SALMON farming will not be allowed to expand “at any expense”, Rural Economy Secretary Fergus Ewing has told an inquiry.

The cabinet secretary was giving evidence before MSPs yesterday when he dismissed suggestions that the Scottish Government has taken a firm line on backing the sector’s expansion plans even while Holyrood committee investigations continue.

Describing himself as a “very strong and public advocate” for aquaculture, Ewing said much criticism of the industry was “unevidenced” and “emotive”, but stated: “We do not accept growth at any expense. Growth must be sustainable.”

Critics of salmon farming say the lucrative sector – which produces the country’s top food export – poses an environmental threat through parasites, disease and the use of chemicals.

Campaigners have called for tighter regulation and tougher scrutiny to protect wild fish stocks and a 42,000-strong petition was handed over yesterday.

Ewing said regulatory changes will see reporting of problems like fish mortalities move from a quarterly to a monthly basis, improving transparency.

He also said Marine Scotland had been tasked with carrying out a review of acoustic deterrent devices (ADDs), which the Hebridean Whale and Dolphin Trust claims could disrupt cetacean species around the coast.

The devices are employed at some salmon farms to keep seals at bay, but the trust claims there is evidence that they could also disrupt wildlife tourism by driving minke whales and other key species away.

On the deaths of captive fish, which can also be caused by treatment for deadly sea lice, Ewing said: “Obviously we all want to drive down the mortality rates.

“Ideally a mortality rate of zero is what any farmer, land or sea, would aspire to, whether it’s farmed salmon, whether it’s lambs, whether it’s dairy cattle. Sadly life shows that it’s extremely challenging.”