These are the plastic items that most kill whales, dolphins, turtles and seabirds

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Lauren Roman, CSIRO; Britta Denise Hardesty, CSIRO; Chris Wilcox, CSIRO, and Qamar Schuyler, CSIRO

How do we save whales and other marine animals from plastic in the ocean? Our new review shows reducing plastic pollution can prevent the deaths of beloved marine species. Over 700 marine species, including half of the world’s cetaceans (such as whales and dolphins), all of its sea turtles and a third of its seabirds, are known to ingest plastic.

When animals eat plastic, it can block their digestive system, causing a long, slow death from starvation. Sharp pieces of plastic can also pierce the gut wall, causing infection and sometimes death. As little as one piece of ingested plastic can kill an animal.

About eight million tonnes of plastic enters the ocean each year, so solving the problem may seem overwhelming. How do we reduce harm to whales and other marine animals from that much plastic?

Like a hospital overwhelmed with patients, we triage. By identifying the items that are deadly to the most vulnerable species, we can apply solutions that target these most deadly items.

Some plastics are deadlier than others

In 2016, experts identified four main items they considered to be most deadly to wildlife: fishing debris, plastic bags, balloons and plastic utensils.

We tested these expert predictions by assessing data from 76 published research papers incorporating 1,328 marine animals (132 cetaceans, 20 seals and sea lions, 515 sea turtles and 658 seabirds) from 80 species.

We examined which items caused the greatest number of deaths in each group, and also the “lethality” of each item (how many deaths per interaction). We found the experts got it right for three of four items.

Film plastics cause the most deaths in cetaceans and sea turtles.
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Flexible plastics, such as plastic sheets, bags and packaging, can cause gut blockage and were responsible for the greatest number of deaths over all animal groups. These film plastics caused the most deaths in cetaceans and sea turtles. Fishing debris, such as nets, lines and tackle, caused fatalities in larger animals, particularly seals and sea lions.

Turtles and whales that eat debris can have difficulty swimming, which may increase the risk of being struck by ships or boats. In contrast, seals and sea lions don’t eat much plastic, but can die from eating fishing debris.

Balloons, ropes and rubber, meanwhile, were deadly for smaller fauna. And hard plastics caused the most deaths among seabirds. Rubber, fishing debris, metal and latex (including balloons) were the most lethal for birds, with the highest chance of causing death per recorded ingestion.

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Read more:
We estimate up to 14 million tonnes of microplastics lie on the seafloor. It’s worse than we thought

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What’s the solution?

The most cost-efficient way to reduce marine megafauna deaths from plastic ingestion is to target the most lethal items and prioritise their reduction in the environment.

Targeting big plastic items is also smart, as they can break down into smaller pieces. Small debris fragments such as microplastics and fibres are a lower management priority, as they cause significantly fewer deaths to megafauna and are more difficult to manage.

Plastic found in the stomach of a fairy prion.
Photo supplied by Lauren Roman

Flexible film-like plastics, including plastic bags and packaging, rank among the ten most common items in marine debris surveys globally. Plastic bag bans and fees for bags have already been shown to reduce bags littered into the environment. Improving local disposal and engineering solutions to enable recycling and improve the life span of plastics may also help reduce littering.

Lost fishing gear is particularly lethal. Fisheries have high gear loss rates: 5.7% of all nets and 29% of all lines are lost annually in commercial fisheries. The introduction of minimum standards of loss-resistant or higher quality gear can reduce loss.

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Read more:
How to get abandoned, lost and discarded ‘ghost’ fishing gear out of the ocean

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Other steps can help, too, including

• incentivising gear repairs and port disposal of damaged nets

• penalising or prohibiting high-risk fishing activities where snags or gear loss are likely

• and enforcing penalties associated with dumping.

Outreach and education to recreational fishers to highlight the harmful effects of fishing gear could also have benefit.

Balloons, latex and rubber are rare in the marine environment, but are disproportionately lethal, particularly to sea turtles and seabirds. Preventing intentional balloon releases and accidental release during events and celebrations would require legislation and a shift in public will.

The combination of policy change with behaviour change campaigns are known to be the most effective at reducing coastal litter across Australia.

