Nearly 475,000 fish lost to sea lice infestations amid challenging environmental conditions

The summer of 2025 has been a difficult one for salmon farming operations in Newfoundland, and the challenges show no signs of letting up. Mowi Canada East, a subsidiary of global aquaculture giant Mowi, has confirmed yet another significant mortality event at its operations on the province's southern coast—the third such incident in just a few months.

What Happened

According to the company's public disclosure, nearly 475,000 Atlantic salmon were affected across two separate farming sites. One location saw 238,246 fish impacted, while the other lost 236,569.

Unlike some mortality events that occur suddenly, this incident unfolded over a period of weeks. The culprit: repeated sea lice infestations that proved difficult to control despite treatment efforts using Health Canada-approved products.

Mowi pointed to a combination of environmental factors that created ideal conditions for sea lice proliferation:

• Prolonged high water surface temperatures that persisted well beyond normal seasonal patterns
• Extended periods without rainfall reducing freshwater runoff into coastal fjords
• Calm wind conditions that failed to drive the surface currents that typically help disperse parasites

"These conditions are ideal for sea lice and other small marine animals to flourish," the company stated in its announcement.

A Pattern Emerging

This latest incident doesn't exist in isolation. It follows two earlier mortality events that have made 2025 a particularly challenging year for Mowi's Newfoundland operations.

In July, the company reported a mortality event at its Little Burdock Cove site near Rencontre East, where 176,249 salmon died due to decreased oxygen levels associated with elevated water temperatures.

Combined with the latest losses, Mowi has seen well over 650,000 fish affected by environmental mortality events in Newfoundland this summer alone.

The Human Element

In its statement, Mowi acknowledged that the losses extend beyond financial calculations. The company expressed that the incident represents "a painful loss for the dedicated and hard-working staff who have cared for and reared these fish for the last year."

The company thanked its employees for their professionalism throughout the difficult period—a reminder that behind every aquaculture operation are people whose livelihoods and daily efforts are directly affected by these events.

Climate as the Common Thread

While each mortality event has its own specific triggers—sea lice in one case, low oxygen in another—the underlying theme connecting them is increasingly difficult to ignore: environmental conditions that fall outside historical norms.

Mowi was direct in its assessment of the situation: "2025 is proving to be an environmentally tough year for everyone on Newfoundland."

That statement reflects a broader reality facing the aquaculture industry globally. Operations that were designed and sited based on decades of environmental data are now contending with conditions that push beyond those parameters. Water temperatures are reaching levels that stress fish and favor parasites. Weather patterns are becoming less predictable. The stable conditions that salmon farming depends on are becoming harder to count on.

Industry Implications

For Mowi, the immediate impact is economic. The company described the incident as a financial loss, coming after what it characterized as "several years of successful incident-free production."

But the longer-term implications extend across the entire salmon farming sector. Operations in regions experiencing climate volatility may need to reconsider everything from site selection to cage depth to treatment protocols. Investment in real-time monitoring systems, predictive modeling, and adaptive infrastructure is likely to increase.

The Newfoundland situation also raises questions about regulatory frameworks and reporting requirements. The company noted that it informed the provincial government as soon as it became aware of the cumulative mortality numbers—a practice that has become increasingly important as transparency demands grow.

Looking Forward

Salmon farming has always involved managing environmental variables. Fish are raised in open water, subject to the conditions around them. Disease, parasites, temperature fluctuations, and oxygen levels have always been part of the equation.

What's changing is the frequency and intensity of challenging conditions. Events that might once have been considered rare are becoming more common. The playbook that worked for previous generations of fish farmers may need to be rewritten.

For companies like Mowi, the path forward likely involves a combination of operational adaptation, technological investment, and honest acknowledgment that the environment they're farming in is changing. How quickly and effectively the industry responds to that reality may determine its long-term viability in regions like Newfoundland.

The fish that were lost this summer cannot be recovered. But the lessons learned from these incidents—about environmental monitoring, treatment timing, and climate adaptation—could help prevent similar losses in the future.