Menhaden population being harvested before it can replenish itself
The Chesapeake Bay Ecological Foundation has comprehensively reviewed menhaden management since the 1950s and found two periods (1960s and 2000s) when landings of older menhaden age-5+ were at record low levels and the stock demonstrated signs of collapse because of recruitment overfishing (When fishing pressure is too heavy to allow a fish population to replace itself).
Atlantic menhaden are the primary prey of East Coast striped bass. Menhaden spawn as they migrate along the Atlantic Coast, and their offspring move into coastal waters, including the Chesapeake Bay where they “recruit” into the population. The menhaden population was ecologically healthy in the 1950s when it was capable of meeting the prey demand of Chesapeake Bay striped bass and supporting a fishery. Catch records from the 1950s show that age-8 fish were fairly common and age-10 fish were also present in the spawning stock. Older menhaden, age-5+, are the most important component of the spawning stock because they produce up to 10 times more eggs than first-spawning age-3 females.
Observations of menhaden older than age-6 since 1965 have been rare. Since 2000, annual landings of age-5+ menhaden have averaged about 1 million fish compared with the annual average of 63 million fish from 1955 to 1963.
Egg production may now be too low to sustain the population. Since the early 1990s, menhaden recruitment has remained at historic lows in Maryland, Virginia and North Carolina, approximately 85 percent of the nursery area. Today, the remaining spawning stock is composed mostly of age-3 fish, which are relentlessly fished in the mid-Atlantic region while at the same time striped bass have recovered to record high levels. As a result, menhaden reduction landings (fish caught for industrial use) reached historic lows.
This has happened because the Atlantic States Marine Fisheries Commission “manages” menhaden in state-controlled waters without size or total catch limits and the National Marine Fisheries Service “regulates” menhaden in federal waters (more than 3 miles offshore) with no harvest restrictions. This lack of management persists because ASMFC failed to establish a “total allowable catch” after the adoption of its new Menhaden Management Plan in 2001. Management measures should have included restoring older age-5+ menhaden to the spawning stock and adopting adequate harvest restrictions to address ecological goals
The oldest fish in the population were decimated on their summer feeding grounds in the Gulf of Maine from 1988 to 1993, leading to the northern fishery’s collapse. In 1988, a Maine company contracted with the Soviet Union to supply menhaden to Russian factory ships. In 1991 alone, 60 million menhaden caught in the Gulf of Maine were processed on the 504-foot Russian factory ship M/V RIGA.
The demise of the population was reflected in menhaden bait landings, which declined 98 percent in the New England region during the early 1990s. An index to estimate egg production was developed by NMFS in the 1980s which indicated that older menhaden from the New England region had the potential to contribute 39 percent of the menhaden egg production. The decimation of the menhaden spawning stock in the Gulf of Maine severely reduced egg production, although recent signs of improved recruitment have been noted in some minor nursery areas north of the Chesapeake Bay.
The broad geographic decline in menhaden landings since then illustrates the magnitude of overfishing that occurred on these older fish. Modeling studies indicate that low menhaden recruitment in the Chesapeake Bay may be caused by inadequate numbers of older fish that historically spawned in the northern region of the Mid-Atlantic Bight.
Older menhaden that spawn north of the Chesapeake Bay are likely to supply most of the Bay’s larvae according to findings of the South Atlantic Bight Recruitment Experiment sponsored by the National Oceanic and Atmospheric Administration’s Coastal Ocean Program. This report states: “The size distribution of the adult population may influence the supply of larvae to particular estuaries along the coast…the magnitude of spawning…may be directly related to the escapement of older/larger fish from the fishery. If this sector of the population is removed by the fishery, then spawning at the extreme north may suffer. This will be seen to be…of greatest significance to the recruitment to the Chesapeake and Delaware Bays.”
Meanwhile, menhaden in the Bay have been under increased pressure from the bait and reduction fisheries, as well as predation by a growing striped bass population.
