Gear type, stock abundance key to more efficient fishing

Diesel and other fossil fuels make modern commercial fishing possible, and have since the late 1880s, when trawlers first started using steam engines.

At the time, the new technology allowed bigger boats to ranger further while fishing deeper and harder – all while independent of the wind and human muscle labor. On-board freezers preserved fish longer, while the engines returned them to market quicker.

But the burning of that fuel use also creates most of the industry’s emissions of greenhouse gases – making fuel use both the industry’s biggest contribution to climate change and its greatest opportunity to raise efficiency.

The amount of fuel used varies greatly across fisheries and gear types. But generally, emissions coming from commercial fishing are lower than those from land-based animal farming.

Some estimates put the emissions from global fisheries at roughly that of farmed chicken, according to Robert Parker, a postdoctoral research fellow at the University of British Columbia’s Institute for the Oceans and Fisheries. 

“While the relative performance of fisheries varies widely…the industry average is relatively low-carbon compared to many land-based systems,” Parker told SeafoodSource.

But certain types fisheries, such as those for lobsters and prawns, and certain gear types may have corresponding emissions as high as those of beef and sheep, which are both much higher than chicken.

According to Parker, the two most important drivers of emissions from fishing are the type of gear used and the health of the fish stock. The gear needed to catch different species makes an enormous difference in emissions. For instance, small pelagic fish, which are found in dense schools in shallower waters, can be caught using very fuel-efficient gear. Crustaceans, by contrast, rarely congregate in dense groups, and are often found on the ocean bottom, requiring inefficient gears such as trawls and traps.

“If two boats go out in the morning and spend the day fishing, and one comes back with a few tons of sardines while the other comes back with 30 kilograms of lobsters, you can imagine that the sardine catch was much more efficient, regardless of the type of gear employed,” said Parker, who has co-authored multiple studies on the greenhouse gas emissions of commercial fishing.

For species that can be caught using multiple types of gear, the choice of which type still makes a large difference. A boat using one type of gear can burn three to five times more fuel than another boat using a different gear, even if they’re targeting the same type of fish, according to Peter Tyedsmer, a professor in the School of Resource and Environmental Studies at Dalhousie University.

But when two fisheries of the same species are targeted using the same gear, it’s the abundance of the fish that drives emissions, Tyedsmer told SeafoodSource. Catching fish from healthy, plentiful stocks requires less fuel than attempting to do so from scarce, overfished stocks.

Rebuilding those overfished stocks would do the most to make fishing more fuel efficient, said Tyedsmer, who has also co-authored multiple studies on fishing emissions. 

“Fisheries are extremely well-positioned to flourish in a carbon-constrained world,” Tyedmers said. “Yes, they generated GHG emissions, but relative to, say, beef, at much lower rates. Moreover, many fisheries have far more capacity to lower their energy use and resulting emissions when biomass is increased — stock status improves — particularly where stocks are in poor shape or overexploited.”

But government efforts to lower emissions have so far focused on using different technology, such as low-drag gears and more fuel-efficient engines, and behavioral changes, such as steaming slower. Such changes to technology and behavior have not generally lowered fuel use per ton of seafood caught, Tyedmers said.

Unlike other industries that cross national borders, such as commercial airlines, governments are not pursuing international accords to regulate fishing-related greenhouse gas emissions.

In fact, many governments have excluded fisheries from emissions control schemes, and have even subsidized fuel use. However, other aspects of fuel use and emissions have been regulated, such as limits on the sulphur content of marine fuels, Parker said.

To better inform consumers and businesses about the greenhouse gas emissions of different types of seafood, the Monterey Bay Aquarium’s Seafood Watch program is developing a web-based tool to calculate the greenhouse gas emissions of fisheries and aquaculture, a spokesman told SeafoodSource.

The tool will calculate emissions up to the dock or farm gate, and will collect data for the use of fuel in wild capture fisheries, the amount of energy used on fish farms and the energy expended in producing feed for aquaculture. Since solid data on greenhouse gas emissions from seafood is limited, the tool won’t have the same specificity of Seafood Watch’s other ratings.

Seafood Watch aims to launch the first version of the tool late this year or early next year.