The Icelandic Orca Project has been ongoing in Vestmannaeyjar since 2008. From that first summer, we have observed killer whales regularly every year and have been collecting a lot of important long-term data. The 6th July 2014 started like a typical day in the field but quickly became extraordinary. We spent several hours on the water with plenty of killer whales around our research boats and were busy collecting photographs and acoustic recordings. Just as we were getting ready to head back to the harbour, we spotted several small dorsal fins in the distance: long-finned pilot whales! We had never observed this species in the area before and locals had not observed them either. It turned out that these new visitors had come to stay. Since that first encounter, we have observed pilot whales every summer. And we are not the only ones noting their presence. The killer whales do not seem to like the approach of these new visitors. We have observed many times that killer whales avoid pilot whales and sometimes flee at high speed. Similar interactions have been reported from other locations in the North Atlantic and we have been puzzled by these interactions ever since we first observed them. Now we got a chance to study them in more detail and we recently published our findings.
Our team in the field collecting data by boat. Photo: Rosemary Connelli
There were two main questions that we wanted to answer: 1) How often do killer whales and pilot whales occur in Vestmannaeyjar and were the two species also seen in other locations around Iceland’s coast? 2) What exactly is happening during the interactions?
We reached out to colleagues around Iceland to gather data on the occurrence of killer whales and pilot whales as well as possible interactions between them. Most of the data we received was collected by researchers and naturalists onboard whale watching tours. We gathered data from six different locations (Vestmannaeyjar, Faxaflói, Breiðafjörður, Steingrímsfjörður, Eyjafjörður and Skjálfandi), spanning the years 2007-2020. Both species had been sighted in all of the locations but there were major differences in how often each species was seen and at which time of the year.
Map of Iceland showing study locations
Killer whales were commonly encountered in Vestmannaeyjar in the south of Iceland during summer and in Breiðafjörður (west Iceland) during winter and spring. In all other locations sightings were infrequent and could occur at any time of the year. Pilot whales were only seen in the summer time, most commonly in Vestmannaeyjar, Breiðafjörður and Steingrímsjörður (northwest Iceland). In most locations sightings increased during the study period, particularly in Vestmannaeyjar.
In Vestmannaeyjar and Breiðafjörður the two species were seen simultaneously. Whenever pilot whales and killer whales were seen together, interactions between them were common. The interactions were very intriguing. Typically, the pilot whales would approach the killer whales, often at high speed. In most interactions that we observed, the killer whales avoided the pilot whales by moving away at moderate speed or they disappeared from view for a while and were then sighted some distance away. However, in about a third of the interactions high-speed chases ensued with both species porpoising (meaning the whale is coming out of the water with the head and leaping forward, as seen in the pictures below).
Pilot whales pursuing killer whales at high speed (porpoising). Photo: Katarína Klementisová
Killer whales moving away from pilot whales at high speed (porpoising). Photo: Curt Hanson
Pilot whales and killer whales during a high speed interaction. Video: Rebecca Bakker
Similar interactions have been reported from Norway and the Strait of Gibraltar, Spain but it remains unclear what exactly is going on. Previous studies have suggested two possible explanations for this behaviour. The first is that the two species are competing for food, habitat or feeding areas. While killer whales in Vestmannaeyjar and Breiðafjörður feed on herring primarily, we have very little knowledge on the diet of pilot whales. The second hypothesis is that pilot whales are exhibiting a mobbing behaviour. Mobbing is a common antipredator behaviour in many animals (e.g. birds or small mammals). In order to avoid an attack, animals may assemble around a predator and cooperatively attack and harass them. Research from Norway shows that pilot whales are strongly attracted to killer whale sounds and will increase group size while moving towards the killer whale sounds. This behaviour is consistent with a mobbing behaviour and it is possible that we are observing the same in Icelandic waters.
In this study we described the occurrence of killer whales and pilot whales around Iceland over time and had the chance to describe their interactions in detail and it raised many new questions that we are hoping to address in future studies. For example, we are very interested in what role sound plays in triggering interactions and have started studies to investigate this further. We are also hoping to gain further insights into the biology and ecology of both species but in particular pilot whales, to better understand their occurrence and behaviour.
This project was a collaborative effort, bringing together data from all around Iceland and we would like to thank our colleagues as well as the whale watching companies that provided us with data or research platforms: Elding Whale Watching, Gentle Giants, Láki Tours, North Sailing, Special Tours, Whale Watching Akureyri
The study is available here: Selbmann A, Basran CJ, Bertulli CG, Hudson T, Mrusczok M-T, Rasmussen MH, Rempel JN, Scott J, Svavarsson J, Wensveen PJ, Whittaker M, Samarra FIP (2022) Occurrence of long‐finned pilot whales (Globicephala melas) and killer whales (Orcinus orca) in Icelandic coastal waters and their interspecific interactions. Acta ethologica, https://doi.org/10.1007/s10211-022-00394-1