1. Projected changes to tuna stocks

2. Based on……..

3. Outline Sensitivity of tuna to features of the ocean
Summary of changes to the ocean
Projected effects on:
Skipjack tuna
Bigeye tuna
Albacore

4. Effects of temperature on tuna
Each tuna species has evolved with a preferred range in temperature
Species
Temperature (°C)
Skipjack
20-29
Yellowfin
20-30
Bigeye
13-27
Albacore
15-21
Impacts vertical & horizontal distribution (habitat and food) & reproduction location and timing
According to life stage sensitivity to SST degree e.g. larvae and adult. Spawning. Affects habitat and
Range of sea surface temperature with substantial catches
Source: Sund et al. (1981)

5. Effects of oxygen on tuna
Sensitive to combined effects of SST O2
Estimated lower lethal limits
Species
Fork length
(cm)
Lower lethal O2 levels (ml l-1)
Skipjack 50
1.87
Albacore
1.23
Yellowfin
1.14
Bigeye
0.40
Increasing tolerance to low O2 values

6. Effects of oxygen on vertical distribution of tuna+
0 m
100 m
Well oxygenated
Skipjack
Albacore
Yellowfin
500 m
Low oxygen
Bigeye
Typical vertical O2
profile

7. Effects of productivity on tuna
Tuna larvae
Zooplankton
Source: Rudy Kloser and Jock Young CSIRO, Australia
Micronekton
Primary production
PP is vital for reproduction and feeding hence tuna move in search of food and better habitat, PP=spatial & vertical distribution. PP supports the food web linking ot tuna (VAL)

8. 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

9. Effects of climate change on tuna
Now that we understand the oceanography a bit better then before, we have spent some years making a model to better understand the projections expected. Spent years working on a model to incorporate these change. Through this model we see changes in fishing grounds and distributions towards eastern for tuna and this poses challenges for fishing operations like purse seinier and long liners.

10. Skipjack projection Cook Islands ~ 10% Cook Islands ~ 15%
Source: Bell et al. 2013

11. Bigeye projection Displacement eastward Larval density Adult biomass
2000
2050
Displacement eastward
Source: Lehodey et al. 2011

12. Albacore projection Sensitive to O2 Larval density Adult biomass
2000
2000
2050
2050
No change in O2
Sensitive to O2
With modeled O2

13. 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
Point to the graph on complexation.

14. Conclusions
Resolution 2°
Resolution 1°
Resolution 0.25 °
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
we expect to be better at these models to get down form coarse scale to finner scale to better capture the oceanic processes. What is important to remember is that even thou there are gaps of knowledge and uncertainty in SEAPODYM, this is currently the only model, which can incorporate all these processes mentioned. Lead the audience thru the diagram. Alex resloution and giving example places in red more tuna then the palces in blue if u go donw from 2 degrees to these with these sort of model we would hope to provide more information to the managers to maange long liners. So as you can see when we go donw from 2 degrees to 0.25 we are better able to see these processes.