Oil Spills and Marine Mammals in British Columbia, Canada: Development and Application of a Risk-Based Conceptual Framework

Abstract

Marine mammals are inherently vulnerable to oil spills. We developed a conceptual framework to evaluate the impacts of potential oil exposure on marine mammals and applied it to 21 species inhabiting coastal British Columbia (BC), Canada. Oil spill vulnerability was determined by examining both the likelihood of species-specific (individual) oil exposure and the consequent likelihood of population-level effects. Oil exposure pathways, ecology, and physiological characteristics were first used to assign species-specific vulnerability rankings. Baleen whales were found to be highly vulnerable due to blowhole breathing, surface filter feeding, and invertebrate prey. Sea otters (Enhydra lutris) were ranked as highly vulnerable due to their time spent at the ocean surface, dense pelage, and benthic feeding techniques. Species-specific vulnerabilities were considered to estimate the likelihood of population-level effects occurring after oil exposure. Killer whale (Orcinus orca) populations were deemed at highest risk due to small population sizes, complex social structure, long lives, slow reproductive turnover, and dietary specialization. Finally, we related the species-specific and population-level vulnerabilities. In BC, vulnerability was deemed highest for Northern and Southern Resident killer whales and sea otters, followed by Bigg's killer whales and Steller sea lions (Eumetopias jubatus). Our findings challenge the typical "indicator species" approach routinely used and underscore the need to examine marine mammals at a species and population level for risk-based oil spill predictions. This conceptual framework can be combined with spill probabilities and volumes to develop more robust risk assessments and may be applied elsewhere to identify vulnerability themes for marine mammals.

Surface-Dwelling Aquatic Insects in Low-Energy Freshwater Environments Are Highly Impacted by Oil Spills and the Surface Washing Agent Corexit EC9580A Used in Oil Spill Response

“…Thin sheens of fish oil (Morandin and O'Hara 2014) and crude oil (O'Hara and Morandin 2010) have been reported to be sufficient to greatly increase feather weight due to the loss in waterproofing, and the result is impacts on seabird buoyancy and flight (Leighton 1993). Oiling and subsequent washing by marine mammals also rids fur of its waterproofing capabilities due to loss of the air‐filled insulating layer as surface tension is reduced, allowing water to penetrate the deeper layers of fur; this can lead to hypothermia, increases in metabolic rate, and increased energy expenditure, all of which can lead to death (e.g., Costa and Kooyman 1981; Engelhardt 1983; Rosenberger et al 2017). Thus it is of value to explore the impacts of other types of oils on strider immobility.…”

A comprehensive petrochemical vulnerability index for marine fishes in the Gulf of Mexico

“…"rebound potential," etc. (Millsap et al 1990;Golden & Rattner 2003;Chin et al 2010;Rosenberger et al 2017). The studies acknowledge that some human judgement, i.e.…”

“…species' sensitivity to oil, functional role of species in an ecosystem, etc. (Millsap et al 1990;Golden & Rattner 2003;Chin et al 2010;Rosenberger et al 2017). Expert opinion can differ on occasion, and Golden and Rattner established that under each index's metric, species might be considered vulnerable due to specific biological traits, e.g.…”

Semi-quantitative risk assessment of marine mammal oil exposure: A case study in the western Gulf of Mexico

“…During a spill at sea, part of the oil rises to the surface, and the volatile components evaporate at a rate that depends both on the type of oil (light: API gravity > 38, medium: API gravity 22-38, or heavy: API gravity< 22; EIA, 2022) and the oceanographic and atmospheric conditions at the time of the incident (Lee et al, 2016). The greatest risk of oil exposure for marine mammals occurs near the surface, either through contact, inhalation, and/or ingestion (Harris et al, 2011;Jarvela Rosenberger et al, 2017). Methods have been designed to assess the likelihood of exposure of marine mammals to oil spills using their biological and ecological traits (e.g., Jarvela Rosenberger et al, 2017).…”

“…The greatest risk of oil exposure for marine mammals occurs near the surface, either through contact, inhalation, and/or ingestion (Harris et al, 2011;Jarvela Rosenberger et al, 2017). Methods have been designed to assess the likelihood of exposure of marine mammals to oil spills using their biological and ecological traits (e.g., Jarvela Rosenberger et al, 2017). However, the risk of exposure during a spill is also strongly influenced by the feasibility of the encounters between the animals and the oil, which is determined by the spatial and temporal distribution of the species and the evolution of the oil spilled (Fox et al, 2016).…”