Curious kids: how do gills work?



David Clode/Unsplash, CC BY

Culum Brown, Macquarie University

How do gills work? Tully, aged 7

Great question, Tully! Animals on land breathe air, which is made up of different gasses. Oxygen is one of these gases, and is made by plants (hug a plant today and say thanks). All animals need to breathe in oxygen to survive.

When the air goes into our lungs, oxygen goes into our blood and is delivered all around the body. Air is light, so it’s easy to move around. This makes it pretty easy to breathe air back and forth — a bit like blowing up balloons and letting them deflate.




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Things are different for fish. Fishes also need oxygen, but rather than getting it from air, they have to get it from water.

But there is less oxygen available in water than air. And to make matters worse for the poor fishes, water is thicker than air, so it takes much more work to move it around. This makes the problem of getting that oxygen in the fishes’ body even harder.

Two goldfish in an aquarium
Fish take in water through their mouths, where it passes over their gills.
Shutterstock

This is why fish need gills

Rather than breathing in and out through the mouth, fish use a one-way system, passing water in one direction over their gills.

Water goes in the mouth, across the gills and out through the opercula (the bony covering protecting their gills).

But gills and lungs are more similar than you might think. Both have really big surface areas which increases the amount of water or air that touches the gill or lung tissue, and so increases the amount of oxygen available.

Water goes in the mouth, across the gills and out the other side.
Shutterstock

What’s more, the walls of the lungs and gills are very thin and loaded with tiny tubes that transport blood (called “capillaries”).

This means the capillaries come into close contact with the air or water outside, letting oxygen pass across the thin walls and into the blood. At the same time, carbon dioxide, which is a waste product from our bodies, passes out.

Gills are also important for controlling how much salt is in the body, but let’s leave that story for another day.


Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au




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Curious Kids: when fish get thirsty do they drink sea water?


The Conversation


Culum Brown, Professor, Macquarie University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Basking sharks travel in extended families with their own ‘gourmet maps’ of feeding spots, genetic tagging reveals



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Catherine S Jones, University of Aberdeen; Leslie Noble, Nord University, and Lilian Lieber, Queen’s University Belfast

Picture the scene. Swimming off Scotland’s west coast during a summer holiday you notice a large dark shark nearly 10 metres long headed towards you. A prominent triangular dorsal fin cuts the surface, the powerful rhythmically beating tail driving it silently through the cloudy green depths. You’re transfixed by a cavernous mouth large enough to swallow a seal.

Musing this may be your last swim, it might be surprising to learn this leviathan of the deep is a harmless yet endangered gentle giant. It has little interest in humans, focusing on some unseen bounty of the warmer summer waters: zooplankton, the tiny creatures found near the surface of the ocean.

This is the basking shark (Cetorhinus maximus), once common off western Europe, feeding on the annual plankton bonanza of the European shelf.

Our recent study suggests holidaymakers and basking sharks have much in common. They make temporary forays into these higher latitudes, travelling familiar routes with extended family, feeding on local fare at well-known places visited on previous trips.

Areas supporting high densities of zooplankton are like tourist traps, drawing basking sharks from across the Atlantic in late spring and summer. Hundreds converge in inshore surface waters on the Scottish west coast, Ireland and Isle of Man.

Once hunted for its oily liver across all oceans, basking sharks in the the north-east Atlantic were primarily targeted, with more than 80,000 slaughtered in the second half of the 20th century. This earned the world’s second biggest fish (after the whale shark) a place on the International Union for Conservation of Nature´s Red List. A critical indicator of biodiversity, this catalogue of species under threat of global extinction makes depressing reading.

Saving our sharks

Conservation management of the basking shark demands knowledge of its ecology and movement patterns. These slow-swimming coastal predators easily traverse the equator and ocean basins, moving from one legislative domain to another. Identifying important feeding sites and routes popular for annual migrations can therefore help countries enact effective protection.

Difficult to track and observe, satellite tagging has revealed shark movements, showing use of the ocean throughout a year. One study suggests that basking sharks have an attachment to particular areas, returning annually to feeding sites, a behaviour known as seasonal site fidelity.

Such localities are candidates for protection, designated Marine Protected Areas (MPAs), and ensure sharks remain undisturbed during sensitive and important life stages. But tagging informs us mainly about individual movements, leaving crucial conservation questions unanswered.

Our study focused on developing genetic markers to identify individuals and establish their migration routes, population connectivity and size. We also wanted to explore basking sharks’ genetic diversity – an indicator of a species’ ability to future proof against environmental change, and kinship of feeding clusters.

But developing tools removed only one obstacle. Another was lack of routine DNA sampling of basking shark groups. A breakthrough came when, in desperation, we discovered skin mucus from a tail swipe against a boat was a DNA source. Routine swabbing of basking shark groups – quickly and with minimal disturbance – provided genetic profiles of more than 400 individuals and a snapshot of those travelling together.

This register identified individuals arriving at summer feeding sites, revealing that sharks were re-sighted within seasons and again in later years, sometimes around the same date at sampling locations only kilometres apart. This supports findings of basking sharks repeatedly visiting feeding sites in the recently designated Sea of the Hebrides MPA. Ominously, our study also indicates the Irish Sea is an important migration route – an area of increasing human activity.

The dorsal fin of a basking shark breaking the surface of the sea.
The distinctive dorsal fin of a basking shark off the coast of Scotland.
Lilian Lieber, Author provided

Family ties

We expected the roaming and mixing of cosmopolitan, filter-feeders that live long lives to erode genetic differences between populations. But regular sampling of feeding groups revealed basking sharks off the coast of Ireland in spring (perhaps having wintered near the US) were genetically distinct from north-east Atlantic populations. This differentiation was explained when genetic snapshots made up family albums.

