Research Document - 2010/116
Ocean disposal in resident killer whale (Orcinus orca) Critical Habitat: Science in support of risk management
By C.L. Lachmuth, J.J. Alava, B.E. Hickie, S.C. Johannessen, R.W. Macdonald, J.K.B. Ford, G.M. Ellis, F.A.P.C. Gobas, and P.S. Ross
Abstract
Resident killer whales in the coastal waters of British Columbia and Washington are heavily contaminated with persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs). The northern and southern populations of resident killer whales are listed, respectively, as threatened and endangered under the Canadian Species at Risk Act (SARA), which protects species at risk from being killed or harmed (section 32) and protects any part of their Critical Habitat from destruction (section 58). The Resident Killer Whale Recovery Strategy identified contaminants, reduced prey and disturbance (noise and physical) as threats to population recovery.
Sediment dredged from the lower Fraser River and other locations is periodically disposed of at marine sites in coastal British Columbia, both within and outside killer whale Critical Habitat. Ocean disposal is regulated by Environment Canada under the Canadian Environmental Protection Act (CEPA). Sediments contain complex mixtures of contaminants, and material intended to be disposed of at sea is screened for a select list contaminants. Because killer whales are long-lived and occupy a very high trophic level, they are at particular risk to accumulating high concentrations of PCBs and related compounds.
This report provides a response to the following questions identified by Fisheries and Oceans Canada SARA and Habitat Managers: Are current Ocean Disposal Rejection/Screening Limits for environmental contaminants (including PCBs, mercury and PAHs) under CEPA 1999 adequate to prevent northern and southern resident killer whale Critical Habitat from destruction, as required by SARA Section 58?; and, Do PCBs in materials deposited in any area of killer whale habitat increase the risk of harm or mortality of northern and southern resident killer whales, as required by SARA Section 32?
In order to answer these questions given the complexity of killer whale ecology and that of their primary prey (Chinook salmon), we developed a novel food web modeling tool. This effort includes the following components: i) the designation of seven geographic areas that relate to management-related priorities (e.g. Critical Habitat) and/or international boundaries in the NE Pacific Ocean; ii) an assignment of time spent in each of these areas by southern and northern resident killer whales and their prey (Chinook salmon and non-salmonid species) based on best available information; iii) the adaptation of sediment-biota PCB bioaccumulation models to killer whales and their prey; iv) a compartmentalized approach to modeling sediment-food web uptake of PCBs within each of the seven areas identified so as to be able to evaluate site-specific impacts of disposal operations; and v) a comparison of model outcomes to three established health effects thresholds for PCBs in marine mammals. The modeling approach is based on the distribution of PCBs among sediments, the water column, and biota, and estimates concentrations that will accumulate in animals throughout a lifetime of exposure. This model does not evaluate the existing PCB distribution and pathways in the BC abiotic environment, but rather predicts the incremental consequences to killer whales of altering bottom sediments to reflect PCB concentrations following a series of disposal scenarios.
Our model indicates that disposal of material with PCB concentrations lower than those in the ambient sediments in the disposal sites would not increase PCB delivery to killer whales. However, the disposal of sediments into Critical Habitat sites from some of the more contaminated sites for which data are available could increase the PCB concentrations in killer whales by as much as 8%. These predictions assume that the sediments and water were in equilibrium, and that the Strait of Georgia was a closed system. Some processes may decrease uptake of PCBs by the food web relative to the model result (e.g. burial by sedimentation and exchange with the open ocean), while others may increase the uptake (e.g. direct uptake of PCBs by food web during disposal operations).
Under current practices, the scrutiny and approval of disposal applications in the Pacific Region is constrained by shortcomings in analytical measurement standards and by the definition of the CEPA Action Level based on only effects at low trophic levels. High Resolution instrumental analysis would reduce Detection Limits by up to 350 times, and improve risk management assessment of disposal applications. The current CEPA Action Level is too high to protect killer whales because PCBs biomagnify. Disposal of sediment containing PCBs at a concentration matching the current CEPA Action Level could hypothetically lead to a 32-fold increase in PCB levels in male southern resident killer whales.
We derived a sediment PCB concentration range that would protect 95% of resident killer whales of 0.012 to 0.200 μg·kg-1, dry weight. Results reveal the profound vulnerability of killer whales to accumulation of persistent contaminants, since only 4/61 (6.6%) sediment sites for which we have PCB measurements in BC and Washington State fall below the least protective of these sediment values. This suggests that there continues to be widespread contamination of resident killer whale habitat by the legacy PCBs.
This newly developed food web model can be employed as a risk management tool in support of SARA protections for killer whales. We suggest that the ambient sediment PCB concentration becomes an important benchmark for a management-based evaluation of risks to killer whales and to killer whale Critical Habitat. Disposal of materials with PCB concentrations lower than ambient in Critical Habitat in areas of high sedimentation will not increase sediment PCB concentrations, might help to bury contaminated sediments, and should not lead to increased PCB concentrations in killer whales. The decision about whether or not to dispose of materials with PCB concentrations that exceed ambient levels in the marine environment, particularly in Critical Habitat, will have consequences for killer whales.
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