Baleen whale distributional patterns and the potential influence of biological and physical processes

Marques, Fernanda F. C. (1996) Baleen whale distributional patterns and the potential influence of biological and physical processes. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (10MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Processes influencing baleen whale distribution have been traditionally inferred from correlations with behavioural, physical or biological variables. Such variables are often not directly linked to any particular process or mechanism, and hypotheses based on well established physical or biological models are rarely tested. In addition, the effects of measurement scale are seldom explicitly considered. -- One way to incorporate reasoning about scale in descriptions of baleen whale distributional patterns is via a comparison of results obtained across a range of spatial and temporal scales. This approach was exemplified through a description of spatial and temporal patterns of humpback, finback and minke whale distribution in Placentia Bay, Newfoundland. A multi-scale comparison of results indicated that local patterns of abundance are unlikely to reflect large-scale, population trends. Spatial patterns of baleen whale distribution were found to be highly variable, and no consistent trends are apparent. Differences in the seasonal timing of humpback and finback abundance are considered to reflect the exploitation of different food resources elsewhere during the spring, and reiterate the importance of the timing of sampling. -- Dimensionless ratios were then used to evaluate the relative importance of somatic growth, demographic and kinematic processes on northwest Atlantic humpback whale biomass concentration. Changes in humpback biomass concentration resulting from changes due to their own locomotory behaviour dominated over all other processes across a wide range of spatial and temporal scales. A review of current research knowledge of northwest Atlantic humpbacks indicated that limited data on growth rates and age structure of the population, calf survival and recruitment are available. -- An examination of humpback whale aggregative response to prey availability as a function of scale indicated that humpbacks were associated with prey at small (2.5-7.5 km) spatial resolutions. This suggests that whales may be continuously tracking prey. Maximum coefficients of association between whales and prey obtained at relatively small spatial scales (10-22.5 km) suggest that studies examining interactions between humpback whales and their prey can be conducted at relatively small scales, but repeated sampling may be necessary before any patterns can be detected. -- Other authors have suggested that episodic oceanographic events influencing prey distribution may indirectly influence baleen whale distribution and movements. An examination of water temperature profiles obtained in Placentia Bay indicated the occurrence of a localized coastal upwelling event during the summer of 1994. This event coincided with observations of large patches of euphausiids and schools of mackerel, and also with the peak in humpback whale relative abundance. These findings are speculated to indicate a potential response of humpback whales to concentrations of prey resulting from changes in oceanographic conditions. Additional experiments are needed to confirm these observations.

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