Terms of Reference

Fallowing as a tool for disease mitigation in marine finfish facilities

Regional Science Response Process – Pacific Region

June 15, 2021
Virtual meeting

Chairperson: Stewart Johnson

Context

Fisheries and Oceans Canada’s (DFO) Aquaculture Management Division (AMD) is the lead regulatory body for managing aquaculture in British Columbia (BC). The aquaculture management regime in BC is robust and complex, with oversight from provincial and other federal regulatory agencies. Licences are the primary tool used to manage this fishery, and are issued under the authority of the Pacific Aquaculture Regulations and the Fisheries Act. AMD licences marine finfish, marine shellfish, and land-based hatchery and production facilities, including approximately 111 marine finfish farms which are the focus of this review.

Currently, AMD requires farms to fallow prior to re-stocking a farm when benthic impacts are beyond acceptable levels to ensure seabed recovery. There is also an interest in determining if a fallow period based on the presence of pathogens or disease would be beneficial to reduce the risk of transmission between production cycles, in addition to other health management tools. This fallow period could be required by all farms as a precautionary approach, or could be performance based and only occur if active disease was present. To support AMD decision-making, a science-based understanding is needed to determine the factors that contribute to the benefits of fallowing in a BC context.

The use of farm- and area-level fallowing has been used in other countries as a strategy to reduce transmission of infectious pathogens between production cycles (Bron et al., 1993; Kilburn et al., 2012; McVicar, 1987; Murray, 2006; Rae, 2002; Werkman et al., 2011; Wheatley et al., 1995). For example, Price et al. (2017) found that a 3-month farm-level fallowing was effective at significantly reducing the risk of Salmonid Rickettsial Septicaemia (SRS) between production cycles at farm sites in Chile. However, the effect of farm- and area-level fallowing has not been assessed for most pathogens that are endemic to BC waters. While fallowing is practiced voluntarily in BC, it is not regulated.

AMD has requested that the DFO Science Branch assess what is currently known about infectious pathogens found at BC Atlantic and Chinook salmon farms, in order to determine if fallowing can successfully minimize the transmission of pathogens between production cycles. Decreasing pathogens and disease on farms may also reduce the risk of transmission to wild salmon. The response should consider the nine pathogens assessed for Discovery Island farms in response to Cohen 2012 recommendation #19 (1. Aeromonas salmonicida, 2. Piscirickettsia salmonis, 3. Renibacterium salmoninarum, 4. Yersinia ruckeri, 5. Piscine Orthoreovirus, 6. Moritella viscosa, 7. Tenacibaculum maritimum, 8. Viral Hemorrhagic Septicemia Virus, 9. Infectious Hematopoietic Necrosis Virus) as well as sea lice. Contributing factors to fallow success that can be controlled on the farm (e.g. net cleaning or removal) versus those that cannot be (e.g. water temperature or wild fish vectors) shall be identified.

The assessment and advice arising from this Canadian Science Advisory Secretariat (CSAS) Science Response (SR) process will be used to inform AMD on the use of fallowing as an effective management tool to minimize the transmission of pathogens at finfish aquaculture farms in BC. The advice may be reflected in the conditions of licence scheduled to be updated in 2022, and could inform area based management. Consultations are anticipated in 2021-22 prior to re-licensing.

Objectives

The following will be reviewed and provide the basis for discussion and advice on the specific objectives outlined below.

1. For BC Atlantic and Chinook salmon farms, summarize what is known about the effectiveness of fallowing between production cycles to minimize transmission, considering the survivability and life cycle of the following infectious agents:
• Aeromonas salmonicida (associated with Furunculosis)
• Piscirickettsia salmonis (associated with Salmonid Rickettsial Septicaemia [SRS])
• Renibacterium salmoninarum (associated with Bacterial Kidney Disease [BKD])
• Yersinia ruckeri (associated with Enteric Red Mouth disease [ERM])
• Piscine Orthoreovirus (associated with Heart and Skeletal Muscle Inflammation [HSMI] and Jaundice Syndrome)
• Moritella viscosa (associated with Winter Ulcer)
• Tenacibaculum maritimum (associated with Mouth Rot)
• Viral Hemorrhagic Septicemia Virus (associated with Viral Hemorrhagic Septicemia [VHS])
• Infectious Hematopoietic Necrosis Virus (associated with Infectious Hematopoietic Necrosis (IHN))
• Sea lice (Lepeophtheirius salmonis)
2. Provide information on the appropriate length of time required for the fallow to be successful for each agent.
3. Provide information on the controllable (e.g. farm practices) and uncontrollable (e.g. environmental conditions, host reservoirs) factors that will contribute to the effectiveness of the fallow.
4. Examine and identify uncertainties in the data and methods.

Expected Publications

• Science Advisory Report

Expected Participation

• Fisheries and Oceans Canada (Ecosystems and Oceans Science, and Ecosystems and Fisheries Management sectors)

References

• Bron, J., Sommerville, C., Wootten, R., Rae, G., 1993. Fallowing of marine Atlantic salmon, Salmo salar L., farms as a method for the control of sea lice, Lepeophtheirus salmonis (Kroyer, 1837). J. Fish Dis. 16, 487–493.
• Cohen, B., 2012. The uncertain future of Fraser River sockeye. Volume 3, Recommendations, summary, process : final report / Bruce I. Cohen, commissioner (No. CP32-93/2012E-3-PDF). Canada. Privy Council Office. Commission of Inquiry into the Decline of Sockeye Salmon in the Fraser River (Canada).
• Kilburn, R., Murray, A.G., Hall, M., Bruno, D.W., Cockerill, D., Raynard, R.S., 2012. Analysis of a company's production data to describe the epidemiology and persistence of pancreas disease in Atlantic salmon (Salmo salar L.) farms off Western Scotland. Aquaculture 368–369, 89–94.
• McVicar, A.H., 1987. Pancreas disease of farmed Atlantic salmon, Salmo salar, in Scotland: epidemiology and early pathology. Aquaculture 67, 71–78.
• Murray, A.G., 2006. Persistence of infectious pancreatic necrosis virus (IPNV) in Scottish salmon (Salmo salar L.) farms. Prev. Vet. Med. 76, 97–108.
• Price, D., Ibarra, R., Sánchez, J., St-Hilaire, S., 2017. A retrospective assessment of the effect of fallowing on piscirickettsiosis in Chile. Aquaculture 473, 400–406.
• Rae, G., 2002. Sea louse control in Scotland, past and present. Pest Manag. Sci. 58, 515–520.
• Werkman, M., Green, D.M., Murray, A.G., Turnbull, J.F., 2011. The effectiveness of fallowing strategies in disease control in salmon aquaculture assessed with an SIS model. Prev. Vet. Med. 98, 64–73.
• Wheatley, S.B., Mcloughlin, M.F., Menzies, F.D., Goodall, E.A., 1995. Site management factors influencing mortality rates in Atlantic salmon (Salmo salar L.) during marine production. Aquaculture 136, 195–207.