A Historical ecology of Salish Sea "resident" killer whales (Orcinus orca) : with implications for management




Osborne, Richard

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The purpose of this study is to explore the implications of the historical perspective when it is linked to the ecological concept of adaptive management. The vehicle for this exploration is a genetically distinct population of killer whales (Orcinus orca), whose core coastal habitat includes the inland waters of Georgia Strait, Juan de Fuca Strait and Puget Sound; a geographic region referred to as the “Salish Sea.” This stock of killer whales, known as the Southern Resident Community, is unique in having a detailed scientific record that spans over two decades and recently this population was listed as “threatened” by the Committee on the Status of Endangered Wildlife in Canada (April 1999). The goal of this study is to take account of the specific ecological history of this killer whale population, and provide an assessment of the resiliency of this stock to withstand present levels of human impacts. In Chapter 1 the academic concepts of historical ecology and adaptive management are reviewed in preparation for their application as theory. Chapter 2 is an inventory of the ecological domain, in which the focal population is assessed by temporally measurable indicators o f its ecological status: population dynamics, feeding ecology, and habitat use. In Chapter 3 temporally measurable indicators of stress such as predation, disease, food resource depletion, toxic exposure, surface disturbance, and underwater noise are examined for their impact upon the carrying capacity of the environment of the whales. Chapter 4 plots both sets of indicators historically as trends in variation from the Sample Mean at different time scales (months, years, decades, centuries), and indexes them in terms of perturbations from the historical norm. In Chapter 5 four basic types of historical trends in environmental impacts are identified that are directly relevant to evaluating the resilience of the management unit. These are: (1) Relic impacts - potential impacts that are no longer present, but may account for present conditions. (2) Adapted impacts - potential impacts that have been around long enough for the management unit to have adapted to them. (3) Cumulative impacts- potential impacts that accumulate slowly in the environment or life history of the management unit before exerting environmental resistance. (4) New impacts - potential impacts with which the management unit has not had previous experience. These four historical criteria allow the manager to identify the most sensitive impacts for present conditions, and identify scales of management for restorative intervention. This resiliency index should have application for most types of ecological systems, or management units, because it describes very generalized types of temporal outcomes, independent of scale and life history pattern of the management unit. In terms of the focal population of killer whales in this study, the historical assessment suggests that: 1) these whales are presently a remnant population due to killing and capture by European settlers from the turn of the century to the 1970s; 2) they have bio-accumulated toxins during the highest historical periods of environmental pollution in the Salish Sea, and this toxic exposure will continue to increase for the whales over the next few decades; 3) this killer whale population has never previously experienced a lack of salmon, so diminishing salmon stocks are potentially a new stress on them; and 4) these killer whales have adapted to vessel traffic and noise for several decades in relation to vessel-based salmon fishing operations, and that this influence has recently been replaced by record levels of whale watching traffic, which potentially poses more severe impacts than fishing vessels because the boats follow the whales, rather than their prey. This historical assessment facilitates the application of “adaptive management” strategies for these whales by providing the basis for predicting the current “resiliency” of this population to adapt to environmental conditions.



Killer whale, Whales, British Columbia, Ecology