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Effects of Water Quality and Land-Use on Wood Turtle Populations
by Brian Zarate
Endangered and Nongame Species Program

The Endangered and Nongame Species Program (ENSP) has embarked on an ambitious wood turtle (Glyptemys insculpta) survey project. With strong documentation on the distribution of state-threatened wood turtles on a presence/absence basis only, we now hope to learn more about the animal's viability and preferences throughout its riparian (the green, vegetated areas on each side of streams and rivers) and upland habitats.

Data collected from this project will assist in modifying and enhancing several aspects of the work we do at the ENSP, including refining our current Landscape Project's critical wood turtle habitat mapping and more effectively managing existing or degraded wood turtle populations.

Using known water quality data from the NJ DEP Division of Water Quality and analyzing current land use practices near to historical wood turtle stream corridors, the study hopes to find correlation between these two physical characteristics and wood turtle occurrence.

Wood turtle
Wood Turtle
photo © Robert Zappalorti

Current records of wood turtle occurrence do little to help us understand how well or poorly a population is doing at a particular site. Many watersheds may contain functionally extinct populations as a result of habitat destruction, water quality degradation, road mortality, nest predation, illegal collection and forestation of open nesting and basking habitat.

A total of 20 sites in central and northern New Jersey have been selected for the surveys. Eighteen of the study sites fit into a category based on their current designation with regard to water quality and land use. Water quality is determined from existing data as non-impaired, moderately impaired, or severely impaired. Land use is characterized as lightly developed or developed. The 18 study sites fit into one of six of the following categories:

a) Non-impaired/Lightly Developed
      1. Hardwick/Stillwater Twp.
      2. Franklin Twp.
      3. Knowlton Twp.
b) Non-impaired/Developed
      4. Branchburg Twp.
      5. Bridgewater Twp.
      6. Byram Twp.
c) Moderately Impaired/Lightly Developed
      7. Montgomery Twp.
      8. Montague Twp.
      9. Mansfield Twp.
d) Moderately Impaired/Developed
      10. Denville Twp.
      11. Roxbury Twp.
      12. Bridgewater Twp.
e) Severely Impaired/Lightly Developed
      13. Roosevelt Boro.
      14. Long Hill Twp.
      15. Scotch Plains Twp.
f) Severely Impaired/Developed
      16. Denville Twp.
      17. Warren Twp.
      18. Hamilton Twp.

Along with the 18 study sites, we have selected 2 control sites with strong, documented wood turtles occurrences to use as a measure against our survey efforts at the study sites:

g) Control
      19. Frankford Twp.
      20. Franklin Twp.

Several parameters have been established to act as a protocol for standardizing our project efforts. Each stream is not surveyed in its entirety, but rather only in a section where both water quality and wood turtle data exist. Using GIS software, aerial photographs are digitally marked around a stream section to realistically reflect the area where biologists will perform their surveys based on first hand, field experience. From this created polygon, the inner area is calculated to reflect the amount of search effort needed at each site, with an average of 2 hours of field survey per acre.

Wood turtles move throughout their home range over the course of the year. The ENSP has refined search efforts to maximize the potential of encountering an animal when it is closest to its home stream where overwintering and spring or fall breeding occur. Dates for surveys will range from March 15 - June 15 and September 15 - November 15. Climactic variables of 45°-80°F under non-precipitating conditions will apply to the surveys as well.

Animals found during the search efforts will be marked with a shell notch for future recapture identification, have location data recorded using Geographic Positioning System information, and released at the point of capture. Information will further be documented on the life phase and general health of the turtle.

Wood turtle and file
Wood turtle and file used to mark shell
Wood turtle and GPS equipment
Wood turtle and Global Positioning System equipment

This is a two-year project that began in March of 2003 and will end in the fall of 2004. After our first year of project work, 53 new wood turtles have been noted during 140 hours of search effort primarily in our non-impaired and moderately impaired water quality sites. To date, no wood turtles have been observed in any of our 6 severely impaired water quality sites.

For information on the natural history of the wood turtle, visit (75kb in PDF format which requires the Adobe Acrobat Reader, available free from Adobe's Website).

This article wil be updated in March, 2005, with the cumulative results of the project - check back then!

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