Killer whale respiration rates

Abstract

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.

Fig 1. Still images from UAV drone video showing datalogger placement and respiration.

Photographs showing the animal-borne datalogger attached with suction cups to a juvenile northern resident killer whale (A113). Views show (A) the whale’s breath immediately after surfacing, (B) mid-blow, and (C) after the blow has dissipated. Photo credit: Keith Holmes.

Fig 2. Histogram of maximum dive depths for HHMM dive types.

Note that dive depths are plotted on a log scale for 4 adult male (n = 4955 dives) and 7 juvenile resident killer whales (n = 3163 dives).

Fig 3. Example of a dive-depth profile from adult male whale D21 illustrating depth categories and track behavioural states predicted by the HHMM.

Panel A represents the depth categories used to classify behavioural states within the HHMM. On D21, sample sizes were logging (n = 27), shallow (< 7.5m, n = 1,687) medium (10–30 m, n = 87), and deep (> 50m, n = 11, see S2 Appendix for details). Panel B represents predicted behavioural states by the HHMM for resting (n = 550 dives), travelling (n = 1005 dives), and foraging (n = 257 dives) on this animal. This adult male whale made 1812 total individual dives recorded on the animal-borne tag.

Fig 4. Respiration rates (breaths min^-1) of 7 juvenile and 4 male resident killer whales while resting, foraging, and travelling.

The number of tracks were resting (70), foraging (38), and travelling (68) for juveniles compared to resting (90), foraging (62), and travelling (68) for adult males. Sample size of whales across all behaviours was n = 7 juveniles and n = 4 adult males.

Fig 5. Individual long dive durations (≥ 1 minute) of 7 juvenile and 4 adult male resident killer whales for different behavioural states (foraging, resting, and travelling).

Individual dive duration was recorded by the CATS tags with behavioural state as predicted by the HHMM. Long dives include 11% of the total dives in juveniles (n = 354 long dives) and 9% of the total dives in adult males (n = 440 long dives). Sample sizes for total individual dives ≥ 1 minute were n = 76-foraging, 190-resting, and 88-travelling dives for juveniles; and n = 93-foraging, 241-resting, 106-travelling dives for adult males.

Fig 6. Distributions of individual dive durations for short dives (< 1 minute) from CATS tags with behavioural state predicted by HHMM (bins = 4 seconds).

Individual dive duration was recorded by the CATS tags with behavioural state predicted by the HHMM. Short dives were 89% of the total dives in juveniles (n = 2899 short dives) and 91% of the total dives in adult males (n = 4515 short dives). Sample sizes for total individual short dives < 1 minute are n = 603-foraging, 950-resting, and 1256-travelling dives for juveniles; and n = 1340-foraging, 1296-resting, 1879-travelling dives for adult males.