Reducing film-like plastics, fishing debris and latex/balloons entering the environment would likely have the best outcome in directly reducing mortality of marine megafauna.

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Read more:
Newly hatched Florida sea turtles are consuming dangerous quantities of floating plastic

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Lauren Roman, Postdoctoral Researcher, Oceans and Atmosphere, CSIRO; Britta Denise Hardesty, Principal Research Scientist, Oceans and Atmosphere Flagship, CSIRO; Chris Wilcox, Senior Principal Research Scientist, CSIRO, and Qamar Schuyler, Research Scientist, Oceans and Atmospheres, CSIRO

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

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Sparkling dolphins swim off our coast, but humans are threatening these natural light shows

Dean Cropp, Author provided

Dr Vanessa Pirotta, Macquarie University

It was 2 am on a humid summer’s night on Sydney’s coast. Something in the distance caught my eye – a pod of glowing dolphins darted towards the bow of the boat. I had never seen anything like it before. They were electric blue, trailing swaths of light as they rode the bow wave.

It was a stunning example of “bioluminescence”. The phenomenon is the result of a chemical reaction in billions of single-celled organisms called dinoflagellates congregating at the sea surface. These organisms are a type of phytoplankton – tiny microscopic organisms many sea creatures eat.

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Dinoflagellates switch on their bioluminescence as a warning signal to predators, but it can also be triggered when they’re disturbed in the water – in this case, by the dolphins.

You can see marine bioluminescence from land in Australia. Places like Jervis Bay and Tasmania are renowned for such spectacles.

But this dazzling night-time show is under threat. Light pollution creates brighter nights and disrupts ecological rhythms along the coast, such as breeding and feeding patterns. With so much human activity close to the shore and at sea, how much longer can we continue to enjoy this natural light show?

Lighting up the world has an ecological price

Light pollution is a well-known problem for inland ecosystems, particularly for nocturnal species.

In fact, a global study published earlier this year identified light pollution as an extinction threat to land bioluminescent species. The study surveyed firefly experts, who considered artificial light to be the second greatest threat to fireflies after habitat destruction.

Artificial light is one of the biggest threats fireflies face.
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At sea, artificial light pollution enters the marine environment temporarily (lights from ships and fishing activities) and permanently (coastal towns and offshore oil platforms). To make matters worse, light from cities can extend further offshore by scattering into the atmosphere and reflecting off clouds. This is known as artificial sky glow.

For organisms with circadian clocks (day-night sleep cycles), this loss of darkness can have damaging effects.

Bioluminescence in Sydney in the wake of the boat the author was on.
Vanessa Pirotta, Author provided

For example it can disrupt animal metabolism, which can lead to weight gain. Artificial light can also change sea turtle nesting behaviour and can disorientate turtle hatchlings when trying to get to sea, lowering their chances of survival.

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Read more:
Lights out! Clownfish can only hatch in the dark – which light pollution is taking away

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It can also disorientate the foraging of fish communities; alter predatory fish behaviour (such as in Yellowfin Bream and Leatherjacks) leading to increased predation in artificial light at night; cause reproductive failure in clownfish; and change the structural composition of marine invertebrate communities.

What are lights along the coast doing to bioluminescent species?
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For zooplankton – a vital species for a range of bigger animals – artificial light disrupts their “diel vertical migration”. This term refers to the movement of zooplankton from the depths of the ocean where they spend the day to reduce fish predation, rising to the surface at night to feed.

What does this mean for bioluminescent species?

Increased exposure to artificial light due to human activities, such as growing cities and increased global shipping movement, may disrupt when and where bioluminescent species hang out.

In turn, this may influence where predators move, leading to disruptions in the marine food web, potentially changing the dynamics of energy transfer efficiency between marine species.

Bioluminescence draws tourists and photographers in Tasmania.
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Bioluminescence usually serves as a communication function, such as to warn off predators, attract a mate or lure prey. For many species, light pollution in the ocean may compromise this biological communication strategy.

And for light-producing organisms such as dinoflagellates, excess artificial light may reduce the effectiveness of their bioluminescence because they won’t shine as bright, potentially increasing their risk of being eaten.

