Predator observations will provide an important piece in the krill distribution and abundance puzzle.

A team of observers will count flying seabirds around the vessel during each transect. Scientists will also deploy underwater listening devices, called ‘sonobuoys’, to listen for whales in the area.

The team will then look to see how their predator observations correlate with krill distribution and density detected by the ship’s echosounders.

“We need to better understand the relationship between krill and predators to fully inform the setting of the precautionary catch limit for CCAMLR,” Voyage Chief Scientist Dr So Kawaguchi said.

“This study will contribute to that, but importantly, it will also help us design a practical, long-term ecosystem monitoring program, that accounts for predators, prey, and the impacts of climate change and a future krill fishery.”

Photo: Black-browed albatross

The ship’s echosounders will be the workhorse of the TEMPO voyage, running constantly throughout the transects. Echosounders, mounted in the ship’s hull, send pings of sound out into the environment below and around the ship. Some of the sound is absorbed by the environment and some bounces off objects (such as krill or fish) allowing the instruments to return a ‘picture’ of what is below.

Downward and sideways looking echosounders will be used to get a three dimensional picture of krill swarms moving under and around the ship, providing information about a swarm’s density, structure and vertical distribution in the water column. Using CCAMLR algorithms and real-time measurements of krill captured in trawls, the team will be able to calculate the biomass of swarms. Biomass measured across the six transects can then be scaled up to provide a biomass estimate for the wider CCAMLR management area.

This animation from echoes detected by the RV Investigator’s echosounders shows a three-dimensional representation of a large krill swarm beneath the ship. The swarm is about 400 metres long by about 200 metres across, with a total depth range of about 100 metres. With a volume of 1 million cubic metres, it contains hundreds of millions of Antarctic krill.

Krill biomass estimates will be improved by looking at the orientation of krill in a swarm, as vertically or obliquely oriented krill will reflect sound differently to horizontally oriented krill.

Australian Antarctic Division krill biologist, Mr Rob King, said studies in the Division’s krill aquarium had provided some insights into schooling behaviour, but that it was time to test whether the findings hold true in the wild.

“It’s the age-old question of how does a bird, or in this case a krill, know when to turn left when its neighbour does,” Mr King said.

“How do krill organise themselves into coherent swarms, and what are the rules about distances and alignment between individuals.”

To try and find out, Mr King and scientists from the University of Sydney, will deploy free-floating stereoscopic cameras directly into krill swarms detected by the echosounders.

The cameras are enclosed within a metal frame, painted white to look like ice. The system will be deployed off the back of the trawl deck, and later retrieved.

“We’ll deploy the swarm study system and then steam away from the area, to see if there’s any change in swarming behaviour when there’s a big ship over the swarm, and when there isn’t,” Mr King said.

“It’s a case of putting the instrumentation down and seeing what we’ll discover.”

Two types of trawls will be conducted during the voyage.

Up to 50 routine trawls will occur in set locations, to quantify the abundance of krill and other smaller zooplankton species (planktonic animals) in the area. This will contribute to a broad picture of ecosystem health.

To support the acoustics work, krill swarms will be fished using a small scientific net. By measuring the length, weight, sex and maturity stage (adults, juveniles) of krill collected from swarms detected by the echosounders, scientists will determine how sound reflects off each animal.

“These measurements will help calibrate the echosounders,” Dr Kawaguchi said.

“The more information you have about the composition of the target organism, the more accurate will be your conversion of the echo to biomass.”

Krill will also be kept in on-board aquariums to measure their growth rates, by measuring the size of their exoskeleton before and after moulting. This information is useful in understanding broader ecosystem productivity – more food means faster growing and healthier krill.

To get a sense of how krill use the sea floor and whether it is an important habitat for them over winter, krill biologist Mr Rob King, will deploy three ‘Krill Observational Moorings for Benthic Investigation’, or KOMBIs for at least 12 months.

The KOMBIs will be anchored to the sea floor between 350 and 1500 metres deep – in shallow habitat, a shelf break and a deep canyon.

The moorings have a sideways looking video camera and lights that will video the sea floor for three to five minutes, every five hours, over the entire year. They also carry a Conductivity, Temperature and Depth (CTD) instrument to measure ocean properties, and an upward looking echosounder and current profiler that will detect krill swimming above the mooring.

“We don’t know where krill go during winter when the sea ice freezes over, and the sea ice cover makes it difficult for us to study and understand their movements,” Mr King said.

“These moorings will allow us to determine how krill use the sea floor and the seasonal sea ice area across space and time, and it will also allow year-round monitoring of krill in some of the main foraging grounds for whales, seals and penguins.”

The moorings are the size of an Australian shipping pallet (1.165 x 1.165 m), and weigh more than 700 kilograms each.

Oceanography is a critical component of the TEMPO voyage, with 82 casts planned for the conductivity, temperature, depth (CTD) instrument.

The CTD carries an array of bottles that will collect water at different depths between the near-surface (10 metres depth) and sea floor at about 4600 metres.

Marine biologist, Dr Karen Westwood, said the CTD and water samples will be used to measure ocean chemistry – including temperature, salinity, oxygen, and nutrients. These measurements will assist with the identification of ocean fronts, which are thought to influence the distribution of krill and the biology in the water column – including the phytoplankton krill feed on.

The water samples will also be used to:

• investigate the distribution and abundance of phytoplankton within the survey area • characterise the phytoplankton species that are favoured by krill as a food source • measure carbon dioxide concentrations to help assess climate change impacts, and • to measure environmental DNA (eDNA).

Seawater is full of DNA shed from organisms moving through the ocean, including bacteria, phytoplankton, krill, fish, penguins and whales.

This environmental DNA or eDNA allows scientists to identify hundreds of species in small water samples, by sequencing the DNA in the sample. Scientists can also measure how much DNA from a target species – such as Antarctic krill – is in the sample.

Geneticist, Dr Leonie Suter, will test the emerging power of this technology to see whether the amount of krill DNA she detects in her seawater samples correlates with the amount of krill detected by the ship’s echosounders.

“We will take water samples using the ship’s seawater line as the ship approaches and moves through a krill swarm, to see how their DNA signal dilutes and spreads horizontally, so we can calibrate our method against what we know was there,” she said.

“We’ll also take surface seawater samples at trawl sites to compare eDNA detection of krill with the trawls.”

Dr Suter will also collect water samples from the sea floor and through the water column, using the CTD instrument.

“We’re interested in comparing what krill eDNA we detect near the sea floor, to what the light trap on the sea floor shows, to see if they match,” she said.

As the technology develops, eDNA may contribute to improvements in krill biomass estimates, and identifying the presence of predators.

To try and detect and catch krill near the sea floor, a deep sea camera and light trap, developed by krill biologist Mr Rob King, will be attached to the conductivity, temperature, depth (CTD) instrument.

The device will switch on for five minutes, as the CTD rests 3–5 metres off the sea floor.

“Previous work suggests deep sea krill are attracted to light within two minutes,” Mr King said.

“We hope to be able to catch any that might be in the area and bring them back to the surface alive, to measure their growth rate, and to check their condition and what they’ve been eating.

“The camera will also tell us what the sea floor habitat looks like, and whether there are krill there, even if we don’t catch any.”