We found that basking shark groups consist of related individuals, indicating a tendency to travel prescribed seasonal migration routes as extended family parties. It would seem the family that feeds together, stays together.

Cetaceans often travel as kin groups, perhaps facilitating learning of migration routes and encouraging cooperative behaviours. This could mean that basking shark groups also exhibit complex behaviours. Certainly, they don’t fit the lone shark stereotype.

Until our study, the perception was that they moved into warmer waters from widespread locations, sniffing out a plankton meal, collecting as groups of unrelated individuals – like gourmands headed into the city, chancing on finding a good restaurant by smell.

Now it looks like basking sharks carry “road maps” of gourmet venues, taking the family along. Perhaps travelling together allows young kin to learn accurate navigation, and maybe many noses are better at sniffing out a meal of densely packed zooplankton.

Conservation biologists fret about genetic variation of threatened species. Large marine creatures have low rates of reproduction and consist of small populations. This means they accumulate genetic variation more slowly than the tiny, populous, rapidly reproducing plankton they eat. That lack of evolutionary currency slows responses to environmental change. In an important conservation milestone, our genetic estimates suggest a north-east Atlantic basking shark population not exceeding 10,000 individuals.

Worse still, most variation is distributed amongst families, so loss of kin groups erodes genetic variation rapidly – as when basking sharks were hunted, and as occurs now during accidental bycatch, when fishing vessels trap unwanted marine creatures in their nets.

Such population size and structure, coupled with tendencies to frequent inshore feeding areas earmarked for development of marine renewables such as windfarms, may not produce a happy outcome without intelligent management of such environments.
When it comes to basking shark conservation we have to remember that in a rapidly changing world, family matters.The Conversation

Catherine S Jones, Senior Lecturer, Biological Sciences, University of Aberdeen; Leslie Noble, Professor of Aquatic Biosciences, Nord University, and Lilian Lieber, Research Fellow in the Bryden Centre, School of Chemistry and Chemical Engineering, Queen’s University Belfast

This article is republished from The Conversation under a Creative Commons license. Read the original article.

How will sharks respond to climate change? It might depend on where they grew up



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Culum Brown, Macquarie University and Connor Gervais

They may have been around for hundreds of millions of years — long before trees — but today sharks and rays are are among the most threatened animals in the world, largely because of overfishing and habitat loss.

Climate change adds another overarching stressor to the mix. So how will sharks cope as the ocean heats up?

Our new research looked at Port Jackson sharks to find out. We found individual sharks adapt in different ways, depending where they came from.

A Port Jackson shark swimming on the sea bed
Port Jackson sharks in Jervis Bay may be better at responding to climate change than those from The Great Australian Bight.
Connor Gervais, Author provided

Port Jackson sharks from cooler waters in the Great Australian Bight found it harder to cope with rising temperatures than those living in the warmer water from Jervis Bay in New South Wales.

This is important because it goes against the general assumption that species in warmer, tropical waters are at the greatest risk of climate change. It also illustrates that we shouldn’t assume all populations in one species respond to climate change in the same way, as it can lead to over- or underestimating their sensitivity.

But before we explore this further, let’s look at what exactly sharks will be exposed to in the coming years.

An existential threat

In Australia, the grim reality of climate change is already upon us: we’re seeing intense marine heat waves and coral bleaching events, the disappearance of entire kelp forests, mangrove forest dieback and the continent-wide shifting of marine life.

The southeast of Australia is a global change hotspot, with water temperatures rising at three to four times the global average. In addition to rising water temperatures, oceans are becoming more acidic and the amount of oxygen is declining.

Any one of these factors is cause for concern, but all three may also be acting together.

Coral bleaching
Oceans act like a heat sink, absorbing 90% of the heat in the atmosphere. This makes marine environments highly susceptible to climate change.
Shutterstock

One may argue sharks have been around for millions of years and survived multiple climate catastrophes, including several global mass extinctions events.

To that, we say life in the anthropocene is characterised by changes in temperature and levels of carbon dioxide on a scale not seen for more than three million years.




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Rapid climate change represents an existential threat to all life on Earth and sharks can’t evolve fast enough to keep up because they tend to be long-lived with low reproductive output (they don’t have many pups). The time between generations is just too long to respond via natural selection.

Dealing with rising temperatures

When it comes to dealing with rising water temperature, sharks have two options: they can change their physiology to adapt, or move towards the poles to cooler waters.

Moving to cooler waters is one of the more obvious responses to climate change, while subtle impacts on physiology, as we studied, have largely been ignored to date. However, they can have big impacts on individual, and ultimately species, distributions and survival.

Juvenile Port Jackson sharks
Juvenile Port Jackson sharks from our study.
Connor Gervais, Author provided

We collected Port Jackson sharks from cold water around Adelaide and warm water in Jervis Bay. After increasing temperatures by 3℃, we studied their thermal limits (how much heat the sharks could take before losing equilibrium), swimming activity and their resting metabolic rate.

While all populations could adjust their thermal limits, their metabolic rate and swimming activity depended on where the sharks were originally collected from.




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With a rise in water temperature of just 3℃, the energy required to survive is more than twice that of current day temperatures for the Port Jackson sharks in Adelaide.

The massive shift in energy demand we observed in the Adelaide sharks means they have to prioritise survival (coping mechanisms) over other processes, such as growth and reproduction. This is consistent with several other shark species that have slower growth when exposed to warmer waters, including epaulette sharks and bonnethead sharks.

Two brown, spiralled shark eggs: one is about half the size of the other
The smaller egg to the left is from Port Jackson sharks near Adelaide, while the right egg is from sharks in Jervis Bay.
Connor Gervais, Author provided

On the other hand, a 3℃ temperature rise hardly affected the energy demands of the Port Jackson sharks from Jervis Bay at all.

Threatening the whole ecosystem

Discovering what drives responses to heat is important for identifying broader patterns. For example, the decreased sensitivity of the Jervis Bay sharks likely reflects the thermal history of the region.




