Variables affecting sediment sulfide concentrations in regulatory monitoring at salmon farms in the Bay of Fundy, Canada

Abstract

Annual monitoring of sediments is conducted under salmon farms in the southwestern New Brunswick (SWNB) area of the Bay of Fundy, Canada, from August to October. We examined the relationships between the average sediment sulfide concentrations at salmon farms monitored from 2006 to 2009 and some variables related to farm operations: farm age, predicted average near-surface current speed, and estimated biomass of salmon at the time of monitoring. Data for all of these variables were available for 87% of salmon farms monitored in these years (farms that had been inactive for >1 yr were excluded). The year of monitoring had no significant effect, so data from all 4 yr were combined. The ability of the 3 variables to predict sulfide concentrations at the time of monitoring was analyzed using a linear model with log-transformation of variables (except farm age). Each variable individually showed a significant correlation with sulfide concentration, but the model including all 3 variables explained only 37% of the variation. Current speed and biomass explained the highest proportions of sulfide variation (together 35%). Almost 30% of monitoring events occurred at farms holding no fish. When these fallowed sites were excluded, the model explained only 24% of sulfide variation, with current speed being the most important predictor variable. Management actions targeted at farm size (biomass) and physical aspects of sites (especially current speed) may help to reduce the risk of causing adverse benthic impacts, but measurable effects may not be observed due to the large amount of sulfide variation that is not explained by these variables.