How old is that dolphin?

Unlike humans or other animal species, dolphins rarely show signs of external aging. We don’t see wrinkles or changes to hair color, so estimating the age of a wild dolphin during a veterinary examination can prove challenging. Knowledge of the dolphin’s age, however, is very important to understand their health and the demographics within wild dolphin populations. Previous methods to estimate dolphin age have relied on tooth extraction and counting the growth layer groups within the tooth, similar to the rings in a tree stump. We wanted to provide an alternative, less invasive, and if possible, more precise methodology that could accurately estimate age throughout the dolphin’s life span.

The aim of this new collaboration was to create a novel methodology to estimate the age in dolphins via radiography of their pectoral flipper following similar principles applied to human hands.

In March 2018, NMMF Conservation Medicine Veterinarian Dr. Ashley Barratclough traveled to Valencia, Spain, to work with Dr. Daniel García-Párraga at Oceanogràfic. The aim of this collaboration was to create a novel methodology to estimate the age in dolphins via radiography of their pectoral flipper following similar principles applied to human hands. In humans, an X-ray of the hand can be used in forensics to identify the age up to the age of 18 by examining growth plate closure within the fingers. Learning from methods used in the human field can help us to advance marine mammal medicine. The collaboration between marine mammal veterinarians and human radiologists has been decisive in facilitating and orienting this work. We collaborated with human radiologist Dr. Luis Martí-Bonmatí and bioinformatics engineer Dr. Roberto Sanz-Requena to extrapolate from the human hand methodology and apply this to dolphin flippers. There is so much potential in the collaboration between veterinarians and human physicians to further advance the field of marine mammal medicine. This is a clear example of how we can improve and better understand the dolphin life cycle by validating and adapting a technique that has been routinely used in the human medical field for over 50 years.

Accurate age estimation allows us to understand the reproductive capabilities of the individual and ultimately understand the population demographics and predicted survival.

Pictured left is a radiograph from a fetus. Pictured right is from a dolphin over 50 years of age showing significant degenerative changes including osteoarthritis. MMPA/ESA Permit 18786-03

The aim of this project is to facilitate accurate age estimation of free-ranging bottlenose dolphins during veterinary physical examinations as part of conservation population health assessments. We aim to use these methods in future health assessments of dolphins impacted by the Deepwater Horizon oil spill to interpret their biological data and understand the health issues experienced in this population. Accurate age estimation allows us to better understand the reproductive capabilities of the individual and ultimately understand the population demographics and predict survival.

Over the last 15 years, a database of 126 radiographs has been compiled from multiple institutions in an unprecedented collaborative effort, to bring Dr. García Párraga’s vision into practice. By analyzing each radiograph individually and assigning a score to each bone, we were able to determine the specific chronological changes that occur during each period of the dolphin’s life. Since male and female dolphins grow at different rates, we had to make two separate formulas to ensure increased accuracy of age estimation. From their pectoral flipper radiographs, a dolphin’s age can be predicted within a few months in young dolphins (<5 years old) to within a few years if the animal is > 25 years old. This technique is an exciting advancement in the field of conservation medicine as it will enable an accurate, less invasive method of estimating dolphin age and subsequently interpreting their veterinary physical exam more accurately.

This novel diagnostic tool could also be applied to diagnose nutritional, developmental, or growth abnormalities, and identify subclinical health issues.

The bones labeled in this radiograph show which bones are included in the scoring system. M stands for metacarpal and P stands for Phalanx. MMPA/ESA Permit 18786-03

This method could also be applied to stranded cetaceans to help understand the reason for stranding and whether there is an age component to the underlying cause. Even museum specimens in marine mammal collections could be aged without needing to destroy or manipulate bone or dental material. Besides invasiveness, one important limitation when working with traditional techniques is that most marine mammal species are protected, and tissues can only be collected or transported under very strict permission. The benefit of different radiographs is that they can be easily distributed worldwide to the requested specialist or even interpreted immediately.

“This is a clear example of how we can improve and better understand the dolphin life cycle by validating and adapting a technique that has been routinely used in the human medical field for over 50 years.”

Dr. Ashley Barratclough

Finally, knowledge of the lifespan and the onset of sexual maturity for each species may allow this model to be applied to other cetaceans with similar bone maturation developmental curves, facilitating age estimation via pectoral radiography in future research.

Read more about this technique in the full research article published in PlosOne. Application of the technique to wild dolphins has already begun in Sarasota, Florida, and will continue in future health assessments.