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Case Study: Sea Turtles
Case Study: Sea Turtles

Context

Five species of sea turtles occur in the mid-Atlantic United States, all of which are listed as Threatened or Endangered under the Endangered Species Act. They were a focus of this study, in part, because few turtles occur in European waters (where most offshore wind energy development has occurred to date), and the effects of this type of development on sea turtles remain poorly understood.

Download Mid-Atlantic Wildlife Studies: Distribution and Abundance of Wildlife along the Eastern Seaboard 2012-2014. This 32-page summary publication explores aspects of the mid-Atlantic ecosystem; describes our survey and analytical approaches; and presents a range of results, featuring several case studies on specific species or phenomena.

The Executive Summary for the technical report is also available here.

 

Take Home Messages

  • There may be species-specific differences in habitat use or movements that were not distinguishable in this study.
  • Digital aerial surveys seem to have higher detection rates of sea turtles than other survey approaches, but application of newer technologies with improved species differentiation is needed.
  • Construction of offshore wind energy facilities in mid-Atlantic WEAs is likely to occur in warmer months and sea turtles will be present during these periods.
 

Background

Sea turtles are long-lived animals with worldwide oceanic distribution. The five species that occur in the mid-Atlantic study area are the Loggerhead Sea Turtle, Leatherback Sea Turtle, Kemp’s Ridley Sea Turtle, Hawksbill Sea Turtle, and Green Sea Turtle. All are listed as Threatened or Endangered under the Endangered Species Act.

Adults migrate seasonally, with some migrations up to 10,000 km. Their body temperatures vary considerably with their environment, limiting sea turtles to waters in specific temperature ranges.

The mid-Atlantic region has large populations of a high diversity of turtles, but there are many existing threats that could cause population declines. These include mortality from bycatch in fishing nets, collisions with vessels, especially those traveling at high speeds, loss of nesting habitat to coastal development, and disturbance or destruction of nests by humans or other animals. Potential concerns from offshore wind energy development include vessel traffic and the effects of noise from seismic profiling, pile driving, and trenching.

 

Survey Methods

Turtles were more frequently observed in digital aerial surveys than in boat surveys, likely in large part because turtles could be detected even when they were fully submerged. Because of these high detection rates, we used only aerial data to develop predictive models of sea turtle distributions.
 

Temporal Variation

Sea turtles were most abundant from May to October, with very few individuals present in winter.
 

Distribution and Abundance

Persistent abundance hotspots for turtles (Testudines spp.) observed in video aerial surveys, March 2012-May 2014. Data are split into only three persistence classes as the 75th and 85th percentile of persistence fell at the same value.
Persistent abundance hotspots for turtles (Testudines spp.) observed in video aerial surveys, March 2012-May 2014. Data are split into only three persistence classes as the 75th and 85th percentile of persistence fell at the same value.
Predicted relative abundance of sea turtles by season, based on two years of digital video aerial survey data (2012-2014). Models used observation data from aerial surveys and remotely sensed environmental covariate data to predict abundance across the study area. Turtles had a dense southerly distribution in the spring, and were dispersed more broadly in the summer. By the fall, they were distributed fairly evenly across the mid-Atlantic in offshore areas.
Predicted relative abundance of sea turtles by season, based on two years of digital video aerial survey data (2012-2014). Models used observation data from aerial surveys and remotely sensed environmental covariate data to predict abundance across the study area. Turtles had a dense southerly distribution in the spring, and were dispersed more broadly in the summer. By the fall, they were distributed fairly evenly across the mid-Atlantic in offshore areas.
 

For More Information

For more information, see Chapters 14, 15, and 17 in the technical report.
 

References

  • Epperly SP, Braun J, Chester AJ, Cross FA, Merriner JV, Tester PA (1995) Winter distribution of sea turtles in the vicinity of Cape Hatteras and their interactions with the summer flounder trawl fishery. Bulletin of Marine Science 56:547–568 
  • Gardner B, Sullivan PJ, Epperly S, Morreale SJ (2008) Hierarchical modeling of bycatch rates of sea turtles in the western North Atlantic. Endangered Species Research 5:279–289. doi: 10.3354/esr00105 
  • James MC, Ottensmeyer CA, Myers RA (2005) Identification of high-use habitat and threats to leatherback sea turtles in northern waters: New directions for conservation. Ecology Letters 8:195–201. doi:10.1111/j.1461-0248.2004.00710.x 
  • Hazel J, Lawler IR, Marsh H, Robson S (2007) Vessel speed increases collision risk for the green turtle Chelonia mydas. Endangered Species Research 3:105–113
 
Photo Credits: Header image © Daniel Calatayud
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