Is the Mean Trophic Level Useful for Fisheries Management in the Northeast US?

The mean trophic level (MTL) has been suggested as an indicator for ecosystem overfishing. Using simulation modeling and empirical analysis of survey and landings data, we discuss the utility of MTL as an indicator for informing fisheries management responses in the Northeast US. Empirical approaches identified weak relationships between MTL and both fishing and environmental drivers, and multispecies modeling revealed that thresholds in the response of MTL to fishery removals were variable and dependent on the fishing pattern among species. However, ceilings on total system removals set using thresholds in MTL were able to improve management performance compared to ceilings set using other ecosystem indicators or when no ceilings were in place. Optimal values for reference points for MTL depended on whether management objectives had yield or conservation focus, though MTL of survey biomass was more effective at achieving objectives than MTL of the catch. Although we acknowledge that further testing is warranted, we conclude that MTL can be considered useful when viewed in concert with other ecosystem indicators and appropriate attention is paid to the effects of fishing history among species.