Tag Archives: threatened species

How the 2016 bleaching altered the shape of the northern Great Barrier Reef

The Conversation

File 20180418 163978 1aql97h.jpg?ixlib=rb 1.1
Staghorn and tabular corals suffered mass die-offs, robbing many individual reefs of their characteristic shapes. ARC Centre of Excellence for Coral Reef Studies/ Mia Hoogenboom

Selina Ward, The University of Queensland

In 2016 the Great Barrier Reef suffered unprecedented mass coral bleaching – part of a global bleaching event that dwarfed its predecessors in 1998 and 2002. This was followed by another mass bleaching the following year.

This was the first case of back-to-back mass bleaching events on the reef. The result was a 30% loss of corals in 2016, a further 20% loss in 2017, and big changes in community structure. New research published in Nature today now reveals the damage that these losses caused to the wider ecosystem functioning of the Great Barrier Reef.

Fast-growing staghorn and tabular corals suffered a rapid, catastrophic die-off, changing the three-dimensional character of many individual reefs. In areas subject to the most sustained high temperatures, some corals died without even bleaching – the first time that such rapid coral death has been documented on such a wide scale.


Read more:
It’s official: 2016’s Great Barrier Reef bleaching was unlike anything that went before


The research team, led by Terry Hughes of James Cook University, carried out extensive surveys during the two bleaching events, at a range of scales.

First, aerial surveys from planes generated thousands of videos of the reef. The data from these videos were then verified by teams of divers in the water using traditional survey methods.

Finally, teams of divers took samples of corals and investigated their physiology in the laboratory. This included counting the density of the microalgae that live within the coral cells and provide most of the energy for the corals.

The latest paper follows on from earlier research which documented the 81% of reefs that bleached in the northern sector of the Great Barrier Reef, 33% in the central section, and 1% in the southern sector, and compared this event with previous bleaching events. Another previous paper documented the reduction in time between bleaching events since the 1980s, down to the current interval of one every six years.

Different colour morphs of Acropora millepora, each exhibiting a bleaching response during mass coral bleaching event. ARC Centre of Excellence for Coral Reef StudiesStudies/ Gergely Torda

Although reef scientists have been predicting the increased frequency and severity of bleaching events for two decades, this paper has some surprising and alarming results. Bleaching events occur when the temperature rises above the average summer maximum for a sufficient period. We measure this accumulated heat stress in “degree heating weeks” (DHW) – the number of degrees above the average summer maximum, multiplied by the number of weeks. Generally, the higher the DHW, the higher the expected coral death.

The US National Oceanic and Atmospheric Administration has suggested that bleaching generally starts at 4 DHW, and death at around 8 DHW. Modelling of the expected results of future bleaching events has been based on these estimates, often with the expectation the thresholds will become higher over time as corals adapt to changing conditions.

In the 2016 event, however, bleaching began at 2 DHW and corals began dying at 3 DHW. Then, as the sustained high temperatures continued, coral death accelerated rapidly, reaching more than 50% mortality at only 4-5 DHW.

Many corals also died very rapidly, without appearing to bleach beforehand. This suggests that these corals essentially shut down due to the heat. This is the first record of such rapid death occurring at this scale.

This study shows clearly that the structure of coral communities in the northern sector of the reef has changed dramatically, with a predominant loss of branching corals. The post-bleaching reef has a higher proportion of massive growth forms which, with no gaps between branches, provide fewer places for fish and invertebrates to hide. This loss of hiding places is one of the reasons for the reduction of fish populations following severe bleaching events.


Read more:
The world’s coral reefs are in trouble, but don’t give up on them yet


The International Union for Conservation of Nature (IUCN), which produces the Red List of threatened species, recently extended this concept to ecosystems that are threatened with collapse. This is difficult to implement, but this new research provides the initial and post-event data, leaves us with no doubt about the driver of the change, and suggests threshold levels of DHWs. These cover the requirements for such a listing.

Predictions of recovery times following these bleaching events are difficult as many corals that survived are weakened, so mortality continues. Replacement of lost corals through recruitment relies on healthy coral larvae arriving and finding suitable settlement substrate. Corals that have experienced these warm events are often slow to recover enough to reproduce normally so larvae may need to travel from distant healthy reefs.

