Orca Whales: Killer Shockwave Hunters of the High Seas

by Robert C. Brears Blog

The orca, or killer whale as it is commonly known, is the top marine predator and possibly the most widespread vertebrate on Earth. It is found in all the world’s oceans, including the Antarctic and Arctic regions.

Regiones: Antártida, Ártico

Destacados: Orca

The orca (aka killer whale), a whale of many oceans

The orca, or killer whale as it is commonly known, is the top marine predator and possibly the most widespread vertebrate on Earth. It is found in all the world’s oceans, including the Arctic and Antarctica.

Black-and-white killer whale coloring

Killer whales, which have rounded heads and blunt beaks, are the largest members of the dolphin family. They are famous for their striking combination of black and white: black backs and flanks, white underbellies. Most of them have a light grey saddle marking just behind their dorsal fin. Orcas have large, elliptical white patches on the side of their heads, just above and behind the eyes. 

Iceland Orca Project

The Icelandic Orca Project monitors the social and foraging behaviour of killer whales regularly seen in Icelandic waters. Orca behaviour can be generally divided into foraging, travelling, socialising, and resting. The behaviours are easy to tell apart. Travelling killer whales head consistently in a specific direction, while socialising whales tend to hang around with a lot of surface activity. Resting killer whales are typically idle at the surface for minutes at a time.

Killer whale shockwave hunting

When Icelandic killer whales feed on herring schools, they encircle their prey to force the school into tighter formations before using their tails to slap the water. This causes a shockwave to stun the fish, enabling the orcas to feed on each fish one at a time. This type of feeding is called “carousel feeding.” However, this type of behaviour is not seen in Iceland, suggesting to scientists that there is a different type of feeding behaviour going on there. Using tagging data, researchers in Iceland found the killer whales feeding on herring schools at the bottom of their dives instead of forcing the fish to the surface. The scientists speculate that this could be due to different water bodies in Norway and Iceland. Norwegian waters are deep in the fjords, while the waters in Iceland, where herring spawning grounds are found, are quite shallow.

Unique Icelandic orca sounds

Studies on the acoustic sounds killer whales make have been ongoing for many years. Orcas make clicks, pulsed calls, and whistles. However, not all whistles are the same across killer whale populations around the world. In fact, orcas in the Pacific produce low-frequency whistles with predominantly downward contours, while Atlantic orca whistles are higher in frequency and have a variety of contour shapes. In comparison, Icelandic killer whales produce a unique call, which is known as the “herding call.” It is a very long and low-frequency call that clearly stands out from other whale calls and can be heard when the orcas are feeding. It is believed that the herding call is used to shepherd the herrings when feeding, forcing the fish into tighter densities and making them easier for the orcas to target with their slapping tails.

Day-and-night killer whale feeding

Scientists have conducted a study on Iceland killer whales to determine if they hunt for herring more during the daylight hours or at night time. Comparing the acoustic data of killer whales during the day and night using autonomous recorders deployed in Iceland over the winter, researchers found that, based on the acoustic detection of underwater tail slaps, the killer whales feed on herring both at night and day. In fact, they spent half of their time at night and nearly 75% of the day feeding on fish. There was a change in their herding call and slapping behaviour, however, with more slapping at night. This indicates that in low-light conditions, orcas rely more on acoustics to herd the herring, showing scientists that killer whales have the ability to adapt their feeding behaviour to different light conditions. 

Real-time orca tracking in Antarctica

Orcas are a major attraction on Antarctica cruises, but they are of deep interest to scientists as well. Since 2005, scientists have been attaching small transmitting tags to the dorsal fins of killer whales in Antarctica. Over 25 of these tags, which weight about 40g (.09 pounds), have been attached on different types of orcas around the Antarctic Peninsula and Ross Sea regions. The tags usually last for more than 100 days on the whales and have tracked individual movements of more than 9,000 kilometres (5,592 miles). The tags transmit data to Argos satellite receivers, resulting in high-resolution tracking. This enables scientists to study ranging patterns, migration, and foraging behaviours, comparing different types of killer whales. In addition, the tracking data enables real-time locations to be given, increasing the understanding of orca prey preferences through more regular observations.

A quick killer whale turnaround

Already the above-mentioned satellite data has provided scientists with valuable insights into the migratory habits of killer whales in the Antarctic region. For instance, there was a rapid migration of a certain type of orca from the Antarctic Peninsula to the edge of the tropics and back in just 42 days. The data showed that this type of orca foraged near the Antarctic Peninsula, then headed off to Uruguay and Brazil in a round trip that was 9,400-km-long (5,840 miles).

Orca wave washing

Scientists (and maybe even a few passengers of Antarctica Peninsula trips) have observed orcas near the Antarctic Peninsula cooperatively hunting together in pack ice, with whales using their tails to “wave wash” seals off ice floes. Over a period of time, researchers observed three different groups of killer whales hunting off the western Antarctic Peninsula. The study observed 16 seals and one Antarctic minke whale falling prey to this tactic. Of the seals successfully hunted, the data showed that 86% of the time it involved killer whales cooperatively creating waves with their tails to produce destabilise the seal. They produced 120 waves during 22 separate attacks and successfully took 75% of the Weddell seals attacked. The statistics also showed that the mean number of waves produced per successful attack was just over four, and the mean length of attack was 30 minutes, while the range was 15 – 62 minutes.

Five quick facts about the killer whale

1. Adult orcas range in size from 5.5 – 9.8 metres long (18 – 32 feet), with males reaching on average 7.3 metres (23 feet) and at least 8,000 kg (17,636 pounds) in weight. Female orcas grow to around 6.2 metres (20 feet) and 4,000 kilograms (8,819 pounds) in weight

2. The adult male orca’s dorsal fin can be up to 1.8 metres tall (5.9 feet) or more, while females and juveniles have a dorsal fin that is around one metre (3.2 feet) tall

3. Killer whale pods can travel in tight formation or be spread across more than one kilometre (0.6 miles), often breathing and diving in a coordinated fashion, with each whale reaching up to 55 km per hour (34 mph) when swimming at full pace

4. Researchers have found that, while Icelandic orcas are very vocal when feeding on herring – they produce a lot of calls and clicks, along with herding calls and tail slapping – they are very silent when travelling, remaining quiet for extended periods of time

5. It is believed killer whales in Antarctica migrate to warmer waters for periodic maintenance of their skin. The warmer waters allow their skin to regenerate without the heat loss that would occur in colder Antarctic waters

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