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Depletion of Food Supply Disrupts Chesapeake Bay Ecosystem

The Chesapeake Bay ecosystem has been disrupted by declining numbers of Atlantic menhaden, bay anchovy and blue crab, important components of the food web. Menhaden and bay anchovy are a vital source of food for fish and fish-eating birds. When abundant, menhaden are important filter feeders that consume large amounts of plankton and organic matter, helping maintain water clarity and quality in the Bay. Low numbers of menhaden and bay anchovy have resulted in a dramatic decline in gulls and loons, along with fewer ospreys in the higher salinity portions of the Bay. In 1984 striped bass were declared a “threatened species” in Maryland tidal waters because the overfished population was at an extremely low level. Maryland’s striped bass fishery was closed in 1985. In 1990 the Atlantic States Marine Fisheries Commission (ASMFC) allowed the fishery to reopen coast-wide. In Maryland’s portion of the Chesapeake Bay (upper Bay) the historical 12″ minimum size was raised to 18″ and the allowable harvest was substantially reduced. This resulted in high striped bass numbers and a dramatic increase in consumption of menhaden, bay anchovy and blue crab. During the early 1990’s older adult menhaden were severely overfished off New England concurrent with intensive fishing on menhaden in Virginia’s portion of the Chesapeake Bay (lower Bay) and off the coast of Virginia and North Carolina. Increased predation by large migratory striped bass and over-harvest of adult menhaden was followed by the ecological depletion (insufficient numbers to meet nutritional needs of dependant predators) of menhaden and the initiation of health problems in Chesapeake Bay striped bass. In 2006 ASMFC responded to concern about menhaden depletion by establishing an annual “harvest cap” on the lower Bay menhaden purse seine reduction fishery (fish harvested for industrial purposes) and initiated a multi-million dollar research program to assess whether menhaden are “locally depleted” in the Chesapeake Bay. (Menhaden reduction landings from the lower Chesapeake Bay during 2006 and 2007 were approximately 50% below the previous 10 year average). In 2007 Maryland Congressman Wayne Gilchrest introduced HR 3841 which could close the Atlantic menhaden purse seine reduction fishery in state and federal waters.

The Chesapeake Bay Ecological Foundation (CBEF) has conducted cooperative striped bass studies with the Maryland Department of Natural Resources (MD-DNR) since the early 1980s. In 2004, CBEF initiated a Predator/Prey Monitoring Program (PPMP) to study aspects of striped bass life history and identify the type of prey and ages of menhaden they consume in mid-Atlantic coastal waters and in the Chesapeake Bay. Over 4,000 striped bass have been examined and analyses of PPMP and MD-DNR data show that following the ecological depletion juvenile menhaden in the upper Bay, striped bass consumed increased numbers of bay anchovy and blue crab. The average weight of striped bass 18″ in length (90% males) caught in the Choptank River during the fall is now less than 70% of their historical weight. The weight of 14″ to 18″ striped bass caught in the Choptank River has increased and decreased with high and low reproduction levels of juvenile menhaden, demonstrating that resident striped bass in this size range are unable to maintain their weight when juvenile menhaden are ecologically depleted. (PPMP studies of striped bass over 18″ caught in the upper Chesapeake Bay determine that feeding activity was high from late fall through spring when menhaden constituted over 80% of their diet by weight, and low during the summer and early fall when their diet consists primarily of bottom dwelling prey, including blue crab). Contrary to published scientific studies, this feeding pattern results in large striped bass over 18″ gaining weight over the colder months and losing weight during the warmer months. Intensive feeding during winter provides essential fat for egg development and spawning success. Large striped bass migrate from New England to their historical winter feeding grounds off Virginia and North Carolina during the fall and feed heavily on young menhaden and bay anchovy since older adult menhaden are ecologically depleted in coastal waters. Now, large numbers of these migratory female striped bass over winter in the upper Bay and compete for food with resident male striped bass. This unprecedented competition for menhaden, blue crab, and white perch further disrupts the Chesapeake Bay ecosystem. State and regional management agencies, including ASMFC, should give first priority to the revision of existing fishery management plans to include ecosystem-based approaches adopted by the Chesapeake Bay Program.

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