Although this paper brings us devastating news of coral death at relatively low levels of heat stress, it is important to recognise that we still have plenty of good coral cover remaining on the Great Barrier Reef, particularly in the southern and central sectors. We can save this reef, but the time to act is now.

This is not just for the sake of our precious Great Barrier Reef, but for the people who live close to reefs around the world that are at risk from climate change. Millions rely on reefs for protection of their nations from oceanic swells, for food and for other ecosystem services.

The ConversationThis research leaves no doubt that we must reduce global emissions dramatically and swiftly if we are save these vital ecosystems. We also need to invest in looking after reefs at a local level to increase their chances of surviving the challenges of climate change. This means adequately funding improvements to water quality and protecting as many areas as possible.

Selina Ward, Senior Lecturer, School of Biological Sciences, The University of Queensland

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

Leave a comment

Filed under Reblogs

Mike Baird is right, culling sharks doesn’t work – here’s what we can do instead

The Conversation

Jane Williamson

New South Wales is the latest Australian state to hear calls for sharks to be culled, in response to a spate of fatal and non-fatal incidents.

NSW Premier Mike Baird has implemented a new surveillance program, while resisting calls for a cull on the basis that it doesn’t work.

Put simply, there is no scientific support for the concept that culling sharks in a particular area will lead to a decrease in shark attacks and increase ocean safety.

Western Australia tried culling sharks with baited drum lines last year. The tactic did not improve the safety of swimmers, surfers or divers – one of the reasons why scientists actively opposed the cull. A similar long-standing policy in Queensland has shown little evidence of effectiveness.

Born survivors

Sharks have inhabited this planet for more than 400 million years, and have survived five mass extinctions. Earth is now entering its sixth – this time caused by humans – and sharks are at the pointy end, with 90% of the species already considered threatened.

It is not just an issue on NSW’s surf breaks. Humanity’s growing demand for protein has put substantial pressure on oceanic systems, and industrial fishing techniques have have reduced predatory fish populations to less than 10% of their historic numbers. Sharks are especially vulnerable because of their low reproductive rates, slow growth and delayed rates of maturity.

The Indo-Australasian region is recognised as a hot-spot for global shark biodiversity, and in in this region Australia trumps all, with more than 36% of all known shark species living in Australian waters.

What’s more, sharks play a pivotal role within the ecosystems they inhabit. As apex predators, they maintain community structure and biodiversity by regulating predator and prey abundance. Even light fishing pressure such as species-target line fisheries can cause dramatic declines in populations of large coastal sharks. Meanwhile, indirect fishing via shark meshing programs can catch a range of targeted and non-targeted species of sharks.

Blanket measures don’t tend to work well as a rule. AAP Image/Dave Hunt

What would a cull do to sharks and ecosystems?

Shark culling is best thought of as an indiscriminate method of removing sharks from our coastal ecosystems. The WA and Queensland culls have led to the capture and death of many non-targeted sharks. We also know that many shark species do not cope with capture well – a recent Australian study found that 100% of hammerheads caught by line fishing will die of stress within an hour of capture.

Similarly, spinner and dusky sharks have very low survival rates within the first few hours of being hooked, and sharks that are hooked and subsequently released do not necessarily survive.

Hooking in the gut is very common. New South Wales’ flagship threatened aquatic species, the greynurse shark, will most probably die over time if hooked in the gut and then released. Stainless steel hooks do not rust out but become encapsulated in the tissue over time, causing starvation, wasting of the body (known as cachexia), and eventual death.

If we remove sharks as top predators from the ecosystem, the effects will filter down to animals lower down the food chain and cause unexpected changes to ecosystems. We are already seeing such changes in areas where sharks are overfished.

Declines in the number of blacktip sharks in North Carolina in the late 1970s and 1980s caused an increase in the relative abundance of cownose rays and a corresponding decrease in scallops over the ensuing decades. Healthy aquatic ecosystems are typified by a complexity of players in the food chain, and removing such macropredators will result in decreasing ecosystem resilience.

What can we do instead of culling?