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Australia’s southeastern coastline is warmed by the East Australian Current, which varies in strength both throughout the year and from year to year. With each generation exposed to these naturally variable conditions, populations along this coastline have likely become more tolerant to heat.

Populations in the Great Australian Bight, in contrast, don’t experience such variability, which may make them more susceptible to climate change.

So why is this important? When sharks change their behaviour it affects the whole ecosystem.

The implications range from shifts in fish stocks to conservation management, such as where marine reserves are assigned.

Sharks and rays generally rank at the top or in the middle of the food chain, and
have critical ecosystem functions.

Port Jackson sharks, for example, are predators of urchins, and urchins feed on kelp forests — a rich habitat for hundreds of marine species. If the number of sharks decline in a region and the number of urchins increase, then it could lead to the loss of kelp forests.

The top of a swimming Port Jackson shark
Port Jackson sharks feed on feed on urchins in kelp forests.
Connor Gervais, Author provided

What’s next?

There’s little research dedicated to understanding how individuals from different populations within species respond to climate change.

We need more of this kind of research, because it can help identify hidden resilience within species, and also highlight populations at greatest risk. We have seen this in action in coral bleaching events in different parts of Australia, for example.

We also need a better handle on how a wide range of species will respond to a changing climate. This will help us understand how communities and ecosystems might fragment, as each ecosystem component responds to warming in different ways and at different speeds.

Steps need to be taken to address these holes in our knowledge base if we’re to prepare for what follows.




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The Conversation


Culum Brown, Professor, Macquarie University and Connor Gervais, Connor Gervais

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Sharks are thriving at the Kermadec Islands, but not the rest of New Zealand, amid global decline




Adam Smith, Massey University

A recent global assessment of shark populations at 371 coral reefs in 58 countries found no sharks at almost 20% of reefs and alarmingly low numbers at many others.

The study, which involved over 100 scientists under the Global FinPrint project, gave New Zealand a good score card. But because it focused on coral reefs, it included only one region — Rangitāhua (Kermadec Islands), a pristine subtropical archipelago surrounded by New Zealand’s largest marine reserve.

It is a different story around the main islands of New Zealand. Many coastal shark species may be in decline, and less than half a percent of territorial waters is protected by marine reserves.

The first global survey of reef sharks shows they are virtually absent in many areas.



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Sharks in Aotearoa

In New Zealand, there are more than a hundred species of sharks, rays and chimaeras. They belong to a group of fishes called chondrichthyans, which have skeletons of cartilage instead of bone.

Some 55% of New Zealand’s chondrichthyan species are listed as “not threatened” by the International Union for Conservation of Nature (IUCN). Not so encouraging is the 32% of species listed as “data deficient”, meaning we don’t know the status of their populations. Most species (77%) live in waters deeper than 200 metres.

Seven species are fully protected under the Wildlife Act 1953. They are mostly large, migratory species such as the giant manta ray. Some are threatened with extinction according to the IUCN, including great white sharks, basking sharks, whale sharks and oceanic white tip sharks.

Basking shark and snorkellers
Basking sharks were once common in some coastal areas in New Zealand.
Martin Prochazkacz/Shutterstock

Historically, basking sharks were caught as bycatch in New Zealand fisheries, and seen in their hundreds in some inshore areas. Sightings of these giant plankton-feeders suddenly dried up over a decade ago. We don’t know why.

Commercial shark fisheries

Eleven chondrichthyan species are fished commercially in New Zealand under the quota management system. Commercial fisheries for school shark, rig and elephant fish took off from the 1970s and now catch around 8,000 tonnes per year in total.

Finning of sharks has been illegal throughout New Zealand since 2014.

Most of New Zealand’s shark fisheries are considered sustainable. But a sustainable fishery can mean sustained at low levels, and we must tread carefully. School shark was recently added to the critically endangered list after the collapse of fisheries in Australia and elsewhere, and there’s a lot we don’t know about the New Zealand population.

We do know sharks were much more abundant in pre-European times. In Tīkapa Moana (Hauraki Gulf), sharks have since declined by an estimated 86%. An ongoing planning process provides some hope for the ecosystems of the gulf.

Protecting sharks

Not surprisingly, the global assessment found a ban on shark fishing to be the most effective intervention to protect sharks. Several countries have recently established large shark sanctuaries, sometimes covering entire exclusive economic zones.

These countries tend to have ecotourism industries that provide economic incentives for protection — live sharks can be more valuable than dead ones.

Other effective interventions are restrictions on fishing gear, such as longlines and set nets.

Waters within 12 nautical miles of the Kermadec Islands have been protected by a marine reserve since 1990. In 2015, the Kermadec Ocean Sanctuary was announced but progress has stalled. The sanctuary would extend the boundaries to the exclusive economic zone, some 200 nautical miles offshore, and increase the protected area 83-fold.

A large population of Galapagos sharks, which prefer isolated islands surrounded by deep ocean, thrive around the Kermadec Islands but are found nowhere else in New Zealand. Great white sharks also visit en route to the tropics. Many other species are found only at the Kermadecs, including three sharks and a sex-changing giant limpet as big as a saucer.

Galapagos sharks
Galapagos sharks were recorded around Raoul Island in the Kermadec archipelago.
Author provided



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New technologies are revealing sharks’ secrets

What makes the Global FinPrint project so valuable is that it uses a standard survey method, allowing data to be compared across the globe. The method uses a video camera pointed at a canister of bait. This contraption is put on the seafloor for an hour, then we watch the videos and count the sharks.

Grey reef, silver tip and hammerhead sharks circle a baited camera station set up near Walpole Island in the Southwest Pacific.

