Tim Essington

Assistant Professor, Aquatic & Fishery Sciences University of Washington

Fishing Through Marine Food Webs and the Need for Multi-Species Fisheries Management

Abstract

A recurring pattern of declining mean trophic level of fisheries landings, termed fishing down the food web, is thought to be indicative of the serial replacement of high trophic level fisheries with less valuable, low trophic level fisheries as the former become depleted to economic extinction. An alternative to this view, that declining mean trophic levels indicate the serial addition of low trophic level fisheries ("fishing through the food web"), may be equally severe as it ultimately leads to conflicting demands for ecosystem services. An analysis of fishery landings throughout the world indicates that the latter mode is far more common, accounting for trends in landings in 21 of the 30 ecosystems in which the mean trophic level of fish landings decline over time. These findings imply that we are imposing multiple and perhaps conflicting demands on our marine ecosystems. I also show that this behavior is expected from any fishing fleet acting to maximize its short-term profits, and that some regulatory structures can actually promote rather than retard this behavior. Highly precise predictions about the nature of species interactions, which are virtually impossible to obtain for complex marine food webs, are not needed to improve decision making. Lastly, I use case studies to demonstrate how foresighted management can avoid the ecological and economic collapses that can accompany unchecked growth of multiple, competing demands for ecosystem services.

Bio

Tim Essington is an Assistant Professor at the School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA. Tim was originally trained as a freshwater ecologist, but quickly became interested in the ecology of marine food webs and the role of human exploitation therein. Working out of the NOAA- Fisheries Honolulu laboratory, he first began exploring relationships between fishing and marine food web structure by embarking on a project to model the response of pelagic systems to longline and purse seine fisheries. Subsequent research projects took him to Stockholm, where he explored how the collapse of cod in the Baltic Sea led to a surge in clupeid stock productivity, and then to New York where he led a research program that identified potential indirect effects of squid fisheries in the U.S. Mid-Atlantic ecosystem that might be caused by alterations in food web structure. Tim now works in ecosystems around the world developing tools to enable more effective management of multi-species fisheries.

Readings

Essington, T.E., Beaudreau, A.H. and Wiedenmann, J. 2006. Fishing through marine food webs. Proc. Nat. Ac. Sci. 103: 3171-3175.

Pauly, D., Christensen, V, Dalsgaard, J., Frose, R. and Torres, F. 1998. Fishing down marine food webs. Science 279: 860-863.

And perhaps some less obvious ones:

Brunner, R.D. 2000. Alternatives to Prediction. in Prediction: Science, decision making and the future of nature. Ed. by D. Sarewitz, R.A. Pielke and R. Byerly. Island Press, Washington D.C. pp 299-313.

Essington, T.E. 2004. Getting the right answer from the wrong model: Evaluating the sensitivity of multispecies fisheries advice to uncertain species interactions. Bull. Mar. Sci. 74: 563-581.

Parkes, G. 2000. Precautionary fisheries managment: the CCAMLR approach. Marine Policy 24: 83-91.