Science Advisory Report 2014/006
Sea Lice Monitoring and Non-Chemical Measures
- Sea lice and fishes co-evolved, so infestations in wild salmonid and non-salmonid fishes are a natural phenomenon. Transmission of sea lice between and within wild fish populations and salmon farms is known to occur, however, the dynamics of transmission will depend on a multitude of environmental and biological factors, and will be site and time-dependent.
- Sea lice dynamics (i.e., development and survival) are influenced by salinity and water temperature (which affect survival, growth, development rate, and reproductive success of sea lice), water movement (tides and currents), behaviour of infective larval stages and motile pre-adult and adult stages, and the abundance and proximity of suitable fish hosts.
- Hydrodynamic water circulation models, which may be useful in examining sea lice dispersal, are available for all salmon farming areas in Canada, and preliminary biophysical models of sea lice dynamics, have been developed for some regions. These tools could then be used to model sea lice dispersion and survival, help define broader management areas for sea lice control, study the dynamics of sea lice infestations and predict where and when sea lice outbreaks might be prevalent.
- Management and regulatory thresholds defining the level of on-farm sea lice per fish, that trigger the application of control measures for managing sea lice infestations, have been shown to be a useful management tool for reducing risk of transfer of sea lice from farmed to wild salmonids in some areas of British Columbia.
- A more flexible, dynamic and risk-based approach to setting thresholds than has been used in the past is recommended. In establishing management thresholds, consideration should be given to biological (e.g., proximity to and timing of wild fish migrations), environmental (e.g., temperature and salinity) and farm management (e.g., stocking levels and treatment options) factors.
- Sea lice monitoring programs currently in use in Canada for both farmed and wild fish are providing useful information, but could be improved. Monitoring programs should be designed to address the specific objective(s) of the monitoring program, and should include defined methods and protocols and a process to evaluate whether the monitoring program is effective in meeting objectives.
- In designing surveys and monitoring programs for sea lice on wild fish populations, ensuring representative sampling of all potential host species and stages, limiting loss of sea lice during capture and handling, and ensuring accurate identification of sea lice to species and life-history stage should be considered.
- Within a defined area, the abundance of sea lice on a farm is positively correlated with the number of neighbouring farms with sea lice, suggesting that the density of farms affects sea lice numbers. Therefore, if sea lice management on adjacent farms or within a management area is not coordinated, the management action may be less effective. Determining the appropriate size and location of a management area (farm, bay, fisheries area, etc.) is key to developing an effective sea lice management strategy, and this is influenced by a number of environmental and management factors (i.e., management objectives, number and location of farms, number and age of fish stocked on farms, distance between farms, local hydrodynamics, water temperature and salinity, farm management practices and logistics).
- Fallowing can be an effective tool to help reduce sea lice levels if it can be conducted at the appropriate management area level rather than by individual farms (i.e., coordinated fallowing of farmed sites), and if there are few wild hosts in the area which could act as a reservoir of sea lice. The effectiveness of fallowing as a sea lice control tool depends on factors such as abundance of wild host species in the area, proximity of farms, and environmental factors that influence sea lice development and dispersal of infective stages. The size of the zone to fallow should consider historical patterns of infestation, hydrodynamic conditions of the area, and when available, information from dispersal modelling.
- Non-chemical approaches to sea lice control, including the use of cleaner fish, sea lice traps, increased bivalve filtering through use of Integrated Multi-trophic Aquaculture (IMTA) approaches, utilization of sea lice-resistant strains of Atlantic salmon, and the use of immunostimulatory feeds have shown promise for helping to control sea lice under experimental conditions, but have generally not been applied commercially in Canada. None of these, individually, is likely to resolve serious infestations, but all may ultimately be part of an integrated sea lice management strategy. Some of these approaches may ultimately become components of an integrated pest control management strategy for sea lice management but more research is required to improve the efficacy of these strategies before they can be used economically on a large scale.
- An integrated, multi-facetted approach to managing sea lice in net-pen sites that is specific to the local area is recommended. Such an adaptive approach can permit customized management strategies to address area-specific issues. Such approaches do not rely on a single tool to control sea lice, but rather encompass several management strategies to improve the likelihood of success. A similar adaptive multilevel approach to pathogen control has been successfully used for bacterial and viral diseases.
This Science Advisory Report is from the September 25-27, 2012 assessment of Sea Lice Monitoring and Non-Chemical Measures. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.
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