454
benthic oil, either directly or via the pelagic food web (see Pulster et al. 2020).
Impacts of the spill on mesopelagic and bathypelagic prey availability remains
unclear (Fisher et al. 2016). Different prey types likely have differing abilities to
metabolize oil-derived compounds. In particular, cephalopods seem less capable of
metabolizing polycyclic aromatic hydrocarbons (PAHs) and more likely to bioaccumulate heavy metals than fish (Reijnders et al. 2009). Trace metals are common
in crude oil and may further concentrate in weathered oil (Gohlke et al. 2011).
Deep-foraging, squid-eating cetaceans including sperm whales and beaked whales
may be at higher risk of long-term exposure to oil-related pollutants through their
prey. Toxicity of oil and oil-related compounds to marine mammals and sea turtles
remains poorly understood.
Lastly, the unknown spatial ranges and movement patterns of most oceanic GOM
marine mammal species and sparse habitat use, abundance, and distribution data for
sea turtles result in broad uncertainty regarding exposure and long-term impacts of
the spill and subsequent environmental pollution on these populations. It remains
unclear to what degree observed animals are resident in or systematically return to
affected habitats. Without coordinated, international GOM-wide monitoring efforts,
it is not possible to determine whether local declines in encounter rates represent
population shifts or population decreases.
26.7 Conclusion
The majority of research on the effects of oil spills on marine mammals and sea
turtles has focused on nearshore species (coastal bottlenose dolphins, killer whales,
and pinnipeds), coastal impacts (coastal strandings, sea turtle nesting beaches), and
surface oiling. The DWH event was a large-volume oil spill that occurred offshore,
with significant subsurface footprint, in poorly understood habitats, and with sparse
baseline data. Long-term offshore monitoring suggests ongoing declines in marine
mammal presence, which may be related to reduced reproductive success as
observed in nearshore proxies. Oceanic species were most heavily and directly
impacted by this spill, but discerning the immediate and long-term effects on oceanic populations requires piecing together a patchwork of sparse observations and
studies. It is clear however that marine mammals and sea turtles were directly
exposed to unprecedented amounts of oil and dispersants and that the acute and
chronic population-level impacts of this exposure were likely high and underestimated based on coastal observations.
Funding Information This research was made possible by grants from the Gulf of Mexico
Research Initiative through its consortium the Center for the Integrated Modeling and Analysis of
the Gulf Ecosystem (C-IMAGE). Funding for HARP data collection and analysis was also provided by the Natural Resource Damage Assessment partners (20105138), the US Marine Mammal
Commission (20104755/E4061753), the Southeast Fisheries Science Center under the Cooperative
Institute for Marine Ecosystems and Climate (NA10OAR4320156) with support through
Interagency Agreement #M11PG00041 between the Bureau of Offshore Energy Management,
K. E. Frasier et al.
benthic oil, either directly or via the pelagic food web (see Pulster et al. 2020).
Impacts of the spill on mesopelagic and bathypelagic prey availability remains
unclear (Fisher et al. 2016). Different prey types likely have differing abilities to
metabolize oil-derived compounds. In particular, cephalopods seem less capable of
metabolizing polycyclic aromatic hydrocarbons (PAHs) and more likely to bioaccumulate heavy metals than fish (Reijnders et al. 2009). Trace metals are common
in crude oil and may further concentrate in weathered oil (Gohlke et al. 2011).
Deep-foraging, squid-eating cetaceans including sperm whales and beaked whales
may be at higher risk of long-term exposure to oil-related pollutants through their
prey. Toxicity of oil and oil-related compounds to marine mammals and sea turtles
remains poorly understood.
Lastly, the unknown spatial ranges and movement patterns of most oceanic GOM
marine mammal species and sparse habitat use, abundance, and distribution data for
sea turtles result in broad uncertainty regarding exposure and long-term impacts of
the spill and subsequent environmental pollution on these populations. It remains
unclear to what degree observed animals are resident in or systematically return to
affected habitats. Without coordinated, international GOM-wide monitoring efforts,
it is not possible to determine whether local declines in encounter rates represent
population shifts or population decreases.
26.7 Conclusion
The majority of research on the effects of oil spills on marine mammals and sea
turtles has focused on nearshore species (coastal bottlenose dolphins, killer whales,
and pinnipeds), coastal impacts (coastal strandings, sea turtle nesting beaches), and
surface oiling. The DWH event was a large-volume oil spill that occurred offshore,
with significant subsurface footprint, in poorly understood habitats, and with sparse
baseline data. Long-term offshore monitoring suggests ongoing declines in marine
mammal presence, which may be related to reduced reproductive success as
observed in nearshore proxies. Oceanic species were most heavily and directly
impacted by this spill, but discerning the immediate and long-term effects on oceanic populations requires piecing together a patchwork of sparse observations and
studies. It is clear however that marine mammals and sea turtles were directly
exposed to unprecedented amounts of oil and dispersants and that the acute and
chronic population-level impacts of this exposure were likely high and underestimated based on coastal observations.
Funding Information This research was made possible by grants from the Gulf of Mexico
Research Initiative through its consortium the Center for the Integrated Modeling and Analysis of
the Gulf Ecosystem (C-IMAGE). Funding for HARP data collection and analysis was also provided by the Natural Resource Damage Assessment partners (20105138), the US Marine Mammal
Commission (20104755/E4061753), the Southeast Fisheries Science Center under the Cooperative
Institute for Marine Ecosystems and Climate (NA10OAR4320156) with support through
Interagency Agreement #M11PG00041 between the Bureau of Offshore Energy Management,
K. E. Frasier et al.