Recovery Strategy for the Transient Killer Whale (Orcinus orca) in Canada
The ‘West Coast transient’ population of killer whales (Orcinus orca) is acoustically, genetically and culturally distinct from other killer whale populations known to occupy waters off the west coast of British Columbia. This population was designated as ‘threatened’ by COSEWIC in 2001, and currently numbers approximately 250 animals. Transient killer whales are long-lived upper trophic level predators that are considered to be at risk because of their small population size, their very low reproductive rate (one calf every five years) and their extremely high levels of chemical contaminants that are persistent, bioaccumulative and toxic. Their high contaminant burdens, which have resulted from bioaccumulation in their prey, combined with other anthropogenic threats such as physical and acoustic disturbance, warrant their protection under the Species at Risk Act, and they are currently listed as Threatened.
There are significant gaps in our knowledge of transient killer whales, and they are not as well understood as resident killer whales. In part, this is because transients can be very difficult to detect, both visually and acoustically, because of their reliance on stealth when foraging on their acoustically sensitive mammalian prey. In inshore waters they are typically seen in small groups of two to six animals, where they most commonly forage for pinnipeds and small cetaceans. Once prey are alerted to the presence of transients in the area, they generally leave the water or become highly evasive. This may explain why transients travel widely across their range.
The population and social dynamics of transient killer whales are not as well understood as those of residents because transients may disperse from their natal group, and individuals may not be seen for extended periods of time. Their year-round distribution and habitat requirements are also not well understood. These gaps must be addressed before a meaningful numerical target for recovery can be established and before critical habitat can be identified. As such, the long-term goal of this recovery strategy is:
To attain long-term viability of the West Coast transient killer whale population by providing the conditions necessary to preserve the population’s reproductive potential, genetic variation, and cultural continuity.
To achieve this goal, interim population and distribution objectives have been established until quantitative objectives can be determined. In addition, recovery objectives to understand and address threats are presented herein. These objectives, established for the next five years and coinciding with the duration of this recovery strategy, will direct the research and recovery activities necessary to achieve the recovery of this population.
- The population size, averaged over the next five years, will remain at or above the current level.
- The number of breeding females in the population, averaged over the next five years, will remain at levels that will provide a neutral or positive growth rate.
- Studies will be undertaken to determine numerical and demographic population objectives that represent long-term viability for this population.
- Transient killer whales will continue to utilize their known range.
- Prey will be available, in quantities adequate to support recovery, throughout the currently known range of transient killer whales.
- Studies will be undertaken to determine how the range is utilized at a population and sub-population level.
Numerous anthropogenic threats have been identified for transient killer whales. The most pressing threats are: 1) chemical contaminants (both legacy and emerging), and 2) physical and acoustical disturbance (both chronic and acute). However, they are also vulnerable to biological pollutants, trace metals, toxic spills, collision with vessels and the effects of culls on their prey.
The first four recovery objectives provide direction for the strategies and approaches that can be used to mitigate and/or eliminate each of the threats facing transient killer whales. The remaining four objectives focus on obtaining information needed to develop a more comprehensive understanding of these threats, which will allow for the refinement of mitigation measures.
- Minimize the exposure to transient killer whales to legacy and emergent pollutants.
- Minimize the risk of prey population reductions from anthropogenic activities, until precise prey needs can be determined.
- Current measures to protect transient killer whales from vessel disturbance will be maintained or modified, if determined necessary from further studies.
- Minimize the exposure of transient killer whales to acute or chronic sound levels in excess of those considered to cause behavioural or physical harm in cetaceans.
- The quantity, quality and distribution of transient killer whale prey necessary to sustain or increase the current population level will be determined.
- A greater understanding of the impacts of contaminants and other biological and non-biological pollutants on transient killer whales will be developed.
- The effects of vessel disturbance on transient killer whales will be evaluated.
- A more comprehensive understanding of the impacts of chronic and acute noise on transient killer whales will be developed.
Strategies are outlined within this recovery strategy to achieve these objectives, many of which are attainable within the next five years. These strategies will also serve to reduce knowledge gaps about transient killer whales and to help identify their critical habitat. Although the transient killer whale population is not expected to achieve high abundances because transients are upper trophic-level predators with a low birth rate, the measures outlined herein will serve to reduce the population’s vulnerability to anthropogenic threats and help ensure that it does not decline to an endangered status.
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