Have you read Julia Baird’s new book? It’s a great introduction to the science behind the ephemeral bioluminescence at sea.
HarperCollins Australia

A 2016 study in the Arctic revealed the critical depth where atmospheric light dims to darkness, and bioluminescence from organisms becomes dominant, was approximately 30 metres below the sea surface.

This means any change to light in the Arctic influences when marine organisms rise to the surface. If there is too much light, these organisms remain deeper for longer where it’s safe – reducing their potential feeding time.

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Read more:
Bright city lights are keeping ocean predators awake and hungry

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What can we do?

Understanding the level at which artificial light penetrates the ocean is tricky, especially so when dealing with mobile sources of light pollution such as ships, which are becoming an almost permanent fixture in some areas of the ocean.

Bioluminescence usually serves as a communication function, such as to warn off predators.
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Pockets of darkness still remain in our oceans. But they are becoming rarer, making light pollution a serious global threat to marine life.

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The glowing ghost mushroom looks like it comes from a fungal netherworld

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The spectacle of glowing dolphins should serve as a timely reminder of our need to conserve the darkness we have left.

Simple steps at home such as switching off lights and reducing unnecessary outdoor lighting, especially if you live near the ocean, is a step in the right direction to doing your bit for nocturnal species.

Dr Vanessa Pirotta, Marine scientist and science communicator, Macquarie University

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

Whales and dolphins found in the Great Pacific Garbage Patch for the first time

Adult and infant sperm whales have been spotted in the Great Pacific Garbage Patch.
Inf-Lite Teacher/Flickr, CC BY-SA

Chandra Salgado Kent, Edith Cowan University

Scientific research doesn’t usually mean being strapped in a harness by the open paratroop doors of a Vietnam-war-era Hercules plane. But that’s the situation I found myself in several years ago, the result of which has just been published in the journal Marine Biodiversity.

As part of the Ocean Cleanup’s Aerial Expedition, I was coordinating a visual survey team assessing the largest accumulation of ocean plastic in the world: the Great Pacific Garbage Patch.

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The ocean’s plastic problem is closer to home than scientists first thought

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When the aircraft’s doors opened in front of me over the Pacific Ocean for the first time, my heart jumped into my throat. Not because I was looking 400m straight down to the wild sea below as it passed at 260km per hour, but because of what I saw.

This was one of the most remote regions of the Pacific Ocean, and the amount of floating plastic nets, ropes, containers and who-knows-what below was mind-boggling.

However, it wasn’t just debris down there. For the first time, we found proof of whales and dolphins in the Great Pacific Garbage Patch, which means it’s highly likely they are eating or getting tangled in the huge amount of plastic in the area.

The Great Pacific Garbage Patch

The Great Pacific Garbage Patch is said to be the largest accumulation of ocean plastic in the world. It is located between Hawaii and California, where huge ocean currents meet to form the North Pacific subtropical gyre. An estimated 80,000 tonnes of plastic are floating in the Great Pacific Garbage Patch.

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Our overall project was overseen and led by The Ocean Cleanup’s founder Boyan Slat and then-chief scientist Julia Reisser. We conducted two visual survey flights, each taking an entire day to travel from San Francisco’s Moffett Airfield, survey for around two hours, and travel home. Along with our visual observations, the aircraft was fitted with a range of sensors, including a short-wave infrared imager, a Lidar system (which uses the pulse from lasers to map objects on land or at sea), and a high-resolution camera.

Both visual and technical surveys found whales and dolphins, including sperm and beaked whales and their young calves. This is the first direct evidence of whales and dolphins in the heart of the Great Pacific Garbage Patch.

Mating green turtles in a sea of plastics.
photo by Chandra P. Salgado Kent, Author provided

Plastics in the ocean are a growing problem for marine life. Many species can mistake plastics for food, consume them accidentally along with their prey or simply eat fish that have themselves eaten plastic.

Both beaked and sperm whales have been recently found with heavy plastic loads in their stomachs. In the Philippines, a dying beaked whale was found with 40kg of plastic in its stomach, and in Indonesia, a dead sperm whale washed ashore with 115 drinking cups, 25 plastic bags, plastic bottles, two flip-flops, and more than 1,000 pieces of string in its stomach.