Baited cameras have been used in a few places in New Zealand but there are no systematic surveys at a national scale. We lack fundamental knowledge about the distribution and abundance of sharks in our coastal waters, and how they compare to the rest of the world.

Satellite tags are another technological boon for shark research. It is difficult to protect sharks without knowing where they go and what habitats they use. Electronic tags that transmit positional data via satellite can be attached to live sharks, revealing the details of their movements. Some have crossed oceans.

Sharks have patrolled the seas for more than 400 million years. In a few decades, demand for shark meat and fins has reduced their numbers by around 90%.

Sharks are generally more vulnerable to exploitation than other fishes. While a young bony fish can release tens of millions of eggs in a day, mature sharks lay a few eggs or give birth to a few live young. Females take many years to reach sexual maturity and, in some species, only reproduce once every two or three years.

These biological characteristics mean their populations are quick to collapse and slow to rebuild. They need careful management informed by science. It’s time New Zealand put more resources into understanding our oldest and most vulnerable fishes, and the far-flung subtropical waters in which they rule.The Conversation

Adam Smith, Senior Lecturer in Statistics, Massey University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The mushroom cloud’s silver lining: how the Cold War is helping the biggest fish in the sea



United States Department of Defense/Wikimedia

Mark Meekan, Australian Institute of Marine Science

It might surprise you to learn that nuclear bomb tests during the Cold War are now helping conserve whale sharks, the largest living fish.

Growing up to 18 metres – longer than the average bus – whale sharks live in all tropical oceans. In Australia, they are found off tropical coasts in the north, particularly in Western Australia.

Whale sharks face a number of threats. Globally they are listed as endangered, and their numbers continue to decline.




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Until recently, key information about the life history of whale sharks was missing, which prevented informed choices about how they were managed. In particular, scientists were not able to accurately assess their age and growth patterns.

Our research, published today in Frontiers in Marine Science, changes that. We examined the skeleton of whale sharks, using carbon from Cold War atomic bomb testing as a “time stamp” to reveal their true age. The findings will help protect these beautiful animals into the future.

Until now, it’s been difficult to assess the age of whale sharks.
Wayne Osborn

Gentle giants

Whale sharks are placid “filter feeders”, which basically means they eat by opening their massive mouths and straining small fish and plankton that pass through the gills.

They are covered in a pattern of stripes and spots that provide camouflage as they bask at the surface. Whale sharks’ gentle nature and striking appearance has made them a drawcard for tourists who pay to snorkel or dive with the animals.

Whale shark ecotourism is big business. At Ningaloo Reef off Western Australia, the industry is worth an estimated A$12.5 million per year.

The industry is also valuable for small island nations such as the Maldives and developing countries including the Philippines and Indonesia. It has lifted thousands of villagers from poverty and provided an impetus for governments to protect whale sharks.




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But all is not plain sailing for these animals. In some parts of the world they are hunted for their fins, meat, oil and skin. The flesh resembles tofu when cooked, and is a popular menu item in parts of Asia, particularly China.

When shipping lanes are established near whale shark habitat, the animals are frequently struck by vessels and either die or suffer propeller injuries such as fin amputation. Their habit of basking at the surface of the ocean during the day puts whale sharks at particular risk of ship strike.

This combined with other threats – such as warming sea surface temperatures due to climate change – has created an uncertain future for these charismatic and valuable animals.

A whale shark carcass on the shore of Teluk Betung beach in West Sumatra, Indonesia, last year. The animal is considered endangered.
RAJO BATUAH/EPA

The silver lining on the mushroom cloud

Just how vulnerable whale shark populations are to these threats is not clear. Growth rates of fish species – or how many years they take to reach a certain size – determine their resilience, and how fast populations are likely to recover if severely damaged.

But determining the age of whale sharks has, to date, been very difficult. Their vertebrae feature distinct bands, similar to the rings of a tree trunk, which increase in number as the animal grows older. But the bands could not conclusively be used to determine age because some scientists believed a ring formed every year, but others suggested one formed every six months.

Cross section of a whale shark vertebra from Pakistan, showing 50 growth bands.
Paul Fanning/ Pakistan node of the UN Food and Agricultural Organisation

To settle the debate, we turned to the radioactive legacy of the Cold War’s nuclear arms race – specifically, carbon-14.

Carbon-14 is a naturally occurring radioactive element. But in the 1950s and early 1960s, nuclear weapons tests by the US, Soviet Union, Great Britain, France and China released enormous amounts of carbon-14 into the air.

It travelled into the world’s oceans, and into every living organism on the planet – including the skeletons and shells of animals.

We analysed the vertebrae of two whale sharks collected many years ago in Taiwan and Pakistan. By counting back from the peak carbon-14 level, we concluded the rings were formed once per year. This meant that for the first time, the age and growth rate of a whale shark could accurately be determined; a 10-metre shark was 50 years old.

We know whale sharks can grow to almost twice the length of the animals we analysed, and have been estimated to live as long as 100 years. The results of our study makes that prediction now seem more likely.

Whale sharks can live as long as 100 years.
Wayne Osborn

What does this mean for whale sharks?

Slow-growing species with long lifespans are typically very susceptible to threats such as fishing. This is because it takes many years for animals to reach reproduction age, and the rate at which individuals are replaced is very slow.

Our study explains why fisheries targeting whale sharks almost immediately collapse: the species is not built to cope with the added pressures of human harvests.

Whale sharks populations take a very long time to recover from over-harvesting. Governments and management agencies must work together to ensure this iconic animal persists in tropical oceans – for both the future of the species, and the many communities whose livelihoods depend on whale shark ecotourism.




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The Conversation


Mark Meekan, Senior Principal Research Scientist, Australian Institute of Marine Science

This article is republished from The Conversation under a Creative Commons license. Read the original article.

