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The sei whale ( Balaenoptera borealis ) is an important species among baleen whales in the North Pacific and plays a significant role in the ecosystem. Despite the importance of this species, information regarding its migration patterns and breeding locations remains limited. To enhance the understanding of the phenology of North Pacific sei whales, we deployed satellite-monitored tags on these whales in the western and central North Pacific from 2017 to 2023. We fitted 55 sei whale tracks to a state-space model to describe the whales’ seasonal movements at feeding grounds and their migratory behavior. The whales typically leave their feeding grounds between November and December, with migration pathways extending from off Japan to the west of the Hawaiian Islands. These southward transits converge in the waters of the Marshall Islands and north of Micronesia between 20° N and 7° N, which appear to be breeding grounds. After a brief stay at these breeding grounds, the whales migrate northward from January to February, reaching their feeding grounds around 30°N by March. To the best of our knowledge, this is the first study to present the phenology of feeding and breeding seasons and the migration pattern of North Pacific sei whales.

Impact assessments for sonar operations typically use received sound levels to predict behavioural disturbance in marine mammals. However, there are indications that cetaceans may learn to associate exposures from distant sound sources with lower perceived risk. To investigate the roles of source distance and received level in an area without frequent sonar activity, we conducted multi-scale controlled exposure experiments ( n = 3) with 12 northern bottlenose whales near Jan Mayen, Norway. Animals were tagged with high-resolution archival tags ( n = 1 per experiment) or medium-resolution satellite tags ( n = 9 in total) and subsequently exposed to sonar. We also deployed bottom-moored recorders to acoustically monitor for whales in the exposed area. Tagged whales initiated avoidance of the sound source over a wide range of distances (0.8–28 km), with responses characteristic of beaked whales. Both onset and intensity of response were better predicted by received sound pressure level (SPL) than by source distance. Avoidance threshold SPLs estimated for each whale ranged from 117–126 dB re 1 µPa, comparable to those of other tagged beaked whales. In this pristine underwater acoustic environment, we found no indication that the source distances tested in our experiments modulated the behavioural effects of sonar, as has been suggested for locations where whales are frequently exposed to sonar.

Antarctic minke whales Balaenoptera bonaerensis are rorquals that migrate to Antarctic waters to forage during the austral summer. Because the species frequents the edges of ice packs in summer, the potential impact of long-term physical environmental changes poses serious conservation concerns. Condition along the ice edge vary regionally, sometimes forming small ice free areas (ice gaps), and little is known about whale movement patterns associated with these small-scale variations in the physical environment. In this study, six minke whales were tracked for an average of 31 days (range 4–77 days) from January to March of 2016 and 2017 between 60° E and 140° E above and off the continental shelf. The tracking data of five animals were fitted to a Bayesian hierarchical switching state-space model assembled from ARGOS data filters to estimate behavioral states. Results show that Antarctic minke whales are likely to search for ice gaps areas and remain there for extended periods until the surrounding ice melts, rather than stay at krill rich shelf breaks or areas with high chlorophyll-a concentration. When no ice gaps were nearby, the whales were likely to move eastward along highly concentrated ice packs to find a gap. Our study found a strong association between minke whale movements and ice dynamics during the summer foraging season in this region.

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. This study used records from 13 satellite tags deployed off Jan Mayen to provide an extensive description of the dive behavior of northern bottlenose whales in the Nordic Seas. Our findings demonstrate that this species has 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 habitat to this population of deep‐sea predators.

Of all animals considered subjects for instrumentation for behavioral or physiological studies, cetaceans probably represent the greatest challenge to the engineer and biologist. The marine environment being harsh to electronics, evasive behavior during tagging approaches and the short time window available to attach instruments, all imply a need for innovative tagging solutions to facilitate better understanding of their life cycle, migration, physiology, behavior, health and genetics. Several animal-attached tag packages holding specific data loggers, e.g., time depth recorders, position, orientation, acoustic and video recorders for short to medium term studies, as well as tags developed for large scale migration telemetry studies are available as off-the-shelf devices, or in many cases as custom made sensor packages. Deployment of those instruments is often the limiting factor for data collection. The Aerial Remote Tag System (ARTS) is a flexible system which can easily be adapted to deploy different tag sensor packages and biopsy collection devices. This paper presents the history and design of the ARTS, and accessories developed for instrumentation and biopsy sampling of cetaceans, such as the recent developed ARTS–LKDart for biopsy sampling. Deployment of archival tags usually requires radio tracking of the instrumented animal, or at least tracking of the tag for recovery. Thus, we also here describe the automatic digital signal processing radio direction finder, the Direction Finder Horten (DFHorten unit).

