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



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Dolphins contribute important knowledge about ocean health.
Shutterstock

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.

The ConversationResearch 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.

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



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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.


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


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).


Read more: Explainer: El Niño and La Niña


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.

The ConversationWith 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. The Conversation

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.

How insight into southern Africa’s dolphins is being deepened


Simon Elwen, University of Pretoria

South Africa has a wide range of oceanographic conditions around the coast. As a result, there is a diversity of cetacean species. These are large-bodied, fast-moving top predators like dolphins and whales. Globally, at least a quarter of these species are listed as endangered. Understanding how these species move and live is crucial to understanding their ecological relationships with the environment.

The E3C – Effect of Climate Change on Cetaceans – project looks at the impact climate change has on these species. The Conversation Africa’s energy and environment editor Ozayr Patel spoke to Dr Simon Elwen, a researcher with South Africa’s University of Pretoria working on the project.

Globally, at least a quarter of whale and dolphin species have been listed as endangered. What are the main reasons?

Many of the large whale species and populations that were subjected to commercial whaling have been very slow to recover, notably the Antarctic blue whale and the North Atlantic right whale. But the majority of large whale populations have been increasing slowly over the past few decades. Species are gradually leaving the threatened lists, thanks to wide-ranging international conservation efforts. The most important of these is the end of whaling, showing that stopping directed take – in other words “not killing animals” – is one of the most effective conservation strategies.

But the bad news is that many dolphin and porpoise populations are the ones now facing extirpation. The Maui’s dolphin of New Zealand and the vaquita of the gulf of California are both critically endangered. The baiji, the Chinese river dolphin, has already been declared extinct due almost entirely to habitat loss in the Yangtze River in China.

What is the state of dolphin species around Africa’s coasts? What threats do they face?

In southern Africa most dolphin populations are thought to be fairly healthy. There are five species that are regularly seen from shore, including the Heaviside’s and dusky dolphin on the west coast and the Indo-Pacific bottlenose and Indian Ocean humpback dolphin, which are found to the east of Cape Point in Cape Town. There are several other species that inhabit the shelf and offshore waters, with the common dolphin being one of the few of these regularly seen close to shore, especially along the south-eastern part of the continent. The only species that is currently thought to be of concern is the humpback dolphin, Sousa plumbea.

The humpback dolphin lives along the southern Cape coast and off northern KwaZulu-Natal province. This entire population in South Africa likely numbers less than 1,000 individuals and lives extremely close to shore, where it regularly encounters humans. This results in things like boat traffic, pollution, habitat loss and prey depletion having an impact on these species.

Why are dolphins, in particular, important in the ocean’s ecosystem?

Dolphins and whales are large, highly mobile top predators. They can eat a lot of food and respond quickly to changes in the environment by moving large distances, depending on the species. As large predators, they can have a top-down role in ecosystems, suppressing the numbers of prey animals. What this means is that sometimes species near the bottom of the food chain, like sardine or anchovy, can increase when medium-level predators are removed by top predators such as seals, sharks and dolphins, a result shown in a number of ecosystems globally.

Dolphins and
whales are known to be top predators.

Simon Elwen

What is unique about the South African coast that makes it so diverse?

South Africa’s marine life at all trophic levels is remarkably diverse, thanks largely to the diversity of habitats available around the coast. It ranges from tropical at the Mozambique border, to temperate along the south coast and cool-temperate along the west coast.

From a mammal point of view, the cold waters of the Benguela ecosystem along the west coast provide a link to sub-Antarctic environments, so some species that are usually only found south of 40 degrees of latitude also occur in the Benguela, like southern right whale dolphins and pygmy right whales.

Commercial fishing practices, gill nets and pollution are viewed as the most serious challenge to dolphins. Are these serious problems in African and South African waters?

To the best of my knowledge, bycatch – the unintentional catching of a species – is thankfully not a major problem in South Africa. There is no gill netting in South Africa. Coastal net fisheries are scarce and most of the large-scale commercial fishing activities in South Africa occur in deeper waters than most of our coastal dolphin species occur.

But entanglement in lobster and octopus trap lines is an increasing concern for large whales in coastal waters. Recent data on organic pollutants in dolphins from the east coast suggests that DDT and polychlorinated biphenyls are still a concern, especially for coastal dolphin species like the humpback and bottlenose.

What effect is climate change having on dolphins?

Essentially, assuming no other changes in the ecosystem – which is somewhat naive – we expect a general pole-ward shift in the distribution ranges of most cetacean species. This isn’t likely to be a major problem for animals that move large distances in the relatively uniform and connected environment of the open ocean. But it will potentially have major impacts on some coastal species, especially those that live in habitats that are “dead ends” in this respect (like the southern coast of Africa).

Along the South African coast, several dolphin species live in the Benguela, which is currently thought to be cooling – against the general trend of climate change – due to increased winds and upwelling of cold water. Right now we don’t really know how adaptable these animals are to massive changes in temperature in either direction, should they occur.

What other major conservation tactics are used to help dolphins survive and thrive?

1) Don’t kill them! In any form, including entanglement or bycatch, hunting or pollutants.

2) Stop polluting the oceans – including noise, plastics and organic pollutants.

3) Stop harassing them – obey the laws and use responsible tour operators.

4) Don’t steal their food – eat sustainably caught fish

You have started a project involving citizen scientists. Why have you taken this route?

Citizen science projects have been extremely successful both locally and internationally. Modern communication methods like mobile phones and the internet allow scientists to rapidly communicate with thousands of interested and knowledgeable observers to increase the number of eyes and ears available to collect data. We can’t be everywhere, and our boat surveys and acoustic methods are limited in the amount of area or time they can cover, so we are trying to take advantage of the large number of keen whale and dolphin watchers around our Cape Town’s coasts to report sightings to us.

Remarkably, the area around Cape Town itself has been quite poorly studied by cetacean scientists in the past. So citizen science offers us a potentially powerful route to massively increase the number of data points of dolphin and whale sightings around the area.

The Conversation

Simon Elwen, Research Fellow, Mammal Research Institute, University of Pretoria

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