Scientists 3D model hundreds of millions of krill in giant swarm with a dramatic ‘gender imbalance’
Scientists followed the calls of blue whales to find the krill swarms they eat. (Australian Antarctic Division: Brett Wilks)
Researchers have created 3D animations of giant krill swarms in the Southern Ocean, discovering a puzzling “gender imbalance” among the tiny crustaceans which sustain the world’s largest animal.
- Scientists are using “echosounder technology” to record 3D animations of giant krill swarms
- The swarms contain hundreds of millions of krill
- The krill trawls are dominated by immature females and female krill that are ready to lay eggs
The Australian Antarctic Division (AAD) scientists aboard the CSIRO Research Vessel Investigator recorded a giant live krill swarm 400 metres long, 200m across and 100m deep, made up of hundreds of millions of krill.
The researchers have been following the calls of blue whales for hundreds of kilometres across the ocean to find the krill swarms that the whales eat.
They used echosounder technology during the voyage off the East Antarctic Coast to create 3D animations of the “super-organisms” for the first time.
Rob King, an AAD krill biologist, said the swarms could take on many different shapes and sizes.
“We target areas for krill research by listening in on blue whales that we’re hearing from hundreds of kilometres across the ocean,” he said.
“Krill swarms can be deep or shallow, dense or diffuse, but little is known about the different swarm types and whether some are more attractive to blue whales than others.
“We’ve got so much more information available on this ship about the fine-scale three-dimensional structure of krill swarms that we can start to answer the question: what sort of krill is a blue whale after?”
An adult blue whale almost exclusively eats krill, and can eat more than 3 tonnes of krill in one day.
Plenty of female krill in the sea, but not near the males
Mr King said the first few krill trawls they had studied were dominated by females krill, with only 20 per cent estimated to be male.
“It’s not preventing them producing fertilised eggs. All of the females that have spawned here in the lab have produced fertilised eggs that have gone onto produce embryos no trouble at all,” he said.
“So the system’s working, but we’re not sure where the males are … so we’re going to be looking for those as the cruise continues.”
In the later trawls, Mr King said they were dominated by males.
“It appears there’s a strong gender imbalance in this area,” he said.
“The picture that is developing now is one of skewed distributions of the sexes, so some trawls dominated by males and others by females.”
Antarctic blue whales can eat up to 4 million krill in one day. (Australian Antarctic Division: David Donnelly)
Joshua Lawrence, an AAD acoustician, said the 3D model helped show the scale of the swarm compared to the ship.
“We can contrast swarms where we’ve got whales, with swarms in areas where there aren’t any whales, to see what differences we can identify,” he said.
“We’re collecting samples of krill from different swarms, to see if there’s any correlation between the three-dimensional structures we’re seeing and the krill’s size, age and population structure.
“It might tell us something about the preferences the whales have for the different three dimensional structures, again that’s something you wouldn’t really be able to do without that three-dimensional information.”