Understanding how individual animals modulate their behaviour and movement patterns in response to environmental variability plays a central role in behavioural ecology. Marine mammal tracking studies typically use physical environmental characteristics that vary, and/or proxies of prey distribution, to explain predator movements. Studies linking predator movements and the actual distributions of prey are rare. Here we analysed satellite tag data from ten humpback whales in the Barents Sea (north-east Atlantic) to examine how their spatial movement and dive patterns are influenced by the geographic and vertical distribution of capelin, which is a key prey species for humpback whales. We used capelin density estimates based on direct observations from a trawlacoustic survey and sun elevation to explore the drivers of changes in movement patterns. We found that the humpback whales’ exhibited characteristic area restricted search movement where capelin density was the highest. While horizontal movements showed both positive and negative individual relationships with sun elevation, humpback whale dive depth was positively correlated with diurnal variations in the vertical distribution of capelin. This suggests that in addition to whales foraging in regions of high capelin density, they also target the densest shoals of capelin at a range of depths, throughout the day and night. Overall, our findings suggest that regions of high capelin density are important foraging grounds for humpback whales, highlighting the central role capelin plays in the Barents Sea marine ecosystem.

Long-distance migration for most species of baleen whales is poorly understood because of the practical difficulties and substantial expense involved in gathering relevant data. Presently, satellite tracking is the only method that delivers the necessary detail and quantitative data on movement patterns on far-ranging marine mammals. In this study, ARGOS satellite tags were deployed on North Atlantic sei whales (Balaenoptera borealis) at the Azores Islands. Data from one whale showed a cumulative 4,102-km movement from tagging at Faial Island in the Azores on 12 April 2005 via the Charlie Gibbs Fracture Zone (CGFZ) to the Labrador Sea where transmissions stopped on 7 June 2005. For a portion of the distance from CGFZ to the Labrador Sea, the whale moved in the prevailing direction of the surface current pattern. Erratic movement in five areas along the movement track indicates feeding behaviour, particularly in the CGFZ. The results show the large-scale movement potential of North Atlantic sei whales from wintering grounds to highly productive potential feeding areas in the Labrador Sea. [PUBLICATION ABSTRACT]

Knowledge about species-specific hearing is vital to assessing how anthropogenic noise impacts marine mammals. Unfortunately, no empirical audiogram exists for any mysticete whale. We therefore developed a catch-and-release method to assess hearing in a small mysticete, the minke whale (Balaenoptera acutorostrata). Stationary lead nets were placed to intercept migratory routes and direct the whales into an ocean basin enclosed by nets and islets, while another net was pulled across the entrance once a whale entered the basin. The minke whales were then slowly corralled into a modified aquaculture pen using a net suspended between two boats. Subsequently, the water volume available to the whales was gradually reduced by raising the pen net by hand until the whales were secured in a “hammock” between the floating pen ring and a raft. From the raft, researchers could access the whales to monitor their health, apply instruments for hearing tests, or perform other research objectives, and then attach tags to monitor the movements and diving behavior of the whale post-release. The method is a slow and controlled procedure, allowing continuous monitoring and quick release of the whales, if needed. In the first three field seasons employing the method, three minke whales were caught for research procedures. Initial hearing measurements using auditory evoked potentials were successfully completed. After release, the whales resumed migration, and dive behavior was considered normal. Our observations demonstrated that minke whales can be guided safely via moored net barriers, corralled into an aquaculture pen, and safely handled for research purposes, before being released back into the wild.