Impact of Industrial Tuna Fisheries on Fish Stocks and the Ecosystem of the Pacific Ocean

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1 Impact of Industrial Tuna Fisheries on Fish Stocks and the Ecosystem of the Pacific Ocean John Sibert John Hampton Pelagic Fisheries Research Program Oceanic Fisheries Programme University Hawaii Secretariat of the Pacific Community

2 Thanks to the folks who actually do the work: Adam Langley Pierre Kleiber Mark Maunder Shelton Harley Yukio Takeuchi Momoko Ichinokawa Tom Polacheck Alain Fonteneau Oceanic Fisheries Programme, SPC, Noumea NOAA Pacific Island Fisheries Science Center, Honolulu Inter-American Tropical Tuna Commission, La Jolla National Research Institute of Far Seas Fisheries, Shimizu CSIRO, Hobart IRD, Sete

3 Outline Preliminary results from an analysis synthesis exercise Based on stock assessment results using all available data Biomass trends Changes in size structure Changes in trophic structure within guild of top predators Regime shifts? Fishery management options Compare with results of simple CPUE analysis

4 Availability of stock assessments Current Assessments Needed Assessments Stock Status Stock Status WCPO Yellowfin 3 Ono 0 EPO Yellowfin 3 Mahi mahi 0 Southern Albacore 3 Oceanic Whitetip Shark 0 Northern Albacore 2 Pacific Bigeye 3 WCPO Bigeye 3 WCPO Skipjack 2 Pacific Swordfish 1 Pacific Blue Marlin 1 Pacific Blue Shark 1 3: current & definitive; 2: current, but needs work; 1: in progress or needs updating; 0: probably insufficient data Used in this presentation

5 Biomass Trends WCPO Yellowfin South Pacific Albacore Pacific Bigeye e+00 1e+06 2e+06 3e+06 4e EPO Yellowfin North Pacific Albacore WCPO Skipjack e e e e

6 Impact of Fishery on Total Biomass Exploited/Unexploited WCPO Yellowfin EPO Yellowfin South Pacific Albacore North Pacific Albacore Pacific Bigeye WCPO Skipjack Year

7 Changes in Size Spectra 's 's 's 's 's 's

8 Impact of Fishery on Size Proportional Biomass Reduction Decade 1950s 1960s 1970s 1980s 1990s 2000s

9 Impact of Fishery on Spawning Biomass Exploited/Unexploited WCPO Yellowfin EPO Yellowfin South Pacific Albacore North Pacific Albacore Pacific Bigeye WCPO Skipjack Year

10 Ecopath Calculations Central Pacific Eastern Tropical Pacific Cox et al., 2002 Olson & Watters, 2003 Species Small Weight (kg) Large Small Large Bigeye Yellowfin Albacore Blue Shark Blue Marlin Swordfish Skipjack Marlins Sharks Bluefin 4.37 Sailfish Average Cox, S., S. Martell, C. Walters, T. Essington, J. Kitchell, C. Boggs, and I. Kaplan Reconstructing ecosystem dynamics in the central Pacific Ocean, I. Estimating population biomass and recruitment of tunas and billfishes. Can. J. Fish, Aquat. Sci. 59: Cox, S., T. Essington, J. Kitchell, S. Martell, C. Walters, C. Boggs, and I. Kaplan Reconstructing ecosystem dynamics in the central Pacific Ocean, II. A preliminary assessment of the trophic impacts of fishing and effects on tuna dynamics. Can. J. Fish, Aquat. Sci. 59: Olson, R. and G. Watters A model of the pelagic ecosystem in the eastern tropical Pacific Ocean. IATTC Bulletin 22:

11 Eastern and Western Food Webs Hinke, J, I. Kaplan, K. Aydin, G. Watters, R. Olson and J. Kitchell Visualizing the food-web effects of fishing for tunas in the Pacific Ocean. Ecology and Society 9:

