Sunday, 29 December 2013

Sea Lice Kill 34% of Wild Salmon Smolts - Ireland, Updated Dec 29, 2013

Cermaq Mainstream lost 15% of its farmed fish to lice in Chile in the last year. In Norway, the annual sea lice loss is pegged at $170 Million in farmed salmon, and $30 M in Scotland. Here in BC, the same companies are still fighting the notion that lice kill wild Pacific salmon fry.

Here is a 2013 paper that show that sea lice kill 34% of wild Atlantic Salmon smolts in Ireland: 

The new paper demonstrates that the impact of sea lice on wild salmon causes a much higher loss (34%) of those returning to rivers in the west of Ireland, than the 1% loss suggested heretofore in the Jackson paper. The new study entitled “Comment on Jackson et al. "Impact of Lepeophtheirus salmonis infestations on migrating Atlantic salmon, Salmo salar L., smolts at eight locations in Ireland with an analysis of lice-induced marine mortality" is published by Krkošek, et al. (2013) in The Journal of Fish Diseases. It 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.

The new paper gives the example that if, in the absence of parasites, final adult salmon recruitment is 6% of smolt production, then the effect of parasite mortality reduces that recruitment to 4%.  According to interpretations used by Jackson et al. (2013), that is a change of 2%.  However, the overall effect is that it reduces the abundance of adult salmon returning to a river from, say, 6,000 down to 4,000; this 1/3 loss of salmon returns could have significant conservation or fishery implications. Krkošek, et al. 2013 emphasise that their purpose is not to downplay factors other than parasites that may also have a large influence on marine survival of Atlantic salmon. They do however highlight that parasites can and, in this case, clearly do have a large effect on fisheries recruitment, irrespective of apparent changes in overall marine mortality over time, and with important implications for the management and conservation of wild salmon stocks.

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