In a new study, published this week in the journal PLOS ONE, researchers have confirmed a long-established assumption - orcas breathe only once between their dives.

Resident killer whales are an ecotype that specializes in eating salmon, particularly Chinook salmon. In comparison, Bigg's killer whales eat larger prey, including other marine mammals such as sea lions, dolphins and other whales.

Killer whale respiration rates
Measuring breathing rates is a means by which oxygen intake and metabolic rates can be estimated to determine food requirements and energy expenditure of killer whales (Orcinus orca) and other cetaceans. This relatively simple measure also allows the energetic consequences of environmental stressors to cetaceans to be understood but requires knowing respiration rates while they are engaged in different behaviours such as resting, travelling and foraging. We calculated respiration rates for different behavioural states of southern and northern resident killer whales using video from UAV drones and concurrent biologging data from animal-borne tags. Behavioural states of dive tracks were predicted using hierarchical hidden Markov models (HHMM) parameterized with time-depth data and with labeled tracks of drone-identified behavioural states (from drone footage that overlapped with the time-depth data). Dive tracks were sequences of dives and surface intervals lasting ≥ 10 minutes cumulative duration. We calculated respiration rates and estimated oxygen consumption rates for the predicted behavioural states of the tracks. We found that juvenile killer whales breathed at a higher rate when travelling (1.6 breaths min-1) compared to resting (1.2) and foraging (1.5)—and that adult males breathed at a higher rate when travelling (1.8) compared to both foraging (1.7) and resting (1.3). The juveniles in our study were estimated to consume 2.5–18.3 L O2 min-1 compared with 14.3–59.8 L O2 min-1 for adult males across all behaviours based on estimates of mass-specific tidal volume and oxygen extraction. Our findings confirm that killer whales take single breaths between dives and indicate that energy expenditure derived from respirations requires using sex, age, and behavioural-specific respiration rates. These findings can be applied to bioenergetics models on a behavioural-specific basis, and contribute towards obtaining better predictions of dive behaviours, energy expenditure and the food requirements of apex predators.
PLOS ONETess M. McRae ,

Like humans, orcas need to breathe more when they are involved in activities that require greater energy consumption, such as hunting or traveling long distances, so that they can obtain more oxygen for their bodies.

"This study was initiated to better understand the energy needs of killer whales resident in British Columbia," the study's first author, Tess McRae, explained to Popular Science.

To monitor the whales in the wild, the team used suction-cup tags placed on 11 orcas residing north and south off the coast of British Columbia, Canada.

The team collected data on diving depths, acoustics and biological data. This combination of in-water and out-of-water data and statistical analysis allowed the team to gain a much better understanding of the orcas' activities.

"Orcas are like sprinters who don't have the marathon endurance of blue and humpback whales to make deep, prolonged dives," says Andrew Trites, professor and co-author of the study, in a statement on EurekAlert.

The team found that orcas spend most of their time on shallow dives and most last less than a minute. The longest dive took an adult male about eight minutes.

Killer whales breathe just once between dives, study confirms
<p>A new study has confirmed a long-held assumption: that orcas take just one breath between dives.</p> <p>The researchers used drone footage and biological data from tags suction-cupped to 11 northern and southern resident killer whales off the coast of B.C. to gather information on the animals&rsquo; habits. Confirming orcas take only one breath between dives allowed the researchers to calculate how many litres of oxygen adults and juveniles consume per minute. This provides another piece of the puzzle in estimating orca energy expenditure, and eventually, how many fish the animals need to eat per day, key to their conservation.</p>
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The whales in the study breathed 1.2 to 1.3 times a minute when they were resting and 1.5 to 1.8 times when they were traveling or hunting.

"Once we know what their breathing rates are, we can calculate the energy and then the food requirements of these whales," says McRae.

Resident orcas off the western coasts of the United States and Canada are threatened and endangered. The reduced availability of salmon, attacks by boats, chemical pollution and noise pollution have all affected these aquatic animals.

"So this is the first step towards finding out how much food these whales need to survive, which is important for their conservation," concludes the study's lead author.