We’ve just discovered two new shark species – but they may already be threatened by fishing



One of the newly discovered sixgilled sawshark species (Pliotrema kajae).
Simon Weigmann, Author provided

Per Berggren, Newcastle University and Andrew Temple, Newcastle University

Finding a species that’s entirely new to science is always exciting, and so we were delighted to be a part of the discovery of two new sixgill sawsharks (called Pliotrema kajae and Pliotrema annae) off the coast of East Africa.

We know very little about sawsharks. Until now, only one sixgill species (Pliotrema warreni) was recognised. But we know sawsharks are carnivores, living on a diet of fish, crustaceans and squid. They use their serrated snouts to kill their prey and, with quick side-to-side slashes, break them up into bite-sized chunks.

The serrated snout of a sixgill sawshark (Pliotrema annae).
Ellen Barrowclift-Mahon/Marine MEGAfauna Lab/Newcastle University., Author provided

Sawsharks look similar to sawfish (which are actually rays), but they are much smaller. Sawsharks grow to around 1.5 metres in length, compared to 7 metres for a sawfish and they also have barbels (fish “whiskers”), which sawfish lack. Sawsharks have gills on the side of their heads, whereas sawfish have them on the underside of their bodies.

A sixgill sawshark (Pliotrema annae) turned on its side, showing gills and barbels.
Ellen Barrowclift-Mahon, Author provided

Together with our colleagues, we discovered these two new sawsharks while researching small-scale fisheries that were operating off the coasts of Madagascar and Zanzibar. While the discovery of these extraordinary and interesting sharks is a wonder in itself, it also highlights how much is still unknown about biodiversity in coastal waters around the world, and how vulnerable it may be to poorly monitored and managed fisheries.

The three known species of sixgill sawshark. The two new species flank the original known species. From left to right: Pliotrema kajae, Pliotrema warreni (juvenile female) and Pliotrema annae (presumed adult female).
Simon Weigmann, Author provided

Fishing in the dark

Despite what their name might suggest, small-scale fisheries employ around 95% of the world’s fishers and are an incredibly important source of food and money, particularly in tropical developing countries. These fisheries usually operate close to the coast in some of the world’s most important biodiversity hotspots, such as coral reefs, mangrove forests and seagrass beds.

For most small-scale fisheries, there is very little information available about their fishing effort – that is, how many fishers there are, and where, when and how they fish, as well as exactly what they catch. Without this, it’s very difficult for governments to develop management programmes that can ensure sustainable fishing and protect the ecosystems and livelihoods of the fishers and the communities that depend on them.

Small-scale fishers of Zanzibar attending their driftnets.
Per Berggren/Marine MEGAfauna Lab/Newcastle University, Author provided

While the small-scale fisheries of East Africa and the nearby islands are not well documented, we do know that there are at least half a million small-scale fishers using upwards of 150,000 boats. That’s a lot of fishing. While each fisher and boat may not catch that many fish each day, with so many operating, it really starts to add up. Many use nets – either driftnets floating at the surface or gillnets, which are anchored close to the sea floor. Both are cheap but not very selective with what they catch. Some use longlines, which are effective at catching big fish, including sharks and rays.




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In 2019, our team reported that catch records were massively underreporting the number of sharks and rays caught in East Africa and the nearby islands. With the discovery of two new species here – a global hotspot for shark and ray biodiversity – the need to properly assess the impact of small-scale fisheries on marine life is even more urgent.

Pliotrema kajae, as it might look swimming in the subtropical waters of the western Indian Ocean.
Simon Weigmann, Author provided

How many other unidentified sharks and other species are commonly caught in these fisheries? There is a real risk of species going extinct before they’re even discovered.

Efforts to monitor and manage fisheries in this region, and globally, must be expanded to prevent biodiversity loss and to develop sustainable fisheries. There are simple methods available that can work on small boats where monitoring is currently absent, including using cameras to document what’s caught.

A selection of landed fish – including sharks, tuna and swordfish.
Per Berggren, Author provided

The discovery of two new sixgill sawsharks also demonstrates the value of scientists working with local communities. Without the participation of fishers we may never have found these animals. From simple assessments all the way through to developing methods to alter catches and manage fisheries, it’s our goal to make fisheries sustainable and preserve the long-term future of species like these sawsharks, the ecosystems they live in and the communities that rely on them for generations to come.The Conversation

Per Berggren, Marine MEGAfauna Lab, Newcastle University and Andrew Temple, Postdoctoral Research Associate in Marine Biology, Newcastle University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Acidic oceans are corroding the tooth-like scales of shark skin



CT scan of a catshark hatchling head. Note the ridged scales.
Rory Cooper, Kyle Martin & Amin Garbout/Natural History Museum London, Author provided

Rory Cooper, University of Sheffield

Shark skin might look perfectly smooth, but inspect it under a microscope and you’ll notice something strange. The entire outer surface of a shark’s body is actually covered in sharp, little scales known as denticles. More remarkable still, these denticles are incredibly similar to human teeth, as they’re also comprised of dentine and enamel-like materials.

Your dentist will no doubt have warned you that acidic drinks like fizzy cola damage your teeth. This is because acid can dissolve the calcium and phosphate in the enamel tooth covering. For the first time, scientists have discovered a similar process acting on the tooth-like scales of sharks in the ocean.




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The carbon dioxide (CO₂) that humans release into the atmosphere doesn’t just heat the planet. As more of it dissolves in the ocean, it’s gradually increasing the acidity of seawater. In the past 200 years, the ocean has absorbed 525 billion tonnes of CO₂ and become 30% more acidic as a result. Now scientists worry that the lower pH is affecting one of the ocean’s top predators.

Denticles have sharp ridges and are arranged in an overlapping pattern, similar to chainmail.
Rory Cooper, Author provided

An unwelcome sea change

Over hundreds of millions of years, the denticles that make up shark skin have evolved to allow sharks to thrive in different environments. Different species have distinct denticle shapes and patterns that enable a range of remarkable functions. I’ve spent the last four years attempting to understand how the development of these scales is genetically controlled in shark embryos, and how their intricate details give each species an edge.

