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AFSC Seminar Series No. 7

Scheduled Seminars

Subject: Fishing Down (and up) Alaskan Food Webs

Speaker: Mike Litzow, AFSC RACE Shellfish Assessment Program
When: Thursday, 6 April 2006, 10:00 am -11:00 pm
Where: Bldg. 4, Traynor Seminar Room, Rm. 2076, AFSC, Sand Point Campus, Seattle

Dear Colleagues,

Please join us for the upcoming seminar by Mike Litzow of the RACE Shellfish Assessment Program in Kodiak. His research centers on the community-level impacts of climate change. He will be presenting his work on the trends of Alaskan fishery trophic levels. Mike is currently working on a community-wide study of animal distribution changes in the Bering Sea for the years 1979-2004, and a study of climate regulation of top-down and bottom-up ecosystem control in Pavlof Bay.

Fishing Down (and Up) Alaskan Food Webs

Mike Litzow
Kodiak Fisheries Research Center
301 Research Court
Kodiak, AK 99615

Dan Urban
Alaska Department of Fish and Game
Division of Commercial Fisheries
211 Mission Road Kodiak, AK 99615

Abstract:
Alaskan fisheries are a model of successful management. However, to our knowledge no study has presented an ecosystem-level, state-wide analysis of the sustainability of Alaskan fisheries. We constructed a time series of Alaskan commercial fishery catches for the years 1893-2004 in order to 1) examine trends in measures of sustainability; and 2) examine the effect of climate variability on Alaskan fisheries. We also examined trends in regional fisheries and fisheries-independent surveys. During the trawl era (1959-2004), trend in the Fisheries in Balance (FIB) index was best described by a logarithmic function, indicating an initial rapid expansion in catch size, followed by slower expansion over the past 30 years. Mean trophic level of statewide fisheries showed linear increase throughout 1959-2004, and did not show the decline characteristic of overfishing. Both trophic level (R² = 0.34) and FIB values (R² = 0.15) were related to the Pacific Decadal Oscillation index, providing evidence of climate effects on Alaskan fisheries. Survey and fisheries data from the Bering Sea and

Gulf of Alaska indicate that these fisheries remain healthy. However, survey trophic level, fishery trophic level and FIB values have all been falling in the Aleutian Islands for 15-20 years. Assigning cause to these patterns is beyond the scope of our study, but we conclude that overfishing should be the leading hypothesis. Increases in Alaskan fishery trophic levels over the last 45 years are similar to increases that preceded fisheries collapses in other areas. We are currently unable to predict the capacity of Alaskan ecosystems to support further increases in fishery trophic level and catch size, nor do we understand the effects of climate change on this capacity. We conclude that Alaskan ecosystems should be considered fully exploited at current harvest levels, and that preventing further increase in trophic level and FIB values should be a management priority.