Subject: Fishing through marine food webs   (video)

Speaker: Tim Essington, School of Aquatic and Fishery Sciences at the University of Washington
When: Thursday, 4 May 2006, 10:00 am
Where: Bldg. 4, Traynor Seminar Room, Rm. 2076,  AFSC, Sand Point Campus, Seattle, Washington

Dear Colleagues,

Please join us for the upcoming seminar by Tim Essington from the School of Aquatic and Fishery Sciences at the University of Washington. Tim’s research focuses on food web interactions involving fish in marine, estuarine, and freshwater habitats. His present research includes analysis of tropical tunas, sharks, and fisheries in the central Pacific, analysis of cod and clupeid dynamics in the Baltic Sea, and identifying trophically mediated trade-offs between fisheries.

The seminar will be transmitted live to Auke Bay Lab and recorded on tape/disk.

Fishing through marine food webs:
A comparative analysis of fisheries expansion

Tim Essington
School of Aquatic and Fishery Sciences
University of Washington
Seattle, Washington

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.

By analyzing trends in fishery landings in 48 large marine ecosystems worldwide, we find that fishing down the food web was pervasive (present in 30 ecosystems), but that the sequential addition mechanism was by far the most common one underlying declines in the mean trophic level of landings. Specifically, only 9 ecosystems showed declining catches of upper trophic level species, compared to 21 ecosystems that exhibited either no significant change (6) or significant increases (15) in upper trophic level catches when fishing down the food web was occurring.

Only in the North Atlantic were ecosystems regularly subjected to sequential collapse and replacement of fisheries. We suggest that efforts to promote sustainable use of marine resources will benefit from a fuller consideration of all processes giving rise to fishing down the food web.


References:

Litzow, M.A., K.M. Bailey, F.G. Prahl, R. Heintz. In press. Climate regime shifts and reorganization of fish communities: the essential fatty acid limitation hypothesis. Marine Ecology Progress Series.

Litzow, M.A. In review. Climate regime shifts and community reorganization in the Gulf of Alaska: how does 1998-1999 compare with 1976-1977? ICES Journal of Marine Science.