Antarctic Feeding Grounds Research Articles

Beyond counting calls: estimating detection probability for Antarctic blue whales reveals biological trends in seasonal calling

We explore the utility of estimating the density of calls of baleen whales for better understanding acoustic trends over time. We consider as a case study stereotyped ‘song’ calls of Antarctic blue whales (Balaenoptera musculus intermedia) on their Antarctic feeding grounds over the course of a year-long, continuous recording from 2014. The recording was made in the Southern Ocean from a deep-water autonomous hydrophone moored near the seafloor in the Eastern Indian sector of the Antarctic. We estimated call density seasonally via a Monte-Carlo simulation based on the passive sonar equation, and compared our estimates to seasonal estimates of detection rate, which are commonly reported in acoustic studies of Antarctic blue whales. The resulting seasonal call densities at our Antarctic site were strongly influenced by seasonally varying noise levels, which in turn yielded seasonal differences in detection range. Incorporating the seasonal estimates of detection area into our analysis revealed a pattern of call densities in accord with historic (non-acoustic) knowledge of Antarctic blue whale seasonal distribution and migrations, a pattern that differed from seasonal detection rates. Furthermore, our methods for estimating call densities produced results that were more statistically robust for comparison across sites and time and more meaningful for interpretation of biological trends compared to detection rates alone. These advantages came at the cost of a more complex analysis that accounts for the large variability in detection range of different sounds that occur in Antarctic waters, and also accounts for the performance and biases introduced by automated algorithms to detect sounds. Despite the additional analytical complexities, broader usage of call densities, instead of detection rates, has the potential to yield a standardized, statistically robust, biologically informative, global investigation of acoustic trends in baleen whale sounds recorded on single hydrophones, especially in the remote and difficult to access Antarctic.

Short Communication: Lateralised lungefeeding behaviour in Southern Hemisphere fin whales at Antarctic feeding grounds

Balaenopterids use dynamic feeding lunges to capture prey, often performing roll manoeuvres which may demonstrate a side preference or laterality. In this study, we use aerial video footage of fin whales (Balaenoptera physalus) feeding at Elephant Island, Antarctica, to investigate laterality in the Southern Hemisphere fin whale subspecies B. p. quoyi. Right‐biased lateralisation was observed in all 63 recorded side lunges, 57 of which displayed visible lunge directions, the majority being clockwise (98.3%). These results complement existing information on lateralised feeding behaviour in Northern Hemisphere fin whales, confirming a strong right‐sided bias across the different fin whale subspecies.

Southern Ocean humpback whale trophic ecology. II. Influence of fasting and opportunistic feeding on skin stable isotope values of migrating whales

Many baleen whale species migrate between low-latitude breeding grounds and high-latitude feeding grounds, with increasing evidence that humpback whales Megaptera novaeangliae utilise supplemental feeding sites in temperate regions while migrating. The diet of whales while migrating is often unknown, and the impact that temperate feeding and/or fasting has on biochemical tracers used to investigate diet remains unclear. The aims of this study were to (1) determine whether prey consumption at supplemental feeding sites could be detected by carbon (13C) and nitrogen (15C) stable isotope analysis of skin; (2) obtain information on diet during migration; and (3) ascertain the impact of potential fasting on stable isotope values of baleen whales. Skin samples were taken from the eastern Australian humpback whale population on Antarctic feeding grounds and 2 sites on the southward migration route (a sub-tropical site and a temperate site) across 2 yr. At the sub-tropical site, 13C and δ15N were consistent with the last place of foraging 5 mo earlier. One exception was the higher (0.5 ‰) δ15N value in 2011, suggesting that in some years, potentially when blubber reserves are insufficient, δ15N may be influenced by fasting. In both years, skin 13C and δ15N values at the temperate site were higher than those from the Antarctic and sub-tropical sites, indicating that a feeding signal from temperate zones had likely been incorporated, with whales feeding on fish and krill. Importantly, supplemental feeding while migrating could affect the interpretation of whale diet on feeding grounds if sampled early in the season.

