Chesapeake DolphinWatch, the citizen-science app that lets Bay boaters and shoreline watchers report bottlenose dolphin sightings, is marking its tenth year with more than 20,000 users and over 12,000 logged sightings — and with researchers turning to new tools to answer the one question the app can’t: how many dolphins actually live in the Chesapeake Bay. (Reporting on the program’s milestone was first published by science writer Wendy Mitman Clarke for the University of Maryland Center for Environmental Science.)
The program was developed by researchers at the University of Maryland Center for Environmental Science’s Chesapeake Biological Laboratory (CBL) in Solomons, in partnership with the Chesapeake Bay Trust, which provided initial grant funding. “I think Helen [Bailey] and I thought it would be a dozen of our closest friends who reported,” said Tom Miller, a CBL fisheries science professor who co-founded the program with Helen Bailey and now leads it. “Now we have really great information on where dolphins are seen in time and space.”
That data has already supported real science: a 2021 peer-reviewed study in PLOS ONE used DolphinWatch sighting reports, cross-checked against underwater acoustic monitoring, to describe seasonal patterns of dolphin presence in the Bay for the first time — finding that dolphin detections consistently peaked in July and August and correlated with water temperature, tidal patterns and salinity.
But sighting counts have a basic limitation: they can’t distinguish one dolphin from another. A report of 100 dolphins in a single river on a summer day, researchers say, could easily include the same handful of animals spotted multiple times as they move through the water — and because more people are out on the Bay in summer than in spring or fall, the sighting data is also skewed toward peak boating season, even though dolphins are present and moving through the Bay’s tributaries year-round.
“The next question almost everyone asks is, ‘Well, how many dolphins are there in the Bay?'” said Jamie Testa, the program’s project coordinator. Answering it matters beyond curiosity — bottlenose dolphins are managed coastwide under the federal Marine Mammal Protection Act by NOAA’s National Marine Fisheries Service, which relies on population estimates to set management policy.
To move toward an actual count, researchers are considering two approaches. One would train a smaller subset of DolphinWatch volunteers to conduct standardized surveys — watching specific locations at specific times, and recording details like distance to the animal and sea conditions — data precise enough to support formal abundance statistics. The other relies on environmental DNA, or eDNA: testing water samples for genetic material that dolphins shed naturally, a technique already used to track other wildlife and, during the COVID-19 pandemic, to monitor infection levels through sewage testing.
“NOAA researchers on the West Coast have had pretty good success with some of their major fisheries measuring eDNA to estimate hake abundance,” Miller said, comparing it favorably against traditional hydroacoustic and net-based population surveys. He said eDNA wouldn’t replace the volunteer network — DolphinWatch participants could be trained to collect water samples themselves. “So we wouldn’t lose that citizen science aspect of it even if we did switch to eDNA.”
Researchers also hope to use genetic testing, in partnership with NOAA, to determine whether the Bay’s dolphins represent a single resident population or several overlapping coastal groups — and to finally incorporate dolphins into the Bay’s ecosystem and food web models, something that has not been done despite their position near the top of the Bay’s food chain. Diet data remains scarce, though a review of stranded dolphins in North Carolina, Maryland and Virginia found they most often fed on weakfish, Atlantic croaker and spot.
Testa said funding for the next phase of research is not guaranteed. “Funding further research projects inspired by what we’ve learned so far is always a challenge, and science dollars are particularly hard to come by right now,” she said. “Our 10 years is a great start, a good foundation, and our motivation to keep going is still very strong.”
