The characteristics of krill swarms in relation to aggregating Antarctic blue whales

Abstract

We model the presence of rare Antarctic blue whales (Balaenoptera musculus intermedia) in relation to the swarm characteristics of their main prey species, Antarctic krill (Euphausia superba). A combination of visual observations and recent advances in passive acoustic technology were used to locate Antarctic blue whales, whilst simultaneously using active underwater acoustics to characterise the distribution, size, depth, composition and density of krill swarms. Krill swarm characteristics and blue whale presence were examined at a range of spatiotemporal scales to investigate sub meso-scale (i.e., <100 km) foraging behaviour. Results suggest that at all scales, Antarctic blue whales are more likely to be detected within the vicinity of krill swarms with a higher density of krill, those found shallower in the water column, and those of greater vertical height. These findings support hypotheses that as lunge-feeders of extreme size, Antarctic blue whales target shallow, dense krill swarms to maximise their energy intake. As both Antarctic krill and blue whales play a key role in the Southern Ocean ecosystem, the nature of their predator-prey dynamics is an important consideration, not only for the recovery of this endangered species in a changing environment, but for the future management of Antarctic krill fisheries.

Distribution of blue whale populations in the Southern Indian Ocean based on a decade of acoustic monitoring

“…Productive Antarctic waters are the main Antarctic blue whale feeding grounds. This subspecies feeds mainly on large Antarctic krill (Euphausia superba) (Kawamura, 1980;Miller et al, 2019). Antarctic blue whale migration is guided by the seasonal presence of krill in summer in high latitudes.…”

Self-organization and information transfer in Antarctic krill swarms

“…In addition, these strong responses in the vertical dimension may relate to krill predator-avoidance strategies or their mode of communication. For instance, many oceanic predators attack predominantly from above or below, rather from the side ( 16,17 ), while the positioning of bioluminescent photophores on the ventral surface mean that signaling between krill occurs predominantly in the vertical plane ( 18 ). The suggestion that the photophores act to counter-illuminate krill and make them less conspicuous to predators attacking from below potentially means that these points are interrelated ( 18 ).…”

Modelling the distribution of a key habitat feature to guide future on‐ground habitat assessment for an endangered specialist songbird

“…Miller et al . 2019). We predicted for future climate scenarios with bioclimatic variables under future climate and kept soil and topographic predictors the same.…”