Modeling sea lice dispersion and estimating encounter rates with juvenile Pacific salmon in the Broughton Archipelago and Discovery Islands

Description

This sea lice dispersion modeling project initiated by the Pacific Salmon Forum and Fisheries and Oceans Canada was carried out in collaboration with the Broughton Archipelago Management Plan (BAMP) project. The objective was to explore means for reducing the potential for sea lice from farmed salmon to infect juvenile pink and chum salmon during the outward migration season.

Sea lice copepodid concentrations were computed by coupled circulation and dispersion models for the Broughton Archipelago and used to estimate encounter rates with juveniles migrating seaward along pre-specified routes.

The model grids were improved to provide increased resolution around farms and coastlines, and various coastal boundary approximations were tested to determine their effects on sea lice retention. A hindcast simulation for May 2008 was compared with a similar run for March 2008 in order to estimate the impact of freshwater on sea lice mortality. A May 2010 run was also compared with May 2008 to assess inter-annual variability.

Methodologies to compare these concentrations and encounter rates with values arising from BAMP’s wild salmon monitoring program were also investigated. In the second year of the project, model coverage was extended to the Discovery Islands area using the circulation component of a viral transmission model that was developed with Aquaculture Collaborative Research and Development Program (ACRDP) funding.

In an effort to provide validation data on larval sea lice abundance and distribution for the Foreman-Stucchi transport and dispersal model, the project was expanded to include a field sampling component. Sampling methods analysis of planktonic-stage sea lice distributions, were applied in the Discovery Passage region.

Findings

The circulation model was refined to improve the heat flux forcing calculation. As a result, the agreement between modelled and observed near-surface temperatures improved. The coupled circulation and dispersion model was used to simulate May sea lice concentrations with increased credibility. Ocean salinities in May 2010 were higher than in May 2008 in both modeled calculations and field observations. The higher salinity in 2010 likely played a significant role in the higher sea lice numbers found on wild juvenile salmon that year.

Publications

Foreman, M.G.G., D.J. Stucchi, K.A. Garver, D. Tuele, J. Isaac, T. Grime, M. Guo. 2012. A circulation model for the Discovery Islands, British Columbia. Atmosphere-Ocean 50(3): doi:10.1080/07055900.2012.686900.

Program Name

Program for Aquaculture Regulatory Research (PARR)

Year(s)

2010 to 2012

Principal Investigator(s)

Mike Foreman, Research Scientist, Fisheries and Oceans Canada, Institute of Ocean Sciences, Pacific Region
Email:  mike.foreman@dfo-mpo.gc.ca

Team Member(s)

Dario Stucchi, Fisheries and Oceans Canada,  Institute of Ocean Sciences, Pacific Region

Darren Tuele, Fisheries and Oceans Canada,  Institute of Ocean Sciences, Pacific Region

Peter Chandler, Fisheries and Oceans Canada, Institute of Ocean Sciences, Pacific Region

Moira Galbraith, Fisheries and Oceans Canada, Institute of Ocean Sciences, Pacific Region