Social structure in migrating humpback whales (Megaptera novaeangliae)

Although largely solitary, humpback whales exhibit a number of behaviours where individuals co-operate with one another, for example during bubble net feeding. Such cases could be due to reciprocal altruism brought on by exceptional circumstances, for example the presence of abundant shoaling fish. An alternative explanation is that these behaviours have evolved through kin selection. With little restriction to either communication or movement, diffuse groups of relatives could maintain some form of social organization without the need to travel in tight-nit units. To try to distinguish between these hypotheses, we took advantage of the fact that migrating humpback whales often swim together in small groups. If kin selection is important in humpback whale biology, these groups should be enriched for relatives. Consequently, we analysed biopsy samples from 57 groups of humpback whales migrating off Eastern Australia in 1992. A total of 142 whales were screened for eight microsatellite markers. Mitochondrial DNA sequences (371 bp) were also used to verify and assist kinship identification. Our data add support to the notion that mothers travel with their offspring for the first year of the calf's life. However, beyond the presence of mother-calf/yearling pairs, no obvious relatedness pattern was found among whales sampled either in the same pod or on the same day. Levels of relatedness did not vary between migratory phases (towards or away from the breeding ground), nor between the two sexes considered either overall or in the north or south migrations separately. These findings suggest that, if any social organization does exist, it is formed transiently when needed rather than being a constant feature of the population, and hence is more likely based on reciprocal altruism than kin selection.     

Recurring patterns in the songs of humpback whales (Megaptera novaeangliae)

Humpback whales, unlike most mammalian species, learn new songs as adults. Populations of singers progressively and collectively change the sounds and patterns within their songs throughout their lives and across generations. In this study, humpback whale songs recorded in Hawaii from 1985 to 1995 were analyzed using self-organizing maps (SOMs) to classify the sounds within songs, and to identify sound patterns that were present across multiple years. These analyses supported the hypothesis that recurring, persistent patterns exist within whale songs, and that these patterns are defined at least in part by acoustic relationships between adjacent sounds within songs. Sound classification based on acoustic differences between adjacent sounds yielded patterns within songs that were more consistent from year to year than classifications based on the properties of single sounds. Maintenance of fixed ratios of acoustic modulation across sounds, despite large variations in individual sounds, suggests intrinsic constraints on how sounds change within songs. Such acoustically invariant cues may enable whales to recognize and assess variations in songs despite propagation-related distortion of individual sounds and yearly changes in songs.     

Non-song acoustic communication in migrating humpback whales (Megaptera novaeangliae)

Humpback whales are renowned for the complex structured songs produced by males. A second, relatively understudied area of humpback acoustic communication concerns un-patterned sounds known as "social sounds," produced by both males and females. These include vocalizations as well as sounds produced at the surface of the water as a result of surface behaviors ( e.g. , breaching, pectoral slapping). This study describes a portion of the non-song social sound repertoire of southward migrating humpbacks in Australian waters, and explores the social relevance of these sounds. On migration, humpback whales travel in social groups of varying compositions. These social groups are not stable in that humpback whales continually change group composition by splitting from, or joining with, other groups. The results of this study suggest that "breaching" and "slapping" have a communicative function. Other sounds such as "underwater blows" and "cries" were heard mainly in competitive groups while other low-frequency sounds such as "grumbles,""snorts,""thwops," and "wops" may function in intra- or inter-group communication. Particular sounds ("grunts,""groans," and "barks") were almost exclusive to joining pods suggesting a role in social integration. Social sounds in humpbacks may have specific social and behavioral functions relating to social group composition, and the mediation of interactions between these social groups.     

