Center of Expertise in Marine Mammalogy: Scientific Research Report 2009-2011

5.0 Species at Risk

5.1 British Columbia's killer whales and ocean disposal practices in Critical Habitat (Peter S. Ross)

The northern and southern populations of resident killer whales in British Columbia are listed as threatened and endangered, respectively, under the Species at Risk Act (SARA), which aims to protect species at risk from being killed or harmed (section 32) and protects any part of their Critical Habitat from destruction (section 58). These resident killer whales have been found to be contaminated with very high levels of polychlorinated biphenyls (PCBs). As hydrophobic chemicals, PCBs are either incorporated into the lipid fraction of the food web, where they biomagnify, or they attach to particles and sediments. High concentrations of PCBs encountered in harbours and industrial areas can provide a source to adjacent food webs.

Environment Canada regulates disposal at sea operations under the Canadian Environmental Protection Act 1999 (CEPA 1999; Disposal at Sea Regulations, Regulations Respecting Applications for Permits for Disposal at Sea). DFO is responsible for the issuance of SARA permits for activities that may harm a listed species or destroy their Critical Habitat. A PCB food web modeling tool was developed to explore disposal scenarios, and to support risk management practices related to killer whales and their Critical Habitat.

Killer whales off the British Columbia coast.

Killer whales off the British Columbia coast.
Photo: B. Gisborn

Disposal of materials with less than ambient sediment PCB concentrations at a receiving site is not expected to increase PCB delivery to killer whales. Disposal of materials containing greater than ambient PCB levels would benefit from an alternative strategy, including disposal at a site with high natural sedimentation rate, as long as this new site is deemed to be depositional and dredge materials are not further dispersed. This modeling effort suggests that a target sediment PCB range of 0.012 to 0.200 μg•kg-1 dry weight would optimally protect long-lived, high trophic level killer whales. However, these protective sediment PCB values are currently exceeded in many parts of coastal BC, underscoring the legacy left by the PCBs used decades ago.

An additional understanding of PCB pathways in coastal waters, including sources, sinks, sedimentation rates, and substrate types in both dredge and disposal sites will better inform risk-based decisions regarding the likely fate and consequences of disposal activities within killer whale Critical Habitat.

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