The increased mussel production is part of industry organization Scotland Food and Drink’s ambition to double Scottish food production by 2030.
Scottish researchers have therefore studied how mussel larvae move in order to give mussel farmers and other shellfish farmers important information on where and how to farm them.
The discovery: everything revolves around the current.
The University of Stirling’s Institute of Aquaculture used genetic testing of mussels at sampling sites along the west coast of Scotland, combined with mathematical modeling to understand where mussels grow well.
Research in this area has been limited so far, according to PhD student Ana Corrochano-Fraile. “Mussel farming has been a bit of a black box”,he said. “The larvae float in the water, we put ropes in the sea and the larvae appear there. If the stock goes down, we don’t know why. If the quality drops, we don’t know why.
The team found that mussel larvae move in currents from south to north. “We have found that within 30 days a hopper cloud can move from the Scottish border near Stranraer to Islay [about 80 miles] for example. They then attach themselves to the substrate – anything solid in the water, which can be ropes – and grow for a year and a half until they start reproducing. The next generation of larvae are carried by the current from Islay to the Outer Hebrides in 30 days – that is much further, as 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 Marine Science Association, as well as with mussel farms at various locations on the west coast, through the Fishmongers’ Company, Scottish Sea Farms Ltd and the Association of Scottish Seafood Growers. They found, for example, that Loch Eil farm larvae leave the loch, but no new larvae enter it, so although Loch Eil has a self-sustaining population, it also contributes to the populations of other places, like Loch Linnhe.
Corrochano-Fraile’s supervisor, computational biologist Dr Michaël Bekaert, said: “We were surprised by how quickly the larvae moved in a short time, as well as their fragility and vulnerability.
“Research shows that if we were to somehow block the current between Scotland and Northern Ireland, or slow it down, we would lose larvae. Likewise, if we were to pollute the sea there, or somewhere like Loch Linnhe, where lots of fresh grubs wash up, it would have a huge impact. To breed quality mussels, like anything else, you need maximum diversity in genes, so you don’t want to lose new genes by messing with the current or polluting.
“We will need to better understand the effects of climate change, but if the current were to move much faster, for example, the larvae could be swept past the Outer Hebrides without stopping at all!”
Forty percent of the UK’s mussels are produced in Scotland, with half growing along the west coast and the rest around Shetland. Mussel farming has a low impact on the environment, as they require no food, grow on ropes, and by nature they even clean the water around them.
“It does, however, mean that they are vulnerable to pollution,”explained Dr. Bekaert. “They will absorb heavy metals, for example. If we give them garbage to eat, they keep it. But if these fast waters are clean, the mussels are clean.
“It is possible to produce a lot of molds at very low cost – environmental and economic. The most expensive part is harvesting and processing them.
Dr. Bekaert added: “This level of detailed oceanographic information is also relevant for other valuable bivalves such as scallops and oysters and, being on a scale of meters rather than kilometers, is even useful for the salmon industry.”
The article, ‘Predictive biophysical models of bivalve larvae dispersal in Scotland’, is published in the journal Frontiers in Marine Science.
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