441
(Soldevilla et al. 2017) and, therefore, may also be at risk of exposure to oil deposited in sediments.
Differences in seasonal presence likely played a role in the extent to which
marine mammal species were directly exposed to DWH oil and dispersants
(Fig. 26.2). Sperm whales, Gervais’ beaked whales, Kogia species, and midfrequency dolphins (in the GOM this group primarily consists of species in the
Stenella genus, categorized based on echolocation click peak frequencies) are found
year-round in the region of the oil spill and were likely directly exposed to oil. In
particular Kogia and mid-frequency delphinid species presence increases in the
summer months, increasing the likelihood of exposure to DWH oil and dispersants.
Risso’s dolphins are seasonally present in spring through summer and therefore
likely experienced direct exposure during the first months of the spill but less exposure as the summer progressed. In contrast, Cuvier’s beaked whale presence is
strongly seasonal near the wellhead with highest occurrence during winter months;
therefore, these populations likely experienced minimal direct exposure during the
spring spill.
26.4.2 Oil Exposure: Sea Turtles
Potential direct impacts to sea turtles from an oil spill differ depending on the life
stage, but all stages are vulnerable to acute toxicity from volatile contaminants,
exposure through inhalation and ingestion, physical impairment from heavy oiling,
and a variety of physiological and clinicopathological impacts of exposure (see
review in Shigenaka 2003). Sea turtles are unlikely to detect oil (Odell and
MacMurray 1986), and in experimental conditions they showed no avoidance
Fig. 26.2 Seasonal patterns in marine mammal presence at a passive acoustic monitoring site in
Mississippi Canyon, located approximately 10 km from the DWH wellhead. The vertical axis indicates the factor by which seasonal presence varies relative to mean presence. Higher values indicate stronger seasonality
26 Impacts of the Deepwater Horizon Oil Spill on Marine Mammals and Sea Turtles
(Soldevilla et al. 2017) and, therefore, may also be at risk of exposure to oil deposited in sediments.
Differences in seasonal presence likely played a role in the extent to which
marine mammal species were directly exposed to DWH oil and dispersants
(Fig. 26.2). Sperm whales, Gervais’ beaked whales, Kogia species, and midfrequency dolphins (in the GOM this group primarily consists of species in the
Stenella genus, categorized based on echolocation click peak frequencies) are found
year-round in the region of the oil spill and were likely directly exposed to oil. In
particular Kogia and mid-frequency delphinid species presence increases in the
summer months, increasing the likelihood of exposure to DWH oil and dispersants.
Risso’s dolphins are seasonally present in spring through summer and therefore
likely experienced direct exposure during the first months of the spill but less exposure as the summer progressed. In contrast, Cuvier’s beaked whale presence is
strongly seasonal near the wellhead with highest occurrence during winter months;
therefore, these populations likely experienced minimal direct exposure during the
spring spill.
26.4.2 Oil Exposure: Sea Turtles
Potential direct impacts to sea turtles from an oil spill differ depending on the life
stage, but all stages are vulnerable to acute toxicity from volatile contaminants,
exposure through inhalation and ingestion, physical impairment from heavy oiling,
and a variety of physiological and clinicopathological impacts of exposure (see
review in Shigenaka 2003). Sea turtles are unlikely to detect oil (Odell and
MacMurray 1986), and in experimental conditions they showed no avoidance
Fig. 26.2 Seasonal patterns in marine mammal presence at a passive acoustic monitoring site in
Mississippi Canyon, located approximately 10 km from the DWH wellhead. The vertical axis indicates the factor by which seasonal presence varies relative to mean presence. Higher values indicate stronger seasonality
26 Impacts of the Deepwater Horizon Oil Spill on Marine Mammals and Sea Turtles