Multivariate analysis of habitat selection by rorqual whales in the Gulf of St. Lawrence, Quebec, Canada
A better understanding of the factors influencing habitat selection by large whales can contribute to improve management and conservation plans. Traditionally such studies have been hindered by the limitations of the oceanographic data, especially when the spatio-temporal scale does not match that of the whale dataset. In this case, we used a computer model of the Gulf of St. Lawrence with very precise resolution in time and space to analyze the fine-scale distribution of four rorqual whale species (blue, fin, humpback and minke whales). For each of 5231 sightings collected from boat surveys between 1996 and 2002, and an equal number of random locations, we computed depth and slope of the seabed, distance to shore, temperature at the surface and at three other depths, salinity, current strength and turbulent kinetic energy. We used principal component analysis to simplify the multivariate dataset and investigate inter-correlation between variables. The results were used to define habitat preferences in environmental space for each species and compare the overlap of their ecological niches. We then used logistic regression to compare the variables associated with random points (representing available habitat) and those associated with whale sightings (habitat used). Using Akaike's Information Criteria, we determined which models best fitted the data. These models all confirmed the influence of static factors like bathymetry but also emphasized the importance of dynamic variables such as temperature and currents. There were strong interactions between factors, underlining the complexity of the relationships linking rorqual whales to oceanographic processes. These findings allow us to better predict which areas constitute potentially important habitat requiring protection. They also encourage other studies of habitat selection to make greater use of dynamic variables and multivariate datasets.
Doniol-Valcroze, T., D. Berteaux & R. Sears. 2006. Multivariate analysis of habitat selection by rorqual whales in the Gulf of St. Lawrence, Quebec, Canada. Oral presentation to the 16th biennial conference on the biology of marine mammals, San Diego, December 11, 16, 2005.