Glider, 22 February 2022
A glider east of Boston records right-whale calls.
The detection is relayed to shore. A single hydrophone can tell that a whale called within earshot. It can’t tell which direction the call came from, or how far it traveled.
Chapter 01
Slow zones today
How one detection in February 2022 became a slow zone.
NOAA slow zone
NOAA centers a slow zone on the glider.
1,600square nautical miles
With no position to go on, the zone is a box about 40 nautical miles on a side around the glider. For the next 15 days, mariners are asked to avoid it or slow to 10 knots. Compliance is voluntary.
Acoustic slow zones, 2022
Most slow zones in 2022 began with a recording.
47 of 77were triggered by acoustic detections
Three of them fell in this part of the Gulf of Maine: east of Boston in February, east of Chatham in March and southwest of Nantucket in November. Each was centered on a single recorder.
Chapter 02
Locating a whale
From detecting a call to knowing where the whale is.
Single hydrophone
A right-whale detector now runs on a microcontroller.
0.90recall at five false alarms per hour
A 2025 study ran a compressed neural network on an ESP32 and tested it in noise it had never seen. A detection on its own still leaves the whale anywhere within earshot.
Bearing from an array
An array of hydrophones can also tell direction.
6–8×as many unnecessary shutdowns without bearing
At offshore wind sites, a call that can’t be placed outside the exclusion zone stops pile driving. A study for the US Department of Energy compared buoys with and without bearing.
Position from three receivers
Bearings from several receivers cross at the whale.
$50K–$1M+per node per year, from a NOAA survey of operators
That gives a position. Doing it in real time takes receivers that work as one network, and that is expensive today. The network behind US slow zones is eleven moored buoys, plus gliders, for the whole East Coast.
Chapter 03
What Sona does
Software that turns detections from a network of low-cost nodes into positions.
Zone centered on the whale
Sona turns each detection into a position.
Every detection comes back as a position with its uncertainty, and the slow zone is centered on that position instead of on a recorder.
Zone sent to ships
Zones go out over AIS and to chart plotters.
83%of vessels slowed after an AIS alert in a NOAA pilot
Mariners have asked to receive zones as shapes on their chart plotters or over AIS. Sona sends them there and records how long each alert took from the first call.
Positions in the three 2022 zones
Inexpensive nodes can cover more of the coast.
Because each node costs little, a network can reach the places where right whales feed and migrate. Every zone it triggers starts from a position.
Other whales and ships
Sona works beyond right whales.
It can locate other whales and passing ships, once the detector is trained on their sounds. Right whales come first because that is where the rules, the deadline and the public data are.
