Fish Farm Lice Kill Wild Salmon/Sea Trout (And farmed fish, too, but we don't really care much about them. Nor do fish farms or they would farm only on land).

BAD NEWS BITES, May 3, 2019, Item:

220. Lice Kill Wild Salmonids - FINR, Norway, science paper. 

The humour in this one is the cautious tone of the scientists because they are in Norway, where the industry shoots bullets through scientists if they don't like their work: https://www.salmon-trout.org/wp-content/uploads/2018/01/Thorstad-Finstad-2018-Impacts-of-salmon-lice-NINA-Report-1449-2.pdf.


"Results from scientific studies on the impacts of salmon lice on Atlantic salmon and sea trout are summarized here. Considerable evidence exists that that there is a link between farm-intensive areas and the spread of salmon lice to wild Atlantic salmon and sea trout. Several studies have shown that the effects of salmon lice from fish farms on wild salmon and sea trout populations can be severe; ultimately reducing the number of adult fish due to salmon lice induced mortality, resulting in reduced stocks and reduced opportunities for fisheries. Depending on the population size, elevated salmon lice levels can also result in too few spawners to reach conservation limits."


And that lice kill wild salmon: "Studies indicate an annual loss of 50,000 adult wild Atlantic salmon to Norwegian rivers because of salmon lice, which corresponds to an overall loss of 10% of the wild salmon because of salmon lice on a national level (i.e., including both farm-free and farm-intensive areas, based on data from the years 2010-2014). Salmon lice from fish farms are identified as one of the two largest threats to wild salmon in Norway."

Note, currently there are only 500,000 wild Atlantic Salmon left in Norway.


In Ireland and Norway: "These studies show that lice-induced mortality in farm-intensive areas can lead to an average of 12-29% fewer adult salmon." And uses 20% as the reasonable death rate, noting that sea trout (searun browns) death rate is higher because they stay near rivers and don't go to sea. They are also much smaller. Later in the paper it says that in Ireland the result is 50% in high lice years.

This paper has eight pages of dozens of lice studies at the end - to cover their butts.

Here is what lice do to salmon/sea trout: "Laboratory and field studies have shown that salmon lice may induce osmoregulatory dysfunction (i.e. problems with the salt balance), physiological stress responses, anaemia, re-duced feeding and growth, increased susceptibility to secondary microbial infections, re-duced disease resistance and increased mortality in individual fish (see references in Fin-stad & Bjørn 2011, Finstad et al. 2011, Thorstad et al. 2015). Mortality starts to occur in the most severely infested fish within 10-20 days of exposure to lice larvae, when the lice have developed into preadult and adult stages."

For all you biochemistry keeners, here is what sea lice do to fish by breaking through the biological barrier - commonly called skin - between the fish and salt water: "Problems with the salt balance are likely caused by both the mechanical damage of the skin and tissue per se and to the overall physiological stress responses (see references in Thorstad et al. 2015). The damage of the skin, mucus surfaces and dermal tissue caused by salmon lice impairs the physical barrier between the fish body and seawater, and results in increased leakage of water from the fish and thereby osmotic and ionic imbalance. "

Lethal levels in lab experiments are: "Eleven attached/mobile salmon lice can cause death of an Atlantic salmon post-smolt of 15 g. Further, 50 attached/mobile lice may cause death of a sea trout post-smolt of 60 g. In sea trout post-smolts (fish body mass 19-70 g), the critical level for a sublethal stress response was found to be 12-13 mobile lice per fish (Wells et al. 2006)."

Now, these levels are far higher than lethal levels among wild fish in the ocean. In BC, 2 or 3 lice will kill a wild fry. And the paper goes right on to confirm this: "These threshold levels are based on effects in relatively short-term laboratory studies, and values are indicative and not absolute. For instance, density dependent mortality by lice may affect estimates of threshold values, and in some cases lead to overestimates. On the other hand, mortality in the natural environment may be higher than in laboratory studies because of additive effects. The effects of salmon lice have, for example, been shown to be more severe for Atlantic salmon post-smolts impaired also by other influences such as suboptimal water quality (Finstad et al. 2007, 2012). Furthermore, compromised fish may in general experience an elevated mortality risk from predators (e.g. Thorstad et al. 2013."

In a telling study of fry in the wild: "Lethal levels from laboratory studies are supported from field observations by Holst et al. (2003). They sampled more than 3000 wild salmon post-smolts in the Norwegian Sea, and found none carrying more than 10 adult salmon lice, suggesting a lethal dose around this level."

And here are a slew of papers on the issue of fish farm lice/wild salmonids: "Since the late 1980s, in parallel with the expansion of fish farming, there have been several reports of marked sea lice outbreaks on salmonids in Nor-way, Canada, Ireland and Scotland (summarized by Revie et al. 2009, Finstad et al. 2011, Thorstad et al. 2015). Salmon lice epizootics are not a common phenomenon for wild salmonids in farm-free areas (Thorstad et al. 2015)."

Confirming that sea lice abundance flows from farmed salmon to wild salmon, not the other way around, as claimed by fish farm companies, is this: "the large disparity in abundance between cultured and wild hosts means that larval production of salmon lice must originate primarily from farmed salmon and not from wild fish (Tully & Whelan 1993, Heuch & Mo 2001, Butler 2002, Heuch et al. 2005, Penston & Davies 2009). This is verified in a new study showing that salmon lice on wild fish in farm-intensive areas have lice with the same resistance to chemicals used in farms (Fjørtoft et al. 2017)."

And how far can those lice be distributed by ocean tidal currents? A long way: 
"Numerical models have shown that salmon lice larvae can be passively dispersed on currents to distances >15 km (Salama et al. 2016) and even >100 km (Asplin et al. 2011, 2014)." Think of this in relation to all the salmon farms in Clayoquot Sound in BC, perhaps 20 km in total.

"Several studies have shown a relationship between the production cycle in salmon farms and salmon lice levels on wild sea trout, with higher lice levels on trout in the second year of the production cycle (Butler 2002, Marshall 2003, Hatton-Ellis et al. 2006, Middlemas et al. 2010, 2013, Gargan et al. 2016a),"

 And: "Salmon lice from fish farms are identified as one of the two largest threats to wild Atlantic salmon in Norway (Forseth et al. 2017)."

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And from BC in 2019, 'catastrophic' wild salmon failure in Broughton/Port Hardy: https://www.facebook.com/alexandra.morton.1671/posts/2550161268545752.