The danger of ghost nets

The most common debris we were able to identify by eye was discarded or lost fishing nets, often called “ghost nets”. Ghost nets can drift in the ocean for years, trapping animals and causing injuries, starvation and death.

Crew sorts plastic debris collected from the Great Pacific Garbage Patch on a voyage in July 2019.
EPA/THE OCEAN CLEANUP

Whales and dolphins are often found snared in debris. Earlier this year, a young sperm whale almost died after spending three years tangled in a rope from a fishing net.

During our observation we saw young calves with their mothers. Calves are especially vulnerable to becoming trapped. With the wide range of ocean plastics in the garbage patch, it is highly likely animals in the area ingest and become tangled in it.

It’s believed the amount of plastics in the ocean could triple over the next decade. It is clear the problem of plastic pollution has no political or geographic boundaries.

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There are some single-use plastics we truly need. The rest we can live without

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While plastics enter the sea from populated areas, global currents transport them across oceans. Plastics can kill animals, promote disease, and harm the environment, our food sources and people.

The most devastating effects fall on communities in poverty. New research shows the Great Pacific Garbage Patch is rapidly growing, posing a greater threat to wildlife. It reinforces the global movement to reduce, recycle and remove plastics from the environment.

But to really tackle this problem we need creative solutions at every level of society, from communities to industries to governments and international organisations.

To take one possibility, what if we invested in fast-growing, sustainably cultivated bamboo to replace millions of single-use plastics? It could be produced by the very countries most affected by this crisis: poorer and developing nations.

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Designing new ways to make use of ocean plastic

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It is only one of many opportunities to dramatically reduce plastic waste, improve the health of our environments and people, and to help communities most susceptible to plastic pollution.

Chandra Salgado Kent, Associate Professor, School of Science, Edith Cowan University

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

It’s teamwork: how dolphins learn to work together for rewards

Two bottlenose dolphins (Tursiops truncatus) cooperate in a button-pressing task requiring precise behavioural synchronization.
Dolphin Research Center, Author provided

Stephanie King, University of Western Australia

Cooperation can be found across the animal kingdom, in behaviours such as group hunting, raising of young, and driving away predators.

But are these cooperating animals actively coordinating their behaviour, or are they simply acting individually to accomplish the same task at the same time?

In a study, published today in Proceedings of the Royal Society B, we showed that bottlenose dolphins actively coordinate their behaviours. That is, they can learn to work together and synchronise their actions to solve a cooperation task and receive a reward.

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Male dolphins use their individual ‘names’ to build a complex social network

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Testing teamwork

For this study, conducted at the Dolphin Research Center in the Florida Keys, we created a task in which pairs of dolphins had to swim across a lagoon and each press their own underwater button at the same time (within a 1-second time window).

Each trial began with both dolphins and their respective trainers located at the opposite side of the lagoon from the buttons, about 11 metres away. The trainers would either both give a “press the button” hand signal at the same time, or one trainer would give the signal first, while the second trainer asked her dolphin to wait up to 20 seconds before giving the signal.

If the dolphins pressed their buttons at the same time, a computer played a “success” sound, and the dolphins returned to their trainers for fish and social praise.

If the dolphins pressed their buttons at different times, a “failure” sound was played and the trainers moved on to the next trial.

The strict timing requirement meant they had to work together. If their goal was simply “press my button”, then when they were sent at different times, they would press at different times. To succeed, they had to understand their goal as “press the buttons together”.

The question, then, was whether the dolphin sent first would wait for the other dolphin before pressing its button, and whether they could figure out a way to coordinate precisely enough to press simultaneously.

Two bottlenose dolphins (Tursiops truncatus) cooperate in a button-pressing task requiring precise behavioural synchronisation.
Dolphin Research Center, Author provided

Swim fast, or coordinate?

We found that the dolphins were able to work together with extreme precision even when they had to wait for their partner. Interestingly, their behavioural strategies and the coordination between them changed as they learned the task.

Keep in mind that the dolphins had to figure out that this was a cooperative task. There was nothing about the situation that told them in advance that the buttons had to be pressed at the same time.

To help them learn, we started by sending them simultaneously and gradually increased the timing difference between them.