Southern Ocean humpback whale trophic ecology. I. Combining multiple stable isotope methods elucidates diet, trophic position and foraging areas

Southern Ocean humpback whales Megaptera novaeangliae are capital breeders, breeding in the warm tropics/subtropics in the winter and migrating to nutrient-rich Antarctic feeding grounds in the summer. The classic feeding model is for the species to fast while migrating and breeding, surviving on blubber energy stores. Whilst northern hemisphere humpback whales are generalists, southern hemisphere counterparts are perceived as krill specialists, but for many populations, uncertainties remain regarding their diet and preferred feeding locations. This study used bulk and compound-specific stable isotope analyses and isoscape-based feeding location assignments to assess the diet, trophic ecology and likely feeding areas of humpback whales sampled in the Ross Sea region and around the Balleny Islands. Sampled whales had a mixed diet of plankton, krill and fish, similar to the diet of northern hemisphere humpback whales. Proportions of fish consumed varied but were often high (2-60%), thus challenging the widely held paradigm of Southern Ocean humpback whales being exclusive krill feeders. These whales had lower 15N values and trophic position estimates than their northern hemisphere counterparts, likely due to lower Southern Ocean baseline 15N surface water values and a lower percentage consumption of fish, respectively. Most whales fed in the Ross Sea shelf/slope and Balleny Islands high-productivity regions, but some isotopically distinct whales (mostly males) fed at higher trophic levels either around the Balleny Islands and frontal upwelling areas to the north, or en route to Antarctica in temperate waters off southern Australia and New Zealand. These results support other observations of humpback whales feeding during migration, highlighting the species’ dietary plasticity, which may increase their foraging and breeding success and provide them with greater resilience to anthropogenically mediated ecological change. This study highlights the importance of combining in situ field data with regional-scale isoscapes to reliably assess trophic structure and animal feeding locations, and to better inform ecosystem conservation and management of marine protected areas.

Australia's east coast humpback whales: Satellite tag-derived movements on breeding grounds, feeding grounds and along the northern and southern migration.

Satellite tags were deployed on 50 east Australian humpback whales (breeding stock E1) between 2008 and 2010 on their southward migration, northward migration and feeding grounds in order to identify and describe migratory pathways, feeding grounds and possible calving areas. At the time, these movements were not well understood and calving grounds were not clearly identified. To the best of our knowledge, this dataset details all long-term, implantable tag deployments that have occurred to date on breeding stock E1. As such, these data provide researchers, regulators and industry with clear and valuable insights into the spatial and temporal nature of humpback whale movements along the eastern coastline of Australia and into the Southern Ocean. As this population of humpback whales navigates an increasingly complex habitat undergoing various development pressures and anthropogenic disturbances, in addition to climate-mediated changes in their marine environment, this dataset may also provide a valuable baseline. At the time these tracks were generated, these were the first satellite tag deployments intended to deliver long-term, detailed movement information on east Australian (breeding stock E1) humpback whales. The tracking data revealed previously unknown migratory pathways into the Southern Ocean, with 11 individuals tracked to their Antarctic feeding grounds. Once assumed to head directly south on their southern migration, five individuals initially travelled west towards New Zealand. Six tracks detailed the coastal movement of humpback whales migrating south. One tag transmitted a partial southern migration, then ceased transmissions only to begin transmitting eight months later as the animal was migrating north. Northern migration to breeding grounds was detailed for 13 individuals, with four tracks including turning points and partial southern migrations. Another 14 humpback whales were tagged in Antarctica, providing detailed Antarctic feeding ground movements.Broadly speaking, the tracking data revealed a pattern of movement where whales were at their northern limit in July and their southern limit in March. Migration north was most rapid across the months of May and June, whilst migration south was most rapid between November and December. Tagged humpback whales were located on their Antarctic feeding grounds predominantly between January and May and approached their breeding grounds between July and August. Tracking distances ranged from 68 km to 8580 km and 1 to 286 days. To the best of our knowledge, this dataset compiles all of the long-term tag deployments that have occurred to date on breeding stock E1.

