Just moments after Miesa Grobbelaar photographed this endangered humpback whale being freed from a chain, the whale “paused and looked at us, as if saying thanks”, she said. The picture of the rescue effort, which was taken near the coast of Ha’apai, Tonga, won the Grand Prize in the .

Grobbelaar and her team of rescuers had answered a distress call about an entangled humpback whale, arriving to find a “heavy rusted chain cutting deep into her tail”, said Grobbelaar in an announcement about her win. They worked “carefully and silently” to free her, until the chain finally snapped, she said.

While humpback whales as a species are no longer considered endangered, with overall numbers having recovered from low levels seen in the mid-20th century due to excessive whaling, there are still some populations at risk, including those found off the coast of Tonga. These still number in the low thousands, which is around 30 per cent lower than before widespread whaling.

“It’s horrific and beautiful, it’s humanity’s relationship with nature at its worst and humanity caring for nature at its best, all at the same time,” said Jarrod Boord, one of the competition’s judges, in the announcement.

The contest, which was open to photographers from Australia, New Zealand, Papua New Guinea and the Solomon Islands, also awarded prizes in other categories, such as this enchanting picture (above) of a Pluteus velutinornatus mushroom, which grows on wood, that won the Plants & Fungi category. Photographer Nic Wooding spotted the hazel-coloured fungi just before it had opened, returning a couple of days later to find it in “immaculate” condition.

Scott Portelli took first prize in the Lands category for his kaleidoscopic time-lapse of stars above a rock face (above) in Windjana Gorge National Park in Western Australia, known for its distinctive red rocks. It took more than 600 photos to show the stars moving during the night sky, from dusk to dawn.

This vibrant photo (above) of a female peacock mantis shrimp (Odontodactylus scyllarus), taken in Bali, Indonesia, by Peter McGee, was awarded third prize in the Water category. The shrimp is guarding her precious cargo of red eggs, while scanning the waters around her.

Brainwave testing of two young baleen whales has revealed they can hear higher frequency sounds than previously thought, forcing researchers to rethink how the ocean’s largest animals respond to predators and human noises.

“This is truly groundbreaking work,” says at Syracuse University in New York, who wasn’t involved in the new study. “Directly measuring the hearing of a wild baleen whale is something the researchers in the field have been working towards for decades
 This is, to my knowledge, the first successful test of this method with a baleen whale.”

But baleen whales include the largest animals on Earth, and the study method of temporarily restraining them for a hearing test isn’t easy. “The body size of most baleen whales is too large for the approach to be effective,” says at the National Marine Mammal Foundation, a nonprofit organisation based in California. So Houser and his colleagues turned to a relatively small baleen species called the minke whale.

The researchers examined the migratory route of minke whales along the coast of Norway and found a natural channel between two islands, where they used net barriers and boats to guide two whales – each about 3 to 5 metres in length – into a fish farm enclosure with a drop-down net door. Researchers then used a roller system to pull up a net and hold the teenage animals partially submerged at the water’s surface.

The hearing test involved placing two gold-plated electrodes with silicone suction cups on each whale’s skin near its blowhole and dorsal fin, which enabled the researchers to record brainwave signals. They measured how the whales’ brains responded to sounds played from an underwater speaker for about 30 minutes for one whale and 90 minutes for the other.

Such experiments revealed that the whales’ auditory brainstems respond to ultrasonic sounds, which are beyond those the human ear can detect, at frequencies as high as 45 to 90 kilohertz – a much broader hearing range than previously believed possible based on ear anatomy and vocalisations.

The corralling and restraining of wild marine mammals is “quite controversial” because of the potential for “significant stress” in the animals, says at Marine Conservation Research, a nonprofit organisation based in the UK. But he described the findings as “very important” in helping understand how baleen whales may evade predators such as killer whales, which hunt using high-frequency echolocation clicks.

Researchers should also rethink how baleen whales are affected by military sonar and commercially available echo sounders used for mapping the seafloor, says Boisseau. “It seems the more we study the hearing of marine mammals, the more we confound our initial assumptions,” he says.

Sperm whale calls are far more complex than we thought – and could be an animal communication system that is the closest thing to human language yet discovered.

The claim is based on an analysis of thousands of exchanges made by east Caribbean sperm whales (Physeter macrocephalus), which were recorded over several years.

“It’s really extraordinary to see the possibility of another species on this planet having the capacity for communication,” says at the Massachusetts Institute of Technology. “We used to believe that we are the only ones.”

Sperm whales are long-lived animals with complex social lives, with females and their young living in small groups. They hunt their prey – mainly squid – using echolocation that involves streams of regular clicks. It was known that the whales often vocalise at each other with short bursts of irregular click patterns lasting a few seconds, but their significance was unclear.

“They dive together, they eat together, they hunt together,” says Rus. “There is so much collaboration and we hear their vocalisations while they do all these activities, so the question is, what does all this stuff mean?”

To investigate, Rus and her team analysed nearly 9000 sperm whale calls that had been recorded using devices stuck to the animals with suction cups, as part of a monitoring project conducted between 2014 and 2018.

Previously, it was thought that this group of whales used 21 different click patterns, known as codas. In the latest analysis, the team found that there are really 18 different basic codas, but they can be changed to give several further levels of complexity.

For instance, sometimes a known coda would have an extra click tagged on either at the start or the end – this often seemed to indicate that it was the listening whale’s turn to speak.

Another discovery is that sometimes known codas are stretched out by slowing them down while maintaining their rhythmic pattern.

Based on these findings, the researchers estimate that there are several hundred possible click patterns, although only 156 were seen in this dataset. They have drawn up a sperm whale “phonetic alphabet” to help them classify future recordings.

The whales also seem to be adding complexity by combining different codas in sequences, in the same way that human language involves adding together different letters to make words.

“Once you have this combinatorial basis, it allows you to take a finite set of symbols [and] compose them to create an infinite number of symbols by following a set of rules,” says , also at MIT. “Now that we have this alphabet, the next thing we’re trying to do is see how they sequence together.”

at the University of Southampton, UK, who wasn’t involved in the work, says the fact that sperm whales use these sounds for echolocation while hunting suggests they can accurately perceive small changes in the intervals between clicks. “There’s logic to assuming those intervals could convey information.”

“It’s always been a mystery how sperm whales, which have quite complex social structures, communicate with each other when their signals are boring sets of pulses,” he says. “This idea that it’s the fine structure within the codas that’s conveying the information is an interesting concept.”

If it is shown that combinations of clicks do convey a wide range of meanings, the sperm whales’ communication abilities would be unique among non-human animals.

Some other species, including various primates, can signal to each other with a small set of calls or movements. For instance, some monkeys use different alarm calls to warn each other about various predators, such as leopards, snakes and eagles, which would require different escape strategies.

But these communication systems are too limited to be classed as language, which is usually defined as unfettered expression of thoughts into signals.