Round-trip migration and energy budget of a breeding female humpback whale in the Northeast Atlantic

Size-specific strategies of sympatric cetaceans to reduce heat loss

Maintaining a stable core body temperature is essential for endotherms. Cetaceans live in a highly thermally conductive medium, requiring special adaptations to reduce heat loss and maintain homeothermy. We employed a combination of aerial photogrammetry and existing data sources to estimate heat loss rates in five sympatric cetaceans of varying sizes, inhabiting the sub-arctic waters (∼3.7°C) of NE-Iceland: harbour porpoises (Phocoena phocoena, 1.0-1.6 m, n=50), white-beaked dolphins (Lagenorhynchus albirostris, 1.1-2.9 m, n=294), minke whales (Balaenoptera acutorostrata, 4.4-8.6 m, n=30), humpback whales (Megaptera novaeangliae, 6.0-14.2 m, n=282) and blue whales (Balaenoptera musculus, 13.2-24.2 m, n=29). Further, we investigated the effect of body size (length), body shape (surface-area-to-volume ratio, SVR), body temperature and blubber thermal conductivity and thickness on heat loss for all species. Smaller species had higher volume-specific heat loss compared with larger species due to their higher SVRs, a fundamental consequence of scaling. Apart from body size, blubber thickness had the largest effect on heat loss, followed by thermal conductivity. Smaller cetaceans seem to rely primarily on physiological and morphological adaptations to reduce heat loss, such as increased blubber thickness and lower thermal conductivity, whereas larger species offset heat loss by having larger bodies and lower SVRs. Our findings provide valuable insights into the thermal biology of these species and its implications for habitat use and prey requirements.

Migration to breeding areas by male sperm whales Physeter macrocephalus from the Northeast Atlantic Arctic

Mature male sperm whales (Physeter macrocephalus) primarily inhabit high latitude regions, travelling to tropical/temperate waters for breeding, where females and juveniles reside in cohesive social groups. Though mating is known to occur at low latitudes, the timing, duration, and routes of adult male migrations between feeding and breeding areas are poorly known. To study movement patterns of adult male sperm whales, 29 individuals were equipped with satellite transmitters in the Northeast Atlantic Arctic (69-79°N). Twelve of these animals undertook southward migrations. Departures from northern latitudes occurred asynchronously from January to October, indicating that sperm whales do not have a well-defined breeding season. Migrating males travelled 40 (± 11) d to reach the breeding areas at latitudes below 45°N. They travelled distances of 3,993-7,951 km. They spent 76 (± 22) d in the south, roaming across an enormous region (˃10 million km2). Dives deeper than 1,000 m occurred both during migration and at the breeding grounds. Two whales were tracked back to Arctic waters. Their trips took 175 and 180 d, with cumulative distances travelled being 16,332 km and 17,669 km, respectively. This study fills important knowledge gaps in the annual cycle of these cosmopolitan giants.

An annual cycle perspective on energetics and locomotion of migratory animals

Animal migrations, or long-distance movements, on land, through water or in the air, are considered energetically costly because of the investment in persistent locomotion typical for migration. Diverse strategies exist to manage these energetic costs. Yet migration is only one stage in an annual cycle and may not be the most energetically costly. To better understand how free-ranging animals adaptively organize energy expenditure and locomotion, an annual cycle perspective is needed. Bio-logging data are collected for a range of animal species and could facilitate a life cycle approach to study energy expenditure. We provide examples from several studies across different taxa, as well as a more in-depth exploration from our own recent research on time activity budgets based on field observations and bio-logging data to estimate daily energy expenditure in a migratory seabird throughout a year. Our research has shown that daily energy expenditure is highest (1.7× average daily energy expenditure) during the spring migration of long-distance migratory gulls, whereas short-distance migrants expend the most energy (1.4× average daily energy expenditure) during the breeding season. Based on the examples provided, we show how bio-energetic models create exciting opportunities to study daily energetics and behaviour of migratory animals, although limitations also still exist. Such studies can reveal when, where and why peaks and lulls in energy expenditure arise over the annual cycle of a migrant, if long-distance movements are indeed energetically expensive and how animals can adapt to fluctuating demands in their natural environment throughout the year.

Interbreeding area movement of an adult humpback whale between the east Pacific Ocean and southwest Indian Ocean

Humpback whales undertake one of the longest known migrations of any mammal. While their migration route generally extends between latitudes, the breeding stocks are longitudinally separated and display high site fidelity to their feeding grounds. While there is an indication of certain breeding stocks overlapping with each other, the current information on the migration routes of humpback whales within the Southern Hemisphere limits our understanding of the extent of this exchange. Presented here is the longest documented great-circle distance between sightings on wintering grounds of two different ocean basins of an adult male humpback whale, involving two breeding stocks in the eastern Pacific (stock G) and southwest Indian Ocean (stock C). These two stocks are separated by a minimum of 120° longitude, and a great-circle distance of 13 046 km. This extreme distance movement demonstrates behavioural plasticity, which may play an important role in adaptation strategies to global environmental changes and perhaps be an evolved response to various pressures, underlining the importance of consolidation of global datasets on wide-ranging marine mammals.

Annual phenology and migration routes to breeding grounds in western-central North Pacific sei whales

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.

Migratory destinations and spatial structuring of humpback whales (Megaptera novaeangliae) wintering off Nicaragua

Understanding the migratory patterns of large whales is of conservation importance, especially in identifying threats to specific populations. Migration ecology, including migratory destinations, movements and site fidelity for humpback whales (Megaptera novaeangliae) remain poorly studied in parts of the range of the Central America population, considered endangered under the United States Endangered Species Act. This study aimed to investigate the migratory destinations of humpback whales sighted at two study sites in Nicaragua, which are part of the Central America population. A ten-year photographic database of humpback whales observed off Nicaragua was combined with citizen science contributions and sightings from dedicated research programs. The resulting image collection was compared with available historical photo identifications and databases using an automated image recognition algorithm. This approach yielded 36 years of photographic identification totaling 431 recaptures in Nicaragua (2006-2008 and 2016-2021) and 2539 recaptures (1986-2020) in both feeding and breeding grounds of 176 unique individuals sighted in Nicaragua. Our results showed that photo-identified whales were recaptured between October and April in breeding grounds and year-round in feeding grounds between British Columbia and California, with peak recaptures between June and October. Our study provided first-time evidence on fine-scale site affinity of individual humpback whales within Nicaraguan waters and to other breeding and feeding grounds.

Don't mind if I do: Arctic humpback whales respond to winter foraging opportunities before migration

Migration patterns are fundamentally linked to the spatio-temporal distributions of prey. How migrating animals can respond to changes in their prey's distribution and abundance remains largely unclear. During the last decade, humpback whales (Megaptera novaeangliae) used specific winter foraging sites in fjords of northern Norway, outside of their main summer foraging season, to feed on herring that started overwintering in the area. We used photographic matching to show that whales sighted during summer in the Barents Sea foraged in northern Norway from late October to February, staying up to three months and showing high inter-annual return rates (up to 82%). The number of identified whales in northern Norway totalled 866 individuals by 2019. Genetic sexing and hormone profiling in both areas demonstrate a female bias in northern Norway and suggest higher proportions of pregnancy in northern Norway. This may indicate that the fjord-based winter feeding is important for pregnant females before migration. Our results suggest that humpback whales can respond to foraging opportunities along their migration pathways, in some cases by continuing their feeding season well into winter. This provides an important reminder to implement dynamic ecosystem management that can account for changes in the spatio-temporal distribution of migrating marine mammals.