This is a huge and complicated issue to address. Prior to urbanization, shallow reefs spread across much of New York Harbor (Waldman 2000), and the Spartina marshes, essential terrapin habitat, of New York Harbor and neighboring Long Island probably supported large terrapin populations. Jamaica Bay was once highly productive in terms of fish and oysters), but although terrapins probably were there in huge numbers, there are apparently no records of terrapins in Jamaica Bay before Stephen Morreale’s surveys in 1991 (Morreale 1992).
Terrapin populations range-wide were decimated in the 1700-1800s when terrapins were hunted and eaten in huge numbers. This intensified through the 1920s when terrapins of the New York/New Jersey area were heavily affected by the trade in terrapin meat, because of proximity of terrapin habitats to major food markets in New York City and Philadelphia, and terrapins’ reputation as high quality meat. Back then, some people reported that terrapins were nearly gone from Long Island.
After the collapse of the soup industry (1920-1930), terrapin populations started recovering in some areas, until large-scale coastal urban development caused massive habitat losses in the 20th century. Subsequent development of New York City led to the loss of most regional Spartina marshes, and like all the others, Jamaica Bay’s Spartina marshes have been hard hit. Terrapins are tightly linked to Spartina, where there is no Spartina, there are no terrapins.
Jamaica Bay has lost a lot of Spartina marsh, and this continues. The NYS DEC says: … between 1857 and 1924, the intertidal [JB] marsh islands area varied in size without trend, with average changes of up to 10 acres per year. During periods of significant storms, there were losses of marsh islands. But during quiescent years, the marsh islands were able to rebuild. …From 1924 to 1974, 780 acres of marsh islands were lost due to direct dredging and filling (which were unregulated activities up to 1974) and 510 acres were lost (approximately 10 acres per year) due to other reasons. …Since 1974, the study shows that the rate of loss of intertidal marsh islands is accelerating. Between 1974 and 1994, 526 acres of marsh islands were lost at an average rate of 26 acres per year. Between 1994 and 1999, 220 acres were lost at an average rate of 44 acres per year. The vegetated intertidal marsh is being converted to nonvegetated underwater lands…Potential contributing factors include sediment budget disruption, sea level rise, dredging, wave energy, erosion, inlet stabilization, mussel dams on the marshes, and eutrophication.(http://www.dec.ny.gov/lands/5489.html). If the marsh loss is not stopped, Jamaica Bay will no longer support terrapins.
Article from Capital New York: