Projected changes to ocean food webs and oceanic
Projected changes to ocean food webs and oceanic fisheries
Based on……. .
Outline • Food webs for tuna • Differences in food webs among provinces of the Pacific Ocean • Effects of CC on provinces and their food webs • Effects of climate change on tuna stocks
Image: Marc Taquet, FADIO, IRD/IFREMER
Tuna food web Food webs are complex
Five oceanic provinces
Five oceanic provinces • Warm pool Normal El Niño
Five oceanic provinces • North and South Gyres (case 3) and equatorial divergence (case 4)
Impact of climate change • Surface area of the provinces ↘ Rich equatorial divergence ↗ Poorer gyres and warm pool
Impact of climate change • Effect on phytoplankton and zooplankton Present present 2035 2050 2100
Impact of climate change • Effect on micronekton Midwater Dee micronekton Deep micronekton Image: Valerie Allain, SPC Shallow micronekton
Now, turning to tuna! Albacore
Tuna habitat – temperature • Each tuna species has evolved with a preferred range in temperature • Impacts vertical & horizontal distribution (habitat and food) & reproduction location and timing Species Skipjack Yellowfin Bigeye Albacore Temperature (°C) 20 -29 20 -30 13 -27 15 -21 Range of sea surface temperature with substantial catches Source: Sund et al. (1981)
Tuna habitat – oxygen Sensitive to combined effects of SST + O 2 Less tolerant to low values Estimated lower lethal oxygen Species Fork length Lower lethal O 2 (cm) levels (ml l-1) Skipjack 50 1. 87 Albacore 50 1. 23 Yellowfin 50 1. 14 Bigeye 50 0. 40 Skipjack Albacore Yellowfin Bigeye Most tolerant to low values
Tuna habitat – oxygen + 0 0 m 100 m Well oxygenated Albacore 500 m Skipjack Yellowfin Low oxygen Bigeye Typical vertical O 2 profile Change in subsurface may have more impact on low oxygen tolerant species
Skipjack projection Vanuatu = +2 Vanuatu = +3 Vanuatu = -12 Unexploited Fishing effort x 1. 5
Bigeye projection 2050 2000 Adult biomass Larval density 2000 2050 Good fishing grounds could be displaced further eastward
Albacore projection 2050 2000 Adult biomass Larval density 2000 No change in O 2 With modelled O 2 2050 Sensative to O 2 so distribution changes
Conclusions • There is still uncertainty about impacts of climate change on tuna • Fishing has a strong impact and will continue to be a major driver of stocks
Conclusions • Improved resolutions of SEAPODYM model are needed to update these preliminary results Resolution 2° Resolution 1° • Better projections can be achieved using an ensemble of models Resolution 0. 25 °
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