Development of an Index of Sea Turtle Abundance Based Upon In-the-Water Sampling with Trawl Gear
Ruth
Ann Welch, BS; Richard A. Vendetti; A.L. Segars, DVM; Kenneth
S. Latimer, DVM, PhD
University of Georgia
College of Veterinary Medicine (Welch, Latimer) and Marine Extension
Program (Vendetti) and the South Carolina Department
of Natural Resources (Segars)
For eight weeks of the summer, Ruth Ann Welch lived aboard the Research
Vessel (R/V) Georgia Bulldog and participated in a multifaceted marine
research project to assess the loggerhead sea turtle population. The
primary objective of the project was to develop and index of sea turtle
abundance using trawl nets. In addition, several species of sharks,
rays, and commercially harvested fishes also were studied.
A typical day began
thirty minutes after sunrise when the three nets were "dogged off" at
a predetermined specific location, then pulled in after thirty minutes
of trawling (Fig. 1). The catch was
sorted by species that were weighed and measured. Blood was taken from
Atlantic sharpnosed sharks and blue crabs for different research projects
(Fig. 2).
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| Figure
1. Nets and doors of trawling apparatus. |
Figure
2. Sorting the catch by species. Many jellyfish
are present. |
When turtles were
captured, a more extensive protocol was followed. First, turtles
were placed in the "turtle chair" where
blood was taken from the cervical sinus (Fig. 3). Multiple measurements
subsequently were taken, including carapace and plastron width and
length and body depth. The turtles were tagged with a pit tag under
the skin of the right shoulder and with metal flipper tags on each
of the front flippers. The turtle’s weight was recorded
and its picture was taken before the turtle was returned to the
ocean.
Blood
samples were processed in the on-boat laboratory. Blood glucose,
packed cell volume, and total protein were determined for each
turtle. The
remaining blood samples were centrifuged and serum was stored
in liquid nitrogen for further analyses (Fig. 4).
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| Figure
3. Collection of a blood sample from a loggerhead
turtle. |
Figure
4. Research laboratory aboard the R/V Georgia Bulldog. |
Once all the catch
was sorted and research samples were obtained, the nets were once
again "dogged off" for another thirty-minute
trawl. Trawls were made until thirty minutes before sunset. An average
of ten to eleven stations were trawled each day.
Over
one hundred loggerhead turtles were captured during the eight-week
period aboard
the R/V Georgia Bulldog. Additionally, three Kemp Ridley’s
turtles (the smallest marine turtle) were captured (Fig. 5).
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| Figure
5. Kemp Ridley turtle, the smallest marine turtle. |
Several
other interesting species (Fig. 6a-g) of fishes, sharks, rays and invertebrates
were caught including pompano, cobia, batfish, nurse sharks, tiger
sharks, roughtailed stingrays, sea horses, octopi, seastars, a bag
of used diving gear, and many old tires. The research data
obtained will enhance our understanding of various marine species
and the environment in which they live as well as promote the
conservation
of marine natural resources.
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| Figure
6a. Lookdown fish (Selene vomer) |
Figure
6b. Scrawled
cowfish (Lactophrys quadricornis) |
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| Figure
6c. Roughback batfish
(Ogcocephalus parvus) |
Figure
6d. Nurse
shark |
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| Figure
6e. Bonnethead shark |
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| Figure
6f. Octopus |
Figure
6g. Basket of white sea urchin (Lytechinus sp.)
with one purple sea urchin (Arbacia sp.) |
Acknowledgement
Picture of the R/V Georgia Bulldog leaving the dock is from http://www.uga.edu/marine_advisory/gabulldog.html |