Smooth Handfish, the First Marine Bony Fish Declared Extinct in Modern Times

The smooth handfish (Sympterichthys unipennis) was declared extinct by the International Union for Conservation of Nature (IUCN) in March of this year. Only one specimen has ever been known to science, collected by the French naturalist François Péron in 1802. However, the fish has not been seen since then, even after thorough regional assessments.

The smooth handfish specimen collected by François Péron in 1802 (Australian National Fish Collection, CSIRO).

The smooth handfish is thought to have once been common in shallow waters around Tasmania and the south coast of Australia. It was a bottom-dweller and, as with other handfish species, it was named for the specialised fins that the fish use to walk across the seafloor.

Several other handfish species are also under threat and could soon suffer the same fate. In 1996, the spotted handfish (Brachionichthys hirsutus) was the first marine fish to be declared critically endangered, though the red handfish (Thymichthys politus) and the Ziebell's handfish (Brachiopsilus ziebelli) have since followed suit. In addition, there are seven species of handfish which have not been seen in over 20 years.

So, what caused their decline?

As Australia and Tasmania were colonised, it is likely that exploitation of the surrounding waters caused a significant impact, with sensitive ecosystems changing at an unexpected rate. Dredging for scallops and oysters, sediment runoff from industrial activity, and climate change would all have been contributing factors and, even now, ecosystems across the region continue to be impacted.

"About 40% of shallow reef species in southern Tasmania are showing rapid population decline, the whole marine system in the south-east has changed substantially in the last 100 years," Professor Graham Edgar, a marine biologist at the University of Tasmania, told the Guardian.

A small section of reef off the coast of Tasmania (Source: John Turnbull).

Why does it matter?

The loss of the smooth handfish is likely an indictor of a much larger issue.

Ocean warming, caused by climate change, makes life extremely difficult for species that require a cold water habitat, as warm water continues to spread further and further south. As a result, many other vulnerable species in the waters around Tasmania could suffer the same fate as the smooth handfish and are currently threatened with extinction.

In addition, as it is so difficult to accurately assess and monitor marine species, it is likely that the smooth handfish actually went extinct decades before this year's official declaration. Knowing that, we have to ask ourselves, how many other fish species may have come and gone without our knowledge?

It is impossible to survey the entire ocean, making it highly likely that a number of marine species have gone extinct before they could even be discovered. This lack of data means that we are unable to evaluate the true extent of biodiversity loss in the oceans. As a result, it is not possible to implement the necessary conservation efforts in time.

A red handfish, relative of the smooth handfish that is currently listed as critically endangered (Source: John Turnbull).

So, the official listing of the smooth handfish as extinct highlights a larger issue that is happening right now in our oceans. If it is assumed that marine species are going extinct at a similar rate to terrestrial ones (as the evidence suggests they are), then ocean biodiversity is under significant threat. We need to act now to reduce the current impacts on marine ecosystems before it is too late and more species follow the smooth handfish into extinction, including those that we may not yet be aware of.

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."

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.