Deep diving by offshore bottlenose dolphins (Tursiops spp.)

Abstract

We used satellite‐linked tags to evaluate dive behavior in offshore bottlenose dolphins (Tursiops spp.) near the island of Bermuda. The data provide evidence that bottlenose dolphins commonly perform both long (>272 s) and deep (>199 m) dives, with the deepest and longest dives being to 1,000 m and 826 s (13.8 min), respectively. The data show a relationship between dive duration and dive depth for dives longer than about 272 s. There was a diurnal pattern to dive behavior, with most dives deeper than 50 m being performed at night; deep diving began at sunset and varied throughout the night. We used the cumulative frequency of dive duration to estimate a behavioral aerobic dive limit (bADL) of around 560–666 s (9.3–11.1 min) in adult dolphins in this population. Dives exceeding the bADL spent significantly longer time in the upper‐most 50 m following a dive as compared with dives less than the bADL. We conclude that the offshore ecotype off Bermuda, unlike the shallow‐diving near‐shore bottlenose dolphin, is a deep‐diving ecotype, and may provide a useful animal model to study extreme diving behavior and adaptations.

Surface and diving metabolic rates, and dynamic aerobic dive limits (dADL) in near‐ and off‐shore bottlenose dolphins, Tursiops spp., indicate that deep diving is energetically cheap

“…With variation in the relative muscle mass of the deep diving ecotype, it is also possible that the relationship between activity and energy cost is different compared with that developed for dolphins during shallow surface swims (Allen et al, 2022). Still, the estimated dADL of 11.1 min for deep dives was reasonably close to the estimated bADL of 9.6–10.4 min in the same dolphins (Fahlman et al, 2023), suggesting that the dynamic gas model used in the current study provides reasonable results also for deep diving dolphins. However, better information of body composition of pelagic dolphins would help improve future modeling studies.…”

“…Although the LMR was higher during ascent and did not change with depth, the rate of change in depth was higher during descent as compared with ascent in Bermuda dolphins (Equation ), suggesting either higher pitch (Figure 2) or higher swim speed due to changes in buoyancy‐related locomotory efficiencies. The dADL in the current study was 11.1 min in the Bermuda dolphins during deep dives (>100 m), which is close to the 9.6–10.4 min estimated from behavior (bADL; Fahlman et al, 2023).…”

“…To illustrate how these differences affect the metabolic cost of different dives, we estimated the LMR for the different phases of a dive to 50 m versus 500 m. For this, we used the changes in descent and ascent rates (Equation ) to estimate the duration and LMR of the descent, ascent, and the total time at the bottom. We used a dive duration of 225 s and 550 s for the dive to 50 m and 500 m, respectively, which are representative dive durations to these depths for these individuals (Fahlman et al, 2023). In this case, the dives to 50 m and 500 m would result in transit times of 206 s and 314 s, respectively.…”

“…The animals residing in and around Sarasota Bay are smaller and shallow‐diving, with average dive depths around 1 m, and dive durations around 40 s (Fahlman, Jensen, et al, 2018; Wells & Scott, 2018). The dolphins residing in Bermuda are of a larger pelagic ecotype which commonly perform dives beyond 200 m and a maximum recorded dive depth of 1,000 m (Fahlman, Jensen, et al, 2018; Fahlman et al, 2023; Klatsky et al, 2007). The shallow‐diving ecotype has lower hematocrit and smaller body size, indicating lower body O 2 stores (Fahlman, Jensen, et al, 2018; Schwacke et al, 2009), but the resting metabolic rate and respiratory tidal volumes do not differ (Fahlman, Brodsky, et al, 2018; Fahlman, McHugh, et al, 2018).…”

“…Three (two male and one female) dolphins were studied off Bermuda in August 2016 (Fahlman, Jensen, et al, 2018; Fahlman et al, 2023). The animals were captured by a break‐away hoop netting technique (Asper, 1975), and briefly restrained for a health assessment, tagging, and sampling.…”