12 Eating your way to the top

13 Trophic Transitions Ecopath Switch + Stock WCPO Yellowfin EPO Yellowfin South Pacific Albacore North Pacific Albacore Pacific Bigeye WCPO Skipjack + Stock WCPO Yellowfin EPO Yellowfin South Pacific Albacore North Pacific Albacore Pacific Bigeye WCPO Skipjack Ontogenetic + Stock WCPO Yellowfin EPO Yellowfin South Pacific Albacore North Pacific Albacore Pacific Bigeye WCPO Skipjack + Stock WCPO Yellowfin EPO Yellowfin South Pacific Albacore North Pacific Albacore Pacific Bigeye WCPO Skipjack Central Pacific Eastern Tropical Pacific

14 Impact of Fishery on (1) 0e+00 2e+07 4e 's 0.0e e e+07 0e+00 2e+07 4e 's 0.0e e e+07 0e+00 2e+07 4e 's 0.0e e e+07 0e+00 2e+07 4e 's 0.0e e e+07 0e+00 2e+07 4e 's 0.0e e e+07 0e+00 2e+07 4e 's 0.0e e e+07 WCPO Ontogentic

15 Impact of Fishery on (2) 0.0e e e 's 0.0e e e e e 's 0.0e e e e e 's 0.0e e e e e 's 0.0e e e e e 's 0.0e e e e e 's 0.0e e+07 EPO Switch

16 Impact of Ecosystem on Fishery Recruitment Anomaly Darwin Tahiti SOI WCPO Yellowfin EPO Yellowfin South Pacific Albacore North Pacific Albacore Pacific Bigeye WCPO Skipjack 5 year centered average 59 month leading average Year

17 Conclusions Impact of fisheries on biomass is variable Expansion of the purse seine fishery has extended fishing mortality to all age classes of some species Some stocks have declined to a point where management intervention is required Some stocks appear to have increased in abundance Fish larger than 150cm have declined to about 20% of their predicted abundance in the absence of fishing Impact on trophic structure within the guild of top predators is not detectable Fishery-independent trends in recruitment and biomass are apparent Estimated increase in skipjack biomass consistent with predictions from food web models Future work Increase number of stocks in analysis Extend skipjack stock assessment to include Examine possibilities for assessments of mahi mahi, ono, and small tunas

18 Fishery Management Options United States Domestic: For yellowfin and bigeye F > M MSY (overfishing is occurring), but B > B MSY (stocks are not overfished) US catch comprises approximately 0.5% longline and 5% purse seine yellowfin catch US longline bigeye catch comprises approximately 1% total longline bigeye catch Unilateral measures by US would be futile International IATTC - measures to reduce mortality on bigeye ineffective to date WCPFC - identified potentially effective management options Reduce fishing effort by all fleets by 15% Shift purse seine effort away from FAD sets to school sets May implement measures at second meeting in December 2005

19 The Claims... large predatory fish biomass today is only about 10% of preindustrial levels. Ransom A. Myers and Boris Worm Rapid worldwide depletion of predatory fish communities Nature 423: I know that the human being and the fish can coexist. George W. Bush CPUE is not a reliable index of abundance Community CPUE a bogus concept Omits of most of data

20 Interpretation of Catch per Unit Effort (1) Albacore South of the Equator CPUE (Fish/100 Hooks) Japan Taiwan Year Hampton, J, J. Sibert, P. Kleiber, M. Maunder, S. Harley Decline of Pacific tuna populations exaggerated? Nature 434:E1-E2.

21 Interpretation of Catch per Unit Effort (2) _ Yellowfin South of 10 South CPUE (Fish/100 Hooks) % Decline by 2900 tonne removal 60% Decline by 8900 tonne removal Total Year Yellowfin Between 10 South and 10 North CPUE (Fish/100 Hooks) Year 0e+00 2e+05 4e+05 Total

22 Selective use of data (1)

23 Selective use of data (2)