Fin whale song characteristics and potential subpopulation identity in the New York Bight.

Fin whale (Balaenoptera physalus) song can follow a highly consistent pattern, and regional differences in song patterns can be a valuable indicator of subpopulation identity and distribution. In the Northwest Atlantic, endangered fin whales are currently managed as a single stock despite previous identification of different regional song patterns, which indicates potential subpopulation structuring and vulnerability to anthropogenic disturbance if not managed accordingly. Here we document fin whale song in the New York Bight (NYB) from 2017 to 2020 using passive acoustic data to identify monthly and yearly trends in song patterns and to explore potential subpopulation structuring. The predominant song pattern observed was highly consistent with the pattern documented almost a decade prior in the NYB, with short inter-note intervals (INI) from fall-winter and long-INIs in the spring. However, in one song year the majority of songs were composed of long-INIs. This change in song pattern could be due to a shift in fin whale behavior or possibly multiple fin whale subpopulations using the NYB. Fin whales in the NYB may be particularly vulnerable to disturbance given the increasing anthropogenic pressures in this region, and further research into subpopulation structuring is needed to ensure adequate management of these endangered whales.

Surface and subsurface oceanographic features drive forage fish distributions and aggregations: Implications for prey availability to top predators in the US Northeast Shelf ecosystem.

Forage fishes are a critical food web link in marine ecosystems, aggregating in a hierarchical patch structure over multiple spatial and temporal scales. Surface-level forage fish aggregations (FFAs) represent a concentrated source of prey available to surface- and shallow-foraging marine predators. Existing survey and analysis methods are often imperfect for studying forage fishes at scales appropriate to foraging predators, making it difficult to quantify predator-prey interactions. In many cases, general distributions of forage fish species are known; however, these may not represent surface-level prey availability to predators. Likewise, we lack an understanding of the oceanographic drivers of spatial patterns of prey aggregation and availability or forage fish community patterns. Specifically, we applied Bayesian joint species distribution models to bottom trawl survey data to assess species- and community-level forage fish distribution patterns across the US Northeast Continental Shelf (NES) ecosystem. Aerial digital surveys gathered data on surface FFAs at two project sites within the NES, which we used in a spatially explicit hierarchical Bayesian model to estimate the abundance and size of surface FFAs. We used these models to examine the oceanographic drivers of forage fish distributions and aggregations. Our results suggest that, in the NES, regions of high community species richness are spatially consistent with regions of high surface FFA abundance. Bathymetric depth drove both patterns, while subsurface features, such as mixed layer depth, primarily influenced aggregation behavior and surface features, such as sea surface temperature, sub-mesoscale eddies, and fronts influenced forage fish diversity. In combination, these models help quantify the availability of forage fishes to marine predators and represent a novel application of spatial models to aerial digital survey data.

Culturally transmitted song exchange between humpback whales (Megaptera novaeangliae) in the southeast Atlantic and southwest Indian Ocean basins.

In migratory marine species, investigating population connectivity and structure can be challenging given barriers to dispersal are less evident and multiple factors may influence individual movement patterns. Male humpback whales sing a song display that can provide insights into contemporary connectivity patterns, as there can be a cultural exchange of a single, population-wide shared song type with neighbouring populations in acoustic contact. Here, we investigated song exchange between populations located on the east and west coasts of Africa using 5 years of concurrent data (2001-2005). Songs were qualitatively and quantitatively transcribed by measuring acoustic features of all song units and then compared using both Dice's similarity index and the Levenshtein distance similarity index (LSI) to quantitatively calculate song similarity. Song similarity varied among individuals and potentially between populations depending on the year (Dice: 36-100%, LSI: 21-100%), suggesting varying levels of population connectivity and/or interchange among years. The high degree of song sharing indicated in this study further supports genetic studies that demonstrate interchange between these two populations and reinforces the emerging picture of broad-scale connectivity in Southern Hemisphere populations. Further research incorporating additional populations and years would be invaluable for better understanding of fine-scale, song interchange patterns between Southern Hemisphere male humpback whales.

Omura's whales (Balaenoptera omurai) off northwest Madagascar: ecology, behaviour and conservation needs.

The Omura's whale (Balaenoptera omurai) was described as a new species in 2003 and then soon after as an ancient lineage basal to a Bryde's/sei whale clade. Currently known only from whaling and stranding specimens primarily from the western Pacific and eastern Indian Oceans, there exist no confirmed field observations or ecological/behavioural data. Here we present, to our knowledge, the first genetically confirmed documentation of living Omura's whales including descriptions of basic ecology and behaviour from northwestern Madagascar. Species identification was confirmed through molecular phylogenetic analyses of biopsies collected from 18 adult animals. All individuals shared a single haplotype in a 402 bp sequence of mtDNA control region, suggesting low diversity and a potentially small population. Sightings of 44 groups indicated preference for shallow-water shelf habitat with sea surface temperature between 27.4°C and 30.2°C. Frequent observations were made of lunge feeding, possibly on zooplankton. Observations of four mothers with young calves, and recordings of a song-like vocalization probably indicate reproductive behaviour. Social organization consisted of loose aggregations of predominantly unassociated single individuals spatially and temporally clustered. Photographic recapture of a female re-sighted the following year with a young calf suggests site fidelity or a resident population. Our results demonstrate that the species is a tropical whale without segregation of feeding and breeding habitat, and is probably non-migratory; our data extend the range of this poorly studied whale into the western Indian Ocean. Exclusive range restriction to tropical waters is rare among baleen whale species, except for the various forms of Bryde's whales and Omura's whales. Thus, the discovery of a tractable population of Omura's whales in the tropics presents an opportunity for understanding the ecological factors driving potential convergence of life-history patterns with the distantly related Bryde's whales.

