Questions spawn menhaden research in Bay
Menhaden in the Bay have proved to be a vexing issue for scientists and managers. Stock assessments of the species, which migrates along the Atlantic coast filtering algae from the water, have found the overall population to be healthy, with more than enough spawning-age fish to maintain the stock.
At the same time, the number of small, young fish has declined to near-historic lows in the Chesapeake for the past decade. Commercial fishing does not appear to be the direct cause of the decline of young fish because the industry generally does not target menhaden younger than 2 years old, which are the preferred food for most striped bass in the Bay.
Some, though, believe that fishing may be reducing the overall population of reproductive-age fish, which could be hurting menhaden reproduction in the Bay region. That’s difficult to determine because there is no distinct “Chesapeake” stock of menhaden—the fish spawn in the ocean as a single population, with their larvae distributed along the East Coast.
As a result, scientists say if heavy fishing pressure in the Bay were affecting reproduction, it should be reflected in declines along the entire coast—not just in the Chesapeake. But anecdotal reports suggest the number of young fish has remained steady, or is increasing, in other areas, especially New England.
The Chesapeake is a particular concern, though, because it has long been considered the “breadbasket” of menhaden production for the entire coast. Reduced production in the Bay could eventually harm the coastwide stock.
A particular concern is that the Bay, rather than being a source of menhaden for other areas, is now serving as a drain to the overall population as fish produced elsewhere migrate in and are caught in the fishery or eaten by striped bass.
To start sorting out those issues, the National Oceanic and Atmospheric Administration’s Chesapeake Bay Office has stepped up support for research related to menhaden in recent years, with major new projects to begin that will study key information gaps identified by the Atlantic States Marine Fisheries Commission. Front and center is a planned study of menhaden larvae that swim into the Bay after being spawned in the ocean. The research will help to determine how many larvae survive for about six months to become “recruits” into the menhaden population. Surveys show that menhaden recruitment in the Bay has been at near record lows for nearly a decade.
No one knows why. One theory is that climate changes may reduce the amount of larvae entering the Chesapeake or set up conditions that reduce their odds of survival.
Some have suggested that the Bay’s growing striped bass population is eating a large number of small menhaden before they are counted in recruitment surveys.
Others suggest that environmental or other changes within the Bay are making it more difficult for larvae to survive.
Other research topics include trying to estimate the total abundance of menhaden in the Bay and the rate at which the fish migrate in and out of the Chesapeake during different times of the year. While recruitment has been low, no one knows whether the actual population in the Bay has been reduced, or whether the recruitment decline has been offset by menhaden from other places moving into the Bay.
Also planned is research to determine the total amount of menhaden being removed from the Bay, including those taken and used for bait, and those caught as bycatch by fishermen targeting other species.
Among NOAA’s other recently supported research have been studies that suggest climate patterns are important in determining the levels of recruitment in the Bay. Generally, the climate has been unfavorable for menhaden recruitment for more than a decade. It has also funded fish population surveys and studies of predator-prey relationships among Bay species.
ASMFC is expected to announce a companion research program in May.
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