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In Depth

| 04/05/18

Consider the lobster’s greenhouse gas emissions


Fishermen are catching lobsters, crabs and shrimp more than ever, in part because wealthier consumers in Asia like eating the tasty animals, but also due to moves by the fishing industry to increasingly focus on healthy stocks of crustaceans as global fish stocks decline.

This is not great news for the climate, as crustacean fishing emits more greenhouse gases per tonne “landed” (the catches that are landed in port) according to a new assessment of global fisheries. Solving the problem will require more sustainable fishing and switching from diesel to cleaner energy.

Marine fisheries have generally been excluded from global greenhouse gas (GHG) assessments due to seafood’s limited emissions compared to livestock. However, researchers with the University of British Columbia’s Institute for the Oceans and Fisheries released one of the first comprehensive assessments of the carbon intensity (emissions per unit of production) of the sector, comparing data on fishery catches from 1990-2011 to estimates of fuel use for the various fishery classes.

Emissions from all fisheries soared by 28 percent over this period in total, they reported in a paper appearing this week in Nature Climate Change, a growth driven largely by the uptick in crustacean harvests. Crustacean fisheries are only six percent of landings, but represent more than 22 percent of emissions. By 2011, the volume of crustaceans caught was up 60 percent on 1990, a greater bump than for any other class of fishery.

National fleets with the worst total GHG emissions profiles were those of China, Indonesia, Vietnam, the US and Japan, accounting for just over a third of landings but almost half of all emissions in 2011. Those with the worst carbon-intensity were Saudi Arabia, Australia and other nations that had disproportionately large crustacean fisheries.

What is so bad about fishing for crabs and lobsters? They deliver relatively low amounts per trip compared to other seafood. Diesel is combusted every time traps are placed, checked and retrieved. Yet the rise in emissions has happened even as boats have become much more fuel efficient. The authors recommend more sustainable fisheries to begin with. If fishermen do not have to sail as far to find fish, they do not have to expend as much diesel. The challenge here comes as more Asian middle class and Africa join the global middle class and start being able to afford more animal protein.

One option is fuel-switching, from diesel-powered boats to ones that run on electricity or alternate fuels. This is not so far off in the future. Corvus Energy, a Richmond, BC-based firm that produces energy storage systems for maritime propulsion, in 2015 unveiled what it claimed to be the world’s first all-electric commercial fishing vessel. The “Karoline” is an 11-metre ship that can run for up to ten hours from its lithium polymer batteries, charged overnight.

Another option is to steadily switch from unsustainable wild fisheries and step away from the danger of overfishing entirely, to fish farming. Already, as of 2016, more fish was farmed than caught in the wild. Fish farming would also have to involve a greater proportion of non-carnivorous fish, as carnivorous farmed fish such as salmon do not always reduce the pressure on wild fish stocks. Coastal-based aquaculture also faces substantial challenges from nutrient pollution, release of lice and pathogens and displacement of local species by more reproductively advantaged species.

Next-generation fish farming, taking place far offshore or indoors and away from sensitive coastal ecosystems, claims to have solved these problems. But with many of the ecosystem services such as water filtration performed by mechanical means instead, both options face a sharp increase in electricity demand. The biggest barrier to uptake of next-generation aquaculture systems is the cost of that clean electricity. If it is more expensive than diesel for fishing boats, they cannot compete.

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