Mixed-stock analysis of humpback whales (Megaptera novaeangliae) on Antarctic feeding grounds

In understanding the impact of commercial whaling, it is important to estimate the mixing of low latitude breeding populations on Antarctic feeding grounds, particularly the endangered humpback whale populations of Oceania. This paper estimates the degree of genetic differentiation among the putative populations of Oceania (New Caledonia, Tonga, the Cook Islands and French Polynesia) and Australia (western Australia and eastern Australia) using ten microsatellite loci and mtDNA, assesses the power of the data for a mixed-stock analysis, determines ways to improve statistical power for future studies and estimates the population composition of Antarctic samples collected in 2010 south of New Zealand and eastern Australia. A large proportion of individuals could not be assigned to a population of origin (> 52%) using a posterior probability threshold of > 0.90. The mixed-stock analysis simulations however, produced accurate results with humpback whales reapportioned to their population of origin above the 90% threshold for western Australia, New Caledonia and Oceania grouped using a combined mtDNA and microsatellite dataset. Removing the Cook Islands, considered a transient region for humpback whales, from the simulation analysis increased the ability to reapportion Tonga from 86% to 89% and French Polynesia from 89% to 92%. Breeding ground sample size was found to be a factor influencing the accuracy of population reapportionment whereas increasing the mixture or feeding ground sample size improved the precision of results. The mixed-stock analysis of our Antarctic samples revealed substantial contributions from both eastern Australia (53.2%, 6.8% SE) and New Caledonia (43.7%, 5.5% SE) [with Oceania contributing 46.8% (5.9% SE)] but not western Australia. Despite the need for more samples to improve estimates of population allocation, our study strengthens the emerging genetic and non-genetic evidence that Antarctic waters south of New Zealand and eastern Australia are used by humpback whales from both eastern Australia and the more vulnerable breeding population of New Caledonia, representing Oceania.

Vocalizing humpback whales (Megaptera novaeangliae) migrating from Antarctic feeding grounds arrive earlier and earlier in the Perth Canyon, Western Australia

Migratory species undertake seasonal, long-distance travel between feeding and breeding grounds, and time their arrivals with high-quality resources. The Breeding Stock D population of humpback whales (Megaptera novaeangliae) migrates from Antarctic to Western Australian waters every austral winter. Based on 16 years (2002-2017) of passive acoustic recordings in the Perth Canyon, Western Australia, the hourly presence/absence of humpback whale vocalizations was used as an indicator of inter-annual changes in migration timing. A trend of earlier arrivals in the Perth Canyon by 1.4 days/year during the northward migration and possibly earlier departures from the Perth Canyon during the southward migration was observed. A distance-based linear model and a generalized linear model (GLM) both identified sea surface temperature (SST) as the most significant predictor for acoustic presence in the Perth Canyon. A 1 °C increase in SST corresponded to a decrease in humpback whale acoustic presence by 4.4 hours/day. Mean SST at the peak of the humpback whale season in the Perth Canyon was 19 °C. Exploratory analysis of the metocean environment of the Antarctic feeding grounds suggested that whales were leaving the Antarctic at the end of the austral summer, as sea ice concentration (SIC) increased and SST decreased. Further research should investigate whether changes in the metocean conditions on Australian breeding grounds correspond to changing departures from the Perth Canyon during the southward migration. If environmental conditions on breeding and feeding grounds change out-of-sync, migrating whales might be unable to arrive at either ground during optimal conditions.

Humpback Whales Have Super Feeding Events in Australian Waters

Each year, the east Australian humpback whale population migrates between their Antarctic feeding grounds, where they spend the summer feeding, to their sub-tropical breeding grounds, where they give birth. Historically, this population was once hunted in both Antarctica and off Australia, however, since whaling ended in the early 1960s, this population has continued to recover. As the population continues to grow, we may now be witnessing “new” behaviors. For the first time, scientists have footage of humpback whales bubble-net feeding and feeding in “super-groups” of 20+ whales in Australian waters. This footage was collected by citizen scientists—regular citizens who help scientists monitor this whale population. These feeding observations are important for understanding how this whale population is changing—not just in numbers but also behaviors—and what we can do to protect whale populations into the future.

First evidence for fin whale migration into the Pacific from Antarctic feeding grounds at Elephant Island.

