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Harbour Porpoise (Phocoena phocoena) Presence Patterns at an Aquaculture Cage Site in the Bay of Fundy, Canada
Abstract: Finfish aquaculture is a prominent industry in the Bay of Fundy, Canada. The distribution of harbour porpoise (Phocoena phocoena) in the Bay during the summer and fall may be impacted by the presence of offshore cages or the activities of workers on the site. Harbour porpoise presence near and within an aquaculture cage site was studied using visual observations during the summer of 2006 and by monitoring echolocation signals using T-PODs during the summer and autumn of 2006 and 2007. At least one harbour porpoise was sighted per hour 61% of the time among or near the cages. Porpoise occasionally surfaced within the cage site when workers were present. Mother-calf pairs used the within-cages area proportionately more than adults and juveniles. The porpoise were temporarily displaced by high disturbance activities such as cage cleaning with pressure hoses, but quickly returned to the area when the disturbance ended. Echolocation activity was lowest during the day, increased in the evening, and peaked between midnight and dawn. This pattern was evident on the offshore and inshore side of the cages and, to a lesser extent, at a non-aquaculture location farther along the coastline (2007 only). In August of both years, the echolocation patterns were similar, even though in 2007 there were no fish in the cages and much less worker activity than in 2006 when all 15 cages contained Atlantic salmon (Salmo salar). Echolocation activity near a T-POD typically lasted for no more than 10 min or for at least 1 h, suggesting that the porpoise were either passing by the area or staying to feed, respectively. The presence of the aquaculture cage site under study did not appear to be displacing harbour porpoise from the area except during short intervals when high disturbance activities such as a food delivery by barge or cage cleaning were occurring.
Key Words: T-POD, aquaculture, behaviour, echolocation, disturbance, displacement, harbour porpoise, Phocoena phocoena
Document Type: Research article
Page Numbers: 203-211