Dolphins Teach Their Peers Innovative Hunting Techniques

Dolphins have been observed chasing small fish into empty shells, bringing these shells to the surface and draining the water until the fish fall into their waiting mouths. Normally such behaviours would be taught to them by their mothers, but it has been shown in a study published in Current Biology that, instead, they learn this particular technique from their peers.

A number of surveys were carried out by Sonja Wild and her colleagues from the Univeristy of Leeds between 2007 and 2018. During this time, they were observing Indo-Pacific bottlenose dolphins (Tursiops aduncus) at the Dolphin Innovation Project's field site in Shark Bay, Western Australia and witnessed 19 dolphins, belonging to three maternal lineages, performing that same hunting technique, known as "shelling."

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The team were surprised to see that the technique was learned on a peer to peer basis. "Dolphins normally learn foraging behaviour from their mothers, but we found that shelling spreads among closely associated individuals outside the mother-calf bond," Wild told New Scientist.

This not only shows that dolphins are able to learn from their peers, but also that they are motivated to do so. It highlights a parallel between dolphins and our closest relatives, the great apes, since chimpanzees also learn tool use from their peers. As such, the team's observations reveal interesting implications on how dolphin communities function.

As Séverine Methion of the Bottlenose Dolphin Institute in Spain explains, "Behavioural studies show that bottlenose dolphins have distinct personalities, self-awareness, and complex social structures, with individuals cooperating and with new behaviours like shelling being passed from one dolphin to another. In a broad context, this transmission of information could be considered culture."

The ability to learn from others is important in helping animals adapt to changing environments and, as is the case here, spreading new behaviours that allow individuals to forage even under conditions where food may be scarce. The research team observed that shelling was more frequent in the dolphins following a heatwave, as the increased death rate in giant gastropods meant that more shells were readily available for them.

This is not the first time that foraging tool use has been witnessed in dolphins. They have also been observed using sponges to cover their beaks, allowing them to effectively dig into the seabed in search of prey. This behaviour was first recorded in the 1980s and was later studied by Dr Janet Mann and her colleagues who published their findings in PLoS One in 2008.

A sponge similar to what would be utilised by dolphins during "sponging."

So far, shelling has only been observed in Indo-Pacific bottlenose dolphins. However, it is entirely possible that this behaviour occurs in other dolphin species and has yet to be witnessed. The team's findings provide exciting potential for future studies that could help us learn more about dolphin behaviour and, more specifically, the ways in which they interact and learn from one another.

Titanichthys, an Ancient Fish that Fed Like a Basking Shark

Scientists have found that Titanichthys, a giant armoured fish (or placoderm) that lived 380 million years ago, used a feeding strategy similar to modern day basking sharks (Cetorhinus maximus), as published in Royal Society Open Science earlier this week. The research team was formed from a collaboration between paleontologists at the University of Bristol and University of Zurich as part of a post-graduate thesis.

Titanichthys, covered in its tough, armoured plates, was one of the largest animals of the Devonian period. It could reach an overall length of over 5 m (16.5 ft) and the length of its lower jaw exceeded 1 m (3 ft).

Artist's interpretation of Titanichthys. Image credit: Mark Witton

However, before now, there was no evidence to suggest how this massive fish fed. It's lower jaw was narrow and lacked dentition or sharp edges that would make it suitable for cutting. As a result, it has long been assumed that Titanichthys was a suspension feeder, filtering large amounts of plankton from the water column by swimming slowly with its mouth wide open. This is a technique known as continuous ram feeding.

But, to further complicate things, there is no fossil evidence to confirm this feeding strategy. Modern suspension feeders, such as basking sharks, have long projections covering their gills, known as gill rakers, to assist in filtering plankton, but no fossilised suspension feeding structures have ever been found for Titanichthys.

Instead, the research team focused on fossilised jaws collected from the Moroccan part of the Sahara Desert for their study. They used biomechanical analysis to compare the lower jaw of Titanichthys to those of other species, testing jaw resilience using a technique known as Finite Element Analysis (FEA). This allowed them to apply forces virtually to each jaw and assess how likely they were to break or bend.