Non-song social call bouts of migrating humpback whales.

The use of stereotyped calls within structured bouts has been described for a number of species and may increase the information potential of call repertoires. Humpback whales produce a repertoire of social calls, although little is known about the complexity or function of these calls. In this study, digital acoustic tag recordings were used to investigate social call use within bouts, the use of bouts across different social contexts, and whether particular call type combinations were favored. Call order within bouts was investigated using call transition frequencies and information theory techniques. Call bouts were defined through analysis of inter-call intervals, as any calls within 3.9 s of each other. Bouts were produced significantly more when new whales joined a group compared to groups that did not change membership, and in groups containing multiple adults escorting a female and calf compared to adult only groups. Although social calls tended to be produced in bouts, there were few repeated bout types. However, the order in which most call types were produced within bouts was non-random and dependent on the preceding call type. These bouts appear to be at least partially governed by rules for how individual components are combined.

Population structure of humpback whales in the western and central South Pacific Ocean as determined by vocal exchange among populations.

For cetaceans, population structure is traditionally determined by molecular genetics or photographically identified individuals. Acoustic data, however, has provided information on movement and population structure with less effort and cost than traditional methods in an array of taxa. Male humpback whales (Megaptera novaeangliae) produce a continually evolving vocal sexual display, or song, that is similar among all males in a population. The rapid cultural transmission (the transfer of information or behavior between conspecifics through social learning) of different versions of this display between distinct but interconnected populations in the western and central South Pacific region presents a unique way to investigate population structure based on the movement dynamics of a song (acoustic) display. Using 11 years of data, we investigated an acoustically based population structure for the region by comparing stereotyped song sequences among populations and years. We used the Levenshtein distance technique to group previously defined populations into (vocally based) clusters based on the overall similarity of their song display in space and time. We identified the following distinct vocal clusters: western cluster, 1 population off eastern Australia; central cluster, populations around New Caledonia, Tonga, and American Samoa; and eastern region, either a single cluster or 2 clusters, one around the Cook Islands and the other off French Polynesia. These results are consistent with the hypothesis that each breeding aggregation represents a distinct population (each occupied a single, terminal node) in a metapopulation, similar to the current understanding of population structure based on genetic and photo-identification studies. However, the central vocal cluster had higher levels of song-sharing among populations than the other clusters, indicating that levels of vocal connectivity varied within the region. Our results demonstrate the utility and value of using culturally transmitted vocal patterns as a way of defining connectivity to infer population structure. We suggest vocal patterns be incorporated by the International Whaling Commission in conjunction with traditional methods in the assessment of structure.

Estructura Poblacional de las Yubartas en el Centro y Occidente del Sur del Océano Pacífico, Determinada por el Intercambio Vocal entre las Poblaciones Resumen La estructura poblacional de los cetáceos se determina tradicionalmente por medio de genética molecular o individuos identificados fotográficamente. Sin embargo, los datos acústicos han proporcionado información sobre el movimiento y la estructura poblacional de una variedad de taxones con menos esfuerzo y menos costo que los métodos tradicionales. Las yubartas macho (Megaptera novaeangliae) producen una demostración vocal sexual, o canto, en continua evolución que es similar entre todos los machos en una población. La transmisión cultural rápida (la transferencia de información o comportamientos entre co-específicos por medio del aprendizaje social) de diferentes versiones de esta demostración entre poblaciones distintas pero interconectadas en el centro y occidente en la región del sur del Pacífico presenta una manera única para investigar la estructura poblacional con base en las dinámicas de movimiento de la demostración del canto (acústico). Al usar once años de datos, con base en la acústica investigamos a una estructura poblacional de la región al comparar secuencias estereotipadas de cantos entre las poblaciones y los años. Usamos la técnica de la distancia Levenshtein para agrupar poblaciones previamente definidas en grupos (con base vocal) basados en la similitud general de su canto en el espacio y el tiempo. Identificamos a los siguientes grupos vocales perceptibles: grupo occidental, una población al este de Australia; grupo central, poblaciones alrededor de Nueva Caledonia, Tonga y Samoa Americana; y región oriental, ya sea un grupo único o dos grupos, uno alrededor de las Islas Cook y el otro cerca de la Polinesia Francesa. Estos resultados son consistentes con la hipótesis de que cada conjunto reproductivo representa a una población distinta (cada una ocupó un nodo terminal único) en una meta-población, similar al entendimiento actual de la estructura poblacional con base en los estudios genéticos y de foto-identificación. Sin embargo, el grupo vocal central tuvo niveles más altos de cantos compartidos entre las poblaciones que en los otros grupos, lo que indica que los niveles de conectividad vocal variaron dentro de la región. Nuestros resultados demuestran la utilidad y el valor de usar patrones vocales transmitidos culturalmente como una forma de definir la conectividad para inferir la estructura poblacional. Sugerimos que los patrones vocales sean incorporados por la Comisión Internacional de Caza de Ballenas en conjunto con los métodos tradicionales de evaluación de la estructura.

