August 7, 1950 the Woods Hole Oceanographic Institution conducted a survey of Great South Bay. The purpose of this study was to attempt to determine the cause of the almost complete cessation of the once prosperous oyster industry. Statistics show that the seed oyster production of the bay declined steadily for ten years prior to 1935 and has subsequently been negligible. The yield of market oysters fell from a maximum of 350,000 bushels in 1929 to 60,000 in 1944 and is now non-existent. Systematic records kept by the oyster companies, notably Bluepoints and Van der Borgh and Sons, provide strong evidence that the failure of oysters to fatten and grow properly is associated with the periodic occurrence in the bay of luxuriant "blooms" of microscopic plants which they have named "small forms" because of their minute size and difficulty of identification. This view is supported by experiments conducted by V. L. Loosanoff and J. B. Engle of the U. S. Fish and Wildlife Service who report that oysters stop feeding in the presence of heavy concentrations of algae. The problem which the investigators were asked to examine was whether evidence could be found that the circulation of water in Great South Bay has altered in such a way as to account for the failure of the oyster industry or whether abnormal chemical conditions arising from pollution or otherwise might provide an alternate or supplementary explanation of the difficulty. The frequent changes in the inlets cutting the beach and particularly the apparent restriction of Fire Island Inlet and the new opening of Moriches Inlet in 1931 suggest that changes in the circulation of water have taken place and have led to various proposals for modifying or supplementing these openings. On the other hand, the duck farms along the tributaries of Bellport and Moriches Bays have increased production substantially during the past twenty years and it has been suspected that pollution resulting from these farms may have provided conditions favorable to the growth of the small form and have thus been responsible for the failure of plantings of market oysters. An examination of records kept by the Coast and Geodetic Survey indicate that the tidal circulation of the bay has been reduced over the years. The change occurred prior to 1930 and thus preceded the decline in oyster production. The results of a survey of the salinity and tidal movement made in 1907-08 for the New York City Water Supply Board, when compared with information obtained last summer, indicate that the change in conditions has been small except in the eastern extremity of the bay. There a most important alteration has taken place. Whereas in 1908 Bellport Bay was relatively fresh, having only 1/3 the salinity of sea water, it now contains about twice as much salt as formerly. This change undoubtedly results from the opening of Moriches Inlet which permits salt water to flow with the rising tide into Bellport Bay from Moriches Bay and Inlet. The opinion is widely held that relatively brackish water is favorable to the production of seed oysters. It is believed, consequently, that the opening of Moriches Inlet may be responsible tor the failure of the seed oyster industry which was formerly centered in Bellport Bay. However, in the greater part of Great South Bay, where formerly market oysters were planted, the change in circulation does not appear to be sufficient to account for the failure of oysters to fatten properly. The results of the chemical studies indicate that the bay water is unusually rich in the products of decomposing organic matter. These materials appear to originate in the tributaries of Moriches Bay and the Carmans River from where they are carried westward across Great South Bay and provide nutriment for the growth of the great population of microscopic plants. These observations point strongly to the duck farms as the source of abnormal conditions in the bay. The survey has thus revealed two conditions which in combination appear to be responsible for the unfavorable conditions affecting the oyster industry. One is the pollution of the bay by wastes from the duck farms which provides nourishment for the great population of microscopic plants, which appear each summer; the other is the local change in circulation occasioned by the opening of Moriches Inlet which has increased the salinity of Bellport Bay. In considering remedial measures both these conditions should be taken into account. Since the state of pollution depends on the balance between the rate at which pollutants are added and their removal by the circulation of water, the conditions might be improved by enlarging the inlets or cutting new openings designed to increase the flushing of the bay. To be effective these engineering works would be prohibitively expensive and their effectiveness and permanence would be uncertain. In addition, they would not restore the low salinity of the eastern end of Great South Bay which appears to favor seed oyster production. A second alternative is to reduce the pollution at its source by preventing the wastes from the duck farms from reaching the water. The manure might become a valuable by-product of the farms if procedures were developed for using it for fertilizer. Even it such procedures did not yield a profit, they might at least pay the costs of preventing pollution. While this expedient might be expected to improve the conditions in the bay as a whole and thus might lead to a restoration of market oyster production, it would not restore the low salinity of Bellport Bay, on which the seed oyster production supposedly depended, unless Moriches Inlet were to be permanently closed. It this were done, the conditions in Great South Bay might be expected to be restored to very nearly those obtaining prior to 1930. A third alternative, which has much to commend it, is to prevent the exchange of water between Great South Bay and Moriches Bay. If this were accomplished the wastes from most of the duck farms would be prevented from reaching Great south Bay. In addition, the waters of Bellport Bay might be expected to become much fresher and the conditions would favor the restoration of seed oyster production in that area. Inasmuch as it is now proposed to bridge the narrows at Smith Point to provide a roadway to Great South Beach, it is suggested that at reasonable additional expense the opening might be filled completely except for a lock for the passage of boats along the intercoastal waterway. Such construction would eliminate, or place under control, the movement of water between the bays and should lead toward a restoration of the conditions required for the production of both market and seed oysters. While this method of improving the conditions, appears to be the most practical one, it should be realized that it would require either the maintenance of Moriches Inlet as an effective opening or the correction of the pollution of Moriches Bay, since otherwise the isolation of Moriches Bay from the ocean would lead to intolerable conditions.