Rising sea temperatures in the Bay of Fundy are blamed for an increasing number of sea lice outbreaks according to the Atlantic Canada Fish Farmers Association.
The association's 2016 annual sea lice management report says temperature increases in the bay jumped two degrees above historical levels in 2009 and the trend has continued over four summers since then, allowing sea lice to grow to maturity in less than half the time.
"We are seeing these record high water temperatures maintained for longer periods and later in the year than we have seen in the past," said the report.
"Increasing ocean temperatures over prolonged periods of time and later in the year are having an impact on the number of sea lice in southwestern New Brunswick."
Sea lice are a naturally occurring parasite found in both farmed and wild fish.
Information not public
The New Brunswick Department of Agriculture, Aquaculture and Fisheries collects data on sea lice counts but does not make the information available.
"Reporting sea lice counts are a requirement for all licence holders," said Jean Bertin, communications person with the department. "These reports are confidential under the Aquaculture Act."
Information about the location and time of sea lice treatments is released however, and it shows a dramatic increase in activity since 2012 when treatments were carried out 50 times in the bay.
By 2016 sea lice treatments were conducted on 124 occasions.
More than 500,000 fish killed
In late July 2016, sea lice killed 252,000 Atlantic salmon at two Gray's Aqua group farms in Passamaquoddy Bay.
Another 284,000 fish were pre-emptively killed to contain the sea lice outbreak.
According to a court document from the province's then-chief veterinarian, Michael Beattie, the average lice counts at the two farm sites ranged from 65 to 135 per fish.
The farm was being managed at the time by George Kinsman of Ernst & Young, after Gray's operations had slipped into receivership.
Kinsman's report, contained in court documents, describes fears the outbreak would cause 600 tons of "rotting biomass" to wash up onto the St Andrews shore line if the outbreak was not contained.