Bay Journal

Fishery management plans need to include food web in formula

  • By Jim Price on November 01, 2002
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The striped bass fishery in the Chesapeake Bay is facing one of the most challenging ecological problems ever presented to fishery managers and scientists along the Atlantic Coast. The population is suffering from poor nutrition and disease, which may be translating into a higher rate of mortality in young fish and a decrease in the percentage of fish that survive to migrate to the coast, or reach the Bay’s 18-inch minimum size limit.

Evidence also suggests that the Bay’s forage base is depleted, yet fishery managers have made no attempt to reduce the harvest of Atlantic menhaden, historically the striped bass’ most important food.

Meanwhile, the Atlantic States Marine Fisheries Commission wants big striped bass for recreational anglers along the East Coast and has developed a new fishery management plan (FMP) to achieve that goal without considering the health of the Chesapeake ecosystem where most of the young fish are produced. Fishery managers have raised the minimum size limit from 12 to 18 inches over the last 20 years and are considering raising it again, creating an even greater demand for menhaden and other forage species as more striped bass would be in the Chesapeake Bay.

The Maryland Department of Natural Resources Gill Net Survey Index for striped bass spawning stock peaked in 1996 and has since been in a decline. Initiated in 1985, the survey is a fishery-independent index of male and female striped bass abundance ages 2 and older.

Also, the Striped Bass Age-1 Index, which is calculated from the DNR Juvenile Finfish Seining Survey, indicated that since 1994, juvenile striped bass have experienced an increased rate of natural mortality.

The 2000 and 2001 index values were about one-half the series’ average. Most alarming is that the 1996 year class — the largest year class of striped bass in the Bay — did not show up in the gill net survey in numbers sufficient to alter the decline in Maryland’s spawning stock index. A separate Marine Recreational Fishery Statistics Survey conducted by the National Marine Fisheries Service, and based on 15.5 million striped bass caught in Maryland’s tidal waters from 1990 to 2001, shows a 44 percent reduction in catch-per-unit effort the last five years.

The stock decline is likely the result of a combination of factors, including starvation and disease. Mycobacteriosis, a disease found in large numbers of striped bass examined by scientists at the University of Maryland and the Virginia Institute of Marine Science, may be contributing to an increase in the striped bass population’s mortality rate. The scientists’ studies estimate that 50–70 percent of the Bay’s striped bass are infected by Mycobacterium. One strain, M. marinum, has been documented as causing death in infected fish. The University of Maryland has identified a new strain, M. chesapeaki, and VIMS has identified a new strain, M. shottsii. The studies have not determined if these strains are as virulent as M. marinum, but many scientists believe it is likely that many mycobacteria infections progress until death occurs. Some suggest the disease is affecting not only the fish living in the Bay, but also the larger migratory fish.

The health of the Bay’s striped bass population may be closely associated with the abundance of juvenile Atlantic menhaden. The recruitment of menhaden has been poor since 1993 and has contributed to the local depletion within the Bay of this valuable forage fish eaten by many top predators.

The industrial fishery in the Bay has harvested an average 300 million pounds of Atlantic menhaden per year since 1970, and is the largest commercial fishery on the East Coast. The Atlantic menhaden catch in the Bay is equal to five times the combined Maryland commercial seafood harvest of shellfish and finfish.

This intensive fishery has limited the food source for the migratory and resident striped bass populations and has altered the Bay’s ecology in ways that aren’t fully understood. According to a DNR study, approximately 70 percent of the Chesapeake’s striped bass population appears to suffer from poor nutrition, contributing to a general decline in growth rates the last 10 years. Striped bass, ages 3–6, which depend on menhaden at this point in their life cycle, have shown the largest decrease in growth. Poor nutrition stresses the population, making it vulnerable to bacterial infections and disease. The DNR’s 2002 Pound Net Survey found that 17 percent of the striped bass had lesions or sores. Some fishery scientists state that it is unacceptable for more than 1 percent of wild fish to exhibit lesions or sores.

National Marine Fisheries Service landings data clearly show a threefold increase in Atlantic menhaden harvests from the Bay, beginning in 1970. Current juvenile seining survey indices, landing data and population estimates indicate that the menhaden population has reached its lowest level on record. And data from Maryland’s pound net catch-per-unit data and the juvenile finfish survey show a low abundance of Atlantic menhaden in the Bay.

But the ASMFC, which is responsible for developing a fisheries management plan for striped bass and Atlantic menhaden, does not agree that there is a localized depletion of the menhaden in the Bay. It is ready to approve Amendment 6, which will update their Interstate Fisheries Management Plan for Striped Bass, which may underestimate the natural mortality rate for striped bass and could allow for the stock to be overfished.

When state and federal agencies develop FMPs, they don’t consider the ecological impacts their decisions have on the interactions between species. The ASMFC made a fundamental mistake in fisheries management by developing an FMP that is intended to produce maximum yields for the industrial fishery that harvests Atlantic menhaden while at the same time trying to rebuild the stocks of predator species such as striped bass, weakfish and bluefish, which depend on menhaden for the major portion of their diet.

Fisheries management and poor recruitment of forage species have reduced the Bay’s carrying capacity and ability to support the biomass of striped bass, weakfish and bluefish that historically used the Chesapeake Bay. Recruitment failure and the decline in juvenile Atlantic menhaden abundance that began in 1993 caused the Bay’s predator finfish population to consume a larger number of bay anchovy, the Bay’s most numerous forage fish. Since 1994, increased predation and recruitment failure has reduced the bay anchovy population to the lowest level ever recorded by the DNR’s Juvenile Finfish Survey.

The Chesapeake Bay Program has spent 20 years working to improve water quality in the Chesapeake Bay, but has not yet kept its promise to develop a FMP for Atlantic menhaden, although the 1987 Bay Agreement called for initiating such plans for major “commercially, recreationally and ecologically valuable species” by 1990. The ASMFC and the Chesapeake Bay Program need to develop FMPs for forage fish that would result in the restoration of the Bay’s food web.

The ASMFC has been successful in developing an FMP for striped bass that has helped to rebuild the population. But Amendment 6 does not allow the flexibility to lower size limits and change quotas for the Chesapeake Bay when dominant (exceptionally large) year classes occur. Amendment 6 needs to be changed to raise the total mortality rate because natural mortality may have increased because of starvation and disease.

Fishery managers need to make timely decisions before Amendment 6 is approved because the striped bass population is facing a serious health threat that could be devastating to the fishery. The public has been told that the striped bass recovery is an example of good fishery management. But the ASMFC doesn’t consider the ecological effects that their FMPs for striped bass and Atlantic menhaden have on the Chesapeake Bay and the results have been devastating to the ecosystem, creating conditions that threaten the health and restoration of the Chesapeake Bay.

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About Jim Price

Jim Price is president of the Chesapeake Bay Ecological Foundation.

Read more articles by Jim Price

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