453
most sensitive parameters for eliciting changes in population growth (Leung et al.
2012). A geospatial assessment of cumulative stressors to evaluate where combined
threats and impacts are greatest was conducted on a GOM-wide scale for Kemp’s
ridleys and loggerheads following the DWH oil spill (Love et al. 2017). This
research showed a range of anthropogenic stressors including incidental bycatch in
commercial and recreational fisheries and habitat degradation, and it demonstrated
that few areas exist in their terrestrial or marine environment without cumulative
impacts from multiple stressors (Love et al. 2017).
26.6 Remaining Knowledge Gaps
Efforts to assess the comprehensive immediate and long-term effects of the DWH
oil spill on pelagic species are limited by a scarcity of pre-disaster baseline data
(Bjorndal et al. 2011; Graham et al. 2011; Trustees 2016). Without the ability to
compare pre-and post-spill measurements, many potential impacts are unquantifiable. Further, effects on these long-lived species may continue to play out over the
coming decades (Schwacke et al. 2017). The assessment of cumulative impacts
must be considered on an ecosystem level, as effects are based on direct mortality,
degradation of habitat, quality and availability of prey resources, and sublethal
impacts such as reduced foraging or reproductive potential (Love et al. 2017).
Developing a better understanding of the spatiotemporal overlap of threats with the
distribution and abundance of sea turtle populations will guide managers to develop
geographically targeted management strategies to mitigate key stressors and restore
injured resources (Love et al. 2017).
No comparable long-term data on marine mammal presence were collected in
the period prior to the 2010 spill. At best, visual survey data give decadal-scale
abundances that cannot be directly applied to understanding the impact of the spill.
In addition, the GOM was not a pristine habitat prior to the 2010 spill; therefore, we
cannot assume that pre-spill population levels were stable or attribute observed
shifts to the DWH event with great confidence. Although a visual marine mammal
survey was conducted prior to the spill in 2009 (Waring et al. 2013), it did not provide the kind of spatiotemporal resolution or precise abundance estimates needed to
quantify acute impacts. Passive acoustic sensors were deployed 26 days after the
initial blowout, so although they did record during the majority of the 152-day spill,
recorders were not in place to capture pre-spill levels, and some immediate effects
may have been missed. Further, passive acoustic sensors have limited detection
ranges (Frasier et al. 2016), and additional research is needed to determine the spatial scale over which the observations from these monitoring locations can be
extrapolated. Efforts to estimate chronic effects by any method have necessarily
relied on uncertain assumptions regarding pre-spill population sizes, health, and
distributions.
Much of the released oil is thought to have been deposited on the seafloor. Little
is known about if and how marine megafauna might be interacting with deep water
26 Impacts of the Deepwater Horizon Oil Spill on Marine Mammals and Sea Turtles
most sensitive parameters for eliciting changes in population growth (Leung et al.
2012). A geospatial assessment of cumulative stressors to evaluate where combined
threats and impacts are greatest was conducted on a GOM-wide scale for Kemp’s
ridleys and loggerheads following the DWH oil spill (Love et al. 2017). This
research showed a range of anthropogenic stressors including incidental bycatch in
commercial and recreational fisheries and habitat degradation, and it demonstrated
that few areas exist in their terrestrial or marine environment without cumulative
impacts from multiple stressors (Love et al. 2017).
26.6 Remaining Knowledge Gaps
Efforts to assess the comprehensive immediate and long-term effects of the DWH
oil spill on pelagic species are limited by a scarcity of pre-disaster baseline data
(Bjorndal et al. 2011; Graham et al. 2011; Trustees 2016). Without the ability to
compare pre-and post-spill measurements, many potential impacts are unquantifiable. Further, effects on these long-lived species may continue to play out over the
coming decades (Schwacke et al. 2017). The assessment of cumulative impacts
must be considered on an ecosystem level, as effects are based on direct mortality,
degradation of habitat, quality and availability of prey resources, and sublethal
impacts such as reduced foraging or reproductive potential (Love et al. 2017).
Developing a better understanding of the spatiotemporal overlap of threats with the
distribution and abundance of sea turtle populations will guide managers to develop
geographically targeted management strategies to mitigate key stressors and restore
injured resources (Love et al. 2017).
No comparable long-term data on marine mammal presence were collected in
the period prior to the 2010 spill. At best, visual survey data give decadal-scale
abundances that cannot be directly applied to understanding the impact of the spill.
In addition, the GOM was not a pristine habitat prior to the 2010 spill; therefore, we
cannot assume that pre-spill population levels were stable or attribute observed
shifts to the DWH event with great confidence. Although a visual marine mammal
survey was conducted prior to the spill in 2009 (Waring et al. 2013), it did not provide the kind of spatiotemporal resolution or precise abundance estimates needed to
quantify acute impacts. Passive acoustic sensors were deployed 26 days after the
initial blowout, so although they did record during the majority of the 152-day spill,
recorders were not in place to capture pre-spill levels, and some immediate effects
may have been missed. Further, passive acoustic sensors have limited detection
ranges (Frasier et al. 2016), and additional research is needed to determine the spatial scale over which the observations from these monitoring locations can be
extrapolated. Efforts to estimate chronic effects by any method have necessarily
relied on uncertain assumptions regarding pre-spill population sizes, health, and
distributions.
Much of the released oil is thought to have been deposited on the seafloor. Little
is known about if and how marine megafauna might be interacting with deep water
26 Impacts of the Deepwater Horizon Oil Spill on Marine Mammals and Sea Turtles