This study presents the first long-distance tracks of fin whales (Balaenoptera physalus) equipped with satellite transmitters off the Antarctic Peninsula. Southern Hemisphere fin whales were severely depleted by twentieth century industrial whaling, yet recently, they have returned to historical feeding grounds off the northern Antarctic Peninsula, forming large aggregations in austral summers. To date, our knowledge only extended to summer behaviour, while information regarding migration routes and the location of breeding and wintering grounds are lacking. During the austral autumn of 2021, we deployed nsatellite transmitters on four fin whales at Elephant Island. Two transmitters stopped working while the animals were still at the feeding grounds, while two continued to transmit during the transition from feeding activity to migration. Both migrating animals left the feeding ground on 15 April 2021, travelling northward into the Pacific and up along the Chilean coast. The most northerly position received before all tags stopped transmitting on 1 May 2021 was at 48°S. These tracks provide initial evidence of seasonal migratory routes and a first indication toward possible locations of winter destinations. This information, even if preliminary, is critical for investigations of population connectivity, population structure and the identification of breeding grounds of Southern Hemisphere fin whales.

Skin condition of fin whales at Antarctic feeding grounds reveals little evidence for anthropogenic impacts and high prevalence of cookiecutter shark bite lesions

Skin condition of fin whales at Antarctic feeding grounds reveals little evidence for anthropogenic impacts and high prevalence of cookiecutter shark bite lesions

First description of migratory behavior of humpback whales from an Antarctic feeding ground to a tropical calving ground

BackgroundDespite exhibiting one of the longest migrations in the world, half of the humpback whale migratory cycle has remained unexamined. Until now, no study has provided a continuous description of humpback whale migratory behavior from a feeding ground to a calving ground. We present new information on satellite-derived offshore migratory movements of 16 Breeding Stock G humpback whales from Antarctic feeding grounds to South American calving grounds. Satellite locations were used to demonstrate migratory corridors, while the impact of departure date on migration speed was assessed using a linear regression. A Bayesian hierarchical state–space animal movement model (HSSM) was utilized to investigate the presence of Area Restricted Search (ARS) en route.Results35,642 Argos locations from 16 tagged whales from 2012 to 2017 were collected. The 16 whales were tracked for a mean of 38.5 days of migration (range 10–151 days). The length of individually derived tracks ranged from 645 to 6381 km. Humpbacks were widely dispersed geographically during the initial and middle stages of their migration, but convened in two convergence regions near the southernmost point of Chile as well as Peru’s Illescas Peninsula. The state–space model showed almost no instances of ARS along the migratory route. The linear regression assessing whether departure date affected migration speed showed suggestive but inconclusive support for a positive trend between the two variables. Results suggestive of stratification by sex and reproductive status were found for departure date and route choice.ConclusionsThis multi-year study sets a baseline against which the effects of climate change on humpback whales can be studied across years and conditions and provides an excellent starting point for the investigation into humpback whale migration.

New insights into prime Southern Ocean forage grounds for thriving Western Australian humpback whales

Humpback whale populations migrate extensively between winter breeding grounds and summer feeding grounds, however known links to remote Antarctic feeding grounds remain limited in many cases. New satellite tracks detail humpback whale migration pathways from Western Australia into the Southern Ocean. These highlight a focal feeding area during austral spring and early summer at the southern Kerguelen plateau, in a western boundary current where a sharp northward turn and retroflection of ocean fronts occurs along the eastern plateau edge. The topographic steering of oceanographic features here likely supports a predictable, productive and persistent forage ground. The spatial distribution of whaling catches and Discovery era mark-recaptures confirms the importance of this region to Western Australian humpback whales since at least historical times. Movement modelling discriminates sex-related behaviours, with females moving faster during both transit and resident periods, which may be a consequence of size or indicate differential energetic requirements. Relatively short and directed migratory pathways overall, together with high-quality, reliable forage resources may provide a partial explanation for the ongoing strong recovery demonstrated by this population. The combination of new oceanographic information and movement data provides enhanced understanding of important biological processes, which are relevant within the context of the current spatial management and conservation efforts in the Southern Ocean.

