Humpback Whale, Megaptera novaeangliae, Feeding Dynamics From the Perspective of the Individual: Insights From Demography, Life History, and Bio-Logging

Studies of fission-fusion societies provide a framework in which to compare the feeding dynamics across demographics, unrestrained by stable associations or relatedness. This study used bio-logger data and surface observations combined with long-term population data from the Gulf of Maine humpback whale, Megaptera novaeangliae, population to investigate the influence of demographics on feeding methods, and time spent feeding, and to determine if a coordinated feeding method, kick-feeding, was a cooperative behavior. The results suggest that demographics did influence the feeding method used and highlighted the need to determine how energetic needs change across the feeding season. Adult females did not spend more time feeding than males, but engaged more often in bottom-feeding, a difference that could put them at greater risk of entanglement in fishing gear set near the substrate. Additionally, the results suggest that kick-feeding was not a form of cooperation, but rather those dynamics were a product of demographics and local population structure. This study highlights the need to account for demographics when interpreting behavior and behavioral risk from anthropogenic activities

From a calfs perspective: humpback whale nursing behavior on two US feeding grounds.

Nursing influences growth rate and overall health of mammals; however, the behavior is difficult to study in wild cetaceans because it occurs below the surface and can thus be misidentified from surface observations. Nursing has been observed in humpback whales on the breeding and calving grounds, but the behavior remains unstudied on the feeding grounds. We instrumented three dependent calves (four total deployments) with combined video and 3D-accelerometer data loggers (CATS) on two United States feeding grounds to document nursing events. Two associated mothers were also tagged to determine if behavior diagnostic of nursing was evident in the mothers movement. Animal-borne video was manually analyzed and the average duration of successful nursing events was 23 s (±7 sd, n = 11). Nursing occurred at depths between 4.1-64.4 m (along the seafloor) and in close temporal proximity to foraging events by the mothers, but could not be predicted solely by relative positions of mother and calf. When combining all calf deployments, successful nursing was documented eleven times; totaling only 0.3% of 21.0 hours of video. During nursing events, calves had higher overall dynamic body acceleration (ODBA) and increased fluke-stroke rate (FSR) compared to non-nursing segments (Mixed effect models, ODBA: F1,107 = 13.57756, p = 0.0004, FSR: F1,107 = 32.31018, p < 0.0001). In contrast, mothers had lower ODBA and reduced FSR during nursing events compared to non-nursing segments. These data provide the first characterization of accelerometer data of humpback whale nursing confirmed by animal-borne video tags and the first analysis of nursing events on feeding grounds. This is an important step in understanding the energetic consequences of lactation while foraging

From a calf’s perspective: humpback whale nursing behavior on two US feeding grounds

Nursing influences growth rate and overall health of mammals; however, the behavior is difficult to study in wild cetaceans because it occurs below the surface and can thus be misidentified from surface observations. Nursing has been observed in humpback whales on the breeding and calving grounds, but the behavior remains unstudied on the feeding grounds. We instrumented three dependent calves (four total deployments) with combined video and 3D-accelerometer data loggers (CATS) on two United States feeding grounds to document nursing events. Two associated mothers were also tagged to determine if behavior diagnostic of nursing was evident in the mother’s movement. Animal-borne video was manually analyzed and the average duration of successful nursing events was 23 s (±7 sd, n = 11). Nursing occurred at depths between 4.1–64.4 m (along the seafloor) and in close temporal proximity to foraging events by the mothers, but could not be predicted solely by relative positions of mother and calf. When combining all calf deployments, successful nursing was documented eleven times; totaling only 0.3% of 21.0 hours of video. During nursing events, calves had higher overall dynamic body acceleration (ODBA) and increased fluke-stroke rate (FSR) compared to non-nursing segments (Mixed effect models, ODBA: F1,107 = 13.57756, p = 0.0004, FSR: F1,107 = 32.31018, p < 0.0001). In contrast, mothers had lower ODBA and reduced FSR during nursing events compared to non-nursing segments. These data provide the first characterization of accelerometer data of humpback whale nursing confirmed by animal-borne video tags and the first analysis of nursing events on feeding grounds. This is an important step in understanding the energetic consequences of lactation while foraging

Caller identification and characterization of individual humpback whale acoustic behaviour.

Acoustic recording tags provide fine-scale data linking acoustic signalling with individual behaviour; however, when an animal is in a group, it is challenging to tease apart calls of conspecifics and identify which individuals produce each call. This, in turn, prohibits a robust assessment of individual acoustic behaviour including call rates and silent periods, call bout production within and between individuals, and caller location. To overcome this challenge, we simultaneously instrumented small groups of humpback whales on a western North Atlantic feeding ground with sound and movement recording tags. This approach enabled a comparison of the relative amplitude of each call across individuals to infer caller identity for 97% of calls. We recorded variable call rates across individuals (mean = 23 calls/h) and groups (mean = 55 calls/h). Calls were produced throughout dives, and most calls were produced in bouts with short inter-call intervals of 2.2 s. Most calls received a likely response from a conspecific within 100 s. This caller identification (ID) method facilitates studying both individual- and group-level acoustic behaviour, yielding novel results about the nature of sequence production and vocal exchanges in humpback whale social calls. Future studies can expand on these caller ID methods for understanding intra-group communication across taxa

Epigenetic aging of humpback whales in three oceans

Age is a key parameter in population ecology, but rarely known in whale populations. We used an epigenetic assay based on DNA methylation levels at three CpG sites to estimate the age of 1,013 humpback whales skin samples obtained from 1993 through 2014. The assay was calibrated with 76 individuals of known age (<1 to 30 years) and had an R2=0.718 (p=2.88e-22) and a standard deviation of 3.562 years. Samples of unknown exact age were obtained from one feeding ground (the Gulf of Maine, n=609), one extralimital wintering area off the southeast U.S. (n=33) and breeding grounds in the North Atlantic (West Indies, n=122), the North Pacific (Hawaii, n=41) and the South Pacific (American Samoa, n=115). The maximum estimated age at the time of sampling was 50.9 years. Two females, both from the Gulf of Maine, reached the maximum observed age of 64 years when later re-sighted (one with a dependent calf in 2016). Whales of both sexes in the Gulf of Maine were younger on average than in those in the West Indies, and whales sampled off the southeast U.S. coast in winter were younger than both North Atlantic feeding and breeding populations. Together, these results suggest a lower tendency of juveniles to undertake or complete migration to the breeding grounds. Age frequency differences among oceanic breeding populations were generally consistent with historical exploitation histories, but not clearly indicative of recovery. This is the first study of age in live humpback whales based on large sample sizes and multiple populations. Epigenetic aging has broad potential to advance understanding of whale biology and ecology and to facilitate conservation. Despite its average precision, we recommend caution when applying this assay to small sample sizes and individual case studie