Living among giants: Habitat modelling of harbour porpoises (Phocoena phocoena) in thenorthern Gulf of St-Lawrence

Abstract:

Habitat preference studies increase the knowledge on the ecology and biology of cetacean species by analysing environmental proxies to achieve an insight into the underlying reasons for using a specific area. The presence of harbour porpoises in the eastern Canadian waters has been studied extensively in the Bay of Fundy but little is known about the Gulf of St. Lawrence stock. A summer population exists along the Quebec shore where the latest bycatch estimations indicate that a large number of porpoises are killed by the fishing industry. Non- systematic survey data collected in the summer seasons from 1997-2003 allowed the study of harbour porpoise distribution in the western Jacques Cartier Strait. Generalized Estimating Equations (GEEs) were used to analyse habitat use in relation to environmental variables derived from an ocean model. Both spatial and temporal variations were found, although porpoise’s occurrence was highly influenced by local upwelling currents. A predictive model was also built using GEEs to investigate the presence of large aggregations. The results suggest that the extent around the Mingan Archipelago in conjunction with southern sea currents and low turbulent waters enhances the probability of occurrence of big groups. However, the confidence in the model is dubious due to poor goodness of fit in the graphical validation, which could not predict more than seven individuals per sighting while groups made up of twenty individuals were observed. Spatial and temporal occurrence of harbour porpoises in the study area raises the hypothesis that it may be a calving and nursing ground. However, further studies with this dataset using different modelling frameworks could obtain better results than those presented here. Future data collection should include population-related data such as behaviour or presence of calves for confirmation of this hypothesis.

Keywords: habitat modelling, Phocoena phocoena, harbour porpoise, generalized estimating equations.

Soley Calvet, Rachel. 2011. Living among giants: Habitat modelling of harbour porpoises (Phocoena phocoena) in thenorthern Gulf of St-Lawrence. Masters research in Marine Mammal Science. Sea Mammal Research unit, Scottish Oceans Institute, University of St-Andrews , Scotland.
Living among giants: Habitat modelling of harbour porpoises (Phocoena phocoena) in thenorthern Gulf of St-Lawrence PDF (6.8 MB)