Humpback whale migrations to Antarctic summer foraging grounds through the southwest Pacific Ocean

Humpback whale (Megaptera novaeangliae) populations typically undertake seasonal migrations, spending winters in low latitude breeding grounds and summers foraging in high latitude feeding grounds. Until recently, a broad scale understanding of whale movement has been derived from whaling records, Discovery marks, photo identification and genetic analyses. However, with advances in satellite tagging technology and concurrent development of analytical methodologies we can now detail finer scale humpback whale movement, infer behavioural context and examine how these animals interact with their physical environment. Here we describe the temporal and spatial characteristics of migration along the east Australian seaboard and into the Southern Ocean by 30 humpback whales satellite tagged over three consecutive austral summers. We characterise the putative Antarctic feeding grounds and identify supplemental foraging within temperate, migratory corridors. We demonstrate that Antarctic foraging habitat is associated with the marginal ice zone, with key predictors of inferred foraging behaviour including distance from the ice edge, ice melt rate and variability in ice concentration two months prior to arrival. We discuss the highly variable ice season within the putative foraging habitat and the implications that this and other environmental factors may have on the continued strong recovery of this humpback whale population.

Application of a multi-disciplinary approach to reveal population structure and Southern Ocean feeding grounds of humpback whales

Obtaining direct measurements to characterise ecosystem function can be hindered by remote or inaccessible regions. Next-generation satellite tags that inform increasingly sophisticated movement models, and the miniaturisation of animal-borne loggers, have enabled the use of animals as tools to collect habitat data in remote environments, such as the Southern Ocean. Research on the distribution, habitat use and recovery of Oceania’s humpback whales (Megaptera novaeangliae) has been constrained by the inaccessibility to their Antarctic feeding grounds and the limitations of technology. In this multi-disciplinary study, we combine innovative analytical tools to comprehensively assess the distribution and population structure of this marine predator throughout their entire migratory range. We used genotype and photo-identification matches and conducted a genetic mixed-stock analysis to identify the breeding ground origins of humpback whales migrating past the Kermadec Islands, New Zealand. Satellite tracking data and a state-space model were then used to identify the migratory paths and behaviour of 18 whales, and to reveal their Antarctic feeding ground destinations. Additionally, we conducted progesterone assays and epigenetic aging to determine the pregnancy rate and age-profile of the population. Humpback whales passing the Kermadec Islands did not assign to a single breeding ground origin, but instead came from a range of breeding grounds spanning ∼3500 km of ocean. Sampled whales ranged from calves to adults of up to 67 years of age, and a pregnancy rate of 57% was estimated from 30 adult females. The whales migrated to the Southern Ocean (straight-line distances of up to 7000 km) and spanned ∼4500 km across their Antarctic feeding grounds. All fully tracked females with a dependent calf (n = 4) migrated to the Ross Sea region, while 70% of adults without calves (n = 7) travelled further east to the Amundsen and Bellingshausen Seas region. By combining multiple research and analytical tools we obtained a comprehensive understanding of this wide-ranging, remote population of whales. Our results indicate a population recovering from exploitation, and their feeding ground distribution serves as an indicator of the resources available in these environments. The unexpected Kermadec Islands migratory bottle-neck of whales from several breeding grounds, variable distribution patterns by life history stage and high pregnancy rates will be important in informing conservation and management planning, and for understanding how this, as well as other whale populations, might respond to emerging threats such as climate change.

Migratory interchange of humpback whales (Megaptera novaeangliae) among breeding grounds of Oceania and connections to Antarctic feeding areas based on genotype matching

