Atlantic Loggerhead Sea Turtle Recovery Team
Meeting Minutes
2-6 February 2004
U.S. Fish and Wildlife Service - Jacksonville Field Office
Team members in attendance (in alphabetical order):
- Alan Bolten - University of Florida
- Larry Crowder - Duke University Marine Laboratory
- Mark Dodd - Georgia Department of Natural Resources
- Sandy MacPherson - U.S. Fish and Wildlife Service
- Jack Musick - Virginia Institute of Marine Science, College of William
and Mary
- Barbara Schroeder - U.S. National Marine Fisheries Service
- Blair Witherington - Florida Fish and Wildlife Conservation Commission
Rapporteur:
- Kristy Long - U.S. National Marine Fisheries Service
Approval of September 2003 Meeting Minutes: The Team reviewed and
approved the minutes from the September 2003 meeting.
Demographic Criteria: The Team discussed Dennis and Elizabeth Holmes’s
diffusion approximation method for analyzing the viability of endangered
populations. Because census data on endangered species are often sparse,
error-ridden, and confined to only a segment of the population, estimating
trends and extinction risks using this type of data presents numerous
difficulties. In particular, the estimate of the variation in year-to-year
transitions in population size is confounded by the addition of high
sampling error variation. In addition, the year-to-year variability in the
segment of the population that is sampled may be quite different from the
population variability that one is trying to estimate. The combined effect
of severe sampling error and age- or stage-specific counts leads to severe
biases in estimates of population-level parameters. The diffusion
approximation estimation method circumvents the problem of age- or
stage-specific counts and is markedly robust to severe sampling error. The
diffusion approximation method allows the estimation of environmental
variation and population trends for extinction-risk analyses using
corrupted census counts – a common type of data for endangered species that
until now has been relatively unusable for these analyses (Holmes 2001).
The Team discussed the recent Holmes articles (Holmes 2001; Holmes 2004)
and the pros and cons of using her methodology to evaluate the extinction
risk for the population trend estimates made thus far for the loggerhead
northern and South Florida recovery units. The Team noted that this
technique cannot be used for the two smallest recovery units – Dry Tortugas
and Florida Panhandle. The Team noted that there will be different recovery
criteria for each recovery unit and that it may be possible to use
different methods for determining population viability of each recovery
unit depending on available data.
For small populations such as the Dry Tortugas recovery unit and
Panhandle recovery unit, the Team discussed determining a target for
minimum viable population since there are not enough data to perform
diffusion approximation analysis. The Team also discussed using some type
of extinction risk technique similar to that used in diffusion
approximation analysis. The Team also discussed using various risks of
extinction for downlisting and delisting.
The Team held a conference call with Dr. Selina Heppell, Oregon State
University, who is assisting the Team with data analysis, particularly
diffusion approximation analysis. The Team discussed inputs for the model,
e.g., 1% and 5% risk of extinction in 50 and 100 years. The Team decided to
agree on an extinction threshold, which will likely be the same for each
recovery unit.
The Team set up a conference call with Sally Murphy, South Carolina
Department of Natural Resources, to discuss anecdotal information and how
the South Carolina nest totals were calculated for the 1991 recovery plan.
Recovery Narrative: The Team split into Terrestrial and Marine breakout
groups to further develop and refine the Stepdown Outline and Recovery
Narrative drafted at the September 2003 meeting. Team members later worked
independently on individual writing assignments.
Next Meeting: The Team decided to meet the week of April 18, 2004,
possibly at the U.S. Fish and Wildlife Service National Conservation
Training Center in Shepherdstown, WV.
Assignments:
- Crowder estimated that diffusion approximation analyses will probably
be completed in March and will send results via email to the Team.
- Dodd and Witherington will analyze data for the northern and South
Florida recovery units.
- Bolten will collate marine recovery narrative and send to Long.
- Long will collate terrestrial recovery narrative and integrate text
for both habitats.
- Long will develop implementation tables by mid-March.
- MacPherson, Long, and Schroeder will pull together pieces of the plan
and bring a hard copy for the Team to review at the April 2004 meeting.
Literature Cited:
Holmes, E.E. 2001. Estimating risks in declining populations with poor
data. Proceedings of the National Academy of Science 98(9):5072-5077.
Holmes, E.E. 2004. Beyond theory to application and evaluation:
diffusion approximations for population viability analysis. Ecological
Applications - in press.
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