Sea lice levels in Norwegian wild Atlantic Salmon appear to be up, say researchers
December 21, 2012, 8:01 am
Preliminary data from a 2012 study of sea lice indicates that the situation could have worsened, rather than improved, across Norway, said the Institute of Marine Research.
Norwegian researchers monitoring sea lice in wild stocks in 2012 also found that the lice could have had a negative effect on wild trout stocks across Norway, and on wild salmon stocks in some areas, the institute said.
Meanwhile, there is little indication that the situation is improving.
“There is little in our data collection that suggests that the sea lice infection on wild salmon has improved from 2010 to 2012,” said Pal Arne Bjorn, project leader for monitoring of salmon lice at IMR.
“On the contrary, it appears that the infection pressure on wild salmon has increased across the whole coast from Hordaland to Troms in the past years.”
The researchers found that infection levels on sea trout were “high, sometimes extremely high”, at several of the monitoring sites in intensive aquaculture areas from Hordaland to Troms.
Salmon smolt was also affected in some areas. Smolt monitored in Hardangerfjord and Sognefjord were found to have relatively high levels of lice in certain weeks of 2012, probably higher than they were in most years since 2000, Bjorn said.
That said, it appears that smolt that started their migration to sea in May had less lice than smolt that started off later in the year.
In the Trondheim fjord’s national salmon fjord, lice levels on salmon smolt were found to be low this year, but the smolt could have been exposed to high infection pressure because high levels of larval mark was found on the sea trout just outside of the national salmon fjord during the smolt migration.
“This can indicate that the synchronized spring de-lousing efforts of farmed fish have not succeeded to keep the infection pressure low enough during the migration of the salmon smolt at the end of May and early June in these areas,” Bjorn said.
In terms of areas, the northern areas of Troms and Finnmark were found to have low to moderate lice pressure on sea trout, with the lice also appearing later during the year. The same was observed for the inner fjords and the large national salmon fjords.
Sea lice grow to 12 milimeters in size for females, and 6 milimeters for male. They feed off salmon and trout’s skin and blood and reproduce throughout the year, but faster when the temperatures increase in the spring.
The IMR’s preliminary conclusions are laid out in its report, ’The salmon situation in wild salmon along the Norwegian coast in 2012′.