Dr Andrew Trites
Modeling the foraging habitat of humpback whales
Knowing how species will respond to environmental variability and climate change requires understanding the factors that influence their distribution and movement patterns. I investigated the processes that drive individuals to concentrate in specific areas of their home range by modeling encounter rates of humpback whales (Megaptera novaeangliae) in relation to environmental variables using GIS tools, generalized additive models, and remote sensing and in situ data. I conducted this work at two foraging areas: the coastal waters of British Columbia, Canada, and the Bransfield and Gerlache Straits, Antarctica.
Humpback whales in British Columbia were strongly associated with latitude and bathymetric features. The relationships with remotely sensed variables reflecting primary productivity were not consistent, but higher numbers of whales seemed to be associated with higher productivity. In fact, the highest concentrations of humpback whales appeared to reflect areas where concentration and retention processes lead to higher biological productivity, including south Dixon Entrance, middle and southwestern Hecate Strait and off Juan de Fuca Strait.
Humpback whales in the Southern Ocean also preferred areas of enhanced biological productivity. In Gerlache Strait, humpback whales were associated with areas of higher chlorophyll-a concentration in the central and northern sections of the strait, which also corresponded to relatively higher temperatures and shallower mixed layer depths for the in situ data. In Bransfield Strait, humpback whales appeared to prefer the near-frontal zones and the deep basins, where surface waters are influenced by the Bransfield Current. Interannual variability in both humpback and minke whale encounter rates in Gerlache Strait was correlated with the Oceanic Niño Index, the oceanic component of ENSO.
In addition to investigating species-habitat relationships with statistical models, I conducted the first study to describe the satellite-monitored movements of humpback whales on their feeding grounds along the Antarctic Peninsula. Results showed considerable individual variation in direction, speed and range of movements, and an overall pattern characterized by short- and long-distance movements between presumed foraging areas with relatively short residency times.
All told, the results of my research show that humpback whale distribution within foraging habitat is influenced by physical and biological variables that enhance biological productivity.
Modeling the foraging habitat of humpback whales. 2010. Dalla Rosa, L. PhD thesis, University of British Columbia, Vancouver. 185 pp. (PDF)
Killer whale (Orcinus orca) interactions with the tuna and swordfish longline fishery off southern and south-eastern Brazil: a comparison with shark interactions. Dalla Rosa, L. and E.R. Secchi. 2007. Journal of the Marine Biological Association of the United Kingdom 87:135-140. (PDF)
Movements of satellite-monitored humpback whales on their feeding ground along the Antarctic Peninsula. Dalla Rosa, L., Secchi, E.R., Maia, Y.G., Zerbini, A.N. and Heide-Jørgensen. 2008. Polar Biology 31(7):771-781. (PDF)
Characteristics of whistles from resident bottlenose dolphins (Tursiops truncatus) in southern Brazil. Azevedo, A. F., A. M. Oliveira, L. Dalla Rosa and J. Lailson-Brito. 2007. Journal of the Acoustical Society of America 121:2978-2983. (PDF)
Southern Hemisphere humpback whales wintering off Central America: insights from water temperature into the longest mammalian migration. Rasmussen, K., D. M. Palacios, J. Calambokidis, M. T. Saborio, L. Dalla Rosa, E. R. Secchi, G. H. Steiger, J. M. Allen and G. S. Stone. 2007. Biology Letters 3:302-305. (PDF)