Vulnerability Framework: Three Oil Categories

Under Canada’s World Class Tanker Safety System Initiative (WCTSS) a national framework was developed to identify marine biological organisms most vulnerable to ship source oil (Thornborough et al. 2017) in the event of an oil spill. The Pacific regional application of this framework (Hannah et al. 2017) and the 2022 update for all oil types (DFO 2023) considered all oil types together and identified 27 highly vulnerable biological groups., However, it was recommended to further define impacts by assessing vulnerability for individual oil types or categories separately for the initial period of an oil spill when the oil is still fresh and floating. Ongoing funding under Oceans Protection Plan was approved in 2022 to carry out this work. Criterion definitions and scoring guidance from the Pacific Application of the vulnerability framework (all oil types) (Hannah et al. 2017) were reviewed to determine where adaptations were necessary to capture the vulnerability of Pacific marine species to three different types of oil: diesel and gasoline1 ; Bunker C2 ; and diluted bitumen2 above. Changes in the definition and guidance for scoring were required for two criteria (‘seafloor or vegetation interacting’ and ‘close association with unconsolidated substrate’ were changed to add ‘in intertidal areas’) to capture that oil floats when fresh. This application is only relevant to the spill phase when each oil type is fresh and floating as identified by the Automated Data Inquiry for Oil Spills (ADIOS) model output. Consequently subtidal groups will likely have lower vulnerability. Oil fate and behaviour modelling informed timelines and exposure considerations for when the scoring results for individual oil types would be most applicable during the initial period of an oil spill response when the oil is fresh and floating. This period can vary from hours to days depending on oil type and environmental conditions. Scoring for individual oil types lowered the total vulnerability score of several subgroups when compared to the scores for all oil types, particularly for diesel and gasoline, which had fifteen fewer subgroups in the high vulnerability category. For both Bunker C and diluted bitumen there were seven fewer subgroups in the high vulnerability category compared to scores for all oil types (DFO 2023). The distribution of vulnerability scores across subgroups was similar to those for all oil types. There was no difference in vulnerability scores between Bunker C and diluted bitumen for each subgroup, but for diesel and gasoline several vulnerability scores for the same subgroups were lower. The lower vulnerability scores for diesel and gasoline are due to the mechanical impairment criterion, as light oils are not expected to smother or clog feeding structures, like the heavier and more viscous Bunker C and diluted bitumen. Oil weathering models were run using the National Oceanic and Atmospheric Administration’s (NOAA) ADIOS tool, to determine weathering timelines for four different weather scenarios. ADIOS model predictions indicated that the majority of weathering is due to evaporation for diesel and gasoline, and both evaporation and dispersion for Bunker C and diluted bitumen. For diluted bitumen there is an initial period of rapid weathering where the diluent is lost through evaporation and then a slower weathering period where dispersion is the main mode of weathering. Scoring the chemical sensitivity criterion was challenging using the existing scoring guidance. Consequently, all subgroups were scored a precautionary 1 (indicated as 1*) for this criterion unless sufficient evidence was found to give them a score of 1. Currently, there is not clear guidance for deriving a score of 0. Oils vary greatly, even within a specific oil type, and many factors impact how an oil behaves in the environment. Also, individual species within a subgroup can vary in terms of their life history, behaviour, and vulnerability to oil. As such, oil fate and behaviour information and predictions from modelling, as well as expected oil impacts and vulnerability, may not apply to all situations. This framework is one tool used by Fisheries and Oceans’ Environmental Incident Coordinators (EICs) in a response scenario. Combining these results with information from other response partners (such as ecological, archaeological, cultural, and socio-economic priorities) provides a strong response strategy. Based on ADIOS modelling predictions, the list of highly vulnerable subgroups determined for each oil type is most applicable within the first six to eighteen hours after a diesel spill, the first hour after a gasoline spill, the first two to five days after a Bunker C spill, and the first two to twelve hours after a diluted bitumen spill. When environmental conditions are such that significant weathering is likely, or if a sufficient amount of time has passed, the oil will behave differently, and the list of highly vulnerable subgroups resulting from the 2022 update for all oil types (DFO 2023) would be most applicable. For the next revision of the framework, the inclusion of how and whether to include chemical sensitivity should be re-evaluated. If the chemical sensitivity criterion is included, we recommend developing clearer guidance and methods to score chemical sensitivity so that clear sensitivity endpoints are established for each possible score, a consistent evaluation rubric is used to filter studies based on their utility to inform chemical sensitivity, and the weighting of sensitivity is more balanced with life history traits (exposure and recovery criteria) in the framework method. Limitations of this application include the binary scoring method and that current scoring guidance does not capture the breadth of effects (e.g., acute, indirect, and cumulative effects) to appropriately delineate differences in vulnerability between oil types. Though limited to considering marine components within DFO’s jurisdiction, the method could be applicable for other jurisdictions (e.g., marine birds). Species are not assessed based on their socio-economic status (fishery and conservation status) or cultural value, as this information is provided by other response partners, in particular Indigenous communities. The application assumes floating oil does not reach subtidal areas, however, under rough conditions wave action may cause oil droplets, oil particulate aggregates, or dissolved oil components to remain in the water column in subtidal areas. Limitations of the modelling outputs include: input variables (e.g., salinity, temperature, wind) may not be representative of all areas in the region or of all seasons (e.g,. freshwater input and stratification); and the assumption of a single point-source release means results may not apply in all release situations (e.g., continuous release).

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