Trophodynamics of krill and its potential role in blue whale feeding in the Perth Canyon, south-east Indian Ocean

Migrating blue whales along the Western Australian coast exhibit feeding behaviour within the Perth Canyon, which is an area of high krill abundance, particularly for Euphausia recurva. The importance of krill in marine food webs has led to a number of trophodynamic studies investigating their fatty acid and stable isotope compositions. In the south-east Indian Ocean, the suppression of upwelling by the dominant Leeuwin Current results in relatively oligotrophic waters, particularly during autumn and winter. Oligotrophic waters tend to be dominated by small autotrophic flagellates (i. e. dinoflagellates) and cyanobacteria. We relate biochemical data obtained for E. recurva, as well as Stylocheiron carinatum and Pseudeuphausia latifrons with their potential food source, phytoplankton, and one of their potential predators, the endangered pygmy blue whale (Balaenoptera musculus brevicauda) sampled in the Perth Canyon. Fatty acids of all three krill species were dominated by polyunsaturated fatty acids (PUFA; ~50%) largely comprised of omega-3 PUFA, which is typical for krill. The high docosahexaenoic acid (DHA) to eicosapentaenoic acid (EPA) ratio reflects a dinoflagellate, rather than a diatom diet, and the high oleic acid (18: 1 9) to vaccenic acid (18: 1 7) ratio is indicative of an omnivorous diet. Stable isotope analysis positions E. recurva as a first, possibly second order consumer (5. 8 - 8. 4 15N)and phytoplankton as the likely source of carbon (-18 to -24 13C) .The fatty acid composition of krill did not match that of the surface phytoplankton sampled, which was low in PUFA and more reflective of degraded and detrital material. This suggests that krill are not feeding at the surface, and may feed closer to the deep chlorophyll maximum. The outer blubber layer sampled from the pygmy blue whale was high in monounsaturated fatty acids (MUFA, 58%) rather than PUFA, and did not reflect the krill fatty acid composition. However, the high DHA to EPA ratio in the blubber indicated a diet originating from dinoflagellates, as found for krill. Stratification of fatty acids across blubber layers is common for marine mammals and the outer blubber layer for some species has been found to not accurately reflect the diet of the animal

Past and present distribution, densities and movements of blue whales <i>Balaenoptera musculus</i> in the Southern Hemisphere and northern Indian Ocean

1Blue whale locations in the Southern Hemisphere and northern Indian Ocean were obtained from catches (303 239), sightings (4383 records of =8058 whales), strandings (103), Discovery marks (2191) and recoveries (95), and acoustic recordings.2Sighting surveys included 7 480 450 km of effort plus 14 676 days with unmeasured effort. Groups usually consisted of solitary whales (65.2%) or pairs (24.6%); larger feeding aggregations of unassociated individuals were only rarely observed. Sighting rates (groups per 1000 km from many platform types) varied by four orders of magnitude and were lowest in the waters of Brazil, South Africa, the eastern tropical Pacific, Antarctica and South Georgia; higher in the Subantarctic and Peru; and highest around Indonesia, Sri Lanka, Chile, southern Australia and south of Madagascar.3Blue whales avoid the oligotrophic central gyres of the Indian, Pacific and Atlantic Oceans, but are more common where phytoplankton densities are high, and where there are dynamic oceanographic processes like upwelling and frontal meandering.4Compared with historical catches, the Antarctic (‘true’) subspecies is exceedingly rare and usually concentrated closer to the summer pack ice. In summer they are found throughout the Antarctic; in winter they migrate to southern Africa (although recent sightings there are rare) and to other northerly locations (based on acoustics), although some overwinter in the Antarctic.5Pygmy blue whales are found around the Indian Ocean and from southern Australia to New Zealand. At least four groupings are evident: northern Indian Ocean, from Madagascar to the Subantarctic, Indonesia to western and southern Australia, and from New Zealand northwards to the equator. Sighting rates are typically much higher than for Antarctic blue whales.6South-east Pacific blue whales have a discrete distribution and high sighting rates compared with the Antarctic. Further work is needed to clarify their subspecific status given their distinctive genetics, acoustics and length frequencies.7Antarctic blue whales numbered 1700 (95% Bayesian interval 860–2900) in 1996 (less than 1% of original levels), but are increasing at 7.3% per annum (95% Bayesian interval 1.4–11.6%). The status of other populations in the Southern Hemisphere and northern Indian Ocean is unknown because few abundance estimates are available, but higher recent sighting rates suggest that they are less depleted than Antarctic blue whales.</li

Habitat associations of cetaceans and seabirds in the tropical eastern Indian Ocean

