23rd October

Scientists at odds over how to interpret sea-lice results

A Canadian scientist claims that errors by the Marine Institute in analyzing its own scientific data means it has substantially underestimated the impact of lice on wild salmon. Dr Martin Krkošek from the University of Toronto’s Department of Ecology and Evolutionary Biology alleges that scientific papers published by the Marine Institute in 2011 and 2013 ‘incorrectly lead the reader to a conclusion that sea lice play a minor, perhaps even negligible, role in salmon survival. Such a conclusion can be supported only if one is prepared to accept at least three fundamental methodological errors’.

Krkošek further claims in his scientific paper published in The Journal of Fish Diseases, 2013 that his‘re-analyses’ of the same data ‘departs substantially from those reported and interpreted’ by the Marine Institute. ‘Whereas they assert that sea lice cause 1% of mortality in Atlantic salmon, the correct estimate is actually a one-third loss of overall adult recruitment,’ he states.

9.4 Salmon cages at Muir Geal Teo

We acknowledge that few smolts survive to return in any wild salmon population and that recent declines in the survival of Irish Atlantic salmon cannot be solely explained by sealice…… our purpose is to highlight that parasites can and, in this case, do have a large effect on fisheries recruitment… with important implications for the management and conservation of wild salmon stocks’.

Recent evaluation by the Marine Institute

The latest scientific paper from the Marine Institute backs up its previous findings and concludes that wild salmon stocks are not affected by the presence of salmon farms: that escaped farm fish have little influence on wild spawning stocks and that sea lice play only a minor role in sea mortality.

It notes also that ‘the key driver’ in the survival of individual [salmon] stocks is more likelyto be a deterioration of the freshwater habitat. Key points from the study:

• conservation limits are being met in many Irish salmon rivers

• steady and sustained improvement in the overall status of Irish salmon stocks

• rivers on the West coast are in general better in this regard, and rivers in the Northwest, West and Southwest River Basin Districts support both angling and commercial draft net fisheries

• no relationship between the presence of salmon farms and difficulties with rivers meeting their Conservation Limits

• absence of any evidence for a negative correlation between salmon stock status and aquaculture operations would suggest that there is also no discernible negative impact from escapees on the stocks studied

• fish farm escapees in Ireland are at a low level and contribute little to spawning stocks

• significant correlation between unpolluted water quality in catchments and the numbers of rivers meeting their Conservation Limits. This would suggest that the quality of freshwater habitat may be a key driver, implicated in the survival of individual wild salmon stocks. a low level and contribute little to spawning stocks

• since the introduction of Conservation Limits in 2007, exploitation of salmon stocks has been reduced. The commercial offshore mixed-stock drift net fishery was closed since 2007. In addition, angling pressure has been curtailed by closure of certain rivers, the introduction of Bye-Laws limiting catches and restrictions to angling for Spring salmon. The improvement of stock status over the study period would suggest that these conservation measures are contributing to stock recovery in a period of low marine survival


In the wake of increasingly bitter attacks by environmental groups on recently published research, the Marine Institute stands over the work of its scientists. Marine Institute statement to Inshore Ireland:

A recent Marine Institute study published in the peer reviewed international Agricultural Sciences journal (June 2013) found no correlation between the presence of aquaculture and the performance of adjacent wild salmon stocks.

The study by Dr Dave Jackson and colleagues at the Marine Institute examined geographic and temporal trends in Atlantic salmon stock abundance at a River Basin District level and evaluated the effect of salmon aquaculture sites and freshwater habitat quality as potential drivers of stock abundance.

This study found no correlation between the presence of aquaculture and the performance of adjacent wild salmon stocks. Freshwater habitat quality was found to have a highly significant correlation with stock status, suggesting that it may be a key driver, implicated in the survival of individual stocks.

The paper, ‘Evaluation of the impacts of aquaculture and freshwater habitat on the status of Atlantic salmon stocks in Ireland’ is available to download for free. An open access fee is payable by the author only after a paper has been peer reviewed and accepted for publication.

Access to quality research is vital to the scientific community and beyond and open access ensures that members of the public and the scientific community can freely access quality research without having to pay a download fee.

The Marine Institute stands firmly over all peer reviewed scientific papers published by its staff and we support open access to high quality research.

Save Bantry Bay comment

With the Marine Institute’s research now dismissed, the government has got to take heed of its own advisors recommendations from 1994, which clearly stated salmon farms should not be placed within 20km of wild salmon rivers.

The government has allowed its own agencies to pull the wool over their eyes. The Marine Institute’s sea lice research has caused controversy after controversy. World expert, Professor Mark Costello, has personally written to Minister Simon Coveney to warn him that he is being fed mis-information. And now a team of international scientists have discredited [Marine Institute] research in a well-respected peer reviewed journal.

Not only is the Marine Institute putting their reputation at considerable risk, but also that of the Irish government as a whole. Save Bantry Bay are asking that government stop blindly pushing their salmon farming agenda, backed by bad science, but instead complete a full Strategic Environmental Assessment as is required by EU law.

Inland Fisheries Ireland comment

Krkošek, et al. (2013) points out fundamental methodological errors made by Jackson et al. (2013). Following a re-analysis of the same data, it shows that it incorrectly concluded that sea lice play a minor, perhaps even negligible, role in salmon survival and that this finding emerged following three fundamental methodological errors.

This new paper conducts a re-analysis of the data with the findings departing substantially from those reported and interpreted by Jackson et al. (2013), and in previous publications that drew on some of the same data (Jackson, et al. 2011a; 2011b). Whereas Jackson et al. 2013 assert that sea lice cause 1% of mortality in Atlantic salmon, the correct estimate is actually a one third loss (34%) of overall returned stocks.

An Taisce comment

As authoritative scientific voices have weighed into the debate regarding fish farming, the plans for a giant 1,130-acre caged-fish installation between the Aran Islands and Clare, along with similar proposals elsewhere along the coast, appear increasingly ill-advised.

The revelations about its research can only strengthen the argument that the Marine Institute is propping up [BIM.s] controversial plans for these vast and intensive fish farms off the coast.

Sea lice have proven difficult to control on farms, especially large farms, because it is difficult to treat all fish simultaneously. Such fish farms are linked to mass fatal infestations of wild salmon and trout in countries such as Ireland, Scotland, Norway and Canada.

With the Marine Institute study now shown to be essentially a wrong-headed attempt to mask the risks posed by sea lice – harboured in great numbers within such farms – it now needs to be withdrawn in full.

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