Article Review: Long-Term Climate Forcing in Loggerhead Sea Turtle Nesting by Kyle S. Van Houtan and John M. Halley

Luckily for Charlestonians, we get the pleasure of having sea turtles nest on our beaches. Another fun fact: the loggerhead sea turtle is also South Carolina’s state reptile. So I was interested in writing about the article by Houtan and Halley (2011) I found about studying past turtle population dynamics to project future estimations based on oceanic climate. Not only does this article discuss implications on how the environment can affect turtles by bottom-up processing, but how populations are affected in addition to anthropogenic reasons.

A little local story for you: this is Caretta. She is the loggerhead sea turtle on exhibit at the South Carolina Aquarium. She is 25 years old and tipping the scale at about 225 lbs. Caretta was not born in an aquarium. Instead, she was hatched on a beach in the southern states and “adopted” by tourists to go live in their bathtub in Montreal, Quebec. I know what you are thinking and yes-these people clearly had success and bright ideas written all over them. Others might say illegality. But that’s for a later debate. Anyway, as you can imagine things like to grow beyond the size of bathtubs so long story short, Caretta is now a celebrity at the aquarium and will never be released back into the wild or contribute to the gene pool. So with these kinds of stories in mind (not to mention light and other sources of pollution, by-catch mortalities, or just straight harvesting) I think it is pretty important to understand current populations and how they could look in the future.

In this article, Van Houtan and Halley were interested in understanding juvenile populations in Japan and Florida by taking into account the North Atlantic Oscillation (relating to Florida conditions) and the Pacific Decadal Oscillation. The North Atlantic Oscillation pattern is important for driving winds and storms from fluctuating atmospheric pressures and the Pacific Decadal Oscillation has more to do with warm or cool surface water temperatures. These climate conditions play a large role in mediating population success. Sea turtles only lay their eggs when conditions are suitable for their development and this often correlates with sea surface temperatures (SST). The reason for also studying juveniles is because they compose the largest amount of the population but little is known about them. The largest proportion of nesting turtles are also juveniles (around the age of 31 yrs) that enter their first breeding and nesting season.

The authors used models to construct an idea of where turtle populations are heading by taking into account the climate and trends in nesting counts from Japan and Florida. They looked at juvenile recruitment and breeding remigration information from the past 55 years such as population counts, climate, and sea surface temperature indexes came from the Fish and Wildlife Research Institute, the Joint Institute for the Study of the Atmosphere and Ocean, NOAA Earth Systems Research Laboratory, and the North Climatic Data Center. From there lots of math and computing took place to create linear models for nest counts. To understand why one might have a hard time explaining from there here is a little sample:

The results were that the nesting patterns found in the turtles follows the climatic trends, populations seem to be on the rise in Florida but are declining in Japan, and there was reduced survivorship to a second nesting event. Other interesting findings were that breeding females in Japan are smaller than those in Florida, which could mean that these turtles are younger, maturing faster, and possibly encountering less intraspecific competition. More information on ocean resources would be valuable to investigate these differences. Overall, Van Houtan and Halley set out to investigate past, present, and future population dynamics in loggerhead sea turtle populations in accordance with the ocean’s oscillation patterns and the effect of the climate. What can be drawn from this research is the importance of understanding the ecology and sensitivity to the environment that can affect the turtles. 

Take home point: Turtles have enough on their plate already without the help of human impacts. So don't steal them.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0019043