Denticles have highly specialised ridges which help reduce drag by up to 10%, allowing sharks to swim further and faster while using less energy. This works in a similar fashion to the ridges in the hulls of speed boats, which help the vessel move more efficiently through the water. In fact, these scales are so effective at reducing drag that scientists and engineers have long tried to create shark skin-inspired materials for boats and aircraft that can help them travel further on less fuel.

A catshark embryo about 80 days after fertilisation.
Rory Cooper, Kyle Martin & Amin Garbout/Natural History Museum London, Author provided

The patterning of denticles also works as a defensive armour, which protects sharks from their environment and from other predators. Some female sharks – such as the small-spotted catshark – have even developed a region of enlarged denticles which provide protection from a male shark’s bites during mating.

The changing chemistry of the ocean has been linked to coral bleaching, but its effect on other marine animals is less clear. To address this, researchers exposed puffadder shysharks – a species found off the coast of South Africa – to different levels of acidity in aquariums, and used a high-resolution imaging technique to examine the effect of acid exposure on their skin. After just nine weeks, they found that increased water acidity had weakened the surfaces of their denticles.

The puffadder shyshark (Haploblepharus edwardsii) is a slow moving species that lives on the sea floor.
Derekkeats/Wikipedia, CC BY-SA

Corrosion and weakening of the denticle surface could degrade the highly specialised drag-reducing ridges, affecting the ability of these sharks to swim and hunt. Many shark species are top-level predators, so if they’re not able to hunt as effectively, this might have an unpredictable impact on the population size of their prey and other animals in the complex marine environment. Some species of shark need to swim constantly to keep oxygen-rich water flowing over their gills and to expel CO₂ – another process which might be hindered by increased drag.




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Sharks belong to an ancient group of vertebrates known as the cartilaginous fishes, which split from the bony fishes – a lineage that later gave rise to humans – roughly 450 million years ago. Sharks, and other cartilaginous fish like rays, arose long before the dinosaurs, and have outlived multiple mass extinction events. But the rate of change in the marine environment over the last few centuries is an unprecedented challenge. These ancient predators may struggle to adapt to the fastest known change in ocean chemistry in the last 50 million years.The Conversation

Rory Cooper, PhD Researcher in Evolutionary Developmental Biology, University of Sheffield

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Shark nets are destructive and don’t keep you safe – let’s invest in lifeguards



New research says there is no reliable evidence that shark nets protect swimmers.
Ben Rushton/AAP

Leah Gibbs, University of Wollongong; Lachlan Fetterplace, Swedish University of Agricultural Sciences, and Quentin Hanich, University of Wollongong

As Australians look forward to the summer beach season, the prospect of shark encounters may cross their minds. Shark control has been the subject of furious public debate in recent years and while some governments favour lethal methods, it is the wrong route.

Our study, published today in People and Nature, presents further evidence that lethal shark hazard management damages marine life and does not keep people safe.

We examined the world’s longest-running lethal shark management program, the New South Wales Shark Meshing (Bather Protection) Program, introduced in 1937. We argue it is time to move on from shark nets and invest further in lifeguard patrol and emergency response.

A scalloped hammerhead caught in a shark net off Palm Beach in Sydney, in March 2019.
HSI-AMCS-N McLachlan

Managing shark bite

In NSW, 51 beaches between Newcastle and Wollongong are netted. The nets don’t provide an enclosure for swimmers. They are 150 metres long and suspended 500 metres offshore. In the process of catching targeted sharks they also catch other animals including turtles, rays, dolphins, and harmless sharks and fish.

Catching and killing sharks might seem a commonsense solution to the potential risk of shark bite to humans. But the story is not so simple.




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A young tiger shark cruising near Coffs Harbour, NSW.
EPA

Multiple factors influence shark bite incidence, including climate change, prey species distribution and abundance, water quality, human population, beach-use patterns, and lifeguard patrols.

Most research and public debate focuses on human safety or marine conservation. Our research sought to bring the two into conversation. We considered a range of factors that contribute to safety and conservation outcomes. This included catch of target and non-target species in nets, damage to marine ecosystems, global pressures on oceans, changing beach culture, human population growth and changes in lifeguarding and emergency response. Here’s what we found.

Fewer sharks, fewer bites

As the graph below shows, shark catch in the NSW netting program has fallen since the 1950s. This includes total shark numbers and numbers of three key target species: white shark (also known as great white or white pointer), tiger shark and bull shark.

Total shark catch per 100 net days 1950-2019.
Authors

This suggests there are fewer sharks in the water, which is cause for alarm. The three target species are recognised by Australian and international institutions as threatened or near-threatened.

Our analysis shows shark bite incidence is also declining over the long term. The trend isn’t smooth; trends rarely are. The last two decades have seen more shark bites than the previous two. This is not surprising given Australia’s beach use has again grown rapidly in recent decades.

But if we take a longer term view, we see that shark bite incidence relative to population is substantially lower from the mid-20th century than during the decades before.

The decline in shark bite incidence is great news. But key points are frequently overlooked when society tries to make sense of the figures.

Shark bite incidents in NSW per million people per decade, including fatalities and injuries.
Authors

Lifeguard patrol and emergency response are key

In NSW, lifeguard beach patrol grew over the same time period as the shark meshing program. More people swam and surfed in the ocean from the early 20th century as public bathing became legal. The surf lifesaving and professional lifeguard movements grew rapidly in response.

Today, 50 of the 51 beaches netted through the shark meshing program are also patrolled by lifeguards or lifesavers. Yet improved safety is generally attributed to the mesh program. The role of beach patrol is largely overlooked.




