Into the Deep to Study Krill

In January, 20 scientists from the Australian Antarctic Program boarded the Research Vessel (RV) Investigator and set out from Hobart, Tasmania, to spend two months working off East Antarctica in the Southern Ocean. Their mission: Determine the biomass of the region’s Antarctic krill—the world’s largest krill species, a keystone of the Antarctic food web, and an important player in the fight against climate change. The research was considered so crucial that it proceeded during the pandemic, under strict protocols, before the widespread availability of vaccines.

The Pew Charitable Trusts

The scientists used acoustics, trawls, seabird and whale observations, oceanography, genetics, and—for the first time—specially designed underwater camera systems and deep-sea moorings to study krill and their undersea environment. Enormous swarms of krill can contain hundreds of millions of individual crustaceans, each no longer than 2 inches, and knowing their biomass is key to managing the fishery for a healthy and thriving marine ecosystem as commercial fishing demand for krill grows. And maintaining krill biomass is also critical for sustaining animals that feed on them, such as penguins, and other key predators such as blue whales and crabeater seals.

“We want to understand how krill are distributed in relation to predators like whales and seabirds, ocean currents, food sources, seafloor habitat, and other krill swarms,” says So Kawaguchi of the Australian Antarctic Division (AAD). “Understanding the environment in which the krill live, and how it is changing, is key to understanding how krill biomass could be affected in the future.”

Feeding and breeding in the icy depths of the Southern Ocean, krill face many threats, from warming waters, melting sea ice, and ocean acidification to concentrated industrial fishing focused in the coastal areas of the Antarctic Peninsula.

Over two months, the voyage explored six large-scale survey lines, gathering data and samples along the ship’s path, across more than 306,200 square miles. A fine-scale “krill box” survey (during which the ship undertook several shorter survey lines within a small area) was also conducted just off the coast from the Australian-operated Mawson research station, where a penguin monitoring program has been operating for many years.

Angus Henderson Australian Antarctic Division/CSIRO

The survey included sampling of phytoplankton and krill genetic fragments—specifically sampling seawater for krill DNA to help the researchers better understand krill distribution and abundance as well as krill predator interactions. The research voyage was supported by The Pew Charitable Trusts, the AAD, the Australian Antarctic Program Partnership, and the Antarctic Science Foundation, and had a grant of sea time (ship time and logistical and technical support) from Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) Marine National Facility on board RV Investigator.

The team shared its data—particularly the krill biomass estimate—with the 26 member governments of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), which manages the Antarctic krill fishery and has a mandate to protect the Southern Ocean’s diverse marine life. To help achieve protection for this spectacular region, Pew and its partners are working with CCAMLR to help it meet its goals of updating its ecosystem-based fisheries management practices and establishing a network of large-scale marine protected areas (MPAs) around Antarctica.

Observing predators was an important component of the project, and the team on board RV Investigator collected information on the distribution and density of air-breathing animals that rely on Antarctic krill, including dolphins and whales, crabeater and leopard seals, and bird species such as Adélie penguins, snow petrels, and southern fulmars.

But the scientists weren’t only counting the predators—they were also recording their sounds. “Recordings give us a more complete understanding of which species are in the survey area, and also what they’re doing,” says AAD scientist Brian Miller, a marine mammal acoustics specialist. Although visual observation can provide part of the picture of how many animals are present in the study area, recordings can fill in information about species present at each recording site and their behavior. Scientists are also able to make recordings at night, in fog, or during whiteouts—conditions in which visual observations simply aren’t possible. Some species are even easier to track by sound than by sight. For example, blue whales and sperm whales frequently make loud calls when underwater, which can be detected much farther away than these animals can typically be seen.

Gavin Macaulay led the krill acoustics research on the ship. A trained engineer, he had developed echosounders and methods to survey the biomass of deep-water orange roughy years earlier when he worked for New Zealand’s Ministry of Agriculture and Fisheries. This technology was used to survey the krill. “We send out sound pulses and measure the strength of the echo that comes back from krill swarms,” Macaulay explains. Then the scientists divide the echo by the amount they expect from an average individual krill, which allows them to figure out the total weight of krill in the survey area. 

In addition to using echosounders to conduct the biomass survey, the acoustics team also deployed a “krill swarm study system” consisting of free-floating cameras within a metal frame that is lowered into swarms of krill. The new visual perspective the system provided helps increase the accuracy of biomass estimates, provides insights into krill behavior, and may offer clues to understand the factors that affect the formation and tenacity of krill schools.

Another research system the scientists used for the first time is called a krill observational mooring for benthic investigation (KOMBI), a device housing a deep-sea camera and echosounder that will record the changes in krill presence on the seafloor. Three KOMBIs were deployed and will remain in place for a year. “These units should provide an indication of how important the seafloor habitat in this region is for Antarctic krill,” says the AAD’s Rob King, who led the team’s krill biology research onboard. The units will help scientists fill in the information gaps during the winter months, when Antarctica is inaccessible to scientists, and deliver other key biological information.

Olivia Johnson Australian Antarctic Division/CSIRO

Krill are unusual because, depending on the conditions, they can function either as a superorganism in a swarm or as an individual. As a swarm, krill communicate, navigate, make collective decisions, and use photophores—light-producing organs. Understanding when they instigate swarming behavior is something the scientists are trying to better understand. “We don’t know how krill vary between swarming versus individual behavior over winter, and the relative importance of the various strategies they use to get through this period,” says King, adding that he hopes the KOMBI project, combined with further studies, will unlock some of these answers.

The scientists captured krill from various depths to compare biological information and help determine whether the seafloor is an important habitat for the crustaceans, and they used trawls to collect krill and gather data on the composition of swarms. This information will help researchers understand the distribution and maturity stage of krill in the water column, which will feed into determining how climate change may be affecting both krill and their predators in the Southern Ocean—data that is crucial to the advancement of effective ecosystem-based management for the krill fishery.

This research and updated biomass estimate will help CCAMLR’s scientists and policymakers this fall as they consider updates to the ecosystem-based management system for the Antarctic krill fishery.

CCAMLR has also committed to creating an MPA network around the continent. Soon, CCAMLR delegates will consider a proposal by Australia, the European Union, France, Norway, the United States, and Uruguay to protect a large section of the East Antarctic region. That MPA—coupled with catch limits that minimize the impacts on predators from localized fishing—would create a climate refuge for krill, penguins, and other wildlife and help preserve the region’s unique marine ecosystem and distinct biodiversity.

Nicole Bransome works on The Pew Charitable Trusts’ protecting Antarctica’s Southern Ocean project.