Projected changes to ocean food
webs and oceanic fisheries
Solomon Islands Government
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
↘ of rich equatorial divergence
↗ of poorer gyres and warm pool
Impact of climate change
present
• Reduced
exchange
between deep,
nutrient-rich
water and
surface waters
future
Impact of climate change
• Effect on phytoplankton and zooplankton
Present
present
2035
2050
2100
Impact of climate change
Image: Valerie Allain, SPC
• Effect on micronekton
Now, turning to tuna!
Tuna habitat – temperature
• Each tuna species has evolved with a preferred
range in temperature
• This preference
affects:
 vertical
& horizontal
distribution of species
 where and when tuna
spawn
Range of sea surface temperature
with substantial catches
Species
Temperature
(°C)
Skipjack
20-29
Yellowfin
20-30
Bigeye
13-27
Source: Sund et al. (1981)
Tuna habitat – oxygen
Estimated lower lethal oxygen
concentration
Species
Length
(cm)
Lower lethal O2
levels (ml l-1)
Skipjack
50
1.87
Yellowfin
50
1.14
Bigeye
50
0.40
Less tolerant to
low O2 levels
Skipjack
Yellowfin
Bigeye
Most tolerant
to low O2 levels
Tuna habitat – oxygen
+
0
0m
100 m Well oxygenated
Skipjack
Yellowfin
500 m
Low oxygen
Bigeye
Typical
vertical O2
profile
Skipjack tuna
Solomon Is = -4
Solomon Is = -3
Unexploited
Fishing effort x 1.5
Bigeye projection
2050
2000
Adult biomass
Larval density
2000
2050
Good fishing grounds
could be displaced further
eastward
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 °