Indiscriminately culling sharks is dangerous to marine ecosystems, not to mention expensive and futile. We would be far better off allocating resources to achieving a greater understanding of the ecology and behaviour of these large predators. We can increase knowledge of why and where sharks are likely to attack humans by tagging sharks and following their movements over time, or through genetic studies that can assess effective population sizes.

Current aerial surveys are unlikely to be a successful strategy, however. Scientific analysis has already discredited aerial programs in NSW. Aerial surveys have only a 12.5% success rate in spotting a coastal shark from a fixed-wing aircraft, and a 17.1% success rate in helicopters. As surveys are only done for a few hours per week, and pass over a particular beach in minutes, these patrols can give the public a false sense of security.

Other non-invasive methods of mitigation are currently being developed, including the use of erratic walls of bubbles to deter sharks, and the development of wetsuits and surfboards that sharks are less likely to mistake as prey.

But ultimately, we also need to take personal responsibility, and reduce the likelihood of an attack by not swimming at dawn and dusk, not entering the water at the mouth of estuaries with poor visibility, or in areas of baitfish. After all, even sharks can make mistakes.

The ConversationJane Williamson is Associate Professor in Marine Ecology

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

 

Leave a comment

Filed under Reblogs

The war on feral cats will need many different weapons

The Conversation

Katherine Moseby and John Read

At the Threatened Species Summit last week in Melbourne, Environment Minister Greg Hunt and Threatened Species Commissioner Gregory Andrews declared war on feral cats.

Cats are thought to be a significant contributor to the decline of many threatened species.

Targets in the released threatened species strategy include culling two million cats by 2020, creating new safe havens for threatened species (cat-free islands and sanctuaries), restoring habitat and emergency intervention for our most critically endangered species.

Excluding cats using fencing is an increasingly important tool used to protect threatened species. New exclusion fencing projects received significant funding under the latest strategy.

One of us (Katherine) was lucky enough to be asked to give a presentation at the summit on alternative methods of controlling feral cats. The following article summarises this presentation and highlights the importance of investing in a broad range of cat control methods.

Cats are highly adaptable and highly variable, hence we must continue to search for their Achilles Heel and invest in a wide range of control methods.

Poison baiting

Widespread poison baiting for cats has come a long way in the last few decades with baits such as Eradicat, Curiosity and a new hybrid Eradicat bait being produced.

These baits were developed after years of research conducted initially by the WA Department of Parks and Wildlife and are a soft meat sausage injected with 1080 poison or containing an encapsulated PAPP (Para-aminopropiophenone) pill. These baits have had most success in island eradications and areas where alternative prey are scarce.

In order to kill a cat using poison baits, cats must first find and then ingest the bait.

Unfortunately, cats hunt mainly using sight and sound so finding an inert sausage is a challenge for a cat.

Large numbers of baits must be laid, the usual density is 50 per square km, 10 times higher than the recommended fox baiting density of 5 per square km.

Despite this, many cats fail to find a poison bait before they break down and are no longer toxic. Even when cats do find baits, up to 80% of encounters do not lead to bait ingestion, with cats often ignoring, sniffing or avoiding baits when detected. This is because cats prefer to catch their own prey and will only ingest a bait when hungry.

Non-target uptake can also be high – species such as crows, goannas and quolls can take more than half of laid baits in some instances.

Successful baiting relies on using large densities of baits in areas with low food availability at the right time of year when cats are hungriest. Practitioners are continuing to develop ways of improving bait uptake and several important baiting programs received funding under the Threatened Species Strategy.

Grooming traps

A recent invention removes the need for cats to be hungry to ingest poison. An automated grooming trap squirts a poisonous paste onto the fur of the cat as it walks past a trap station, which it then ingests through compulsive grooming.

Cats are fastidious groomers and pen trials have found 9 out of 10 cats will ingest the paste when it is squirted on their fur. The trap uses an array of sensors to restrict triggering to target species and is currently being developed for field trials around Australia. The grooming traps have a silent activation, can store up to 20 doses and can sit unattended for months at a time.

Although unlikely to be used in broadscale applications, the grooming trap may be critical for protecting small threatened species populations and reducing the impacts of cats in areas where food availability is high.

The grooming trap received much needed funding for further development at the Threatened Species Summit.

