Defining the risk of sea lice infections: Analysing the early life history population dynamics of sea lice on Atlantic salmon aquaculture sites in the Bay of Fundy

Description

This project sought to better understand the distribution and dynamics of sea lice larvae on Atlantic salmon farms in the Bay of Fundy. This information could help identify specific times for treatment or farm management techniques to target sea lice larvae and reduce the overall frequency and/or severity of sea lice infestations on  salmon farms. As sea lice are currently one of the major issues affecting salmon farming in the Bay of Fundy, very little is known on the early life history of this species, making this study crucial to successfully managing this industry. The project was designed to combine both lab and field components to understand the mechanisms behind the infection dynamics of larvae attaching to their host fish.

There are signs on the east coast of Canada that resistance of sea lice to the current suite of therapeutant treatments is developing, resulting in more intense infection pressures on farmed salmon. A better understanding of the early life history of sea lice may allow for the development of more effective alternative approaches to parasite control.

Findings

The sea lice larvae present on farms were primarily (non-infective) nauplii and were distributed in random, patchy clusters that were highest in concentration adjacent to the fish cages. Shoreline zones of the Passamaquoddy Bay, NB region, several hundred meters to kilometers away, were found to be sea lice larval reservoirs. These zones possessed large concentrations (millions) of infectious copepodid larval sea lice that pose an infection risk to farms and potentially to wild species. Oceanographic observations showed potential routes of reinfection back to the fish farms through tidal and wind-driven flows. Results also indicated the primary route of successful attachment for infectious copepodids is likely through the mouth of a salmon.

If these observations are generally applicable to the mechanism of infection for coastal salmon farms, then an early warning system could be potentially implemented. This warning system could monitor for impending sea lice infections as well as an assessment of the effectiveness of sea lice control measures within a certain geographic area. It may also allow researchers to search for “hotspots” for larval retention, which will help in site selection. Reducing the infection rate of sea lice on salmon could result in significant benefits to all sectors of the aquaculture industry.

Program name

Aquaculture Collaborative Research and Development Program (ACRDP)

Years

2017 – 2020

Principal investigator

Shawn Robinson, Research Scientist, Fisheries and Oceans Canada, St. Andrews Biological Station, Maritimes Region
Email: shawn.robinson@dfo-mpo.gc.ca

Team member(s)

• Jonathan Day, Biologist, Fisheries and Oceans Canada, St. Andrews Biological Station, Maritimes Region

Collaborator(s)

• Keng Pee Ang, Vice President, Feed and Nutrition, Cooke Aquaculture Inc.