Behavioral responses of humpback whales (Megaptera novaeangliae) to whale-watching vessels on the southeastern coast of Australia

This study assessed the short-term responses of humpback whales to whale-watching vessels during their southward migration along the south coast of New South Wales (NSW), Australia. The behavior of pods was recorded from commercial whale-watching vessels during tours and compared to pods observed in the absence of vessels from the shore in the same area. While some individuals showed obvious signs of horizontal avoidance, others approached vessels, initiating interactions. Calf pods were more sensitive to the presence of vessels than non-calf pods. Dive times and the overall percentage of time whales spent submerged were higher in the presence of vessels, but respiration intervals did not differ. Some surface behaviors occurred less often in the presence of vessels. Whales' responses differed according to whether vessels were operating in accordance with regulations or not. Whales were more likely to avoid a vessel moving within the permitted 100 m approach limit than vessels outside the limit. Whales showed some behavioral changes when vessels operated in accordance with whale-watching regulations, compared with whales in the absence of vessels. Pods that showed no obvious horizontal responses to vessels changed their diving and surface activity when compared with pods in the absence of vessels. Because the long-term impacts of effects of vessels are unknown, management of the humpback whale-watching industry should adopt a conservative approach. Improved knowledge of long-term impacts of multiple exposures to vessels is required to inform management of the effects of whale-watching.     

Global diversity and oceanic divergence of humpback whales (Megaptera novaeangliae)

Humpback whales (Megaptera novaeangliae) annually undertake the longest migrations between seasonal feeding and breeding grounds of any mammal. Despite this dispersal potential, discontinuous seasonal distributions and migratory patterns suggest that humpbacks form discrete regional populations within each ocean. To better understand the worldwide population history of humpbacks, and the interplay of this species with the oceanic environment through geological time, we assembled mitochondrial DNA control region sequences representing approximately 2700 individuals (465 bp, 219 haplotypes) and eight nuclear intronic sequences representing approximately 70 individuals (3700 bp, 140 alleles) from the North Pacific, North Atlantic and Southern Hemisphere. Bayesian divergence time reconstructions date the origin of humpback mtDNA lineages to the Pleistocene (880 ka, 95% posterior intervals 550–1320 ka) and estimate radiation of current Northern Hemisphere lineages between 50 and 200 ka, indicating colonization of the northern oceans prior to the Last Glacial Maximum. Coalescent analyses reveal restricted gene flow between ocean basins, with long-term migration rates (individual migrants per generation) of less than 3.3 for mtDNA and less than 2 for nuclear genomic DNA. Genetic evidence suggests that humpbacks in the North Pacific, North Atlantic and Southern Hemisphere are on independent evolutionary trajectories, supporting taxonomic revision of M. novaeangliae to three subspecies.     

Genetic differentiation between humpback whales (Megaptera novaeangliae) from Atlantic and Pacific breeding grounds of South America

Humpback whales wintering in tropical waters along the Atlantic and Pacific coasts of the South American continent are thought to represent distinct populations or “stocks.” Here we present the first analysis of genetic differentiation and estimates of gene flow between these breeding stocks, based on both mitochondrial DNA (mtDNA) control region sequences (465 bp) and 16 microsatellite loci from samples collected off Brazil (n = 277) and Colombia (n = 148), as well as feeding areas near the western Antarctic Peninsula (n = 86). We found significant differentiation between Brazilian and Colombian breeding grounds at both mtDNA (F_ST = 0.058) and microsatellite (F_ST = 0.011) markers and corroborated previous studies showing genetic similarity between humpbacks from Colombia and those from Antarctic Peninsula feeding areas. Estimates of long‐term gene flow between Brazil and Colombia were low to moderate, asymmetrical, and mostly mediated by males. Assignment procedures detected some cases of interchange and individuals of admixed ancestry between breeding grounds, indicating limited mixing of individuals between these stocks. Overall, results highlight the differentiation of humpback whale breeding populations with adjacent feeding grounds. This appears to be a remarkable example of fidelity to seasonal habitat in the absence of any contemporary barriers.     

Comparing multiple sampling platforms for measuring the behavior of humpback whales (Megaptera novaeangliae)

Multiple platform approaches for measuring the behavior of marine mammals may strengthen data quality and quantity. However, if this approach is chosen, reconciliation of behavioral measures between each platform is required. This study compared typical measures of humpback whale (Megaptera novaeangliae) behavior collected from three different sampling platforms; land‐based, boat‐based, and digital tags (Dtags), to explore similarities and/or discrepancies in data. Visual observations from land‐based platforms significantly underestimated group blow rate when compared to boat‐based platforms, whereas broad‐scale spatial movements (speed and course traveled) were measured similarly by these two platforms. Dtags were used to define dive behavior based on a time and depth criteria, where bouts of short shallow respiration dives (≤80 s and ≤10 m) were separated from longer, deeper dives (>80 s and >10 m). At a group level, land and boat platforms agreed on the number of long dives but land platforms missed bouts of short dives. At an individual level, the number of short and long dives observed by boat‐based platforms agreed with Dtag recordings. This study highlights the importance of data exploration prior to analyses in multiple platform studies to identify potential discrepancies and appropriately account for any biases.     

