Long-Term Depth Records of Satellite-Tagged Northern Bottlenose Whales Reveal Extraordinary Dive Capabilities

Abstract

Studying the baseline behavior of deep-diving mammals can substantially improve our understanding of these species' ecology and provide important benchmarks to evaluate effects of changes in climate and anthropogenic activities. Despite being the most abundant beaked whale in the Arctic and subarctic, information on the behavior of northern bottlenose whales (Hyperoodon ampullatus) is limited. This study used records from 13 satellite tags deployed off Jan Mayen in June-July 2014-2016 to provide an extensive description of the dive behavior of Hyperoodon for the Nordic Seas. A total of 8372 dives, collected over 224 days (or 5376 h), were analyzed. The whales performed extreme dives of up to 2288 m deep and 98 min long-deeper and longer than previously reported for behavior in presumed undisturbed contexts. Individuals spent on average 18% of the time at depths shallower than 40 m, and 22%, 47%, and 12% in epi-, meso-, and bathypelagic dives, respectively. Epipelagic dives averaged 123 m (s.d.: 46 m) in depth and 11 min (5 min) in duration. Mesopelagic dives averaged 441 m (217 m) and 24 min (11 min) and were performed at a mean rate of 1.46 h^-1. Bathypelagic dives averaged 1487 m (366 m) and 55 min (13 min) and were performed at a mean rate of 0.23 h^-1. The distribution of dive depths was less bimodal than typically reported for other beaked whales, and all dive profiles contained periods of continuous, consecutive deep dives. Benthic diving occurred at meso- and especially bathypelagic depths and was individual specific, varying from 8% to 51% of the animal's bathypelagic dives. Overall, our findings demonstrate that northern bottlenose whales have extraordinary capabilities to dive, and presumably feed, throughout the water column including at the sea floor. High rates of deep dives highlight the importance of the Iceland and Norwegian Seas to this population of deep-sea predators.

Keywords: beaked whale; biotelemetry tags; cetacean; deep‐diving; dive behavior.

FIGURE 1

Aerial photograph of a group of northern bottlenose whales ( Hyperoodon ampullatus ) swimming at the surface. Photographer: Patrick Kagerer.

FIGURE 2

Map of the waters near Jan Mayen, showing the locations of the satellite tag deployments on northern bottlenose whales that were analyzed in this study. Bathymetry data for the map were obtained from the ETOPO 2022 global relief model (NOAA 2022).

FIGURE 3

(a) Boxplots of dive durations measured by satellite tags on northern bottlenose whales in 2016 per oceanographic zone (b) scatterplot of maximum depth and duration of the dives measured in 2016 (c) boxplots of maximum dive depths per oceanographic zones throughout all deployments (2014, 2015, 2016). Note the depth axis is positive downwards.

FIGURE 4

Dive profiles (black lines) reconstructed from dive summary information, containing the (a) longest dive (98 min; ID 161593) and (b) two deepest dives (both to 2288 m; ID 161588) in the data set. Turquoise dots: Seafloor depth; red asterisks: Dives considered benthic (< 100 from the charted seafloor depth).