Increasing mussel production is part of the ambition of trade association Scotland Food and Drink to double Scottish food production by 2030.
Researchers in Scotland have therefore investigated how mussel larvae move to give mussel and other shellfish farmers important insights into where and how to farm them.
The discovery: it’s all about the flow.
The Institute of Aquaculture at the University of Stirling used genetic testing of mussels at sample sites along the west coast of Scotland in combination with mathematical models to understand where mussels grow well.
Research in this area has so far been limited, says PhD student Ana Corrochano-Fraile. “Mussel farming has been a bit of a black box”,he said. “The larvae float in the water, we lay ropes in the sea and larvae appear there. If the stock goes down, we don’t know why. If the quality deteriorates, we don’t know why.”
The team found that mussel larvae move in the current, from south to north. “We found that in 30 days a cloud of larvae can move from the Scottish border at Stranraer to Islay [about 80 miles] for example. They then attach themselves to the substrate—anything stuck in the water, which could be ropes—and grow for a year and a half until they start to reproduce. The next generation of larvae is carried on the current from Islay to the Outer Hebrides in 30 days – that’s a lot further, because the current is faster there.”
She added: “Knowing where mussels come from and where they go tells us a lot about the best and worst locations for farms.”
The researchers worked with the Scottish Association of Marine Science, as well as mussel farms in several locations on the west coast, through the Fishmongers’ Company, Scottish Sea Farms Ltd and the Association of Scottish Seafood Growers. For example, they found that Loch Eil farm larvae leave the loch, but no new larvae come in, so while Loch Eil has a self-sustaining population, it also contributes to populations in other locations, such as Loch Linnhe.
Corrochano-Fraile’s supervisor, computational biologist Dr. Michael Bekaert, said: “We were surprised by how quickly the larvae moved in a short time, as well as how fragile and vulnerable they are.
“The research shows that if we somehow blocked or slowed the flow between Scotland and Northern Ireland, we would lose larvae. Likewise, if we polluted the sea there, or somewhere like Loch Linnhe, where many washing up fresh larvae would have a huge impact.To grow quality mussels, as with anything, you need maximum diversity in the genes, so you don’t want to lose fresh genes by tampering or polluting the flow.
“We will need to better understand the effects of climate change, but if the flow were much faster, for example, the larvae could be swept past the Outer Hebrides without stopping!”
Forty percent of Britain’s mussels are produced in Scotland, half along the west coast and the rest around Shetland. The mussel farming has a low impact on the environment as they do not require food, grow on ropes and are naturally bivalves, they even clean the water around them.
“However, this means that they are vulnerable to pollution,”explains Dr. Bekaert. “For example, they will absorb heavy metals. If we feed them garbage, they keep it. But if these fast-flowing waters are clean, the mussels are clean too.
“It is possible to produce a lot of mussels at a very low cost – environmentally friendly and economical. The most expensive is to harvest and process them.”
dr. Bekaert added: “This level of detailed oceanographic information is also relevant to other valuable clams such as scallops and oysters and, because it is on a scale of meters rather than kilometers, is even useful for the salmon industry.”
The newspaper, ‘Predictive biophysical models of the distribution of bivalve larvae in Scotland’, is published in the journal Frontiers in Marine Science.