Bad news if you think that switching to shrimp and lobster will ease your carbon footprint: Their fisheries are the most carbon intensive in the sea. A new study has found that in some cases catching crustaceans can produce as much CO2 per kilogram of edible protein as beef and lamb, and that perhaps you should plump for pelagic fish like anchovies and herring instead. 

Normally, it is recommended that environmentally conscious consumers give up on carbon-intensive meats such as beef and pork and go for foods that have a lighter footprint, such as wild fish and other seafood. 

But weirdly, there has never been a full assessment of the greenhouse gas emissions from fisheries, with estimates to date based on generalized information from a smattering of case studies. Now, a new study published in Nature Climate Change has looked at every single fishery in the world and assessed their carbon output. While most of them are pretty good, there are some you might want to think twice about.

To put things into perspective, it is thought that around 25 percent of global greenhouse gas emissions globally can be traced back to the food industry. This new research focused largely on how much fuel is used by fishing boats in each fishery, as this is by far the main source of carbon in the industry. It found that in 2011, fisheries worldwide used 40 billion liters of fuel, generating a total of 179 million tonnes of carbon dioxide.

This might sound like a heck of a lot but – and here’s the good news – that is only around 4 percent of the total emissions from global food production. However, these emissions are not spread evenly within the fishing industry.

So, while shrimp and lobster only account for around 6 percent of seafood landed, they actually account for a whopping 22 percent of CO2 emissions. This all comes down to the extra drag on fishing vessels as they set, check, and move pots, all of which has a fuel cost. This is then coupled with the fact that not much of a lobster is edible, and so in reality crustaceans emit a whopping 89kg CO2-eq per kg of protein, way more than chicken or pork, and in line with the lower estimates of carbon-intensive beef and lamb. 

"So on average, crustacean fisheries produce more emissions than most other fisheries, and more than chicken or pork production on land, and in some cases more than ruminants like beef and lamb," explains Robert Parker, co-author of the study, to IFLScience in an email. He also points out that "there is a lot of variation within those fisheries too," with Australian rock lobster fisheries using up more fuel than their American lobster equivalent. 

Interestingly, the study found that while in general carbon emissions for food production have been decreasing, the same cannot be said for fishing. While the catch level has remained relatively stable between 1990 and 2011, the amount of carbon emitted has jumped by 28 percent. This is particularly worrisome as boats have become more fuel efficient over this time. 

This might have to do with the fact that over this same period, the amount of crustaceans caught has increased by 60 percent. The authors note that while the carbon cost of shrimp and lobster might be sizable, it is not as big for smaller pelagic fish. Perhaps, then, we should consider eating them instead.