Population spatial structuring on the feeding grounds in North Atlantic humpback whales (Megaptera novaeangliae)

Population spatial structuring among North Atlantic humpback whales Megaptera novaeangliae on the summer feeding grounds was investigated using movement patterns of identified individuals. We analysed the results from an intensive 2-year ocean-basin-scale investigation resulting in 1658 individuals identified by natural markings and 751 individuals by genetic markers supplemented with data from a long-term collaborative study with 3063 individuals identified by natural markings. Re-sighting distances ranged from <1 km to >2200 km. The frequencies ( F ) of re-sighting distances ( D ) observed in consecutive years were best modelled by an inverse allometric function ( F =6631 D ^−1.24, r ²=0.984), reflecting high levels of site fidelity (median re-sighting distance <40 km) with occasional long-distance movement (5% of re-sightings >550 km). The distribution of re-sighting distances differed east and west of 45°W, with more long-distance movement in the east. This difference is consistent with regional patterns of prey distribution and predictability. Four feeding aggregations were identified: the Gulf of Maine, eastern Canada, West Greenland and the eastern North Atlantic. There was an exchange rate of 0.98% between the western feeding aggregations. The prevalence of long-distance movement in the east made delineation of possible additional feeding aggregations less clear. Limited exchange between sites separated by as little as tens of kilometres produced lower-level structuring within all feeding aggregations. Regional and temporal differences in movement patterns reflected similar foraging responses to varying patterns of prey availability and predictability. A negative relationship was shown between relative abundance of herring and sand lance in the Gulf of Maine and humpback whale movement from the Gulf of Maine to eastern Canada.     

Spondylitis in a humpback whale (Megaptera novaeangliae) from the southeast Pacific

A 7.25 m long male humpback whale (Megaptera novaeangliae) with spondylitis was found beached on August 13, 1994 at Ancon, Ecuador (2 degrees 23' S, 80 degrees 47' W). The condition involved at least 11 vertebrae, 7 lumbar (L4 to L11) and 4 caudal (Ca1 to Ca4). Partial fusion of vertebrae was observed as a result of intervertebral bony proliferation, likely impeding full motion. The relatively young age of this specimen and the severity of the deformities suggest an infectious, rather than degenerative, process. The gross findings are most consistent with some type of spondyloarthritis. Although this condition has previously been identified in a number of cetacean species, the pathogenesis, population impact and ecologic implications have not been fully assessed. This is the third case described for humpback whales and the first for a humpback whale from the SE Pacific.     

Habitat preference reflects social organization of humpback whales (Megaptera novaeangliae) on a wintering ground

Habitat preference is driven by a complex interaction among behavioural patterns, biological requirements, and environmental conditions. These variables are difficult to determine for any species but are further complicated for migratory marine mammals, such as humpback whales Megaptera novaeangliae . Patterns of habitat use in relation to social organization potentially exist for this species on their wintering grounds. Using an integrated GIS approach, we examined the degree to which spatial patterns of habitat stratification are correlated within different humpback whale group types from 6 years of sighting data (1996–2001) collected on the Antongil Bay, Madagascar, wintering ground. Stratification of humpback whale sightings by behavioural classification showed significant variation in depth and distance from shore. Distribution by depth could not be described as a function of group size but could be described as a function of social organization, with mother–calf pairs showing a strong preference for shallower water compared to all other group types. Group size and social organization seem to be factors in distribution by distance from shore. Significant diurnal patterns in distribution by depth and distance from shore also exist, where mother–calf groups maintain a relatively stable distribution and pairs and competitive groups are the most variable. Patterns of habitat preference on this wintering ground appear to be guided by social organization, where distribution by depth and distance from shore highlight areas critical to conservation.     

