Evaluation of light traps as a monitoring and control tool for planktonic-stage sea lice

The original plan for this project was to test the usefulness of light traps as a monitoring and control tool for sea lice. Present control strategies minimize production of planktonic sea lice by limiting the density of their parasitic parent population (e.g., by adding the pesticide SLICE® to fish feed when parasites on penned fish exceed a triggering abundance). However, the treatment is expensive, and cannot be administered close to harvest date. Both adult and planktonic sea lice are positively phototactic (they swim toward a point source of light). This behavior can be exploited to physically trap the sea lice. We planned to deploy light traps within and near fish pens in the Broughton Archipelago and, by comparing trap capture rates with ambient densities of planktonic sea lice (sampled by pump), estimate the mortality or removal rate per trap. However, because there were no accessible farms with significant lice loads, we modified our plan by reducing the number of light trap deployments, and increasing the effort for net tow surveys of the entire area. In spring 2009, average concentrations of planktonic lice were considerably lower than in 2007 and 2008. Only two sites had moderately high concentrations, both located along the north margin of Queen Charlotte Strait (seaward of the Knight/Tribune inlet corridor).

For further information, please contact: project leader, David Mackas, at Dave.Mackas@dfo-mpo.gc.ca.