440
26.4 Acute Effects
We consider acute effects of the DWH oil spill on marine megafauna as those effects
that caused immediate harm during the spill and response. This section focuses
primarily on effects experienced in oceanic habitats, as coastal impacts have been
reviewed extensively elsewhere. Primary acute effects include immediate injury and
death from oil and chemical exposure, response activities, and strandings.
26.4.1 Oil Exposure: Marine Mammals
In an oil spill, marine megafauna can be exposed to oil and related compounds
through surface slicks when breathing or resting at the air/sea interface (Trustees
2016) and through interaction with subsurface plumes during dives and foraging
events. Oil compounds can be taken up through the skin, breathed into the lungs, or
ingested with prey (Schwacke et al. 2013). Exposure studies conducted in the 1970s
focused on polar species including pinnipeds, sea otters, and polar bears and found
a range of effects including eye and skin lesions associated with continued exposure, uptake, distribution and accumulation of oil compounds into body tissues and
fat reserves through oil ingestion (Englehardt 1977; Engelhardt 1982), and thermoregulation problems associated with oiling. Marine mammals and turtles were
observed in oil-impacted areas during the DWH spill response while the well
remained uncapped (Wilkin et al. 2017).
There is limited prior information on the effects of oil spills on marine mammal
populations. Early oil spill studies noted that a wide range of marine mammal species including baleen whales, dolphins, and pinnipeds did not appear to avoid oilcontaminated waters (Goodale et al. 1981; Spooner 1967; Geraci 1990a, 1990b)
despite the fact that captive bottlenose dolphins could detect and avoid oil in experimental settings (Geraci 1990a). In the case of the DWH oil spill, the acoustic record
shows little evidence for near-term avoidance of the wellhead area by marine mammals (see Sect. 26.5).
Marine mammals were exposed to oil at the sea surface but also likely at depth.
Deep-diving pelagic species including sperm whales and beaked whales forage at
depths of 1000 m or more and likely interacted with the deep plume which formed
at approximately 1100 m (Hildebrand et al. 2012). The deep plume formation is
largely attributed to dispersant use (Kujawinski et al. 2011) and has not been
reported in previous spills; therefore, it likely represents a new route of exposure for
deep-diving cetaceans. A large amount of released oil did not reach the surface and
likely was eventually deposited on the seafloor (Romero et al. 2017). GOM marine
mammal species are not typically benthic foragers; however, bay, sound, and estuary bottlenose dolphins may use benthic hunting tactics (e.g., Lewis and Schroeder
2003; Rossbach and Herzing 1997), which could increase their exposure to deposited oil. In addition, GOM Bryde’s whales appear to forage at or near the sea floor
K. E. Frasier et al.
26.4 Acute Effects
We consider acute effects of the DWH oil spill on marine megafauna as those effects
that caused immediate harm during the spill and response. This section focuses
primarily on effects experienced in oceanic habitats, as coastal impacts have been
reviewed extensively elsewhere. Primary acute effects include immediate injury and
death from oil and chemical exposure, response activities, and strandings.
26.4.1 Oil Exposure: Marine Mammals
In an oil spill, marine megafauna can be exposed to oil and related compounds
through surface slicks when breathing or resting at the air/sea interface (Trustees
2016) and through interaction with subsurface plumes during dives and foraging
events. Oil compounds can be taken up through the skin, breathed into the lungs, or
ingested with prey (Schwacke et al. 2013). Exposure studies conducted in the 1970s
focused on polar species including pinnipeds, sea otters, and polar bears and found
a range of effects including eye and skin lesions associated with continued exposure, uptake, distribution and accumulation of oil compounds into body tissues and
fat reserves through oil ingestion (Englehardt 1977; Engelhardt 1982), and thermoregulation problems associated with oiling. Marine mammals and turtles were
observed in oil-impacted areas during the DWH spill response while the well
remained uncapped (Wilkin et al. 2017).
There is limited prior information on the effects of oil spills on marine mammal
populations. Early oil spill studies noted that a wide range of marine mammal species including baleen whales, dolphins, and pinnipeds did not appear to avoid oilcontaminated waters (Goodale et al. 1981; Spooner 1967; Geraci 1990a, 1990b)
despite the fact that captive bottlenose dolphins could detect and avoid oil in experimental settings (Geraci 1990a). In the case of the DWH oil spill, the acoustic record
shows little evidence for near-term avoidance of the wellhead area by marine mammals (see Sect. 26.5).
Marine mammals were exposed to oil at the sea surface but also likely at depth.
Deep-diving pelagic species including sperm whales and beaked whales forage at
depths of 1000 m or more and likely interacted with the deep plume which formed
at approximately 1100 m (Hildebrand et al. 2012). The deep plume formation is
largely attributed to dispersant use (Kujawinski et al. 2011) and has not been
reported in previous spills; therefore, it likely represents a new route of exposure for
deep-diving cetaceans. A large amount of released oil did not reach the surface and
likely was eventually deposited on the seafloor (Romero et al. 2017). GOM marine
mammal species are not typically benthic foragers; however, bay, sound, and estuary bottlenose dolphins may use benthic hunting tactics (e.g., Lewis and Schroeder
2003; Rossbach and Herzing 1997), which could increase their exposure to deposited oil. In addition, GOM Bryde’s whales appear to forage at or near the sea floor
K. E. Frasier et al.