Striped bass suffer as overfishing eats away at their prey, menhaden
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The Atlantic Coast striped bass fishery reopened in 1990 after a five-year moratorium with new restrictions adopted by the Atlantic States Marine Fisheries Commission that established an annual quota and raised the striped bass minimum size limit in the Bay from 12 inches (roughly age-2), to 18 inches (roughly age-4). These measures altered the striped bass population’s size structure and dramatically increased their forage demand in the Bay.
Since then, forage size Atlantic menhaden (ages 0-2), an essential part of the striped bass diet, have declined 74 percent 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 300 percent more menhaden in the Bay before the menhaden purse seine (reduction) fishery began concentrating its efforts in Virginia’s portion of the Bay in the mid-1960s.
From 1955 to 1965, the annual menhaden reduction fishery harvest from the Bay averaged 107 million pounds, or approximately 11 percent of the total coastal landings. During the 1990s, average landings by the menhaden reduction fishery increased to 379 million pounds or approximately 58 percent of the total coastal landings.
The ASMFC is allowing age-2 menhaden to be overfished by the reduction fishery, which annually reduces their numbers to a level inadequate to serve the important 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 of the Maryland Department of Natural Resources.
Since 1997, striped bass have shown a high prevalence of anomalies (skin abrasions, lesions or bacterial infections). Most of the Bay’s striped bass suffer from poor nutrition and approximately half of the population is infected with the disease, Mycobacteriosis.
In 1997, the Chesapeake Bay Ecological Foundation notified the DNR and the U.S Fish & Wildlife Service that 12 percent of the 190 striped bass examined in a striped bass cooperative survey had external sores and lesions. Most of the striped bass also had no fat in their body cavities and showed signs of poor nutrition.
Dr. Steve Jordan of the 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 not characteristic of values obtained from wild fish in 1990-1991.”
By 2002, a DNR striped bass pound net tagging survey found that 17 percent of the striped bass had external anomalies, the highest percentage since the Baywide 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 have warned fishery managers that Mycobacteriosis has infected approximately 50 percent of the striped bass population, one strain of which is known to cause death. A University of Maryland study by Dr. Anthony Overton from 1998 to 2001 indicates that 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, of the Connecticut Marine Fisheries Division, contained an analysis of striped bass mortality and tagged-based exploitation rates and 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 striped bass in the Bay.
The ASMFC has failed to take action that could prevent growth overfishing by the menhaden reduction fishery. Growth overfishing is defined, according to research funded by the National Oceanographic and Atmospheric Administration, as “when fishing pressure on smaller fish is too heavy to allow the fishery to produce its maximum poundage.”
Since the mid-1960s, the menhaden fishery, which processes fish into meal and oil, has concentrated its effort in Virginia’s portion of the Bay. This intensive fishery is the largest commercial fishing operation on the Atlantic Coast. Fishery scientists, fishermen and the environmental community are concerned that Atlantic menhaden are being overfished, causing a depletion of forage size menhaden in the Chesapeake Bay.
ASMFC’s Interstate Fishery Management Plan for Atlantic menhaden fails to comply with national standards specified in the Magnuson Act, the first standard of which is 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.”
Omega Protein Corp., which is based in Houston, TX, and operates the reduction fishery in the Bay from Reedville, VA, has been allowed to overfish age-2 menhaden in the Bay and nearby coastal waters.
During the past decade, 87 percent of the reduction fishery harvest (as well as 48 percent of a separate, and smaller, menhaden bait fishery harvest) that came from the Chesapeake Bay, by numbers, were forage size menhaden (ages 0-2). Approximately 45 percent of the estimated total populations of ages 2-4 menhaden—which represent more than 99 percent of the spawning stock biomass—are removed annually by the purse seine fisheries.
Historically, this huge biomass of menhaden was an important component of the Bay’s ecology. Atlantic menhaden improved water clarity by consuming an enormous amount of nutrients, and provided essential forage for older striped bass, bluefish and weakfish.
This intense fishing pressure has influenced the age structure of menhaden over the past four decades by removing excessive numbers of age-2 forage-size menhaden, thus 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 in 2002 examined striped bass data collected by the DNR from 1955-1959, before the reduction fishery concentrated its 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.” At that time, the estimated Atlantic coast population of forage size menhaden (ages 0-2) averaged 795 billion. Griffin’s modeling using data for the same time period estimated menhaden made up 77 percent of the Bay’s ages 3-6 striped bass diet.
In 1995, Kyle Hartman and Stephen Brandt published the results of a bioenergetics modeling study, conducted from 1990 to 1992, which concluded: “Total prey demand by age-3 striped bass exceeded supply by 80 percent, while demand by age-4 through age-6 striped bass was 101–103 percent higher than supply.”
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 made up 65 percent of the Bay’s ages 3-6 striped bass diet.
Anthony Overton in 2001 suggested that prey supply, availability and size were not able to support the production of older striped bass in the Bay. Forage size menhaden declined to an average of 233 billion fish from 1998 to 2001. Overton’s bioenergetics modeling study reported that menhaden made up 21 percent of the Bay’s ages 3-6 striped bass diet during 1998 to 2001.
Older striped bass consumption shifted from menhaden to bay anchovy, blue crab and alternative prey in an attempt to survive because of the reduced number of forage-size menhaden and overfishing by the reduction fishery which also contributed to the collapse of their forage base.
Bioenergetics modeling studies completed in 2001 indicate that by the time the Bay’s striped bass reach age-6, they annually consume 38 percent less forage and weigh approximately 40 percent less than they did from 1955 to 1959.
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 bait fishery harvest was approximately 65 million pounds; the reduction fishery harvest was 382 million pounds, of which 80 percent were forage size menhaden (ages 0-2).
National Marine Fisheries Service 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 percent of the estimated Atlantic coast population of age-2 menhaden with 65 percent 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 percent below 1955-1959 levels, explaining why older striped bass are unable to meet their forage demand.
The NMFS and ASMFC are making a mistake by attempting to maintain a 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.
ASMFC and the NMFS need to exercise their responsibilities to restore the ecological balance between striped bass and Atlantic menhaden to achieve the ecological objectives and goals of their striped bass and Atlantic menhaden FMPs. This would also allow ASMFC’s Atlantic Menhaden FMP to comply with the most important standard of the Magnuson Act to “…prevent overfishing while achieving, on continuing basis, the optimum yield, which will provide the greatest overall benefit to the nation.”
The purse seine fishery should be directed to target the older age-3 plus menhaden, which would protect the striped bass forage base, help rebuild the menhaden stock and prevent growth overfishing.
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