Giant krill swarms in 3D
Krill swarms in 3D
On-screen text: In the Southern Ocean, scientists are finding krill by following the blue whales that eat them.
ROB KING: It's fascinating to be on a voyage where we're targeting areas to research by focusing in on blue whales that we're hearing from hundreds of kilometres across the ocean.
On-screen text: For the first time, the RV Investigator's echosounders are being used to 'see' giant krill swarms underwater.
JOSH LAWRENCE: So the animation is showing us a three-dimensional representation a large krill swarm we passed over earlier in the voyage. The swarm was about 400 metres long by about 200 metres across and it kind of came up in this multi-level swarm that was a total depth range of about 100 metres, but with the three-dimensional view you can see that it's all connected and it's all one enormous swarm.
On-screen text: With a volume of a million cubic metres, this single swarm contains hundreds of millions of Antarctic krill.
ROB KING: What sort of krill is a blue whale after? Because krill isn't just an individual. Krill is a super organism.
JOSH LAWRENCE: It might tell us something about the preferences that 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.
On-screen text: Each swarm recorded by the echosounders is also sampled for its krill.
ROB KING: There's a whole bunch of female krill here that are ready to lay eggs. There's also a lot of developing juvenile krill that are maturing. But what's really interesting is that those krill are mainly females so it appears there's a strong gender imbalance in this area. 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 on to produce embryos, no trouble at all. So the system is working but we're not sure where the males are, so we're going to be looking for those as the cruise continues.
For the first time on an Australian research vessel, giant krill swarms are being captured in 3D using state-of-the-art echosounder technology in the Southern Ocean.
A live krill swarm 400 metres long, 200 metres across, and 100 metres deep has been recorded by a team of Australian Antarctic Program scientists on board the CSIRO Marine National Facility research vessel Investigator.
The ENRICH* voyage is mid-way through its seven week expedition off the East Antarctic coast, following the calls of blue whales to find the krill swarms that they eat.
Krill biologist with the Australian Antarctic Division, Rob King, said krill is not only an individual animal, but also a super-organism.
“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?” Mr King said.
Antarctic blue whales almost exclusively eat krill. In one day, an adult blue whale can eat up to 4 million krill, more than 3 tonnes. To do this, they must feed in areas where they can find high concentrations of krill.
Acoustician Joshua Lawrence of the Australian Antarctic Division is using the multibeam echosounders on RV Investigator to ‘paint a picture’ of the size, shape and density of krill swarms.
“With a three-dimensional model, you can really get to grips with the scale in terms of the depth and the size of the ship relative to the swarm.”
“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,” Mr Lawrence 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.”
Mr King said at this time of year, krill are in reproductive mode.
“What we’re seeing from the krill trawls so far is many female krill that are ready to lay eggs, and also a lot of trawls dominated by immature females.”
“It’s fascinating to be on a voyage where we target areas for krill research by listening in on blue whales that we’re hearing from hundreds of kilometres across the ocean,” Mr King said.
*ENRICH stands for 'Euphausiids (krill) and Nutrient Recycling In Cetacean (whale) Hotspots'