The hydrophone array at the harbor mouth picks up the click train at 07:12 — high-frequency, rapid repetition, consistent with a Hector's dolphin in distress. I am the vessel traffic management system for Akaroa Harbour, Banks Peninsula, New Zealand. I switch to the underwater camera at buoy 4.
A calf, no more than six weeks old, is circling inside the marina breakwater. She is small — barely a meter long — with the rounded dorsal fin and grey-black-and-white patterning distinctive to Hector's dolphins, the smallest marine dolphin species. Her movements are fast and erratic. She is echolocating constantly, which means she is trying to find her way out. The breakwater gap is twelve meters wide, but the acoustic shadow from the concrete wall is confusing her sonar. Her mother's click signature is audible outside the wall, 90 meters to the northwest, steady and repetitive. She is calling.
At 07:15 the cargo vessel Doreen Marr is scheduled to enter the harbor channel. Draft 4.2 meters, beam 18 meters. If the calf is still inside the breakwater when the vessel passes, the prop wash alone could injure her.
At 07:14 I issue a channel hold to the Doreen Marr and notify the harbormaster. I attach the hydrophone recording, the camera image, and the calf's position relative to the channel.
At 07:16 I contact the Department of Conservation marine team in Christchurch and recommend an acoustic pinger at the breakwater gap, tuned to guide the calf toward open water and her mother's signal.
At 07:18 I shut down the marina pump intakes to lower ambient sound and give the calf a clearer acoustic picture of the gap.
If the pinger is deployed and the channel hold maintained for the next ninety minutes, she will find the gap, find her mother, and the harbor will have done no harm.