NORTHERN BOTTLENOSE WHALES

We have studied northern bottlenose whale behaviour in Iceland and Scotland in an attempt to explain unusual coastal occurrences which can have deadly consequences for these animals.
Northern bottlenose whales
Whilst most cetaceans lead lives mysterious to human knowledge, beaked whales are especially enigmatic. Diving to feed for hours at a time in offshore regions, beaked whales are incredibly difficult to study.

The northern bottlenose whale (NBW) is no exception. One of the largest beaked whales, NBWs are found in cold temperate and sub-Arctic waters of the North Atlantic. Like all beaked whales, NBWs are deep divers, with the record being 2339 m for 94 minutes! It’s thought they dive to feed (mostly fish and squid, also sea cucumbers and starfish!) or possibly to evade predators.

Unlike most beaked whale species, NBWs are very curious and will often approach boats. Partly because of this, NBWs were commercially hunted, with more than 60,000 whales caught in the 19th and 20th centuries. Whilst populations have recovered in some areas, numbers are likely well below pre-exploitation levels.

NBWs also face modern threats from humans. For example, they are very sensitive to underwater noise, particularly naval sonar. As far as we know, they respond to sonar by diving deep and away from the source. This deep diving can lead to the formation of dangerous gas bubbles within their tissues, commonly known as the bend (as in humans). If severe, this may lead to death.

Iceland 2018
2018 was a tragic year for beaked whales in the northeast Atlantic, with over 100 beaked whales found dead along the west coast of the British Isles. At the same time, pods of northern bottlenose whales were appearing in shallow waters all around North Iceland – unprecedented for this species.

We were running our first field season in Skjálfandi Bay and helped to monitor NBWs in an effort to understand why they were there. Because this research wasn’t planned, our methods were quite opportunistic. We noted the location of each sighting, monitored behaviour and took photos for photo-identification purposes. This wouldn’t have been possible without the whale-watching companies. Working under the University of Iceland, we monitored whales from North Sailing boats and every company contributed their sightings.

Sadly, by the end of 2018, six animals had died (or were found dead) in the bay – at least five of those were females. This included a live stranding of three sub-adults – at the time, the largest recorded NBW stranding. This was accompanied by clear signs of distress, such as breaching in extremely shallow water, swimming in tight circles and erratic movements. NBWs were sighted for 49 days in a coastal area, where we should never see them. Full details can be found in this 2020 paper. We still can’t explain these unusual occurrences. However, the first day of sighting in north Iceland (June 25th, 2018) coincided with the start of Operation Dynamic Mongoose, a major NATO anti-submarine exercise in the Norwegian Sea.

Scotland 2020
2020 was another sad year for NBWs. After the largest recorded NBW stranding in Ireland in June, at least six animals were sighted around the west coast of Scotland between August and October. These whales were frequently sighted in narrow, south-facing sea lochs. Sadly, these animals looked underweight and appeared distressed (breaching, erratic movement, very short dives). Their prospects weren’t helped by Joint Warrior, a naval exercise held in the same area.

On a weekend in September, before Joint Warrior, we tracked the movement of three whales in Gareloch using a theodolite. Specifically, by measuring the vertical and horizontal angle between the observer and the whale, you can calculate the whale’s position. We wanted to understand why the whales weren’t leaving the loch – perhaps a seafloor feature or something else. We also collaborated with Denise Risch, a cetacean acoustician, who deployed a hydrophone in the loch at the same time to listen to NBW vocalisations. Results expected in 2021.

Throughout the two months, these whales were monitored constantly by British Divers Marine Life Rescue. Despite huge efforts from BDMLR, sadly four animals died, including two live strandings. NBWs, like other beaked whales, are incredibly difficult to rescue once stranded. The cause of stranding or death is still unknown for each animal.