When one dolphin figured out the game first, if their partner was sent first on a particular trial, they knew that the partner (who had not figured out the game) was not going to wait.

So in the early phases, we found that many successes were achieved not by the first dolphin waiting, but by the second dolphin swimming extremely fast to catch up.

But once both animals understood the task, this behaviour disappeared and the timing of their button presses became extremely precise (with the time difference between button presses averaging just 370 milliseconds).

This shows that both partners now understood that they didn’t need to swim fast to succeed; instead, they needed to synchronise their actions.

Wait for it… a delayed start but the dolphins still work together.

Synchrony in the wild

In the wild, dolphins synchronise their behaviour in several contexts. For example, mothers and calves will surface and breathe at the same time, and males in alliances will perform the same behaviours at the same time in coordinated displays.

Triple synchronous dive by a trio of allied male bottlenose dolphins (Tursiops aduncus) in Shark Bay, Western Australia.
Stephanie King / The Dolphin Alliance Project, Author provided

The synchrony in these displays can be remarkably precise, and is thought to actively promote cooperation between partners.

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Tackling the kraken: unique dolphin strategy delivers dangerous octopus for dinner

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The results of our study suggest that this behavioural synchronisation that dolphins show in the wild may not be a hardwired response to a specific context, but may in fact be a generalised ability that they can apply to a variety of situations.

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Kelly Jaakkola, director of research at the Dolphin Research Center, contributed to this research and this article. She can be contacted at kelly@dolphins.org.

Stephanie King, Branco Weiss Research Fellow, University of Western Australia

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

What whales and dolphins can tell us about the health of our oceans

Dolphins contribute important knowledge about ocean health.
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Stephanie Plön, Nelson Mandela University

From the poles to the equator, marine mammals such as seals, dolphins and whales, play an important role in global ecosystems as apex predators, ecosystem engineers and even organic ocean fertilisers. The ocean off the coast of South Africa is home to a high diversity of these mammals and is recognised as a global marine biodiversity hotspot.

Marine mammals are often referred to as “sentinels” of ocean health. Numerous studies have explored the effects of both noise and chemical pollution, habitat degradation, changes in climate and food webs on these marine apex predators. Yet the interplay of these factors isn’t well understood.

Our research on the unfortunate dolphins incidentally caught in shark nets off South Africa’s KwaZulu-Natal coast has helped fill in some of the gaps. By assessing the health of these dolphins we have provided valuable baseline information on conditions affecting coastal dolphin populations in South Africa. This is the first systematic health assessment in incidentally caught dolphins in the Southern Hemisphere.

But to gain a fuller picture of the health of marine mammals in these waters I am now combining this contemporary field research with historical data, like the collection at the Port Elizabeth Museum Bayworld.

The combination of data on diet, reproduction, population structure and health helps us gain a better understanding of the pressures and changes these apex predator populations face. And it helps us understand it in relation to global change, including both climate change and pressures brought about by human behaviour.

My research sheds light on multiple factors: pollutant levels, parasites, and availability of prey, all have an impact on individuals as well as populations.

Understanding the health of these animals also gives us insight into the state of the world’s oceans. This is relevant because oceans affect the entire ecosystem including food security, climate and people’s health. This degree of connectedness is highlighted by recent discoveries about how whales act as ecosystem engineers.

The accumulation of this knowledge is important because the planet’s oceans aren’t being protected. Recent popular documentaries such as “Sonic Sea” and “Plastic Ocean” have highlighted their exploitation and pollution.

What’s missing

Without baseline knowledge it’s challenging to establish the potential effects that new anthropogenic developments (those caused by human behaviour) have on local whale and dolphin populations.

For example, we know that whales are sensitive to shipping noise, so what potential impact could a new deep water port have on mothers and their calves? Could it drive them away from these nursery areas, or could it lead to an increased risk of whales and ships colliding? To answer this and monitor the change that a new port brings with it, we are investigating the soundscape of two bays in the Eastern Cape (one with a new port, one without) in parallel with baleen whale mother-calf behaviour.

