Northeast US Continental Shelf LME

The Northeast US Continental Shelf Large Marine Ecosystem (LME) is characterized by its temperate climate. It extends from the Gulf of Maine to Cape Hatteras along the Atlantic Ocean and is a very productive LME. Intensive fishing is the primary driving force of changes in fisheries biomass yields, with climate as the secondary driving force. Efforts to examine changing ecosystem states and the relative health of this LME are underway in four major sub areas:

• the Gulf of Maine
• Georges Bank
• Southern New England, and
• the estuarine-dominated waters of the Mid-Atlantic Bight.

This LME is structurally very complex, with marked temperature and climate changes, winds, river runoff, estuarine exchanges, tides, and circulation regimes.

The Gulf Stream and its complex circulation with meanders and rings greatly influence the productivity of this continental shelf LME. The gyre systems of the Gulf of Maine and Georges Bank, and the nutrient enrichment of estuaries in the southern half of the LME contribute to the maintenance of relatively high levels of phytoplankton and zooplankton prey for planktivores including fish larvae, menhaden, herring, mackerel, sand lance, butterfish, and marine birds and mammals. According to SeaWiFS global primary productivity estimates, the Northeast U.S. Continental Shelf LME is considered a Category I (>300 gC/m2-yr), highly productive, ecosystem. Since 1977, the NOAA Northeast Fisheries Science Center has monitored this LME for estimates of primary productivity and chlorophyll-a. Productivity varies in the 4 major sub-areas, and also from season to season.
Fisheries scientists retrieve plankton samples in a bongo net. Photo: Jerry Prezioso/NOAA Fisheries

Catch composition of this LME is quite diverse. Intense foreign fishing in the late 1960s and early 1970s led to the precipitous decline in fish stock biomass. Significant flips occurred among dominant species with dogfish and skates increasing in abundance in the 1970s, as groundfish and flounders declined. A decrease of dogfish and skates has been observed since 1990, while an increase in crustacean catches has been noted in recent years. Rebuilding of fish stocks through the application of adaptive management strategies is having great success. The recovery trend of George's Bank yellowtail and haddock observed in the late 1990s is linked to reductions in the exploitation rate. The New England Fishery Management Council (NEFMC) imposed strict restrictions on the fishing of groundfish, and there are efforts now to reduce the currently high fishing mortality on lobsters. The closure of half of the U.S. portion of Georges Bank to scallop harvesting to protect groundfish stocks has contributed to an increase in sea scallop stock biomass Although there is not yet a full understanding of fish and fisheries within the context of ecosystem structure and function, advances have been made towards an ecosystem-based strategy for recovering and sustaining lost fish biomass in this LME.

This LME is under considerable stress from growing near-coastal eutrophication resulting from high levels of phosphate and nitrate discharges into drainage basins, which lead to nearshore plankton blooms. For this LME as a whole, water clarity is good, levels of dissolved oxygen and the condition of coastal wetlands are fair. The levels of eutrophication and sedimentation and the condition of benthos and fish tissue should be improved. Benthic community degradation, fish tissue contamination and eutrophication are increasing. Coastal contamination is especially high along the urbanized and densely populated areas and in poorly flushed waters. Flux levels of zinc, cadmium, copper, lead and nickel are highest in the southern New England region, reflecting the level of urbanization and industrialization. Heavy metal concentrations in demersal fish, crustaceans and bivalve mollusks continue to be monitored as biological indicators.

The population of the coastal counties of the Northeast coast increased over 50% between 1970 and 2000. Major river systems contribute nitrates to estuaries and coastal systems from agricultural practices, atmospheric deposition and sewage. Pollution has reduced the utilization by humans of several coastal resources. Improvements have been made in sewage treatment facilities and the treatment of storm water. Overfishing continues to be a problem although the management councils with input from NOAA are adapting ecosystem management approaches that have initiated recovery of some of the major commercial fish stocks, including yellowtail flounder, haddock and scallops. Regulatory measures are aimed at a managed recovery of depleted fish stocks through reductions in sea days, increased minimum mesh sizes, expanded closed areas, and trip limits for depleted cod and haddock stocks. The New England Fishery Management Council's multispecies fishery management plans aim to eliminate the overfished condition of cod, yellowtail flounder and haddock. Other coordinated programs with participation from states, academic institutions, the private sector, and the federal government are underway to improve monitoring and management strategies and actions aimed at mitigating the detrimental effects of habitat loss, coastal pollution, and eutrophication within this LME.