433
Leatherback (Dermochelys coriacea) and surface-pelagic juvenile loggerhead
turtles (Caretta caretta) and green (Chelonia mydas), Kemp’s ridley (Lepidochelys
kempii), and Atlantic hawksbill (Eretmochelys imbricata) sea turtles are found in
offshore waters in the GOM, while larger neritic juvenile and adult turtles are found
in the continental shelf and nearshore/coastal waters; inshore areas host juvenile
and adult Kemp’s ridleys, loggerheads, and greens (Wallace et al. 2010, 2017). All
five species are listed as endangered or threatened under the Endangered Species
Act of 1973. Hatchlings emerge from nesting beaches and disperse into surfacepelagic developmental habitats in convergence zones, using Sargassum communities as a foraging resource that affords protection from predation and potential
thermal benefits (Bolten 2003, Witherington et al. 2012, Mansfield et al. 2014).
Foraging strategies differ by species, with the adult diet of green turtles dominated
by seagrasses and algae, loggerheads feeding upon a broad range of pelagic and
benthic invertebrates, hawksbills specializing primarily on sponges, Kemp’s ridleys
feeding mostly on crabs, and leatherbacks depending on cnidarians (see Bjorndal
1997 for a comprehensive review).
Loggerheads and to a lesser extent Kemp’s ridleys and green turtles nest on
northern GOM beaches in spring and summer months, although the Kemp’s ridley’s
primary nesting beaches are found in the western Gulf in Tamaulipus and Veracruz,
Mexico.
26.2 A Context of Chronic Impacts
The Deepwater Horizon (DWH) oil spill is one chapter in a long history of direct
and indirect anthropogenic impacts on marine mammal and sea turtle populations in
the GOM. The primary sources of stressors are summarized below.
26.2.1 Direct Harvest
Exploitation of GOM megafauna dates back to the Maya and Aztecs, who intensively harvested sea turtles and manatees (Lange 1971). Impacts were likely mainly
limited to coastal zones until the late 1700s when the American whaling industry
reached Gulf waters (Darnell 2015). Whalers primarily targeted sperm whales, with
pilot whales as secondary targets, and reported that the waters of the mouth of the
Mississippi River constituted one of the most profitable whaling grounds (Reeves
et al. 2011). Reports of sightings and takes of “finback” whales taken in the region
likely refer to the Gulf Bryde’s whale, and these reports indicate that the range of
this species included most of the Gulf (Reeves et al. 2011), although the current
population appears to be restricted to a small region near Desoto Canyon (Soldevilla
et al. 2017).
26 Impacts of the Deepwater Horizon Oil Spill on Marine Mammals and Sea Turtles
Leatherback (Dermochelys coriacea) and surface-pelagic juvenile loggerhead
turtles (Caretta caretta) and green (Chelonia mydas), Kemp’s ridley (Lepidochelys
kempii), and Atlantic hawksbill (Eretmochelys imbricata) sea turtles are found in
offshore waters in the GOM, while larger neritic juvenile and adult turtles are found
in the continental shelf and nearshore/coastal waters; inshore areas host juvenile
and adult Kemp’s ridleys, loggerheads, and greens (Wallace et al. 2010, 2017). All
five species are listed as endangered or threatened under the Endangered Species
Act of 1973. Hatchlings emerge from nesting beaches and disperse into surfacepelagic developmental habitats in convergence zones, using Sargassum communities as a foraging resource that affords protection from predation and potential
thermal benefits (Bolten 2003, Witherington et al. 2012, Mansfield et al. 2014).
Foraging strategies differ by species, with the adult diet of green turtles dominated
by seagrasses and algae, loggerheads feeding upon a broad range of pelagic and
benthic invertebrates, hawksbills specializing primarily on sponges, Kemp’s ridleys
feeding mostly on crabs, and leatherbacks depending on cnidarians (see Bjorndal
1997 for a comprehensive review).
Loggerheads and to a lesser extent Kemp’s ridleys and green turtles nest on
northern GOM beaches in spring and summer months, although the Kemp’s ridley’s
primary nesting beaches are found in the western Gulf in Tamaulipus and Veracruz,
Mexico.
26.2 A Context of Chronic Impacts
The Deepwater Horizon (DWH) oil spill is one chapter in a long history of direct
and indirect anthropogenic impacts on marine mammal and sea turtle populations in
the GOM. The primary sources of stressors are summarized below.
26.2.1 Direct Harvest
Exploitation of GOM megafauna dates back to the Maya and Aztecs, who intensively harvested sea turtles and manatees (Lange 1971). Impacts were likely mainly
limited to coastal zones until the late 1700s when the American whaling industry
reached Gulf waters (Darnell 2015). Whalers primarily targeted sperm whales, with
pilot whales as secondary targets, and reported that the waters of the mouth of the
Mississippi River constituted one of the most profitable whaling grounds (Reeves
et al. 2011). Reports of sightings and takes of “finback” whales taken in the region
likely refer to the Gulf Bryde’s whale, and these reports indicate that the range of
this species included most of the Gulf (Reeves et al. 2011), although the current
population appears to be restricted to a small region near Desoto Canyon (Soldevilla
et al. 2017).
26 Impacts of the Deepwater Horizon Oil Spill on Marine Mammals and Sea Turtles