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Some sharks have declined by 92% in the past half-century off Queensland’s coast


So, claims that shark bite has declined at netted beaches might instead be interpreted as decline at patrolled beaches. In other words, reduced shark interactions may be the result of beach patrol.

More good news is that since the mid-20th century the proportion of shark bites leading to fatality has plummeted. This is most likely the result of enormous improvements in beach patrol, emergency and medical response.

A surfer treated by paramedics after a shark bite near Ballina in NSW.

It’s time to move on from shark nets

Debate over shark management is often polarised, pitting human safety against marine conservation. We have brought together expertise from the social sciences, biological sciences and fisheries, to move beyond a “people vs sharks” debate.

There is no reliable evidence that lethal shark management strategies are effective. Many people oppose them, institutions are moving away from them, and threatened species are put at risk.




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The NSW Department of Primary Industries, manager of the shark meshing program, is investing strongly in new non-lethal strategies, including shark tagging, drone and helicopter patrol, personal deterrents, social and biophysical research and community engagement. Our study provides further evidence to support this move.

Investing in lifeguard patrol and emergency response makes good sense. The measures have none of the negative impacts of lethal strategies, and are likely responsible for the improved safety we enjoy today at the beach.The Conversation

More lifeguards would help prevent shark bite.
AAP

Leah Gibbs, Senior Lecturer in Geography, University of Wollongong; Lachlan Fetterplace, Environmental Assessment Specialist, Swedish University of Agricultural Sciences, and Quentin Hanich, Associate Professor, University of Wollongong

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Shark nets and culls don’t necessarily make Australian beaches safer



AAP Image/Sea Shepherd Australia

George Roff, The University of Queensland and Christopher Brown, Griffith University

Most of the 24 million annual visitors to Queensland don’t notice the series of seemingly innocuous yellow buoys at many popular beaches. Beneath the waves lies a series of baited drumlines and mesh nets that aim to make Queensland beaches safe from the ominous threat of sharks.

Earlier this week the Queensland government lost a legal challenge in the Federal Court to continue its shark culling program in protected areas of the Great Barrier Reef, and Fisheries Minister Mark Furner has written to the federal government to request legal changes to keep the program operating.




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Since the Queensland Shark Control Program began in 1962, more than 50,000 sharks have been removed from Queensland beaches at a cost of some A$3 million per year.

While proponents of the program argue the absence of human deaths at beaches with shark control gear is proof of the program’s success, leading shark experts are not so sure.

Can shark control programs control sharks?

Large sharks roam across very large swathes of the ocean.
Photo courtesy of Juan Oliphant, Author provided

Through a series of baited drumlines and mesh nets, shark control programs aim to reduce local populations of large sharks, thereby reducing the number of times humans and shark meet along our coastline.

This approach assumes that the risk of shark bites directly correlates with the number of sharks, yet evidence for this is surprisingly lacking. As part of its safety at the beach program, the Queensland government states that:

Scientists believe that resident sharks may learn that nets and drumlines placed in their local areas represent an obstacle and actively avoid them. This in itself deters and reduces the local population of large sharks in that particular area.




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There are two problems with this logic. First, large apex sharks are not local to individual beaches – satellite tracking data indicates they are highly mobile, moving thousands of kilometres across coasts, reefs and open oceans every year. Sharks tagged in the Whitsundays and Cairns have travelled thousands of kilometres throughout the Great Barrier Reef and beyond.

Second, there’s no clear evidence that sharks avoid drumlines. In fact, baited drumlines and nets actively attract, not deter, large sharks. Similar programs in Hawaii were stopped after an expert review concluded their effectiveness had been overstated.

Do shark control programs make our beaches safer?

Nets do not place an impenetrable barrier between swimmers and sharks. It is true only one death has occurred at beaches with nets and drumlines, but over the same period there were 26 unprovoked non-fatal incidents.

While a reduction in fatalities is often attributed to the success of the shark control program, it could also be that reduced response times and better medical interventions are more successful at saving lives in recent decades.

Culls, nets and baited drumlines are a blunt tool, unable to completely remove the threat of people and sharks meeting on our beaches. Advances in technology and improved education of swimmers may be a more effective way to create safer beaches in Queensland with less ecological cost.

Smart technology

Modern technology allows us to help people avoid sharks, by modifying our behaviour at beaches. Shark-detecting drones are being trialled on New South Wales beaches as part of that state’s A$16 million shark management strategy, allowing for real-time monitoring of popular coastal areas.

Technology like drones and smart buoys are increasingly good at spotting sharks.
Matt Pritchard/Wikimedia Commons

Underwater “clever buoys” installed at NSW beaches in place of baited drumlines allow for real-time detection of sharks using sonar technology, instantly notifying lifeguards of the location, size and direction of sharks. Solar-powered, beach-based shark warning systems operate on remote beaches in Western Australia, cutting the response time between shark sightings and authorities alerting beachgoers from nearly an hour to a matter of minutes.

Education about shark behaviour can also help. Sharks are more active in certain places, like river mouths, and at certain times, such as at dawn and dusk.

In fact, the Queensland government is prioritising research into shark and human behaviours. This research could support education that mitigates the risk of shark interactions, without causing ecological harm.

Earlier this year the Queensland government committed to a A$1 million annual funding boost towards trialling alternative technologies. Adoption of modern innovations and better education for the general public would improve beach safety while avoiding the expensive and ineffective methods of culls, baited drumlines, and nets.

The cost of shark control programs

While we will never have an exact idea of how many sharks used to roam the eastern coastline, historical estimates from shark control programs suggest that the number of large sharks has declined by 72-97% in Queensland and by as much as 82% in NSW since the middle of the 20th century.

