Aquaculture for all
The Fish Site presents: The Vienna Sessions - Conversations about aquaculture. 9 video interviews with aquaculture thought leaders. Watch here.

Sea Lice Study Accused Of Being Inconclusive

Salmonids Health Biosecurity +5 more

CANADA - A paper published suggesting that sea lice do not harm wild Pacific salmon does not provide conclusive evidence and fails to convince when weighed against the full scope of previous science on the subject, according to Watershed Watch Executive Director, Craig Orr.

He said that what the study does do is confirm that salmon farms are the “main source” of lice on wild juvenile salmon.

This result supports what environmental groups and independent scientists have been saying for years: farms are the primary source of lice infecting juvenile out-migrating wild salmon – a fact salmon farming companies and government continually deny, he says in a Coastal Alliance for Aquaculture Reform (CAAR) article.

Watershed Watch is a founding member of Coastal Alliance for Aquaculture Reform.

Mr Orr says that independent researchers in BC, who have been studying this issue for years, were never given access to the on-farm data provided to the researchers who conducted this study.

"It begs the question as to why this particular group of researchers was given privileged access to on-farm data, while others seeking the same data had to resort to launching Freedom of Information requests, only to be denied because the data are in a private database controlled by the salmon farmers’ industry association," Mr Orr writes.

He adds that scientists are raising concerns about the methods used to analyse data in the new study such as:

  • The authors aggregated data and did not use spatial or temporal controls which likely weakened/skewed analyses of productivity trends.
  • The data were not collected to answer specific hypotheses concerning sea lice impacts on wild salmon, the most rigorous way to approach a science study.
  • The report largely ignores the potential of sea lice as vectors for disease transmission with associated lethal or sub-lethal effects from farmed to wild fish.
  • Only adult female lice were examined as the indicator of total abundance of lice on a farm in a specific period of time. Lice in larval stage, a stage in which lice are most abundant, were largely ignored.
  • The authors claim sea lice from farms are not a significant factor driving the decline of pink salmon in the Broughton Archipelago, but fail to name the missing link, and refer to anecdotal observations that sea lice may be a food source for juvenile salmon.
  • Looking at trends in wild adult salmon is problematic because of multiple variables such as different geographical factors and different times of the year.

Mr Orr says the biggest criticism of the paper’s findings lies in the stark contrast of the conclusions with respect to other published science linking salmon farming and lice to declines in pink salmon as well as coho, sea trout, and wild Atlantic salmon. Previous papers strongly suggest sea lice from salmon farms negatively affect wild salmonids.

Further Reading

- You can view the full report by clicking here.

Further Reading

- Go to our previous news item on this story by clicking here.