Otters on one sea loch have gone almost entirely nocturnal

Otters on a west coast sea loch have shifted almost entirely to night-time activity, ending a long-standing local reputation for reliable daylight sightings.

Camera trap data shows daytime activity falling from 71% of records in 2019 to 6% this year. Total activity is unchanged, which indicates the animals are still there and still feeding, on a different clock.

Coastal otters are normally tidal rather than nocturnal, working the low water regardless of the hour. Shifting to darkness means feeding against the tide roughly half the time, which is less efficient.

What changed

The loch shore now receives an estimated 40,000 visits a year, up from a few thousand. Most are quiet, well-behaved and brief. The cumulative effect is that there is somebody on the shore for most of the daylight hours between April and September.

Otters tolerate a great deal of human presence individually. What they do not tolerate is no gap.

“Every single person there is being respectful. They keep their distance, they keep the dog on the lead. And there are two hundred of them a day, in sequence, from eight in the morning until nine at night.”

A researcher on the monitoring project

The tour problem

Two operators previously running daytime otter-watching trips have moved to evening and night excursions using thermal imaging.

The study is direct about this. If the response to a species avoiding people by moving into the dark is to follow it into the dark, the animals have nowhere left to go, and the loch’s otters will have exchanged a difficult daytime for a difficult night without gaining anything at all.

The recommendation is unglamorous: a voluntary access agreement leaving the shore clear before nine in the morning. Similar arrangements work elsewhere and depend entirely on people knowing about them.