Dissolved oxygen (DO) levels were monitored in two marine Atlantic salmon (Salmo salar L.) cage sites on the south coast of Newfoundland (Canada) during the summer and fall of 2008 and 2009. In 2008, sites A and B had cages with stocking densities of approximately 9 kg m À 3 . In 2009, site A was being fallowed while stocking density at site B was of 10 kg m À 3 . During 2008 and 2009, few hypoxic events (de¢ned as DO o6 mg L À 1 O 2 ) were recorded at site A; however, at site B intermittent hypoxic events (46 mg L À 1 O 2 ) were observed. Our study provides a description of intermittent hypoxia occurring in salmon cages. These hypoxic events occur mostly during the summer season and last for as long as 2.5 months. Fish swimming behaviour show that water layers exhibiting low DO did not cause avoidance behaviour. This con¢rms results found by other authors. Site B exhibited low water currents below 5 m suggesting that caution should be taken before considering an increase in stocking densities in cages. Questions remain about the e¡ect of this intermittent hypoxia on ¢sh health and growth, and will be the focus of future research.

The seasonal and geographical patterns of spawning for Georges Bank cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) are estimated using composite distributions of stage I eggs derived from the Marine Resources Monitoring, Assessment and Prediction (MARMAP) data set (1977–1987). The inferred mean spawning locations are compared with patterns in particle residence times derived from a three‐dimensional prognostic circulation model that estimates the tidal and seasonal mean circulation. The comparisons indicate that cod and haddock spawning occurs at times and locations characterized by model residence times in excess of 35 d. The results are discussed in the context of fish population regulation theory, particularly the member/vagrant hypothesis and the concept of abundance‐dependent vagrancy.

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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.