Southeastern Pacific humpback whales (Megaptera novaeangliae) and their breeding grounds: Distribution and habitat preference of singers and social groups off the coast of Ecuador

Understanding the distribution, habitat preference, and social structure of highly migratory species at important life history stages (e.g., breeding and calving) is essential for conservation efforts. We investigated the spatial distribution and habitat preference of humpback whale social groups and singers, in relation to depth categories (<20 m, 20–50 m, and >50 m) and substrate type (muddy and mixed) on a coastal southeastern Pacific breeding ground. One hundred and forty‐three acoustic stations and 304 visual sightings were made at the breeding ground off the coast of Esmeraldas, Ecuador. Spatial autocorrelation analysis suggested singers were not randomly distributed, and Neu's method and Monte Carlo simulations indicated that singers frequented depths of <20 m and mixed substrate. Singletons, and groups with a calf displayed a preference for shallower waters (0–20 m), while pairs and groups with a calf primarily inhabited mixed bottom substrates. In contrast, competitive groups showed no clear habitat preference and exhibited social segregation from other whales. Understanding the habitat preference and distribution of humpback whales on breeding and calving grounds vulnerable to anthropogenic disturbance provides important baseline information that should be incorporated into conservation efforts at a regional scale.     

Non-lethal entanglement of humpback whales (Megaptera novaeangliae) in fishing gear in northern Southeast Alaska

Aim Entanglement in fishing gear is recognized as a potentially significant source of serious injury and mortality for humpback whales (Megaptera novaeangliae) in some parts of their range. In recent years, the number of humpback whales reported to have been entangled in Alaska has increased. In 2003–04 we quantified the prevalence of non‐lethal entanglements of humpback whales in northern Southeast Alaska (SEAK) with the ultimate goal of informing management discussions of the entanglement issue for the Central North Pacific stock of humpback whales. Location The near‐shore waters of northern Southeast Alaska. Methods We photographed individual humpback whales’ caudal peduncles as they dived and then examined the photographs for scars indicative of a previous entanglement. Results The percentage of whales assessed to have been non‐lethally entangled at some time in their lives ranged from 52% (minimal estimate) to 71% (conditional estimate) to 78% (maximal estimate). Of these, the conditional estimate is recommended because it is based solely on unambiguous scars. Eight per cent of the whales in one portion of the study area (Glacier Bay/Icy Strait) acquired new entanglement scars between 2003 and 2004, although the sample size was small. Calves were less likely than older whales to have entanglement scars, and males may be at higher risk than females. Whales with more photographs and/or photographic coverage may be more likely to be assessed as having been entangled than whales with fewer photographs and/or coverage. Main conclusions Caudal peduncle scars reveal that the majority of humpback whales in northern SEAK have been entangled. Comparison with statistics on reported entanglements suggests that most whales apparently shed the gear on their own, unless humans are disentangling whales much more often than is reported. While cumulative estimates of the percentage of whales with entanglement scars (e.g. the conditional estimate) provide useful baseline information, future efforts should focus on monitoring the annual rate of entanglement scar acquisition as a more powerful measure of contemporary entanglement rates. Our findings indicate that entanglement of humpback whales in fishing gear in SEAK is a management issue warranting increased attention. A proactive approach is needed to address the problem and to identify and implement preventive measures.     

The potential beginning of a postwhaling recovery in New Zealand humpback whales (Megaptera novaeangliae)

Between the 1940s and 1970s Southern Hemisphere populations of humpback whales (including eastern Australia and Oceania populations) were hunted to near extinction by extensive commercial whaling activities in Antarctica, with fewer whales taken in shore whaling operations in New Zealand, Australia (including Norfolk Island) and Tonga. Variable rates of recovery of these populations have been documented, ranging from recovery to prewhaling numbers in eastern Australian humpbacks to very little sign of recovery in many Oceania populations. Here we analyze recent sighting data collected over 12 yr, from annual surveys in Cook Strait, New Zealand. The data show an increase in sightings, at an estimated rate of 13% (95% CI of 4.9% and 21.7%) in 2015, of humpback whales migrating through Cook Strait. The wide confidence intervals preclude substantive conclusions about the rate of increase but suggest humpback whales are returning to this region in increasing numbers, indicating an influx of immigrants from neighboring areas, namely eastern Australia.