6 The U.S. Northeast shelf large marine ecosystem:Zooplankton trends in fish biomass recovery

Abstract

As the application of ecosystem-based management of marine fish and fisheries evolves, it will be necessary to extend the scope of stock assessment methodologies to include indicators of trends in lower level food chain components of ecosystems. Zooplankton as a ubiquitous food chain component can be used as an indicator of changing trends in ecosystem states pertinent to ecosystem effects on fish management actions. Spatial and temporal biomass and species diversity of zooplankton have been examined in a continental shelf ecosystem for indications of variability in abundance levels associated with effort reduction management actions for the recovery and sustainable maintenance of depleted bottom fish stocks. Analyses were conducted on 19,000 zooplankton samples collected seasonally over two decades from the U.S. Northeast Shelf ecosystem (1977 to 1999). Fish stock results were obtained from the Northeast Fisheries Science Center's bottom trawl survey indices of spawning biomass of selected demersal (cod, haddock, yellowtail flounder) and pelagic (herring and mackerel) fish species. The emerging pattern of the zooplankton component of the ecosystem showed biomass values close to or above the 22-year median from the late 1980s through the 1990s, during the recovery of herring and mackerel in the mid-1980s, and the initiation of recovery of demersal stocks as indicated by strong year-classes of haddock and yellowtail flounder in the late 1990s following reductions in fishing effort. The zooplankton component of the ecosystem has not undergone any significant decline during the rebuilding of the fish stocks and is being used as an indicator of stability in the lower trophic levels of the NE Shelf ecosystem food web during the fish-stock recovery period.