05. Projected changes to tuna stocks

Report
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 + O2
Estimated lower lethal limits
Species
Fork length Lower lethal O2
(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 O2 values
0
Effects of oxygen on vertical
distribution of tuna
+
0m
100 m Well oxygenated
Albacore
500 m
Skipjack
Yellowfin
Low oxygen
Bigeye
Typical
vertical O2
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
Adult biomass
2000
2000
2050
2050
Displacement
eastward
Source: Lehodey et al. 2011
Albacore projection
Larval density
Adult biomass
2000
2000
2050
2050
No change in O2
Sensitive to O2
With modeled O2
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
• Improved resolutions of
SEAPODYM model are needed to
update these preliminary results
• Better projections can be achieved
using an ensemble of models and
better spatial reporting of catches
Resolution 2°
Resolution 1°
Resolution 0.25 °

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