U.S. Tuna Fisheries: a trifecta of sustainable practices at odds with climate change mitigation / by Francisco Blaha

Many people sent me versions of an article that came originally in the New Scientist arguing that Sustainable tuna fishing is bad for climate, since the pole&liners and longliners consume more fuel than purseiners per tonne of product. This just shows that there are no magic bullets in fisheries, and everything in life has advantages and disadvantages.

 burning out your ecolabel...

burning out your ecolabel...

The new scientist quoted a poster presented at the American Geophysical Union fall meeting by Brandi McKuin and J Elliott Campbell from University of California Merced. They recognise that environmental concerns have given rise to eco-label initiatives in the seafood industry and a shift to more sustainable fishing practices. So they looked at sustainable practices employed by U.S. tuna fisheries and find the term “sustainably sourced” changes when climate forcing is added to the criteria.

Specifically, there are three sustainable practices at odds with climate change mitigation:

1) The use of selective fishing gear reduces bycatch but increases fuel use;

2) Fishing within exclusive economic zones is more equitable to coastal fishermen, and allows the high seas to serve as an ecological bank, but fishing within these regions means fisheries are subject to more stringent fuel sulphur laws thereby diminishing the cooling effects of sulphate aerosols and increasing climate forcing; and

3) Removing sulphur from fuels improves air quality, but there are added emissions from the refinery process. 

They used ship registry data, historical sulphur levels in fuels; gear-specific fishery fuel use data collected from the literature, historical gear-specific tuna landings data, and a range of global warming potentials to estimate the climate forcing of U.S. tuna fisheries over the last fifteen years.

And they found that for tuna caught within exclusive economic zones, the net fuel-related climate forcing has more than doubled over the last fifteen years.  Thanks to a drop in purse seining in the US tuna fishery since about 1990, the team estimates that catching a tonne of tuna takes about three times as much fuel today as it did 25 years ago.

The also normalised the fuel-related Climate forcing results to a unit of tuna protein and compared these results to other farmed sources of protein.

And they found that tuna caught within exclusive economic zones has the highest climate impact of all land-based protein sources considered, with the exception of beef. 

But none of this is really new… my friend Bob Gillet already wrote in 2009 (Fisheries in the Economies of the Pacific Island Countries and Territories) the following:

”tuna longliners have the highest fuel consumption per tonne of catch—on average, over four times as much as purse seiners. Small-scale coastal fisheries fall between the two, consuming about twice as much fuel per ton as purse seiners. The costs of fuel per dollar of catch value show similar differences, but less pronounced because prices of some fish products have increased more than others.
The financial impact of fuel price increases of longliners is still greater than that of purse seiners, but the difference is very much smaller than that in specific fuel consumption per tonne of catch, because of increases in fish prices. Artisanal fishers are the most financially exposed of all the fleets analysed.”

Furthermore, every time I get confronted by recreational fisherman saying that their fishery is so much more sustainable and at a much higher ecological high ground than the commercial one. I bring the fuel consumption issue to the table, outboards are terrible in fuel consumption and liquefy their exhausts into the water. If you were to quantify fuel-related Climate forcing results to a unit of animal protein obtained, recreational fishing would be the worst by far, yet that is never taking into consideration

Anyway, back to the study presented. Personally, I would have separated the type of tunas by “destiny” (canning or sashimi), since the values are very different and this is reflected by the harvesting gear.

Purseine is a bulk fishery and the quality of the fish brought on board is not individually handled, generalized by the freezing method of brining (holding the fish in a refrigerated hypersaline seawater solution) , which brings the fish to -12C at the best, since the brine will get too thick to be pumped around the boat and re-refrigerated below those temperatures. The “quality” of the resulting tuna is far from fantastic, therefore we used mostly for canning.

On the other side, longliners aim to the sashimi market, hence the fish is treated individually and in a whole different way (ikied, bled, gutted) and then frozen (depending on the boat) to -30C or -50C and maintained at that temperature.

The fuel consumption of a longliner is not just determined by the main engine consumption over miles travelled, but also by the capacity and “power” of the refrigeration equipment on board that has to be fed by every time bigger generators.

As a consequence, a tonne of skipjack is 1800 USD in Bangkok, less than an 80kg yellowfin in avg day in Tokio… and definitely less than the 1st Bluefin tuna of the season there (300000 USD!)

The point of all this: everything has advantages and disadvantages (as my dad’s said when I told him I was getting married), and we have to navigate ethical choices since there is no one perfect way. With science, we can determine what king of management of a fishery will lead to long-term sustainability of food production. Fisheries policy can set up the harvesting regimes needed, and MCS will help stakeholders to obey the rules set. Furthermore, science can (and should) evaluate the environmental impacts of a fishery (including fuel-related Climate forcing results). Yet, it would be imposible for science, policy and MCS to tell you what environmental impacts are low enough – that is a question of individual choice and public policy via political pressure.

And I know this will sound terrible, but the only guaranteed way to have no impact on our environment is for all of us (humanity) to disappear (fast and at once). All other options imply compromises