Another example is understanding how changes in the Sardine run over the past 15 years have affected the diets of these mammals. The Sardine run is an annual phenomenon when large shoals of Sardine migrate northwards along the coast into KwaZulu-Natal waters to spawn. Using long-term data and samples from the Port Elizabeth Museum research collection, we have been able to establish that over the the past 20 or so years the main predator in the Sardine run – the long-beaked common dolphin – has shifted its diet to mackerel. Although such changes in diet can have potential impacts on the health of the dolphins, parallel investigations on the trophic level these animals feed at (using isotope data from teeth) and the body condition of the dolphins (using long-term data on blubber thickness), indicated no adverse effects to the dolphins.

Our analysis highlights how marine mammals may be used as indicators of environmental change and why research is important.

Finding answers to intricate questions on environmental change is not always easy. But a better understanding and knowledge of the environment these animals live in has to be incorporated into studies contributing to their conservation and management. Such studies are becoming increasingly relevant as they highlight the fast degradation of the marine environment.

For example, a recent study identified antibiotic resistant bacteria in both sea water samples and exhaled breath samples from killer whales. This suggests that the marine environment has been contaminated with human waste which in turn has significant medical implications for humans.

Gaining such information is particularly important given the rapid changes taking place in the oceans, such as those on South Africa’s southern and eastern coastline. This includes increasing coastal development, new deep water ports being built or expanded, and parts of the deep sea being explored for oil and gas.

To assess these changes and what they mean for the environment, baseline studies need to be carried out so that potential effects can be assessed. Whales and dolphins are increasingly being recognised as indicators of ocean health in this endeavour.

And a continuation of the research we did on dolphins caught in nets will help document the cyclic changes that can be seen as normal variation in a population. This could prove important for assessing future catastrophic events, such as the Deep Horizon oil spill.

What next

The oceans absorb over 25% of the world’s carbon pollution as well as heat generated by global warming. They also produce at least 50% of the planet’s oxygen, and are home to 80% of all life on earth. Yet only 5% of this vital component of our planet has been explored.

Research on whales and dolphins contributes important knowledge about ocean health. Historical data increasingly provides a guideline to teasing out natural variations in populations and assessing the contribution that multiple factors have on these animals. In time, this will ensure that policy makers are being given sound scientific information. It will also provide us with a good barometer of the overall health of our oceans.

Stephanie Plön, Researcher, Earth Stewardship Science Research Institute, Nelson Mandela University

This article was originally published on The Conversation. Read the original article.

El Niño in the Pacific has an impact on dolphins over in Western Australia

Leaping bottlenose dolphins.
Kate Sprogis/MUCRU, Author provided

Kate Sprogis, Murdoch University; Fredrik Christiansen, Murdoch University; Lars Bejder, Murdoch University, and Moritz Wandres, University of Western Australia

Indo-Pacific bottlenose dolphins (Tursiops aduncus) are a regular sight in the waters around Australia, including the Bunbury area in Western Australia where they attract tourists.

The dolphin population here, about 180km south of Perth, has been studied quite intensively since 2007 by the Murdoch University Cetacean Unit. We know the dolphins here have seasonal patterns of abundance, with highs in summer/autumn (the breeding season) and lows in winter/spring.

But in winter 2009, the dolphin population fell by more than half.

A leaping bottlenose dolphin.
Kate Sprogis/MUCRU, Author provided

This decrease in numbers in WA could be linked to an El Niño event that originated far away in the Pacific Ocean, we suggest in a paper published today in Global Change Biology. The findings could have implications for future sudden drops in dolphin numbers here and elsewhere.

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Read more: Tackling the kraken: unique dolphin strategy delivers dangerous octopus for dinner

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A Pacific event

The El Niño Southern Oscillation (ENSO) results from an interaction between the atmosphere and the tropical Pacific Ocean. ENSO periodically fluctuates between three phases: La Niña, Neutral and El Niño.

During our study from 2007 to 2013, there were three La Niña events. There was one El Niño event in 2009, with the initial phase in winter being the strongest across Australia.

The blue vertical line shows the decline in dolphin numbers (d) during the 2009 El Niño event.
Kate Sprogis, Author provided

Coupled with El Niño, there was a weakening of the Leeuwin Current, the dominant ocean current off WA. There was also a decrease in sea surface temperature and above average rainfall.

