Seasonality and Distribution
The PCDP has recorded nearly 600 sightings of dolphins over the past 10 years, with most sightings occurring from June through August when water temperatures are warmest (Jacoby 2025).
Using both boat-based observations and hydrophones, the PCDP has documented dolphins from the middle of the Chesapeake Bay to 45 miles up the Potomac River near Colonial Beach, VA, spanning waters up to 143 feet deep and 4.7 miles from shore (Jacoby 2025).
This map shows every sighting of dolphins by PCDP from 2015-2025 in blue and sightings reported by members of the community in pink. If you click on the photo or this link, you can explore the sightings!
Behavior and Ecology
The PCDP has observed dolphins mostly traveling, followed by foraging, socializing, and resting. Dolphins in the area feed on several fish species, including spot and weakfish, which are known to be a favorite of dolphins in the Mid-Atlantic region. The PCDP has also documented mating behaviors and even a birth, indicating the area’s importance for both breeding and birthing (Jacoby 2025).
While it is not uncommon for the PCDP to see a lone dolphin, the group sizes average around 26 and can get as large as 260 (Jacoby 2025)! This is much larger than other areas along the U.S., like Sarasota, FL, where average group sizes are approximately 7. The PCDP is currently investigating the social structure and long-term associations of these dolphin groups.
Population Dynamics
Abundance and Site Fidelity
During sightings, the PCDP photographs the dorsal fin of every dolphin in the group. The unique shape and markings of an individual’s fin allows the PCDP to keep track of individuals within and across years. To date, >2000 dolphins have been recorded in the Potomac River-Chesapeake Bay and 21% return year after year (Jacoby 2025).
Bill Clinton in 2025
Photo taken by Verena Conkin in 2025 under NOAA NMFS info should be: under NOAA NMFS General Authorization No. 19403 and 23782
Bill Clinton in 2015
Photo taken by Eric Patterson under NOAA NMFS info should be: under NOAA NMFS General Authorization No. 19403 and 23782
In the above images, Photo ID allowed us to track this dolphin over the course of a couple of years.
Demography
Knowing the demographic structure of a population is necessary for responding to threats and developing management strategies.
Shea O’Day (Georgetown ‘26) and Verena Conkin flying the drone during the 2024 field season
Reproductive females are especially important because they are key indicators of a population’s overall health. To date, the PCDP has identified >300 mothers and 400 calves, with most births occurring between May and June (Jacoby 2025). The PCDP is currently investigating female reproductive histories, stages of calf development, and aggression towards calves in early life.
Using Unoccupied Aerial Systems (UAS or “drones”), PCDP is able to obtain a more complete picture of demographic structure by measuring the body size of individuals from aerial images and inferring their age (calf, juvenile, or adult) and sex.
Drones also provide valuable data on behavior and individual characteristics since many behaviors and interactions happening just below the surface are not visible from any other perspective.
Social Behavior & Disease Risk
After the 2013-2015 Unusual Mortality Event our project focused on discovering how morbillivirus spreads among these dolphins and which dolphins are more at risk of contracting and spreading the disease.
Melissa Collier photographs as two pairs of dolphins surface and breathe synchronously, a behavior that facilitates both social bonding and disease transmission. Video courtesy of Milan Dolezal. Taken under NOAA NMFS Permit No. 23782
Our research has found that juvenile (4-10 years of age) and adult male dolphins have more synchronous breathing contact than adult females and calves.
This suggests that they are at higher risk for contracting and spreading morbillivirus.
These findings reflect the National Marine Fisheries Service stranding data (Collier et al., 2023).
Figure 3. Collier et al., 2023.
Top Left: The average number of synchronous breathing contacts for adult male, adult female and juvenile dolphins based on our data collection.
Bottom Left: A mixing matrix that shows the proportion of synchronized breaths that we observed between each demographic group. We found that dolphins tend to "sync" most with dolphins of their own age/sex class.
Right: A contact network that uses these findings to demonstrate how dolphins are connected based on their synchronized breathing patterns. Circles represent dolphins and lines between them represent a synchronized breathing interaction. We show an example of an individual's (large circles) synchrony network for each demographic group (isolated to the right of the network) to highlight the differences in contact among age and sex. We can use this network to simulate how disease can spread in PCDP dolphins.