Higher than usual salmon deaths
In 2012, a king salmon farm in Waihinau Bay, Marlborough Sounds reported higher than usual fish deaths to MPI. Affected fish had been eating less, were lacking in energy and had lesions on their skin. In the following summers, fish deaths occurred again in the same area.
MPI has been looking at a number of factors that could be involved in the fish deaths, such as the environment, management at the farm and the presence of bacteria.
After the first reported deaths in 2012, MPI took samples and analysed records from the affected farm. Samples were tested at MPI's Animal Health Laboratory (AHL) for a range of pathogens (organisms that cause disease) that infect salmon. None were found, and we concluded that environmental factors probably caused the deaths.
By 2015, the AHL had developed new diagnostic tests for fish pathogens. Further testing discovered 2 bacteria – that hadn't previously been found in New Zealand – in samples from salmon farms in Pelorus Sound and Queen Charlotte Sound. The 2 bacteria were:
- a Rickettsia-like organism that lives inside fish cells
- Tenacibaculum maritimum – a bacterium that causes ulcers in fish skin.
The Rickettsia-like organism is listed as an unwanted organism under the Biosecurity Act 1993.
These bacteria do not pose a known risk to human health. In addition, the management and quality control procedures required at salmon processing plants ensure no affected fish are distributed for human consumption.
MPI believes the bacteria could have contributed to the fish deaths, in combination with a range of other factors. A second investigation report was published in May 2017.
Controls to prevent spread
In April 2016, to prevent the bacteria from spreading, MPI put legal controls on the movement of salmon and equipment from affected areas. The controls are set out in a Controlled Area Notice.
Two areas have been identified as 'Contained Zones': the outer Pelorus Sound and Queen Charlotte Sound. It's illegal to move salmon farming equipment out of the Contained Zones. It's illegal to move farmed salmon out of the Contained Zones unless it's going straight to a processor or laboratory for testing. In December 2019, the Controlled Area Notice was updated to also allow the legal movement of dead salmon to a specific composting facility.
Find out more
- [PDF, 475 KB]
- Find out about unwanted organisms in New Zealand
- MPI and salmon farmers examine summer fish mortality issue – media release
- Aquaculture biosecurity readiness
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