What does the number 400 have to do with tuna? Thoughts on World Tuna Day | WWF

What does the number 400 have to do with tuna? Thoughts on World Tuna Day

Posted on 17 May 2013    
Could tuna this small survive acidic seas?
© Jose Ingles
A week ago, the world’s CO2 concentration in the atmosphere just breached the 400 parts per million level for the first time in the history of mankind.

It dampened my enthusiasm to celebrate the World Tuna Day (May 2) even though this event has seen two large tuna fisheries get MSC certified for two consecutive years.

Crossing the 400 threshold means nothing for many of us because the impacts of CO2 from 350 to 400 cannot be felt. It is a level set by science as a target limit for us to reduce and eventually reverse further increase in CO2 without much social and economic cost. Allowing CO2 to breach this level means that it will be harder and much more expensive for us to bring down CO2 levels without compromising life, property, and health. The last geologic time when we had CO2 levels this high was some 2 million years ago!

What does this number mean to tuna—to our seafood?

The temperature of the earth the last time CO2 levels were this high was inhabitable for any life form. Because our oceans absorb much of the CO2, our seas are expected to become acidic—a condition that could weaken, if not dissolve, the fragile skeletons of many marine organisms, and consequently turn the marine ecosystem into a lifeless sea.

And how will tuna be affected? As the seas become warmer, tropical tuna will invade what are today cooler climates. There is growing scientific evidence that skipjack tuna move eastward from the Western Pacific during episodes of warmer seas. This means that fishers in the Western Pacific Ocean could probably lose their fish, bringing economic dislocation to fishers and countries dependent on this seafood.

This change in ocean temperature could likewise affect the availability of food for newly-spawned tuna. Food sources for baby tuna may either shift to other areas or even die. This could ultimately weaken the future replenishment of tuna stocks.

For fishers, extreme weather is expected, compromising their ability to go out and fish safely at sea.
So what can we do?

We need to build a robust population of tuna stocks (called resiliency) to overcome such oceanic perturbations and perhaps buy time for tuna to adapt to these changes by applying better tuna management practices.

For us consumers, this means raising a louder voice to call on our governments to put in measures to rebuild tuna stocks—measures that should have been put in place a long time ago. Perhaps, this increase in CO2 levels would prove to be enough reason to realize this call.

Posted by Jose Ingles (Jingles)
Could tuna this small survive acidic seas?
© Jose Ingles Enlarge
Tuna being auctioned in General Santos City
© Jose Ingles Enlarge
We need to ensure that future generations will have enough fish to eat
© Jose Ingles Enlarge
With declines in tuna stocks, do fishers really have nothing to fear?
© Jose Ingles Enlarge

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