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Our appetite for shellfish risks pushing mussels and scallops into extinction
Bivalves have been touted as a food of the future – but wild populations might not last that long.
New research has revealed the areas of the world where demand for the molluscs is highest, allowing for conservationists to make plans to bolster species survival and food security.
Our demand for shellfish suppers is putting bivalves at risk of extinction.
While seafood is generally a greener source of protein than meat from land, increasing demand is putting bivalves such as mussels, scallops and oysters at a higher risk of being wiped out. Despite this, the scale of the issue has been largely unappreciated.
Now, a new study has revealed humanity is eating its way through over 800 different bivalve species – over 90% more species than previously thought. As the most populous species are being put under more pressure, it raises the risk that less resilient species will soon end up on our plates, exposing them to a greater risk of extinction.
Dr Katie Collins, the Museum’s Curator of Benthic Molluscs and a co-author of the research, says, ‘While the most currently desirable edible bivalves are inherently pretty low-risk, by targeting them we increase their risk factor, and make them vulnerable - we need to start managing them now so that we can protect them and their less stable relatives.’
‘To do this, we need better data and better consideration of how we can have a good relationship with the bivalves we want to keep eating long into the future.’
The findings of the study were published in the journal Nature Communications.
Mussels are a more efficient source of protein than other meats like beef, chicken or pork. Image © Foodio/Shutterstock.
Why are bivalves an important food?
With the world’s population having recently passed the eight billion mark, and not expected to level off until the 2080s, the search for sustainable sources of protein is more important than ever.
Bivalves and other molluscs, such as squid and octopuses, have been identified as one of the animal groups which could be best able to support growing numbers of humans.
‘Compared to beef, chicken or pork, bivalves are a much more efficient source of protein,’ Katie says. ‘Bivalves take nutrients directly from the water column, and don’t need additional feeding to be able to thrive.’
‘Their filter feeding also offers a number of beneficial ecosystem services, as they can take pollutants out of the water column and provide habitat for other wildlife.’
With demand for bivalves on the rise, the risk of overfishing is becoming increasingly likely. However, with the United Nations’s Food and Agriculture Organisation (FAO) measuring the catch of just 81 species, the risks to many of these animals are going unnoticed.
To improve this list, the researchers pored through a variety of reports and studies to identify what bivalves are being eaten by humans. They found in total that 801 species are eaten, but believe there are probably more exploited species out there.
‘It’s difficult to identify which bivalves are being eaten because they’re generally reported using their common names,’ Katie explains.
‘For example, what might be called a cockle in the UK is very different to one from the south Pacific, but they get lumped together in the same category, while the species Mercenaria mercenaria is known by at least three different common names depending on its size.’
‘There are also a number of other discrepancies in our sources, including one species recorded with the name “simmered with soy sauce and sugar”!’
Farming bivalves could be one way to reduce the pressure of fishing on wild populations. Image © meunierd/Shutterstock.
Finding the most exploited bivalves
By comparing the known species, the researchers could then start to identify how vulnerable the different bivalves were to extinction.
While a Red List assessment is considered the gold standard, this is a long process and so the team instead looked to estimate the baseline vulnerability of species to identify groups and areas where Red Listing should be a priority.
Unsurprisingly, the most exploited bivalves were the largest species that lived closest to shore. However, these species also have some of the lowest baseline extinction risk because they live over large areas and are tolerant of a range of temperatures.
That said, with limited information on how many of these bivalves are being harvested each year, the researchers don’t know if their extinction risk has been growing in recent years.
‘We have to assume that if the most stable species are driven extinct that demand for bivalves won’t let up,’ Katie says. ‘In this case, we’ll probably start eating the next most stable species, and the next, and gradually move towards less resilient species.’
These more vulnerable species tend to be found around the coastline of central America and the west coast of Africa. Of these species, scallops are especially at risk as their species tend to be quite unstable, with lineages that last for a short period of time.
One potential option to protect these threatened bivalves is to increase the amount raised in aquaculture. While the number of farmed molluscs has increased by an average of 3.5% every year for the past 20 years, bigger increases will be needed to meet our demand for these animals.
These increases are not out of the question, as aquaculture in China has seen the production of some farmed bivalves, such as scallops, increase by over 80% in just a decade.
‘Bivalve aquaculture offers a promising solution to help protect vulnerable bivalves while maintaining access to food,’ Katie says. ‘There are certainly challenges to this, but these are being worked on.’
‘By thinking about sustainable aquaculture now, we can ensure that we can have a better source of protein without jeopardising wild populations and marine ecosystems.’
