Chesapeake Bay Forage Base Collapse & Interactions of Striped Bass & Atlantic Menhaden
Report prepared by the Chesapeake Bay Ecological Foundation, Inc. at the request of the Secretary of the Maryland Department Of Natural Resources submitted to the Maryland Department Of Natural Resources
The Atlantic coast striped bass fishery re-opened in 1990 following a five year moratorium. New restrictions adopted by the Atlantic States Marine Fisheries Commission (ASMFC) established an annual quota and raised the striped bass minimum size limit in the Chesapeake Bay from 12” (age-2), to 18” (age-4). These measures altered the striped bass population’s size structure and dramatically increased their forage demand in the Bay. Forage size Atlantic menhaden (ages 0-2), an essential part of the striped bass diet, subsequently declined 74% over the past decade and are no longer found throughout the Bay in sufficient numbers or adequate size to supply the forage demand of striped bass. Striped bass consumed larger prey and more menhaden were available as prey in the Bay prior to the menhaden purse seine (reduction) fishery concentrating its efforts in Virginia’s portion of the Bay during the mid-1960s. From 1955 to 1965, the annual menhaden purse seine (reduction) fishery harvest from the Bay averaged 107 million pounds or approximately 11% of the total coastal landings. During the 1990’s, average menhaden purse seine (reduction) fishery landings increased to 379 million pounds or approximately 58% of the total coastal landings. Most of the Bay’s striped bass now suffer from poor nutrition and approximately 50% of the population is infected with a disease called Mycobacteriosis. The ASMFC has allowed age-2 menhaden to be overfished by the purse seine fishery, which annually reduces their numbers to a level inadequate to serve the vital ecological role they once played along the coast and in the Bay.
An outbreak of disease among striped bass has coincided with the decline of their forage base. Striped bass with sores and lesions (Ulcerative Dermatitis) were first documented in 1994 by Dr. Eric May, Maryland Department of Natural Resources (MD-DNR). In 1997, James Price, president, Chesapeake Bay Ecological Foundation, notified the MD-DNR and the U.S Fish & Wildlife Service that 12% of the 190 striped bass examined in a Striped Bass Cooperative Survey had external sores and lesions. Most of the striped bass had no fat in their body cavities and showed signs of poor nutrition. Dr. Steve Jordan, MD-DNR, reported that striped bass collected in the 1998-2002 fall surveys had: “Weight at length, tissue moisture and lipid levels (that) were not significantly different from wild fish starved for two months at Horn Point Laboratory and were characteristic of the values obtained from wild fish in 1990-1991”. Since 1997, striped bass have shown a high prevalence of anomalies (skin abrasions, lesions, or bacterial infections). By 2002, a MD-DNR striped bass pound net tagging survey found that 17% of the striped bass had external anomalies, the highest percentage since the bay-wide survey began in 1997. Anomalies are cause for concern because they indicate nutritional stress and disease. Fishery scientists and pathologists from the University of Maryland and Virginia Institute of Marine Science (VIMS) have warned fishery managers that Mycobacteriosis has infected approximately 50% of the striped bass population, with one strain known to cause death. A University of Maryland study by Dr. Anthony Overton from 1998 to 2001 indicates Mycobacterium infections in striped bass originated in the Bay, affecting the health and survival of both resident and migratory fish. A 2003 report by Victor Crecco, Connecticut Marine Fisheries Division, that analyzed striped bass mortality and tagged-based exploitation rates found a dramatic rise in natural mortality rates after 1997 for 18 inch plus striped bass from the Chesapeake Bay. This could suggest that natural mortality from starvation and disease has reduced the number of older male striped bass in the Bay.
The ASMFC has failed to take action that could prevent growth overfishing by the menhaden purse seine (net that encircles large numbers of fish) fishery. Growth overfishing is defined, according to research funded by the National Oceanographic and Atmospheric Administration (NOAA) as “When fishing pressure on smaller fish is too heavy to allow the fishery to produce its maximum poundage.” Since the mid 1960’s, the menhaden purse seine (reduction) fishery, which processes fish into meal and oil, concentrated its effort in Virginia’s portion of the Bay, harvesting mostly small, immature fish. This intensive fishery is the largest commercial fishing operation on the Atlantic coast. Fishery scientists, fishermen and the environmental community are concerned that menhaden are being overfished causing a depletion of forage size menhaden and damage to the Chesapeake Bay’s ecosystem.
ASMFC’s Interstate Fishery Management Plan (FMP) for Atlantic menhaden fails to comply with national standards specified in the Magnuson Act, e.g. The first standard to “…prevent overfishing while achieving, on a continuing basis, the optimum yield for each fishery.” Optimum yield, according to research funded by NOAA, is defined as “the amount of fish which will provide the greatest overall benefit to the nation”. The Atlantic Menhaden FMP doesn’t limit the number or size of fish that can be caught by the menhaden purse seine fishery. Omega Protein Corporation, based in Houston, Texas, has a monopoly over the menhaden purse seine (reduction) fishery in the Chesapeake Bay, and has been allowed to overfish age-2 menhaden in the Bay and nearby coastal waters. This massive removal of menhaden from the Bay has been equal in biomass to five times Maryland’s annual commercial seafood harvest. During the past decade, 48% of the purse seine (bait) fishery harvest and 87% of the purse seine (reduction) fishery harvest from the Chesapeake Bay by number were forage size menhaden (ages 0-2). Approximately 45% of the estimated total populations of ages 2-4 menhaden, which represent over 99% of the spawning stock biomass, are removed annually by the purse seine fishery. The Bay’s annual menhaden purse seine (reduction) fishery landings have averaged 315 million pounds since 1965. Historically, this huge biomass of menhaden was an integral component of the Bay’s ecology.
