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Reviewing 1998 - Year of the Menhaden
In 1998 the plight of the pint-sized, filter-feeding Atlantic menhaden, whose condition says much about the broader health of the mid-Atlantic's coastal ecosystem, took center stage. Initially at issue was recruitment—an 8 year trend of too few menhaden surviving their first year—as well as allocating the rights to catch a disproportionately mature population. Early on, there was finger pointing. Recreational fishermen, for whom menhaden are important food-chain links, blamed commercial fishermen for over-harvesting. Commercial fishermen attributed the shortfall to a record sized striped bass population moving through the ecosystem and preying upon menhaden. Both arguments are probably correct: the geographic concentration of menhaden fishing is in the Chesapeake Bay, where blue crab populations and other alternate forage for striped bass are dwindling. But the recruitment mystery stands unsolved and more significant than the longstanding debate over who or which species gets to kill how many fish.
At several scientific meetings there was general agreement that environmental factors in the Chesapeake and North Carolina estuaries and associated rivers, the heart of the menhaden recruitment zone, are key to recruitment attrition. Salinity conditions in the Chesapeake, resulting more from rainfall and runoff patterns than from the general decline of the bay's marine ecology, have favored the comb jellyfish (sea-nettle). The comb preys on small animals called mesozooplankton, which juvenile menhaden also require before they metamorphose and begin feeding on algae as adults. Mesozooplankton populations have declined up to 90% at the mouth of the Bay. The production and distribution of algae, which are limited by the lack of light as well as by the availability of nutrients, may also play a part. Several years of heavy rainfall, resulting in murkier waters, may have altered algae production and distribution, affecting zooplankton populations.
In North Carolina an EPA study found widespread toxic sediments throughout estuaries that are vital for menhaden recruitment. Much of the spawning population gathers each fall off North Carolina's outer banks. During the winter larvae are transported by the tides into estuaries where as juveniles they spend much of their first year. The EPA study found geographical connections between long-lasting toxics that do not break down in the environment, and the absence of benthic invertebrates which form the base of food chains. Toxics were particularly concentrated in primary nursery areas for many fish species (see October 1998 Atlantic CoastWatch). Scientists are beginning to study the degree to which toxics may be affecting fish immune systems and recruitment.
1998 also highlighted menhaden's unique capacity to remove excess nutrients from the water column. Much has been done, with federal funds available for stream buffering and other such efforts, to prevent nutrient rich runoff. But it is far more difficult to rebuild the ability of marine ecosystems to absorb nutrients. Menhaden serve as roving filters, converting algae into energy and thus reducing nutrient loads. Able to process up to four gallons of water per minute, they gather where nutrients in the form of algae are concentrated. Marine biologist Sara Gottlieb, while completing her M.S. degree at the University of Maryland, estimated that for Chesapeake Bay, this ecological function is worth up to $90 million per annum counting only nitrogen and not the other nutrient, phosphorous, that the algae also contain. The commercial value of the fishery ranges between $20-128 million.
In 1998 the stock assessment and policy processes governing the menhaden fishery also came under review. An external review panel mandated by the Atlantic States Marine Fisheries Commission recommended sweeping changes including dismantling the Atlantic Menhaden Advisory Committee and increasing participation through smaller more specific scientific committees, including one on ecological functions. Other recommendations included linking yields to recruitment, and requiring the fishery to take into account the menhaden's life cycle and distribution. Should the concern and findings of 1998 become policy in 1999, it may well be that this largely under-recognized and heavily utilized little fish, Brevoortia tyrranus, will begin its recovery.
Gottlieb's paper at URL: cbl.umces.edu/~gottlieb/thesis/, or visit www.chesbay.org, www.cbf.org or www.nfi.org/media/menI0299.htm |
