435
et al. 1997), as well bycatch rates and competition for prey species (Darnell 2015).
Sea turtles and marine mammals are incidentally caught and killed in trawl, gillnet,
hook-and-line, and longline fishing gear, and fishery bycatch is considered the most
serious global threat to marine megafauna (Lewison et al. 2004; Wallace et al. 2010,
2013).
Marine mammals and turtles are affected by entanglement in gear and marine
debris, with possible effects including injury and drowning (Walker and Coe 1989;
Plotkin and Amos 1990). Loggerhead, green, hawksbill, and Kemp’s ridley sea turtles take refuge as juveniles in Sargassum rafts and are particularly susceptible to
entanglement in trash and ingestion of plastics (Witherington et al. 2012).
26.2.5 Oil and Gas Development
Oil and gas development in the GOM is linked to a variety of chronic impacts
including occasional small- and large-scale spills (Asl et al. 2016; SERO n.d.), leaking infrastructure, chemical releases related to extraction activities (Neff 1990; Neff
et al. 2011a, b), persistence of weathered oil and related compounds in the environment (Van Vleet and Pauly 1987; Botello et al. 1997; Van Vleet et al. 1984),
increased vessel activity, and the construction and removal of offshore platforms (Gitschlag et al. 1995). Some amount of natural crude oil seepage also occurs
from an estimated 914 natural seep zones in the GOM (MacDonald et al. 2015). Oil
from small-scale releases and seeps weathers and spreads in the pelagic ecosystem,
accumulating in offshore convergence zones. These zones, which aggregate drifts of
Sargassum and other macroalgae species, act as vital habitats for surface-pelagic
juvenile turtles, putting them at particular risk for exposure to oil accumulating in
these zones (Witherington et al. 2012; Bolten 2003).
26.2.6 Nesting Beach Impacts
Turtle populations have susceptibilities related to their reliance on nesting beaches,
which are impacted by coastal development, beach erosion, light pollution, dredging, beach re-nourishment programs and armoring, climate change and sea level
rise, as well as native and exotic predators (Lutcavage et al. 1997). Current efforts
to protect nesting beaches and rescue nests began in some areas as early as the
1950s, and successful nesting beach conservation efforts can result in rapid local
population increases (Troëng and Rankin 2005; Hayes 2004).
26 Impacts of the Deepwater Horizon Oil Spill on Marine Mammals and Sea Turtles
et al. 1997), as well bycatch rates and competition for prey species (Darnell 2015).
Sea turtles and marine mammals are incidentally caught and killed in trawl, gillnet,
hook-and-line, and longline fishing gear, and fishery bycatch is considered the most
serious global threat to marine megafauna (Lewison et al. 2004; Wallace et al. 2010,
2013).
Marine mammals and turtles are affected by entanglement in gear and marine
debris, with possible effects including injury and drowning (Walker and Coe 1989;
Plotkin and Amos 1990). Loggerhead, green, hawksbill, and Kemp’s ridley sea turtles take refuge as juveniles in Sargassum rafts and are particularly susceptible to
entanglement in trash and ingestion of plastics (Witherington et al. 2012).
26.2.5 Oil and Gas Development
Oil and gas development in the GOM is linked to a variety of chronic impacts
including occasional small- and large-scale spills (Asl et al. 2016; SERO n.d.), leaking infrastructure, chemical releases related to extraction activities (Neff 1990; Neff
et al. 2011a, b), persistence of weathered oil and related compounds in the environment (Van Vleet and Pauly 1987; Botello et al. 1997; Van Vleet et al. 1984),
increased vessel activity, and the construction and removal of offshore platforms (Gitschlag et al. 1995). Some amount of natural crude oil seepage also occurs
from an estimated 914 natural seep zones in the GOM (MacDonald et al. 2015). Oil
from small-scale releases and seeps weathers and spreads in the pelagic ecosystem,
accumulating in offshore convergence zones. These zones, which aggregate drifts of
Sargassum and other macroalgae species, act as vital habitats for surface-pelagic
juvenile turtles, putting them at particular risk for exposure to oil accumulating in
these zones (Witherington et al. 2012; Bolten 2003).
26.2.6 Nesting Beach Impacts
Turtle populations have susceptibilities related to their reliance on nesting beaches,
which are impacted by coastal development, beach erosion, light pollution, dredging, beach re-nourishment programs and armoring, climate change and sea level
rise, as well as native and exotic predators (Lutcavage et al. 1997). Current efforts
to protect nesting beaches and rescue nests began in some areas as early as the
1950s, and successful nesting beach conservation efforts can result in rapid local
population increases (Troëng and Rankin 2005; Hayes 2004).
26 Impacts of the Deepwater Horizon Oil Spill on Marine Mammals and Sea Turtles