Of their findings, lead author, Sam Coatham, said in a press release, "We have found that Titanichthys was very likely to have been a suspension feeder, showing that its lower jaw was considerably less mechanically robust than those of other placoderm species that fed on large or hard-shelled prey. Consequently, those feeding strategies (common amongst its relatives) would probably have not been available for Titanichthys."

The FEA revealed that the lower jaw of Titanichthys was far less resistant to stress and, therefore, more likely to break than the jaws of other placoderms, such as the better-known Dunkleosteus. As such, the jaws would not have been able to withstand feeding on larger prey as this would exert too much mechanical stress for them to handle.

This is similar to what is seen in both sharks and whales. The jaws of modern suspension feeders are less resistant to stress than their actively hunting relatives. Building on this finding, further analysis that compared the distribution of stress in the jaws showed similar patterns in both Titanichthys and the basking shark.

Basking shark suspension feeding at the water's surface

The team believes that several other extinct species would have also been suspension feeders, including other placoderms and even a species of plesiosaur. They have already identified promising areas for future research to better understand the development of suspension feeding.

"Our methods could be extended to identify other such species in the fossil record and investigate whether there were common factors driving the evolution and extinction of these species. We suggest a link between oceanic productivity and the evolution of Titanichthys, but this should be investigated in detail in the future. An established link could have implications for our understanding of the conservation of modern suspension feeders," Mr Coatham explained.

With so many of today's large suspension feeders being either vulnerable or endangered, the findings of this study, and of the future research it inspires, could prove useful in better protecting these species and minimising the factors that are currently impacting them.

Algal Blooms are Turning Antarctica Green

The beginnings of a new ecosystem is forming in Antarctica, with green algae blooming across the surface of melting snow, a study published in Nature Communications this week has reported. These blooms could spread further in the future as climate change causes more snow to melt, creating the slushy conditions needed for the algae to thrive. Already, in some areas, the algae is so dense that the bright green snow can be seen from space.

A green snow algae bloom. Image used under Creative Commons Attribution 4.0 International License.

The research team, made up of biologists from the University of Cambridge and the British Antarctic Survey, used both satellite data and ground observations to detect and measure green snow algae on the Antarctic Peninsula. For the satellite data, images were taken between 2017 and 2019 using the European Space Agency's Sentinel 2 satellite. Meanwhile, ground observations were conducted by the team at Ryder Bay, Adelaide Island and Fildes Peninsula, King George Island.

The final product of their hard work was the first ever large-scale algae map of the Antarctic Peninsula, which can now be used as a baseline to assess the rate at which algal blooms are forming across the continent due to climate change. The current green algal blooms could prove to be a source of nutrition for other species and they are already forming relationships with with fungal spores and bacteria.

"It's a community. This could potentially form new habitats. It's the beginning of a new ecosystem," explained Dr Matthew Davey, one of the lead researchers and a plant physiologist and chemical ecologist at the Department of Plant Sciences, University of Cambridge.

The research team identified 1,679 separate blooms of green snow algae, covering an astounding area of 1.9 sq km. They estimated that these blooms absorb roughly 479 tonnes of carbon dioxide a year, which is equivalent to the emissions of around 875,000 average UK car journeys. However, this is a relatively small amount on the global scale and is unlikely to make a significant impact on our carbon footprint.

Plus, the warming climate could have a negative impact on the algae regardless of the amount of atmospheric carbon it absorbs. "If it warms up a bit, you get a lot more blooms. If it warms up a lot, the whole system could crash completely because there's no snow," Dr Davey told New Scientist.

There are two factors that currently determine where the algal blooms are located. The temperature needs to be warm enough to turn the snow to slush. The largest blooms are located on the areas of the peninsula and surrounding islands that are warming the fastest and have an average temperature of just over 0°C. Also, there must be a nutrient source for the algae, such as penguin guano. Over 60% of the blooms found during the study were within 5 km of a penguin colony.

As useful as the team's findings are, green snow algae can only give a limited view of the bigger picture regarding the carbon cycle in Antarctica. Future studies will include red and orange algae, both of which were too difficult to detect for this initial study, and will measure blooms across the whole of Antarctica. This will give a better understanding of the total amount of carbon held in Antarctic snow algae, which could prove to be an effective carbon sink in the future for reducing carbon dioxide in the atmosphere.