Humpback whales (Megaptera novaeangliae) congregate to breed during the austral winter near tropical islands of the South Pacific (Oceania). It has long been assumed that humpback whales from Oceania migrate primarily to Antarctic feeding grounds directly south (International Whaling Commission Management Areas V and VI); however, there are few records of individual movement connecting these seasonal habitats. Based on genetic samples of living whales collected over nearly two decades, we demonstrate interchange between the breeding grounds of Oceania and Antarctic feeding Areas V, VI, and I (i.e., from 130°E to 60°W), as well as with the eastern Pacific (Colombia), and the migratory corridors of eastern Australia and New Zealand. We first compared genotype profiles (up to 16 microsatellite loci) of samples collected from Oceania breeding grounds to each other and to those from the eastern Pacific. The matching profiles documented 47 individuals that were present on more than one breeding ground, including the first record of movement between Oceania and Colombia. We then compared the 1179 genotypes from the breeding grounds to 777 from the migratory corridors of east Australia and New Zealand, confirming the connection of these corridors with New Caledonia. Finally, we compared genotypes from breeding grounds to 166 individuals from Antarctic feeding Areas I–VI. This comparison of genotypes revealed five matches: one between New Caledonia and Area V, one between Tonga and Area VI, two between Tonga and Area I (western edge), and one between Colombia and Area I (Antarctic Peninsula). Despite the relatively small number of samples from the Antarctic, our comparison has doubled the number of recorded connections with Oceania available from previous studies during the era of commercial whaling.

The Hunt Fellowship: Inspiring acoustics professionals of the future

Students may exit a Ph.D. program feeling fatigued, and sometimes a bit directionless professionally. These feelings combined with the challenging academic job market could be part of the reason for this time period being one of the biggest “leaks in the pipeline,” for women scientists in particular. The flexibility and generosity of the Hunt Fellowship can be inspiring at this crossroads of a young scientist’s career. As the 2009–2010 Hunt Postdoctoral Research Fellowship recipient, I studied the acoustic behavior of humpback whales on their Antarctic feeding grounds, working under the mentorship of Dr. Whitlow Au (University of Hawaii) and Dr. Douglas Nowacek (Duke University). This project followed seamlessly from my dissertation, yet brought me to new ecosystems and reinvigorated my research questions with surprising data. The signal processing skills I gained in acoustic and animal movement analysis solidified my interest in quantitative acoustic behavior research and I made strong connections with several interdisciplinary research groups. This all fueled my career path toward my current Research Faculty position at Moss Landing Marine Laboratories, using similar sound and movement tags to study the effects of anthropogenic noise on cetaceans in general.

Temporal stability and mixed-stock analyses of humpback whales (Megaptera novaeangliae) in the nearshore waters of the Western Antarctic Peninsula

Southern Hemisphere humpback whales breed in tropical waters and migrate to Antarctica to forage. While the breeding grounds are well defined, the population structure on Antarctic feeding grounds is poorly described. The Western Antarctic Peninsula (WAP) is of particular interest, where rapidly changing environmental conditions could alter prey distribution or migration pathways. To examine changes in the population of whales around the WAP, we used mitochondrial DNA (mtDNA) and 15 microsatellite loci. We compared our WAP dataset to a dataset collected 18 years earlier, and identified new haplotypes for the region, but found no significant difference between the datasets. We compared whales from the WAP to breeding populations in Oceania, Colombia, and Brazil. We used an Analysis of Molecular Variance to confirm significant genetic differentiation between the WAP and each breeding ground (overall F ST = 0.035/0.007 mtDNA/microsatellite, p < 0.001) except Colombia. Bayesian mixed-stock analyses showed a large apportionment to Colombia (mtDNA 93.0%; CL 91–99%; microsatellites 86%; CL 72–93%) and a small apportionment to French Polynesia/Samoan Islands (mtDNA 2.9%; CL 0.0–11.5%; microsatellites 8.9%; CL 0–22%), supporting the strong connection between Colombia and the WAP. Assignment tests allocated 81 individuals to Colombia and two to French Polynesia/Samoan Islands. No other breeding grounds had significant apportionments. Direct connectivity of French Polynesia to the WAP was confirmed with the first genotype match of French Polynesia to a feeding area. Continued genetic monitoring will highlight the complex patterns of humpbacks in this rapidly changing climate. Our results serve as a baseline for humpback whale population structure, illustrate mixed-stock analysis as a useful tool for migrating wildlife, and aid in future management considerations for humpbacks.

Quantifying the energy stores of capital breeding humpback whales and income breeding sperm whales using historical whaling records.

