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 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)

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

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

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)

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 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.

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

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

Albacore projection Sensitive to O2 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 Point to the graph on complexation.

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.