Science Serving Maryland's Coasts
Thomas Miller, Ph.D.
Chesapeake Biological Laboratory
Ecosystem Consequences of Single Species MSY Fishing Policies in the Chesapeake Bay
Fishing at maximum sustainable yield (MSY), theoretically, maintains the population at a size that maximizes production by removing only its surplus-production. However, the central assumption in MSY policies that excess production is "surplus" has been challenged. MSY policies do not consider the ecosystem consequences of removing this production. For example "surplus" production may also play a role in enhancing the resilience of individual populations and in supporting the production of predators. Here we determine the ecosystem impacts of fishing individual and small groups of species at their MSY in the Chesapeake Bay. Surplus-production assessment models and stock assessments were used to determine the MSY fishing mortality rate (Fmsy). The consequences of Fmsy policies for blue crab, striped bass, white perch, Atlantic menhaden, and Atlantic croaker were examined using the Ecopath with Ecosim (EwE)-based Chesapeake Bay Fisheries Ecosystem Model (CBFEM) developed by Christensen et al. (2009). We compared abundances of species within the ecosystem under a continuation of current exploitation patterns to abundances under MSY policies for the 5 target species individually and combined. We also examined MSY policies for a broader range of 10 species including bluefish, weakfish, summer flounder, alewife and herring, and oyster. We found that fishing multiple species and fishing menhaden at MSY had widespread impacts on the ecosystem through loss of the top predator striped bass. This suggests that applying MSY fishing policies to an entire ecosystem is an unsustainable level of exploitation, and that forage fish, that are either highly connected or constitute a large proportion of the biomass in the system, serve an important role in the ecosystem as prey to top predators. We conclude that the MSY for forage fish is lower than their individual MSY and that the MSY for the ecosystem is less than the sum of the individual species MSYs
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