In a recent experiment by Cornell University, 12 decoy dolphin carcasses made of cloth and other materials were dropped at various locations on Dauphin Island, Alabama.
Each metre-long body was filled with sand and anchored to the ground with ropes.
Why? To help conserve real-life dolphins, say researchers in a new study published in the journal Marine Mammal Science.
Stranded marine mammals provide valuable information about how species die and the causes of those deaths. But carcass detection rates by the public or trained observers is not well known, says Jennifer Bloodgood, corresponding author of the study and assistant professor of practice at Cornell University.
Each metre-long body was filled with sand and anchored to the ground with ropes.
To try and find out more about how often strandings are reported, researchers planted decoy carcasses of bottlenose dolphins on both popular and isolated beaches, as well as remote and more trafficked marsh areas.
Each decoy dolphin was tagged with a phone number, which members of the public could call when they found one of the dolphins.
“How many people are reporting the animals is really important, because stranding networks rely on the public as their primary source of information for stranded animals,” says Bloodgood.
“The public only found 58% of the decoy dolphins overall, so that tells us a lot about the potential real number of actual stranded dolphins,” says Bloodgood, which means that for every 100 dolphins found, there may be close to twice as many that don’t get reported.
“The study tells us about the cryptic mortality and where we should put efforts for doing more dedicated searches,” adds Bloodgood.
The results revealed that the public found half the decoy dolphins in the off-season and two-thirds in the high season; they only found 17% of the decoys in low-trafficked marsh areas.
The rates of discovery were higher with trained staff, who found 75% of the decoys in the off-season and 83% of them during the high season.
Use of the drone proved slightly better overall than the traditional methods, such as walking, ATV and kayak, though some decoys were found by walking that weren’t spotted by the drone.
Bloodgood says the findings from the study are important because they highlight which habitats staff members should focus their limited time and resources on. For example, fewer decoys were detected at remote marsh areas, meaning this habitat may merit more scrutiny by trained observers.
“And, it’s important because we need to have better estimates of the total number of animals that are dying to really understand the effects of a specific cause of death,” Bloodgood adds.
“If we don’t know how many animals are stranded in the first place, it makes it difficult to try and estimate and extrapolate deaths to larger population numbers.”
Find out more about the study: Stranded marine mammal detection by the public, trained responders, and drones using decoy carcasses.
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