ENSO is known to affect the strength of the south-ward flowing Leeuwin Current.

During La Niña, easterly trade winds pile warm water on the western side of the Pacific Ocean. This westerly flow of warm water across the top of Australia through the Indonesian Throughflow results in a stronger Leeuwin Current.

During El Niño, trade winds weaken or reverse and the pool of warm water in the Pacific Ocean gathers on the eastern side of the Pacific Ocean. This results in a weaker Indonesian Throughflow across the top of Australia and a weakening in strength of the Leeuwin Current.

A chart showing sea surface temperature (SST) anomalies off Western Australia. Note the extremes for the moderate El Niño in 2009 (blue rectangle), and the strong La Niña in 2011 (red rectangle)
Moritz Wandres, Author provided

The strength and variability of the Leeuwin Current coupled with ENSO affects species biology and ecology in WA waters. This includes the distribution of fish species, the transport of rock lobster larvae, the seasonal migration of whale sharks and even seabird breeding success.

The question we asked then was whether ENSO could affect dolphin abundance?

What happened during the El Niño?

These El Niño associated conditions may have affected the distribution of dolphin prey, resulting in the movement of dolphins out of the study area in search of adequate prey elsewhere.

A surfacing bottlenose dolphin.
Kate Sprogis/MUCRU, Author provided

This is similar to what happens for seabirds in WA. During an El Niño event with a weakened Leeuwin Current, the distribution of prey changes around seabird’s breeding colonies resulting in a lower abundance of important prey species, such as salmon.

This in turn negatively impacts seabirds, including a decrease in reproductive output and changes in foraging.

In southwestern Australia, the amount of rainfall is strongly connected to sea surface temperature. When the water temperature in the Indian Ocean decreases, the region receives higher rainfall during winter.

High levels of rainfall contribute to terrestrial runoff and alters freshwater inputs into rivers and estuaries. The changes in salinity influences the distribution and abundance of dolphin prey.

This is particularly the case for the river, estuary, inlet and bay around Bunbury. Rapid changes in salinity during the onset of El Niño may have affected the abundance and distribution of fish species.

In 2009, there was also a peak in strandings of dead bottlenose dolphins in WA (between 1981-2010), but the cause of this remains unknown.

Of these strandings, in southwest Australia, there was a peak in June that coincided with the onset of the 2009 El Niño.

Specifically, in the Swan River, Perth, there were several dolphin deaths, with some resident dolphins that developed fatal skin lesions that were enhanced by the low-salinity waters.

What does all this mean?

Our study is the first to describe the effects of climate variability on a coastal, resident dolphin population.

A group of bottlenose dolphins.
Kate Sprogis/MUCRU, Author provided

We suggest that the decline in dolphin abundance during the El Niño event was temporary. The dolphins may have moved out of the study area due to changes in prey availability and/or potentially unfavourable water quality conditions in certain areas (such as the river and estuary).

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Read more: Explainer: El Niño and La Niña

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Long-term, time-series datasets are required to detect these biological responses to anomalous climate conditions. But few long-term datasets with data collected year-round for cetaceans (whales, dolphins and porpoises) are available because of logistical difficulties and financial costs.

Continued long-term monitoring of dolphin populations is important as climate models provide evidence for the doubling in frequency of extreme El Niño events (from one event every 20 years to one event every ten years) due to global warming.

With a projected global increase in frequency and intensity of extreme weather events (such as floods, cyclones), coastal dolphins may not only have to contend with increasing coastal human-related activities (vessel disturbance, entanglement in fishing gear, and coastal development), but also have to adapt to large-scale climatic changes.

Kate Sprogis, Research associate, Murdoch University; Fredrik Christiansen, Postdoctoral Research Fellow, Murdoch University; Lars Bejder, Professor, Cetacean Research Unit, Murdoch University, Murdoch University, and Moritz Wandres, Oceanographer PhD Student, University of Western Australia

This article was originally published on The Conversation. Read the original article.

Tackling the kraken: unique dolphin strategy delivers dangerous octopus for dinner

Kate Sprogis, Murdoch University and David Hocking, Monash University

For wild predators, catching, killing and eating prey can sometimes be a risky business. We can see this on the African savannah, where a well-aimed kick from a zebra can spell trouble for a hungry lion.