Cetacean energy stores are known to vary according to life history, reproductive status and time of year; however, the opportunity to quantify these relationships is rare. Using a unique set of historical whaling records from Western Australia (1952–1963), we investigated energy stores of large cetaceans with differing life histories, and quantified the relationship between total body lipid and length for humpback whales (Megaptera novaeangliae) (n = 905) and sperm whales (Physeter macrocephalus) (n = 1961). We found that total body lipid increased with body length in both humpback and sperm whales, consistent with size-related energy stores. Male humpback whales stored 2.49 kl (15.6 barrels) (31.9–74.9%) more lipid than male sperm whales of equivalent length, to fuel their annual migration. Relative lipid stores of sperm whales (males) were constant throughout the year, while those of humpback whales varied with reproductive class and sampling date. Pregnant female humpback whales had higher relative energy stores than non-pregnant females and males (26.2% and 37.4%, respectively), to fuel the energy demands of gestation and lactation. Those that reached the sampling site later (en route to their breeding grounds) carried higher lipid stores than those that arrived earlier, possibly reflecting individual variation in residency times in the Antarctic feeding grounds. Importantly, longer pregnant females had relatively larger energy stores than the shorter pregnant females, indicating that the smaller individuals may experience higher levels of energetic stress during the migration fast. The relationships we developed between body lipid and length can be used to inform bioenergetics and ecosystem models when such detailed information is not available.

Genetic characterization and population genetic structure of the Antarctic minke whale Balaenoptera bonaerensis in the Indo-Pacific region of the Southern Ocean

The population genetic structure of the Antarctic minke whale in the Antarctic sector corresponding to the Indo-Pacific was investigated using the mitochondrial DNA control region sequence (338 bp) and microsatellite DNA at 12 loci. Whale samples were obtained in JARPAII (Japanese Whale Research Program under Special Permit in the Antarctic—Phase II) surveys performed during the austral summer seasons of 2005/06 to 2010/11. The “Indian Sector” comprised the area between 35° and 130°E, while the “Pacific Sector” was between 165°E and 145°W. The mtDNA/nDNA sample sizes in the Indian and Pacific sectors were 1210/1372 and 795/882 animals, respectively. The level of genetic diversity was high for both genomes, and was similar for the two sectors. In both sectors, the mismatch distribution for whales did not suggest a population at equilibrium. Results of a heterogeneity test showed significant genetic differences between whales in the two sectors, suggesting that different populations inhabit the Pacific and Indian sectors of the Antarctic. Microsatellite DNA analyses showed more dispersal in males than females, and also some degree of annual variation. Significant departure from Hardy–Weinberg equilibrium suggested some geographical overlap of the populations in the feeding grounds. The two populations identified in the Antarctic feeding areas of the Indian and Pacific sectors could be related to the suggested breeding areas in the eastern Indian Ocean and western South Pacific, respectively. The segregation of the populations in the Antarctic feeding grounds could be explained by the fidelity of whales to specific areas with krill concentrations.

Potential energy gain by whales outside of the Antarctic: prey preferences and consumption rates of migrating humpback whales (Megaptera novaeangliae)

The humpback whale (Megaptera novaeangliae) makes annual migrations from Antarctic feeding grounds to tropical breeding grounds. The extent to which it feeds during migration is unknown, but thought to be very low. Whether an animal feeds during migration is likely dependent on prey availability and on the ease with which it can capture the available prey. This study used digital tags (DTAGs) and concurrent prey sampling to measure how changes in the depth and type of prey influenced the lunge feeding rates and the amount of energy consumed by migrating humpback whales. Whales targeting krill lunged at significantly higher rates than whales targeting fish; however, the depth of the prey did not influence lunge rate. The observed lunge rates when feeding on krill, to the best of our knowledge, are higher than any previously reported rates of whales feeding. Estimates of the energetic content of the prey ingested revealed that whales may consume between 1.2 and 3.4 times their daily energy requirements per day while feeding on krill during migration, but less when feeding on fish. This suggests that whales may begin to restock energy supplies prior to reaching the Antarctic. Determining how often this high rate of energy intake occurs along the migratory route will assist with understanding the contribution of migratory energy intake to annual energy budgets.