Trends in cetacean abundance in the Gully submarine canyon, 1988–2011, highlight a 21% per year increase in Sowerby’s beaked whales ( Mesoplodon bidens )

• Published in: Canadian Journal of Zoology
• Main Author: Whitehead, Hal
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2013
• Subjects: Animal Science and Zoology; Ecology, Evolution, Behavior and Systematics; The Gully; Mesoplodon bidens
• Online Access: http://dx.doi.org/10.1139/cjz-2012-0293; http://www.nrcresearchpress.com/doi/full-xml/10.1139/cjz-2012-0293; http://www.nrcresearchpress.com/doi/pdf/10.1139/cjz-2012-0293

Long time series of abundance data have advanced ecological understanding. I examined trends in incidental sightings of cetaceans in the Gully and neighbouring submarine canyons on the edge of the Scotian Shelf during summers between 1988 and 2011. There were a total of 2938 h of sighting effort in good conditions. I fit Poisson models to the sighting count data, and examined the support for models that included parameters representing monthly variations in abundance, trends over years, and different sighting rates in the different canyons. Sowerby’s beaked whales (Mesoplodon bidens (Sowerby, 1804)) were sighted 3.5 times more often in the Shortland and Haldimand canyons, compared with the Gully. For all other species, the best-supported models did not include differential sighting rates between canyons. The sighting rates of four species decreased over the 23 years of the study, while three species increased. Some of these trends may be related to changes in overall population size or variation in food resources, but a remarkable 21%/year increase in Sowerby’s beaked whale is perhaps most plausibly explained by a reduction in anthropogenic disturbance.