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The Hardangerfjord Salmon Lice Project
Salmon lice infection level in wild sea trout was investigated in May, June and August 2009. Sea trout were sampled inside the farm free national salmon fjord (Etne), in the intensively farmed middle part (Rosendal) as well as in inner Hardangerfjord(Granvin). Results indicate high infection pressure in middle Hardanger both in May and especially June, but also inside the national salmon fjord in June. Low infection pressure were observed in inner fjord at all sampling points. Atlantic salmon post smolts were also captured by trawl, both in middle fjord, outer fjord as well inside the national salmon fjord in May. Preliminary results shows relatively low infection risks in May, but increasing in May/June. Trawled sea trout showed similar results, while caged hatchery reared salmon smolts showed low lice levels. In addition, sea trout smolts emigrating from the River Guddal in 2008 and 2009 were pit-tagged, and split in two groups, one treated with emamectin by injection, while the other group was nontreated.
To continue the data series of lice counts from farmed salmon, the Hardangerfjord Fish Health Network (HFN) coordinated collection of data from fish farms in the spring of 2009.
Specially trained personnel (telleteams) visited 20 sites in all areas of the fjord in the spring and summer. The current situation in lice control in Norway, where salmon lice resistant to emamectin benzoate (Slice), pyrethoids( Alpha-Max and Beta-Max), have been found on the coast from Lofoten to Rogaland, has forced fish farmers to be very careful when choosing medicines for delousing. The HFN recommends the use of Slice only for the coordinated winter delousings in December-January, in any case, one treatment with this substance per year at each site. The data gathered in the current project will enable us to compare the efficiency of this years treatments and overall efforts to the ones of previous years, to see if the precautionary and strategic use of Slice has produced as low lice numbers as before. Statistical methods for comparing the accuracy of lice counts from the counting teams and the farmers will now also be explored.
The aim of WP3 is to understand the environmental conditions affecting the salmon lice populations. We have been able to participate on regular cruises, typically every second month, collecting hydrographical and current data. Also the development of the numerical model for salmon lice growth and advection, which relies heavily on model results of hydrography and currents, is done in collaboration with similar IMR activities. The recent results indicate that the water temperature during the winter might be more important than we expected for the development of the salmon lice population present in the fjord in May when the wild smolt migrate out the Hardangerfjord. Model results confirm our previous findings that the salmon lice can potentially spread far (>100 km), fast (> 2 km/h) and that the variability can be huge. We are yet working on how clustering of fish farms in the Hardangerfjord will affect the abundance and distribution of salmon lice. Based partly on efforts in this project we have presented scientific advice to the National Food Safety Authorities about potential spreading of salmon lice resistant to slice in fall 2008 as well as advice on best practice for synchronized delousing on fish farms for the winters 2009 and 2010.
Another aim was to complete the compilation and analysis of sea lice counts from salmon farms in the Hardangerfjord to establish epidemiological patterns of infections suitable for use in a DDE (differential difference equation) mathematical model. The work took place in close collaboration with the HFN and required extensive work to ensure the quality and validity of the final data to be used in the analyses. An Access data base was established and two characteristic epidemiological sea lice profiles were derived based on Hardangerfjord data from 69 salmon farms between 2004 and 2007. One profile was for lice infestation on sites stocked in autumn while the other was for sites stocked in spring. In collaboration with Grallator these profiles enabled various populations and environmental parameter sets to be investigated in a mathematical model that could describe each of the profiles. A first approximation which adequately models the sea lice infestation patterns on salmon farms in the Hardangerfjord has been identified, and this will form the basis of ongoing research into optimal lice control strategies in years to come.
The results from the proposed project will be communicated to the management authorities, to fisheries associations and to local users of the study area. Other important target groups for the results are national and international R&D groups. Results will be published both in peer-reviewed journals, and in Norwegian national journals. Information will be disseminated through talks on national and international meetings and symposia as well.