Shark nets, culls and baitlines are expensive and ineffective.
Nicole McLachlan, Author provided

NSW and Queensland shark control programs combined have removed more than 1,445 white sharks from the eastern Australian coastline since the middle of the 20th century. To put this in context, current estimates indicate that the eastern population of white sharks sits at around 5,460 individuals in total.




Read more:
Sharks: one in four habitats in remote open ocean threatened by longline fishing


The idea that sharks numbers have boomed in recent years represents a classic example of shifting baseline syndrome. The number of sharks on our beaches may seem to have grown since the late 1990s, but it is a fraction compared with a 1960s baseline, and long-term trends indicate that declines are ongoing.

The number-one priority at our beaches is keeping swimmers safe. At the same time, we have a responsibility to protect threatened and endangered species. There are smarter ways to manage both humans and sharks that will make our beaches safer and help protect sharks.The Conversation

George Roff, Postdoctoral Research Fellow, The University of Queensland and Christopher Brown, Senior Lecturer, School of Environment and Science, Griffith University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Poor Filipino fishermen are making millions protecting whale sharks



Whale sharks at Oslob are now part of a new ecotourism industry.
Wayne Jones, Author provided

Judi Lowe, Southern Cross University

A group of the world’s poorest fishermen are protecting endangered whale sharks from being finned alive at Oslob in the Philippines.

The fishermen have stopped fishing and turned to tourism, feeding whale sharks tiny amounts of krill to draw them closer to shore so tourists can snorkel or dive with them.

Oslob is the most reliable place in the world to swim with the massive fish. In calm waters, they come within 200m of the shore, and hundreds of thousands of tourists flock to see them. Former fishermen have gone from earning just a US$1.40 a day on average, to US$62 a day.




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Our research involved investigating what effect the whale shark tourism has had on livelihoods and destructive fishing in the area. We found that Oslob is one of the world’s most surprising and successful alternative livelihood and conservation projects.

A drone shot of whale shark tourism, about 100 metres from shore. The small boats with one person are feeders. The longer boats are for the tourists swimming with face masks to see the whale sharks.
Luigi Borromeo

Destructive fishing

Illegal and destructive fishing, involving dynamite, cyanide, fish traps and drift gill nets, threatens endangered species and coral reefs throughout the Philippines.

Much of the rapidly growing population depend on fish as a key source of protein, and selling fish is an important part of many people’s income. As well as boats fishing illegally close to shore at night, fishermen use compressors and spears to dive for stingray, parrotfish and octopus. Even the smallest fish and crabs are taken. Catch is sold to tourist restaurants.

Despite legislation to protect whale sharks, they are still poached and finned alive, and caught as bycatch in trawl fisheries. “We have laws to protect whale sharks but they are still killed and slaughtered,” said the mayor of Oslob.

“Finning” is a particularly cruel practice: sharks’ fins are cut off and the shark is thrown back into the ocean, often alive, to die of suffocation. Fins are sold illegally to Taiwan for distribution in Southeast Asia. Big fins are highly prized for display outside shops and restaurants that sell shark fin products.

Whale sharks come close to the coast to feed on krill.
Andre Snoopy Montenegro, Author provided

To protect the whale sharks on which people’s new tourism-based livelihoods depend, Oslob pays for sea patrols by volunteer sea wardens Bantay Dagat. Funding is also provided to manage five marine reserves and enforce fishery laws to stop destructive fishing along the 42km coastline. Villagers patrol the shore. “The enforcement of laws is very strict now,” said fisherman Bobong Lagaiho.

Destructive fishing has declined. Fish stocks and catch have increased and species such as mackerel are being caught for the first time in Tan-awan, the marine reserve where the whale sharks congregate.

The decline in destructive fishing, which in the Philippines can involve dynamite and cyanide, has also meant there are more non-endangered fish species for other fishers to catch.

Strong profits means strong conservation

The project in Oslob was designed by fishermen to provide an alternative to fishing at a time when they couldn’t catch enough to feed their families three meals a day, educate their children, or build houses strong enough to withstand typhoons.

“Now, our daughters go to school and we have concrete houses, so if there’s a typhoon we are no longer afraid. We are happy. We can treat our children to good food, unlike before,” said Carissa Jumaud, a fisherman’s wife.

Creating new forms of income is an essential part of reducing destructive fishing and overfishing in less developed countries. Conservation donors have invested hundreds of millions of dollars in various projects, however research has found they rarely work once funding and technical expertise are withdrawn and can even have negative effects. In one example, micro-loans to fishermen in Indonesia, designed to finance new businesses, were used instead to buy more fishing equipment.

Former fisherman Jesson Jumaud with his daughter Kheny May, who now goes to school. The profits of whale shark tourism mean they now have a brick house, and Jesson was able to buy a motor bike. He can feed their family three times a day with good food.
Judi Lowe, Author provided

In contrast, Oslob earned US$18.4 million from ticket sales between 2012 and 2016, with 751,046 visitors. Fishermen went from earning around US$512 a year to, on average, US$22,699 each.

Now, they only fish in their spare time. These incredible results are the driving force behind protecting whale sharks and coral reefs. “Once you protect our whale sharks, it follows that we an have obligation to protect our coral reefs because whale sharks are dependant on them,” said the mayor.

Feeding whale sharks is controversial, and some western environmentalists have lobbied to shut Oslob down. However, a recent review of various studies on Oslob found there is little robust evidence that feeding small amount of krill harms the whale sharks or significantly changes their behaviour.




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Oslob is that rare thing that conservation donors strive to achieve – a sustainable livelihoods project that actually changes the behaviour of fishermen. Their work now protects whale sharks, reduces reliance on fishing for income, reduces destructive fishing, and increases fish stocks – all while lifting fishermen and their families out of poverty. Oslob is a win-win for fishermen, whale sharks and coral reefs.The Conversation

Judi Lowe, PhD Candidate, Southern Cross University

This article is republished from The Conversation under a Creative Commons license. Read the original article.