Orcas only need one breath between dives

Killer whales are one of the most capable apex predators on the planet and can single-handedly take on great white sharks, attack boats and have close matrilineal family ties. Now a new study combined tag data, physiology, drone imagery and statistical analyzes to confirm a long-held assumption. Orcas take only one breath between their dives. The findings are described in a study published May 15 in the journal PLOS ONE and could have some important conservation implications.

The study observed 11 northern and southern resident killer whales off the coast of British Columbia, Canada. Resident killer whales are an ecotype that specialized in eating salmon, particularly large, fatty and nutritious Chinook salmon. For comparison, temporary killer whales or Biggs killer whales will eat larger prey including other marine mammals including sea lions, dolphins and other whales.

“This research was actually initiated to better understand the energy needs of British Columbia’s killer whales,” wrote study co-author and master’s candidate from the University of British Columbia (UBC). Tess McRae tells PopSci. “Our northern orcas are endangered and our southern orcas are endangered. So it is very important for us to know how much energy these whales use, and, on the other hand, how much food these whales need to survive.”

[Related: How crafty orca whales hunt near submarine canyons.]

Like humans, orcas need to breathe more when they are engaged in higher energy activities, such as hunting for food or traveling long distances, so they can get more oxygen into their bodies. To monitor the whales in the wild, the team used tags from eleven orcas to collect data including diving depths, acoustics and biological data.

“It’s essentially like putting a Fitbit on the animals,” study co-author and postdoctoral researcher at UBC Dr. Beth Volpov tells PopSci. “But because they move in the wild, we can’t measure it directly. Studies have used drones or studies have used data loggers, but we combined them and synchronized them with the exact whales. When a whale is tagged, we view that whale from above down to the second.”

After a certain time, the suction cups detach, float to the surface and are collected by researchers. This data is used in combination with drone images taken by drone pilot Keith Holmes and the Hakai Institute. McRae could study this drone footage and assess what behaviors the whales exhibited and count the number of breaths they performed during different behaviors.

“The drone footage is very fascinating to look at, but the challenging part for scientists is moving from a few video clips to meaningful numbers and data analysis,” says Volpov. “And that’s where our collaboration with the statistics department helped enormously: translating the video into meaningful numbers to find out what’s going on.”

The team used a deep static analysis by co-author of the study and PhD student Evan Sidrow from UBC’s statistics department to get a more accurate analysis of killer whale breathing rates. The team found that orcas spend most of their time making shallow dives. Most last less than a minute. The longest dive lasted about 8.5 minutes for one adult male. The whales in the study took 1.2 to 1.3 breaths per minute when resting and 1.5 to 1.8 while traveling or hunting. By comparison, people take about 15 breaths per minute at rest and 40 to 60 during exercise.

[Related: Toothed whales turned their vocal fry into a hunting superpower.]

“Orcas are like sprinters that don’t have the marathon endurance of blue whales and humpback whales to make deep and prolonged dives,” says co-author of UBC professor Dr. Andrew Trites said in one rack.

This mix of above- and below-water data and statistical analyzes gave the team a much better understanding of the orca’s activities.

The killer whales that live off the west coast of the United States and Canada are threatened or endangered threatened for countless reasons. Reduced availability of salmon, ship strikes, chemical pollution and noise pollution have all taken their toll on these whales. From December 2023there are an estimated 74 orcas left in the south. Northern resident killer whales are still endangered, but are doing better by approx 300 individual whales.

“Once we know what their breathing rate is, we can calculate the energy and then calculate the food requirements for these whales,” says McRae. “So this is the first piece of insight into how much food these whales need to survive, which is important for their conservation.”