The purse seine (reduction) fishery has influenced the age structure of menhaden over the past four decades by harvesting excessive numbers of age-2 forage size menhaden, altering the predator-prey relationship of striped bass and menhaden in the Chesapeake Bay and along the Atlantic coast. A bioenergetics (diet and growth) modeling study by Jennifer Griffin, (2002) examined striped bass data collected by MD-DNR from 1955-1959, before the purse seine (reduction) fishery concentrated their efforts in the Bay. Griffin stated: “Atlantic menhaden was the primary prey of striped bass in the Chesapeake Bay in the early 1950s…predation demand was only slightly below prey supply throughout the modeled year for all ages”. Hartman and Brandt’s (1995) bioenergetics modeling study, conducted from 1990 to 1992, concluded: “Total prey demand by age-3 striped bass exceeded supply by 80%, while demand by age-4 through age-6 striped bass was 101-103% higher than supply”. Overton (2001) suggested prey supply, availability and size were not able to support production of older striped bass in the Bay.
The estimated Atlantic coast population of forage size menhaden (ages 0-2) averaged 795 billion from 1955 to 1959. Bioenergetics modeling using data for the same time period estimated menhaden comprised 77% of the Bay’s ages 3-6 striped bass diet (Griffin 2001). Forage size menhaden declined to an average of 544 billion fish during 1990-1992 and according to Hartman and Brandt’s bioenergetics modeling data, they comprised 65% of the Bay’s ages 3-6 striped bass diet. Forage size menhaden declined to an average of 233 billion fish from 1998 to 2001. Overton’s bioenergetics modeling study reported that menhaden comprised 21% of the Bay’s ages 3-6 striped bass diet during 1998 to 2001. The Atlantic coast population of forage size menhaden (ages 0-2) declined to 158 billion fish in 2000, 80% less than from 1955-1959, according to population estimates by the National Marine Fisheries Service (NMFS).Increased predation and overfishing by the purse seine fishery contributed to the decline of the Atlantic menhaden population in the Bay during the 1990s, causing consumption by older striped bass in the Bay to shift from menhaden to bay anchovy, blue crab and alternative prey in an attempt to survive. Bioenergetics modeling studies completed in 2001 indicate that by the time the Bay’s striped bass reach age-6, they annually consume 38% less forage and weigh approximately 40% less than they did from 1955 to 1959.
The ASMFC continues to focus on increasing the striped bass stock without considering the ecological impact striped bass forage demand has on other species. Atlantic menhaden are no longer available as an abundant source of forage; Maryland and Virginia juvenile indices and pound net catch per effort in the Potomac River and Maryland’s portion of the Bay are at their lowest level on record. Predation rates on blue crab, the most important fishery for the Bay’s watermen, have dramatically increased; Overton’s bioenergetics modeling study reported that blue crab contributed more than 17% to the diet of ages 4-6 striped bass from 1998 to 2001. Blue crab spawning stock abundance also declined over the past decade, according to Virginia and Maryland trawl surveys; estimates for 2000 and 2001 are the lowest on record. Also, Overton reported that age-3 striped bass consumption of bay anchovy increased 500% over the past decade and at the same time bay anchovy declined to the lowest level on record, according to finfish surveys conducted by the MD-DNR and Virginia Institute of Marine Science. Most alarming is that increased predation on bay anchovy has reduced their total biomass and limited the crucial role they play in the Bay’s food web.
Under the Atlantic Coastal Fisheries Cooperative Management Act, Virginia and North Carolina do not comply with the goal and fail to achieve primary objectives of ASMFC’s Atlantic menhaden FMP, to “protect and maintain…the forage base” and “the important ecological role Atlantic menhaden play along the coast”. In 2002 the purse seine (bait) fishery harvest was approximately 65 million pounds; the purse seine (reduction) fishery harvest was 382 million pounds, of which 80% were forage size menhaden (ages 0-2). NMFS landings data verify that age-2 menhaden are being overfished by the Virginia purse seine fishery in the Chesapeake Bay region of the Atlantic coast. According to research funded by NOAA, overfishing is defined as “harvesting at a rate greater than that which will meet the management goal”. During the past decade the purse seine fishery has annually removed approximately 45% of the estimated Atlantic coast population of age-2 menhaden with 65% of the harvest being taken from the Chesapeake Bay region. These findings confirm that the purse seine fishery continues to significantly deplete age-2 menhaden even though recent population estimates are more than 50% below 1955-1959 levels. A bioenergetics modeling study, conducted by Hartman and Brandt from 1990 to 1992, suggests that growth conditions for striped bass are now much less favorable than they once were in the Chesapeake Bay “…management measures that permit increased escapement and presumably increased migration of age-1 and older menhaden to the Chesapeake Bay will benefit the production of striped bass, bluefish and weakfish”. Overton stated: “The consumption of Atlantic menhaden has declined significantly from 1959 to 2001 concurrent with a greater dependence on benthic pathways (bottom dwelling organisms) as an energy source for striped bass. Managers must consider new approaches such as managing the abundance and health of prey for top predators”.
The NMFS and the ASMFC are making a mistake by attempting to maintain a declining purse seine (reduction) fishery that targets forage size menhaden (ages 0-2) while trying to rebuild stocks of predator species that depend on menhaden as an essential portion of their diet. The striped bass recovery is at risk because their forage base has collapsed and most of the striped bass in the Bay suffer from poor nutrition and disease. The ASMFC and NMFS need to implement management measures to maintain the forage base for coastal predator species in order to achieve the ecological objectives and goals of their FMPs. This would help restore the striped bass forage base and the Chesapeake Bay’s ecosystem, since menhaden play a vital role in top-down control consuming zooplankton and phytoplankton, the bay’s primary production.
Written by James E. Price, President