Humpback whale song on the Southern Ocean feeding grounds: implications for cultural transmission.

Male humpback whales produce a long, complex, and stereotyped song on low-latitude breeding grounds; they also sing while migrating to and from these locations, and occasionally in high-latitude summer feeding areas. All males in a population sing the current version of the constantly evolving display and, within an ocean basin, populations sing similar songs; however, this sharing can be complex. In the western and central South Pacific region there is repeated cultural transmission of song types from eastern Australia to other populations eastward. Song sharing is hypothesized to occur through several possible mechanisms. Here, we present the first example of feeding ground song from the Southern Ocean Antarctic Area V and compare it to song from the two closest breeding populations. The early 2010 song contained at least four distinct themes; these matched four themes from the eastern Australian 2009 song, and the same four themes from the New Caledonian 2010 song recorded later in the year. This provides evidence for at least one of the hypothesized mechanisms of song transmission between these two populations, singing while on shared summer feeding grounds. In addition, the feeding grounds may provide a point of acoustic contact to allow the rapid horizontal cultural transmission of song within the western and central South Pacific region and the wider Southern Ocean.

Temporal stability and change in the social call repertoire of migrating humpback whales.

Quantifying the stability of a species vocal repertoire is fundamental for further investigations into repertoire function and geographic variation. Changes to the repertoire of sounds used in the song displays of male humpback whales have been well studied. In contrast, little is known about the stability of this species' non-song vocal calls. The stability of the social call repertoire of east Australian humpback whales was investigated from 1997, 2003-2004, and 2008. Out of 46 qualitatively defined call types, 19 were classified as "song-unit calls" that tended to change with the song, and 15 were "inconsistent" and only found in one or two years. Twelve call types were "stable" and present in all years and were commonly produced (64.2% of calls). Stable calls tended to vary in some of the measured call parameters but there was no clear trend between years. This result could indicate that minor changes to calls are not permanent, but reflect individual differences in call production or the graded nature of calls within different social environments. This research has clearly identified stable calls in the call repertoire of humpback whales and while their function is not well understood, their stability suggests an important role in social interactions.

Quantifying humpback whale song sequences to understand the dynamics of song exchange at the ocean basin scale.

Humpback whales have a continually evolving vocal sexual display, or "song," that appears to undergo both evolutionary and "revolutionary" change. All males within a population adhere to the current content and arrangement of the song. Populations within an ocean basin share similarities in their songs; this sharing is complex as multiple variations of the song (song types) may be present within a region at any one time. To quantitatively investigate the similarity of song types, songs were compared at both the individual singer and population level using the Levenshtein distance technique and cluster analysis. The highly stereotyped sequences of themes from the songs of 211 individuals from populations within the western and central South Pacific region from 1998 through 2008 were grouped together based on the percentage of song similarity, and compared to qualitatively assigned song types. The analysis produced clusters of highly similar songs that agreed with previous qualitative assignments. Each cluster contained songs from multiple populations and years, confirming the eastward spread of song types and their progressive evolution through the study region. Quantifying song similarity and exchange will assist in understanding broader song dynamics and contribute to the use of vocal displays as population identifiers.

Dynamic horizontal cultural transmission of humpback whale song at the ocean basin scale.

Cultural transmission, the social learning of information or behaviors from conspecifics, is believed to occur in a number of groups of animals, including primates, cetaceans, and birds. Cultural traits can be passed vertically (from parents to offspring), obliquely (from the previous generation via a nonparent model to younger individuals), or horizontally (between unrelated individuals from similar age classes or within generations). Male humpback whales (Megaptera novaeangliae) have a highly stereotyped, repetitive, and progressively evolving vocal sexual display or "song" that functions in sexual selection (through mate attraction and/or male social sorting). All males within a population conform to the current version of the display (song type), and similarities may exist among the songs of populations within an ocean basin. Here we present a striking pattern of horizontal transmission: multiple song types spread rapidly and repeatedly in a unidirectional manner, like cultural ripples, eastward through the populations in the western and central South Pacific over an 11-year period. This is the first documentation of a repeated, dynamic cultural change occurring across multiple populations at such a large geographic scale.