But the same can also be true in the ocean, where some prey types are far from helpless seafood.

In particular, a large octopus can be a risky prey for predators to tackle. This is especially so for marine mammals, such as dolphins, which don’t have hands to help them keep control of this clingy, eight-armed prey.

Our new research highlights the development of complex behaviours that allow dolphins to eat octopus, thereby improving their ability to survive and reproduce.

It’s another example of a strategy that helps to drive the success of dolphins in coastal environments around Australia.

Dangers of eating octopus

In 2015 an adult male bottlenose dolphin was found dead on a beach in Bunbury, southwest Australia.

Wild dolphins face many threats in today’s oceans, yet it was a gruesome surprise when we found octopus arms hanging out of the stranded dolphin’s mouth.

An examination by a veterinary pathologist revealed that this otherwise healthy dolphin, known as “Gilligan” to the research team, had suffocated to death while trying to eat an octopus.

As strange as it sounds, this is not the first recorded case of a dolphin choking to death on an octopus in southwest Australia. There have also been several observations from around the world of dolphins facing difficulties while tackling octopus.

So what is it that makes octopus so hard to handle?

Octopus can grow quite large, with some species bearing muscular arms reaching more than a metre long. Each of their eight arms have powerful suction cup-like suckers on the underside, which are normally used to help octopus capture their own prey while crawling along the seafloor.

But when attacked by a dolphin, these suckered arms also help octopuses to defend themselves by latching onto the dolphin’s smooth skin.

When this happens, dolphins have been observed leaping rapidly out of the water before crashing onto the surface in an attempt to dislodge an octopus.

The real problem is that these arms stay active even after an octopus has been mortally wounded. So even while a dead octopus is being processed, the suckers may still be able to find something to stick onto.

Australia’s octopus-eating dolphins

But we’ve observed some wild bottlenose dolphins that have found a way to handle and feed on octopus, with the findings published today in Marine Mammal Science.

These observations were made between March 2007 and August 2013, while we were conducting boat surveys to study the dolphins living off Bunbury’s coast.

Over this time, we observed 45 octopus handling events by dolphins. Most were performed by adults (male and female), although we also saw four juveniles and two calves performing this behaviour.

Bottlenose dolphin tossing octopus off Bunbury, Western Australia.

During these events, dolphins were observed shaking and tossing octopus around at the water’s surface. In some instances, the prey was gripped in the teeth before being slapped down onto the water.

This likely helped both to kill the octopus and to tear it into smaller, more digestible pieces. In other instances, the octopus was tossed across the surface of the water before being recaptured and tossed again.

By tossing the octopus across the water, dolphins avoid letting the octopus latch onto their bodies. This behaviour also likely assists in wearing out the octopus’s reflex responses that make the suckered arms so dangerous to swallow.

Once the prey has been battered and tenderised enough that the arms are unresponsive, it is then safe for the dolphins to proceed with swallowing their catch.

It’s quite a process the dolphins have developed to deal with the octopus. They have a short, fused neck which means they have to arch their whole body to toss their prey out of the water.

Given the danger, why eat octopus at all?

When we looked closely at when these observations were made, we found that the dolphins were targeting octopus more frequently over winter and spring. These cooler times of year are also the octopus’s breeding time.

Octopus are semelparous, which means they slowly become weaker and then die in the weeks after they finish breeding. It is possible that as they become weaker, they also become easier to catch, making them a relatively easy meal for any opportunistic dolphins swimming by.

At the end of the day, octopus are just part of the broad diet eaten by wild bottlenose dolphins.

Dolphins have also been found to use several other highly specialised feeding behaviours, including processing cuttlefish by popping out the cuttlebone, stranding themselves while hunting fish, and using a marine sponge as a tool to probe the seafloor while searching for buried fish hiding in the sediment.

Octopus shaking and tossing is yet another example that illustrates how intelligent and adaptable these charismatic marine predators are.

Kate Sprogis, Research associate, Murdoch University and David Hocking, Research associate, Monash University

This article was originally published on The Conversation. Read the original article.

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