REsearch Goals
Abundance
One of the first things we learned about the South Florida aggregation is that there are many more hawksbills than were expected! So far, just over 300 individuals have been captured and documented between Jupiter and Key West, and we continue to encounter new ones on a regular basis. Though not abundant compared to other sea turtle species in Florida, this expanding database indicates how supportive the reefs of Florida are for young hawksbill turtles, which has a regional significance for their overall recovery.
Population Structure
Most of the hawksbills found in South Florida are sub-adults, or “teenagers”. As with other sea turtles, their life-stage often dictates their general whereabouts. We call the reefs of South Florida “developmental habitat” for young turtles who will someday depart as young adults to join the rest of the reproductive population in the region. It is essential to the future of the species that this especially vulnerable segment of the population finds safe refuge as it passes through this challenging life-stage. We are particularly interested in monitoring the balance between males and females in the population, as warming nest temperatures can tilt the gender of the hatchlings toward an increasingly high proportion of females.
Movements and Growth
Among the most basic questions biologists often ask about any species is the extent of its range and the time it takes the offspring to reach maturity. Because sea turtles are notoriously difficult to follow, we employ basic marking techniques that can include external flipper tags, internal microchips, and even satellite tracking devices to gain insight into habitat use, social interactions, and time to maturity. Young hawksbills tend to take up residence is fairly small areas for extended periods of time, which has permitted us to re-encounter and re-evaluate dozens of known individuals as they grow toward maturity.
all within close proximity to where they were captured. Those that have been re-measured after at least one year grew (on average) 2.5 cm per year. These results suggest that at least some of the hawksbills found in the study site may remain there for the duration of their sub-adult life- stage, which is likely to be around 15 years.
Origins
Female sea turtles are famous for traveling long distances to return to their natal beach to nest. This marvelous trait allows us to genetically “fingerprint” sea turtle populations due to subtle differences in DNA sequences that have developed between various regional sub-populations. Since we know that the hawksbills of Palm Beach did not come from Florida (hawksbills don’t nest with any regularity here), we were curious about their origins, and by extension, their future destinations. Turns out, most hatched on the beaches of Mexico's Yucatan
Peninsula, but some appear to have come from as afar away as Brazil!
Hawksbill Physiology
Many aspects of physiological function and well-being are revealed in the various components and constituents of blood. Much like a blood panel we may provide to a doctor, the blood we collect from hawksbills allows us to evaluate how a number of organ systems and the body as a whole are functioning. Our studies of blood cells, blood analytes, and other metabolically relevant compounds contained in the turtles’ blood enable us to evaluate developmental patterns, assess overall health, identify potential exposure to contaminants, and examine the relationships between diet and metabolic function.
Gender Ratios
In an ever-fluctuating environment, understanding how sea turtle population structure changes over time is critical to their long-term management. Based on the link between sea turtle gender and nest temperatures (hatchlings become increasingly female-biased in warmer nest environments), we have had the unique opportunity to monitor the ratio of males and females in the SE Florida aggregation over a twenty-year span. Because they don’t reveal their gender externally until they reach maturity, we use the relative concentration of testosterone present in their blood to assign a young turtle as a male or female. The first time we reported on the proportions of males and females in S. Florida (2007), we found a female-biased group, with about twice as many females as males. Since most of those turtles were hatched in the early 1990’s, we recently repeated the study to see if the next generation of hawksbills arriving in Florida was any different. Using updated techniques, we tested the blood of several dozen ‘new’ arrivals to Florida, and are pleased to report that although the group is still female-biased, it is less so than it was back then, indicating that there are still plenty of males entering the system. Next, we will be testing some new techniques for gender determination using alternative components (e.g. lipids, DNA, RNA) present in their blood.
Fibropapillomatosis (FP)
One of the most challenging issues present today concerning sea turtle health is a disease known as fibropapillomatosis, or FP. Often exemplified by large external vascularized tumors, the disease is closely associated with a virus known as ChHv5 and also degraded marine environments. It is still not known exactly what metabolic cascade of events must occur for the tumors to form, but the disease is most prevalent, by far, in green turtles even though the virus appears to be ubiquitous among sea turtles, including hawksbills. Our team has never encountered a hawksbill with tumors, yet about 20% are carrying the virus. Our efforts to assess baseline ChHV5 rates in outwardly healthy looking hawksbill turtles helps to reveal if they are exposed yet don’t develop tumors (serve as ‘carriers’), have a unique resistance to the virus and/or the disease, or even if they are exposed at all or perhaps eliminate it from their bodies after exposure. Further study concerning the etiology of FP across species that share overlapping environments (which young greens and hawksbills often do) will help unravel the mystery of this debilitating disease.
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