Projected changes to tuna stocks Based on Outline
Projected changes to tuna stocks
Based on……. .
Outline • Sensitivity of tuna to features of the ocean • Summary of changes to the ocean • Projected effects on: – Skipjack tuna – Bigeye tuna – Albacore
Effects of temperature on tuna • 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)
Effects of oxygen on tuna • Sensitive to combined effects of SST + O 2 Estimated lower lethal limits 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 Increasing tolerance to low O 2 values
0 Effects of oxygen on vertical distribution of tuna + 0 m 100 m Well oxygenated Albacore 500 m Skipjack Yellowfin Low oxygen Bigeye Typical vertical O 2 profile
Effects of productivity on tuna Zooplankton Tuna larvae Micronekton Primary production Source: Rudy Kloser and Jock Young CSIRO, Australia
Effects of climate change Summary of changes to ocean and food webs • Warmer sea surface temperatures • Increase in oxygen-poor areas • Slower currents south of equator and stronger EUC • Changes in areas of ecological provinces • Reduced production of phytoplankton, zooplankton and micronekton
Effects of climate change on tuna
Skipjack projection Cook Islands ~ 10% Cook Islands ~ 15% Source: Bell et al. 2013
Bigeye projection Larval density 2000 2050 Adult biomass 2000 2050 Displacement eastward Source: Lehodey et al. 2011
Albacore projection Larval density Adult biomass 2000 2050 No change in O 2 Sensitive to O 2 With modeled O 2
Conclusions • Eastward distribution of skipjack and bigeye • But still much uncertainty about impacts of climate change on tuna • 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 can be achieved using an ensemble of models and better spatial reporting of catches Resolution 0. 25 °
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