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Evaluating the effectiveness of fallowing as a mitigation tool at predominantly hard-bottom aquaculture sites in Newfoundland



Atlantic salmon aquaculture sites in Newfoundland are located predominantly over hard ocean substrates where it is difficult to consistently obtain sediment samples. The primary mitigation measure to manage impacts from uneaten food and faeces is to fallow (leave the site without fish) at the end of a production cycle. Optimal fallowing times and the factors that can influence the rate of benthic community recovery remain key knowledge gaps important to the environmental management of the industry.

This project set out to examine the recovery processes at aquaculture sites undergoing different periods of fallowing by evaluating how the length of the fallowing period influences the distribution of bio-indicator species, Beggiatoa and Opportunistic Polychaete Complexes (OPC). Results from the Canadian Science Advisory Secretariat (CSAS) process, 'Potential Impacts of Finfish Aquaculture on Hard Bottom Substrates and Development of a Standardized Monitoring Protocol' (Canadian Science Advisory Secretariat Science Advisory Report - CSAS-SAR 2014/017) suggested that these were acceptable indicators of organic deposition over a range of substrates. This study examined the changes in flocculent matter Footnote1 and non-indicator species during fallowing. The biological basis for changes in the distribution of Beggiatoa and OPC during fallowing was examined to determine if the observed changes occurred in a predictable manner across aquaculture sites on the south coast of Newfoundland. Factors associated with changes in the distribution of bio-indicators and the composition of epifauna Footnote2 were also be described. The outcome of this research improves our understanding of the processes of benthic recovery in the Newfoundland and Labrador Region during fallowing. In particular, the results shed light on the degree of benthic recovery associated with various lengths of fallowing, the biological processes underlying OPC dynamics in association with organic matter degradation, and the effectiveness of fallowing as a mitigation strategy in the region.


Information from all performance indicators is needed to accurately evaluate finfish aquaculture impacts. Multivariate analysis revealed that aquaculture production led to rapid changes in epibenthic communities with the development of bacterial mats and opportunistic polychaetes. No clear intermediate stages between aquaculture impacted and reference sites were discernable. Bacterial mats and opportunistic polychaetes were typically observed up to 100 m, and occasionally up to 160 m from cages. After 15 months of fallowing, bacterial mats and opportunistic polychaetes remained present at sites and were occasionally accompanied by other taxa, suggesting incomplete site recovery. A new species of dorvilleid polychaete, Ophryotrocha cyclops, was observed on the rocky seafloor under NL salmon aquaculture sites. O. cyclops consumed both fish pellets and flocculent matter-associated with bacteria, which contributed to the overall recovery process. O.cyclops has temperature and oxygen limitations suggesting caution in interpreting its absence as an absence of aquaculture impact.


Salvo F., Wiklund H., Dufour S.C., Hamoutene D., Pohle G. and Worsaae K.,  2014. A new annelid species from whalebones in Greenland and aquaculture sites in Newfoundland: Ophryotrocha cyclops, sp. nov. (Eunicida: Dorvilleidae). Zootaxa, 3887(5), 555-568. DOI: 10.11646/Zootaxa.3887.5.3

Salvo F., Hamoutene D., and Dufour S.C., 2014. Trophic analyses of opportunistic polychaete (Ophryotrocha n. sp.) at salmonid aquaculture sites. Journal of the Marine Biological Association of the United Kingdom, DOI: 10.1017/S0025315414002070.

Hamoutene D., Salvo F., Bungay T., Mabrouk G., Couturier C., Ratsimandresy A. and Dufour S., 2015. Assessment of Finfish Aquaculture Effect on Newfoundland Epibenthic Communities through Video Monitoring. North American Journal of Aquaculture 77(2), 117-127. DOI: 10.1080/15222055.2014.976681

Salvo F.; Dufour S., Hamoutene D., Parrish, C., 2015. Lipid Classes and Fatty Acids in Ophryotrocha cyclops, a Dorvilleid from Newfoundland Aquaculture Sites: e0136772. PLoS ONE10.8.

Hamoutene D., Salvo F., Donnet S., Dufour S., 2016. The usage of visual indicators in regulatory monitoring at hard-bottom finfish aquaculture sites in Newfoundland (Canada). Marine Pollution Bulletin. DOI:10.1016/j.marpolbul.2016.04.028.

Salvo F., Dufour S., Hamoutene D., 2017. Temperature thresholds of opportunistic annelids used as benthic indicators of aquaculture impact in Newfoundland (Canada). Ecological Indicators 79, 103-105.

Program Name

Program for Aquaculture Regulatory Research (PARR)


2014 - 2017

Principal Investigator(s)

Dounia Hamoutene
Research Scientist, Aquaculture Section, Northwest Atlantic Fisheries Centre
80 East White Hills Road St. John’s, Newfoundland and Labrador

Team Member(s)

Kimberley Burt

Flora Salvo

Collaborative Partner(s)

Suzanne Dufour, Memorial University of Newfoundland

Robert Sweeney, Sweeney International Marine Corp and SIMCorp Marine Environmental

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