There is an increasing demand for integrated pelagic surveys to support ecosystem-based management of marine environments and their associated marine life. The Browse Basin in the tropical eastern Indian Ocean was surveyed using ship line transects to determine habitat associations of cetaceans and seabirds with submarine topography and local oceanographic conditions during winter and spring 2008. Fourteen species of cetaceans, including the data deficient pygmy blue whale, and 23 species of seabirds were encountered throughout the basin. Aggregations of both cetaceans and seabirds were observed at two significant submarine topographic features, Scott Reef and Browse Cliffs, particularly during spring when encounters and abundances of odontocetes were far greater. The attraction of cetaceans and seabirds to Scott Reef and Browse Cliffs was likely foraging-related given these features were associated with upwelling and elevated biomass of krill and fish. Sub-mesoscale sea surface temperature and chlorophyll a fronts also occurred in vicinity to Browse Cliffs and the shelf environment. The Browse Basin is an important, and potentially predictable, foraging ground for a variety of top predators, and their occurrence would have implications for the current and future management practices of oil and gas industries operating in the region

Water temperature correlates with baleen whale foraging behaviour at multiple scales in the Antarctic

How baleen whales locate prey and how environmental change may influence whale foraging success are not well understood. Baleen whale foraging habitat has largely been described at a population level, yet population responses to change are the result of individual strategies across multiple scales. This study aimed to determine how the foraging behaviour of individual whales varied relative to environmental conditions along their movement path. Biotelemetry devices provided information on humpback whale (Megaptera novaeangliae) movement at two spatial scales in East Antarctica, and a mixed modelling approach was used at a medium scale (tens of kilometres) to determine which environmental factors correlated with a change in foraging behaviour. Water temperature was linked to a change in foraging behaviour at both spatial scales. At the medium scale, warmer water was associated with the resident state, commonly assumed to represent periods of foraging behaviour. However, fine-scale analyses suggested that cooler water was associated with a higher feeding rate. Variation in whale foraging behaviour with changes in water temperature adds support to the hypothesis that whales may be able to track environmental conditions to find prey. Future research should investigate this pattern further, given the predicted rise in water temperatures under climate-change scenarios

From sea ice to blubber:linking whale condition to krill abundance using historical whaling records

Krill (Euphausia superba) are fundamentally important in the Southern Ocean ecosystem, forming a critical food web link between primary producers and top predators. Krill abundance fluctuates with oceanographic conditions, most notably variation in winter sea ice, and is susceptible to environmental change. Although links between local krill availability and performance of land breeding, central place foragers are recognised, the effects of krill variability on baleen whales remain largely unclear because concurrent long-term data on whale condition and krill abundance do not exist. Here, we quantify links between whale body condition and krill abundance using a simple model that links krill abundance to sea ice extent. Body condition of humpback whales (Megaptera novaeangliae) caught in west Australian waters between 1947 and 1963 was estimated from oil yields in whaling records. Annual estimates of krill abundance in the Southern Ocean where those whales foraged (70°–130°E) were correlated significantly with contemporary annual winter sea ice extent. We hindcast sea ice extent for the whaling period from reconstructed temperature data and found that whale body condition was significantly correlated with hindcasted winter sea ice extent, supporting the hypothesis that variations in body condition were likely mediated by associated krill fluctuations. As humpback whales migrate and breed on finite energy stores accrued during summer foraging in the Antarctic, changes in sea ice and concomitant changes in krill abundance have long-term implications for their condition and reproductive success

Data from: High suckling rates and acoustic crypsis of humpback whale neonates maximise potential for mother–calf energy transfer

1. The migration of humpback whales to and from their breeding grounds results in a short, critical time period during which neonatal calves must acquire sufficient energy via suckling from their fasting mothers to survive the long return journey. 2. Understanding neonate suckling behaviour is critical for understanding the energetics and evolution of humpback whale migratory behaviour and for informing conservation efforts, but despite its importance, very little is known about the details, rate and behavioural context of this critical energy transfer. 3. To address this pertinent data gap on calf suckling behaviour, we deployed multi-sensor Dtags on eight humpback whale calves and two mothers allowing us to analyse detailed suckling and acoustic behaviour for a total of 68·8 h. 4. Suckling dives were performed 20·7 ± 7% of the total tagging time with the mothers either resting at the surface or at depth with the calves hanging motionless with roll and pitch angles close to zero. 5. Vocalisations between mother and calf, which included very weak tonal and grunting sounds, were produced more frequently during active dives than suckling dives, suggesting that mechanical stimuli rather than acoustic cues are used to initiate nursing. 6. Use of mechanical cues for initiating suckling and low level vocalisations with an active space of <100 m indicate a strong selection pressure for acoustic crypsis. 7. Such inconspicuous behaviour likely reduces the risk of exposure to eavesdropping predators and male humpback whale escorts that may disrupt the high proportion of time spent nursing and resting, and hence ultimately compromise calf fitness. 8. The small active space of the weak calls between mother and calf is very sensitive to increases in ambient noise from human encroachment thereby increasing the risk of mother–calf separation