Climate Change and Range Shift

What is the climate like in Fiji islands and Kiribati?
How is tuna population distribution shifting in response to climate change?


Let's explore!

Although Fiji islands have a wet season as mentioned in a previous section "About Fiji and Kiribati Islands" section, Fiji has a warm tropical climate. The usual temperature range is from 31°C (88°F) to 26°C (79°F) as demonstrated on the figure below.

                                      Figure A: Annual Average Temperature and Precipitation in Fiji Islands


From late December to early March, there is a rainy season in Kiribati (you may refer to the bars that represent monthly precipitation on the figure below) and Fiji islands follow a same trend. Kiribati enjoys a equatorial maritime climate and average annual temperature is 28 degrees Celsius (86 degrees Fahrenheit).

                                               
                                 Figure B: Annual Average Temperature and Precipitation in Tarawa, Kiribati 


So, we see that climate in Fiji islands and Kiribati are similar. What is happening in the Pacific Islands? Is something wrong with the climate? and how do tuna respond to this change?
From 1993 to 1995, there was a dramatic decline in number of catch of tuna in all tuna species. There are several factors that are responsible for this noticeable change, but it is not limted to climate change alone (overfishing, change in oxygen availability in water, and unemployment in tuna fishery may have played an important role also). What is going on here?   

 

                               Figure C: Catch of Tuna in Fiji islands by species from 1980 to 1998. (Unit: Metric tons)


 Catch of tuna in Kiribati showed a simliar trend around the same period of time (1995). What have caused a dramatic dropdown of tuna fishery in Fiji islands and Kiribati? Why are tuna shifting their habitat range?

                                Figure D: Catch of tuna in Kiribat by species from 1980 to 1998. (Unit: Metric tons.)

As one can notice from the graphs above, Skipjack tuna species take up the largest portion in tuna fishery. Their densely populated habitat is located in the western equatorial Pacific Warm pool with Sea Surface Temperature (SST) of 29 degrees Celsius and also includes areas that are slightly warmer.

                                       Figure E: Tuna Migration and Climate Variability

NOTE:

(a) demonstrates the skipjack tuna catch (shaded and cross-hatched areas indicate January ~ June catch of 200,000) and mean Sea Surface Temperature (SST)

(b) and (c) represent the scale of tuna migration during La Niña and El Niño period.

It is noticeable from the figure that there is a link between the location of the warm pool and El Niño Southern Oscillation and it changes accordingly with the occasional events of El Niño and El Niña.

There is a difference in catch area between the first half of 1989 (La Niña, shown by cross-hatch-cetered around Palau and the Federated States of Micronesia) and first half of 1992 (El Niño, shown by shading-abundance had shifted the east to Kiribati).

The link between distribution shift of skipjack tuna and El Niño and El Niña has shown that climate change has a significant impact on range shift pattern of tuna, which is closely related to opportunities for commercial fishing.

Although the effect on the size and location of the warm pool in western and central Pacific by projected climate change is unknown, it can be theorized from the data that further climate change will drive the tuna population eastwards.

                                     Figure F: Distribution of Bigeye and Skipjack adult tuna in the past and expected based on current data set (Lehodey, P 2010)

In the Western and Central Pacific Ocean, tuna fishery has experienced expansion in the past 30 years. Year of 2007 marked a peak, the total value of the catch of various tuna species including skipjack, Yellowfin, and Bigeye was about 4 billion USD. This was approximately 2.4 tons of tuna. It brought economic benefits to a considerable extent in Pacific Island countries.

Now, how will this climate change have a economic impact?

Is climate change helping some countries, but not others?

Let's move onto the next section "economic impacts of climate change."

                                





References


1.Aaheim, Asbjørn and Sygna, Linda “Economic Impacts of Climate Change on Tuna Fisheries in Fiji Islands and Kiribati” June 22 200 CICERO Report 2000:4 Online

2. Lehodey, P. (2000) “Impacts of climate change on tuna fisheries in the tropical Pacific

Ocean”, Draft, Oceanic Fisheries Programme, Secretariat of the Pacific Community,
Noumena, New Caledonia.

 
3. Lehodey, P., Senina I., Sibert J., Bopp L, Calmettes B., Hampton J. Murtugudde R. (2010). Preliminary forecasts of population trends for Pacific bigeye tuna under the A2 IPCC scenario.
Progress in Oceanography. 86:302-315.


*The diagrams and graphs used in this section were borrowed from the scholarly articles above otherwise known as "Reference."