06. Tuna food webs and tuna

Report
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 + O2
Less tolerant to
low values
Estimated lower lethal oxygen
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
Skipjack
Albacore
Yellowfin
Bigeye
Most tolerant
to low values
Tuna habitat – oxygen
+
0
0m
100 m Well oxygenated
Albacore
500 m
Skipjack
Yellowfin
Low oxygen
Bigeye
Typical
vertical O2
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 O2
With modelled O2
2050
Sensative to O2 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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