Climate Change Impacts on Ocean Food Webs and Tuna Fisheries
Explore the projected changes to ocean food webs and oceanic fisheries, focusing on the effects of climate change on tuna stocks and habitats. Understand the differences in food webs among Pacific Ocean provinces and the sensitivity of tuna habitats to oceanic variables, all illustrated with informative visuals.
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Presentation Transcript
Projected changes to ocean food webs and oceanic fisheries
Outline Food webs for tuna Differences in food webs among provinces of the Pacific Ocean Effects of CC on provinces and their food webs Sensitivity of tuna habitats to oceanic variables Effects of climate change on tuna stocks
Tuna food web Food webs are complex
Five oceanic provinces Warm pool Normal El Ni o
Five oceanic provinces North and South Gyres (case 3) and equatorial divergence (case 4)
Impact of climate change Surface area of the provinces of rich equatorial divergence of poorer gyres and warm pool
Impact of climate change present future Exchanges between deep rich water and surface poorer waters of nutrients reaching the surface where photosynthesis can occur
3. The impact of climate change Effect on phytoplankton and zooplankton present present 2035 2050 2100 of phytoplankton and zooplankton
3. The impact of climate change Effect on micronekton Image: Valerie Allain, SPC of micronekton
Tuna habitat temperature Each tuna species has evolved with a preferred range in temperature Species Temperature ( C) 20-29 20-30 13-27 15-21 17-20 Impacts vertical & horizontal distribution (habitat and food) & reproduction location and timing Skipjack Yellowfin Bigeye Albacore Sth. bluefin Range of sea surface temperature with substantial catches Source: Sund et al. (1981)
Tuna habitat oxygen Sensitive to combined effects of SST + O2 Less tolerant to low values Estimated lower lethal oxygen Skipjack Albacore Yellowfin Bigeye Species Fork length (cm) 50 50 50 50 Lower lethal O2 levels (ml l-1) 1.87 1.23 1.14 0.40 Skipjack Albacore Yellowfin Bigeye Most tolerant to low values
Tuna habitat oxygen + 0 0 m 100 m Well oxygenated Skipjack Albacore Yellowfin Low oxygen 500 m Bigeye Typical vertical O2 profile Change in subsurface may have more impact on low oxygen tolerant species
Better understanding of oceanography = better expected projections
Skipjack tuna Samoa +7% Samoa +10% Unexploited Fishing effort x 1.5
Albacore projection 2000 2000 Adult biomass Larval density 2050 2050 No change in O2 Sensative to O2 hence distribution changes With modelled O2
Conclusions There is still uncertainty about impacts of climate change Fishing has a strong impact and will continue to be a major driver of stocks
Conclusions Resolution 2 Improved resolutions of SEAPODYM model are needed to update these preliminary results Resolution 1 Better projections of key ocean variables for tuna can be achieved using an ensemble of models Resolution 0.25
