1. Skeletochronological Analysis of
Kemp’s Ridley (Lepidochelys kempii) Sea
Turtles Stranded Following the
Deepwater Horizon Oil Spill
Kayleigh Boose
Mentors: Larisa Avens (NOAA) and Demian Chapmen (MCP)
Marine Conservation and Policy Symposium 2015
NMFS, Office of Protected Resources

2. Threatened/
Endangered
EndangeredThreatened/
Endangered
Endangered
Vulnerable Endangered
Threatened/
Endangered

3. Kemp’s Ridley (Lepidochelys kempii)
• Smallest sea turtles – 60-70cm SCL
(Plotkin, 2007)
• Often considered the most
endangered species (Lutz and Musick, 1997)
• Primary nesting at Rancho Nuevo,
Tamaulipas Mexico – arribadas (Lutz and
Musick, 1997)
• Nesting behavior historically
dangerous
Credit: Kayleigh Boose

5. Sea Turtle Movement
• Interact with humans
on land and at sea
• Bone formation during
spring/summer
• Temperature
dependent growth
Nearshore foraging areas (juvenile
and adult turtles)
Oceanic
juvenile
stage
Breeding area
Inter-nesting area
Nesting beach
Periodic oceanic
foraging
North
South
Seasonal
migrations
Hatchlings
migrate
offshore
Credit: Larisa Avens

6. Deepwater Horizon Oil Spill
• April 20, 2010 - Macondo well blowout(Griggs, 2011)
• July 15, 2010 – wellhead capped
• >200 million gallons
• Gulf of Mexico – very productive ecosystem
http://www.eoearth.org/view/article/161185/

8. Motivation for Studying

9. Motivation for Studying
• Long-term effects of oil on sea turtles are not well-understood
• Kemp’s ridley distribution overlaps with oiled areas
• Kemp’s ridley conservation before the spill was a success!
• Growth rates are hypothesized to have decreased as a result of the spill
Credit: NOAA/FWCC
(Blair Witherington)
Credit: Florida Fish and
Wildlife Conservation
Commission

10. Skeletochronology
• Analyze growth marks (GM) in bones
Resorption Core
123
Wide Zones – rapid growth
and bone formation
LAGs (Lines of Arrested Growth)
– little/no bone growth 1 Growth Mark (GM)
= 1 wide zone + 1 LAG

11. Methods

12. Methods

13. Methods: Age Estimates
Assigning Age:
Sep-Nov: LAG count + 0.25
Dec-Feb: LAG count + 0.50
Mar-May: LAG count + 0.75
Jun-Aug: LAG count
2008 -
annulus
2009
2010
2007 - hatching
Lk SKM20100624_02
• 3 years old
• Stranded in June

14. Methods: Age Estimates
Assigning Age:
Sep-Nov: LAG count + 0.25
Dec-Feb: LAG count + 0.50
Mar-May: LAG count + 0.75
Jun-Aug: LAG count
2008 -
annulus
2010
2011
2012
2007 - hatching
2009
Lk JMI20120319_01
• 4.75 years old (LAG
count – 0.25 year)
• Stranded in March –
2012 LAG = full
diameter

15. Methods: SCL Estimates & Growth Rate
7.775873
Calculate SCL
from diameter
= 20.7 cm
Use the difference
between SCL(1) and
SCL(2) to find growth rate
25.9 – 20.7 = 5.2 cm
growth between 2008
and 2009
9.794892
Calculate SCL
from diameter
= 25.9 cm

16. Application to Conservation and the Future
• Sea turtles are long-lived
• Stable Isotope Analysis
• Combining Skeletochronology and Stable Isotopes
• Public education and outreach
• Interactive display and activity for Marine Science Day at Oregon State
University Hatfield Marine Science Center
• Summer camp for high school students through the OSU STEM Academy

17. Questions?

18. References
Avens, L., and L. Goshe. “Comparative skeletochronological analysis of Kemp’s ridley (Lepidochelys kempii) and loggerhead
(Caretta caretta) humeri and scleral ossicles.” Marine Biology 152.6 (2007): 1309-1317.
Avens, L., L.R. Goshe, C.A. Harms, E.T. Anderson, A. Goodman Hall, W.M. Clause, M.H. Godfry, J. Braun-McNeill, B. Stacy, R.
Bailey, and M.M. Lamont. “Population characteristics, age structure, and growth dynamic of neritic juvenile green
turtles in the northeastern Gulf of Mexico.” Marine Ecology Progress Series 458 (2012): 213-229.
Avens, L., LR. Goshe, M. Pajuelo, K.A. Bjorndal, B.D. MacDonald, G.E. Lemons, A.B. Bolten, and J.A. Seminoff.
“Complementary skeletochronology and stable isotope analysis offer new insight into juvenile loggerhead sea
turtle oceanic stage duration and growth dynamics.” Marine Ecology Progress Series 491 (2013): 235-251.
Avens, L., L.R. Goshe, L. Coggins, M.L. Snover, M. Pajuelo, K.A. Bjorndal, and A.B. Bolten. “Age and size at maturation- and
adult- stage duration for loggerhead sea turtles in the western North Atlantic.” Marine Biology (2015).
Griggs, J.W. “BP Gulf of Mexico Oil Spill.” Energy Law Journal, 32:57 (2011): 57-79.
In J. Wyneken, K. Lohmann, & J. Musick (Eds.), (2013). The Biology of Sea Turtles, Volume III (pp. 97-135). Hoboken: CRC
Press.
NMFS. Sea Turtles. (2011, June 11). Retrieved August 2, 2015.
In P.L. Lutz & J. Musick (Eds.), (1997). The Biology of Sea Turtles (pp. 1-29; 137-155; 288-404). Boca Raton: CRC Press.
In P. Plotkin, (2007). Biology and conservation of ridley sea turtles (pp. 7-23; 45-59; 89-107; 213-231; 231-253; 253-297; 297-
325). Baltimore: Johns Hopkins University Press.