Oysters vs lice
IMTA (integrated multi-trophic aquaculture) is the farming of multiple commercially-important species from different trophic levels at the same site in an orientation that enables waste nutrient recycling while optimizing space usage and productivity. This “engineered ecosystem” endeavours to create a more ecologically-balanced aquaculture farm than typical monoculture methods that are currently the norm. The benefits of IMTA are multi-faceted, ranging from environmental to socio-economic.
One particularly interesting potential benefit of IMTA currently under investigation is whether culturing filter-feeding bivalves at salmon farms could help reduce the numbers of sea lice larvae in the water. Allie Byrne, a graduate student with the University of Victoria on Vancouver Island, is studying the potential of Pacific oysters as a sea lice mitigation tool. In collaboration with Grieg Seafood BC Ltd, and supervised by Dr Chris Pearce with Fisheries & Oceans Canada (DFO) and Dr Steve Cross with the University of Victoria, Ms Byrne has been culturing oysters at a salmon farm south of the Broughton Archipelago – an area historically under considerable scrutiny for the perceived threat of sea lice from cultured Atlantic salmon having a negative effect on wild migrating Pacific salmon species.
She examined oyster growth and larval sea lice densities and compared numbers at the farm to a control site away from the farm. Her research showed that oysters may benefit from being in proximity to the salmon cages and identified optimal placement to maximize growth. Earlier laboratory work in Dr Pearce’s lab at DFO showed that oysters are able to ingest sea lice larvae, but larval densities in the oyster cages on the Grieg site didn’t show a measurable difference from control pens without oysters or the oyster reference site (away from the farm). Ms Byrne postulates that “ingestion of these relatively rare copepod larvae in the field is likely only detectable at a finer scale”. She is now employing genetic tools in order to determine whether sea lice DNA is detectable in the digestive tracts of the oysters. Interestingly, her work also corroborates several other studies which show declining larval numbers coinciding with SLICE treatments and declining water salinity.
