Simulated Short-Term Impacts of the Atlantic Menhaden Reduction Fishery on Chesapeake Bay Water Quality

Atlantic menhaden Brevoortia tyrannus support an intense fishery in Chesapeake Bay, an estuary that is impaired by eutrophication and excess phytoplankton biomass. Since Atlantic menhaden are filter-feeding fish that consume plankton, including phytoplankton, fishery removals may negatively affect water quality and may therefore hinder bay restoration efforts. We performed a simulation to estimate the short-term (monthly and annual) water quality impacts caused by the reduction fishery harvesting its current total allowable catch of Atlantic menhaden in Chesapeake Bay (109,020 metric tons/year). A theoretical loss in net nitrogen removal (Nt) due to the fishery was estimated for each month, and the simulation was repeated for several scenarios to account for uncertainties associated with Atlantic menhaden feeding behavior. The largest potential impact of the fishery (i.e., absolute value of Nt) occurred in August for all scenarios, but depending on the value assumed for average feeding rate the fishery was estimated to have either a positive impact or a negative impact on water quality. The sum of Nt across months ranged from -5.78 x 105 to 1.85 x 107 kg of N/year, indicating that the harvested Atlantic menhaden could have contributed up to 0.38% or removed up to 12.19% of the estimated total nitrogen load for Chesapeake Bay. This large range probably captures all possible scenarios of Atlantic menhaden feeding intensity; however, the current understanding of their feeding rates as related to phytoplankton composition in Chesapeake Bay suggests that average feeding rates are relatively low and that the probable impact of the fishery on water quality is negligible.