The Bay is the harvest center for both the bait and reduction industry fisheries and is also the most important nursery area for menhaden that spawn during their spring and fall migration along the Atlantic coast. The bait fishery targets older menhaden than the reduction industry, and has become increasingly important, growing to 20 percent of the total harvest by weight and accounting for about 35 percent of the older age 4+ menhaden landed. Virginia landings now account for more than 50 percent of the total menhaden bait harvest after the collapse of the New England menhaden bait fishery. New Jersey’s menhaden bait landings have declined 50 percent since the mid-1990s.
Since the 1950s, the proportion of total Atlantic Coast menhaden reduction landings from the Chesapeake Bay has increased from 20 percent to 60 percent. Despite that concentration of effort, total reduction landings have declined from an average of 290,000 metric tons (mt) (1985–2000) to 165,470 mt (2002–2005).
The reduction fishery largely depends on age-2 menhaden, but landings of that age class have declined 73 percent from the 1990–1993 average of 1.1 billion fish. Still, in 2005, approximately 72 percent of the reduction landings by number were sub-adult menhaden (ages 0-2). The massive removal of menhaden from the Chesapeake Bay, mostly age-2 fish, raises concern that excessive numbers are being caught before they reach spawning age.
By 2005, reduction landings fell to 146,860 mt, the lowest harvest since the NMFS began keeping records in 1940. This seems to have fulfilled a concern raised in a 1991 NMFS publication, Marine Fisheries Review titled: “Assessment and Management of Atlantic and Gulf Menhaden Stocks.” The summary cautioned: “The expansion of fishing on the spawning stock in New England waters concurrently with increasing fishing pressure on pre-spawning menhaden off Virginia and North Carolina in the fall prompts concern for maintenance of the Atlantic menhaden resource.” Even more alarming, from 1993–2005, the average percentage of age 3+ menhaden—spawning age fish—in the landings increased almost threefold compared with the previous 30-year average.
In reviewing Menhaden Stock Assessments and Peer Review Process reports, it’s apparent that ASMFC relies too heavily on single species modeling and has failed to manage the fishery, even though comprehensive scientific data and analysis indicate that menhaden have been overfished and a healthy spawning stock biomass does not exist. Renowned fishery scientist, John Boreman, as quoted in “Striper Wars,” (2005), “The biggest danger for (fish) population modelers is when you start to believe your own models, and not take them for what they really represent, which is just…your hypothesis about what’s happening out there…But you can get so wrapped up in the model…you start to believe it’s truth, no matter what, instead of…questioning whether the data and assumptions hold up.”
Being harvest-data dependent, the model now relies solely on reduction landings from the Mid-Atlantic Bight, and has not been sensitive to severe stock contractions documented in bait landings submitted by individual states north and south of the Chesapeake Bay.
Since the early 1990s, schools of adult menhaden have been scarce in the New England region, age-5+ fish have become a minor component of the spawning stock, and landings have fallen to the lowest level on record. Nonetheless, because of its dependence on models, ASMFC continues to state: “Menhaden are not overfished and overfishing is not occurring on a coastwide basis.”
A new model developed by the NMFS may not help. It uses assumed, age-specific fixed natural mortality rates for estimating annual menhaden spawning stock biomass, which has not been adjusted for changes in natural mortality over time.
Striped bass populations have grown, and diet studies since 2003 show older striped bass prefer larger, age 1+ menhaden. ASMFC has overlooked previous studies indicating the importance of age-1+ menhaden to the striped bass diet and has failed to incorporate recent diet data into its model.
When managing a forage species, caution is needed because the model will significantly overestimate spawning stock biomass if the natural mortality rates (predation) used are too low. Ironically, the NMFS’ new models continues to estimate menhaden spawning stock biomass levels that are supposed to guarantee good recruitment, even though the data underlying the ASMFC assessment indicates a healthy spawning stock does not exist and menhaden recruitment has continued to remain low for more than a decade.
Now the menhaden population appears unsustainable because of the reduced number of older fish in the spawning stock, the disproportionately high percentage of spawning stock being harvested and the protracted low levels of recruitment.
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