Marine & Environmental Sciences Faculty Proceedings, Presentations, Speeches, Lectures

The Numerical Hatchling Orientation Value Index

Event Name/Location

28th Annual Symposium on Sea Turtle Biology and Conservation, Loreto, Mexico, January 22-26, 2008

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On urban sea turtle nesting beaches light pollution disrupts hatchling sea turtles natural sea finding abilities and is a major cause of hatchling disorientation and mortality. The severity of hatchling disorientation events ranges widely within Broward County, FL, USA. The Hatchling Orientation Index (HOI), as described by Dr. Blair Witherington, assesses to what extent hatchlings disorientate or deviate from their direct path to the sea. As described in his 1996 presentation, we measured the angular deviations and the deviation of the mode of hatchling tracks from the most direct bearing to the ocean and developed a numerical Hatchling Orientation Value (HOV). The numerical HOV is based on the premise that the severity of a disorientation event will increase exponentially as the hatchlings deviates from the most direct path to the sea. The values of this index are the summations of components based on the left and right angular range deviations as well as the modal deviation of hatchling tracks to the sea. The values of the numerical HOV range from 1 to 10 for a modal deviation of 0 to 90 degrees. Index values increase from 10 to 120 when the modal direction was greater than 90 degrees of deviation from the ocean direction. Values ranging from about 4 to 20 corresponded with the Witherington classification of moderate disorientation and values from 20 to 120 corresponded with a classification of severe disorientation. The index was used to assess the severity of hatchling disorientation in Broward County, Florida. HOV sample nests were assigned prior to the start of nesting season as defined by the Florida Fish and Wildlife Conservation Commission Sea Turtle Conservation Guidelines. Preliminary data from the 2006 and 2007 nesting season indicate a slight decrease in the severity of hatchling disorientation events in problem lighting zones within the county. This data suggests that local enforcement of existing lighting ordinances has contributed to decreased disorientations events.


NOAA Technical Memorandum NMFS-SEFSC-602

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