Get rid of rabbits, get rid of cats

Widespread indirect methods of reducing cat impacts are also important. Recent work has found that the Rabbit Haemorrhagic Virus Disease (RHVD) (otherwise known as Rabbit Calicivirus) released in 1995 has had a significant positive impact on many desert threatened mammal species.

The range of species such as the Plains Mouse, Dusky Hopping Mouse and Crest-tailed Mulgara has increased by as much as 70 fold in the last 20 years due largely to reduced predation.

RHDV reduced rabbit abundance by up to 95% in the arid zone of Australia which resulted in a natural steep decline in feral cats and foxes, the main predator of rabbits in that region.

The increase in vegetation cover coupled with a massive decline in predation pressure has allowed these native rodents and marsupials to recover.

This would undoubtedly be one of the most significant recoveries of threatened species in Australia. RHVD was relatively cheap, for an initial investment of only $12 million. The agricultural benefit alone totalled more than A$6 billion and the benefits to threatened species have been dramatic but remain unquantified.

Other researchers have also found that by manipulating fire and stock grazing pressure, broadscale indirect benefits can be achieved for threatened species through a reduction in susceptibility to cat predation.

These indirect benefits include making it more difficult for cats to hunt by increasing ground cover, and increasing the productivity of the landscape thereby allowing native species to increase their reproductive output and tolerate higher predation pressure.

Serial cats

All cats are not created equal and recent work in the Flinders Ranges National Park has highlighted the impact of catastrophic cats on reintroduction programs. The reintroduction of the western quoll resulted in nearly a third of the quolls being killed by feral cats.

A quoll killed by a feral cat in the Flinders Ranges, South Australia. Melissa Jensen, Author provided

DNA analysis indicated that quolls were killed by large male cats with most cats responsible for multiple kills (Moseby, Peacock and Read,in press,Biological Conservation). These specialist hunters could be targeted by making their prey toxic, in other words employing toxic Trojans (poison capsules implanted under the skin of prey species where they remain stable) to control specialist cats.

Poison capsules can be implanted under the skin of prey species where they remain stable. If a cat kills and ingests a toxic Trojan, the capsule will break down in the acidic environment of the cat’s stomach releasing the poison and preventing it from killing more individuals. Research is continuing into this poison delivery device which may result in improved targeted cat control.

Get smart

Finally, an ARC linkage grant between the University of New South Wales and Arid Recovery is researching ways to improve the anti-predator behaviour of threatened species.

Our native species did not evolve with introduced cats and foxes and hence may exhibit inappropriate or ineffective anti-predator responses. This prey naivety can lead to high susceptibility even to low levels of exotic predators.

Containing our threatened species on off-shore islands or behind fences is potentially exacerbating the issue as they are not exposed to mammalian predators and can develop “island syndrome” where they fail to recognise predators as dangerous.

The project involves trialling “in situ” predator training where low levels of predators are added to populations of threatened species for extended periods to improve their anti-predator behaviour.

The theory is that natural selection and learning will lead to improved survival and behaviour of successive generations of threatened species.

Whilst this may be a long term endeavour, ways of facilitating co-existence and increasing the resilience of our native species to exotic predators are urgently needed as it is likely that the wily feral cat is here to stay.

The authors would like to acknowledge the following for contributions. Poison Baits – Dave Algar, Michael Johnston, Keith Morris; Grooming traps- Invasive Animals CRC; Broadscale indirect methods – Reece Pedler, Peter Bird, Rob Brandle Rick Southgate, Rachel Paltridge, Sarah Legge; Specialist Hunters – Dave Peacock; Improving Prey Responses – Mike Letnic, Dan Blumstein, Bec West. Ecological Horizons has received funding from Sporting Shooters, FAME, Bush Heritage and SA and Australian Govt for development of Feral Cat Grooming Traps.

The ConversationKatherine Moseby is Associate Lecturer, Ecological and Environmental Sciences at University of AdelaideJohn Read is Associate Lecturer, Ecology and Environmental Sciences at University of Adelaide.

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.


Leave a comment

Filed under Reblogs

Feral feast: cats kill hundreds of Australian animals

The Conversation

By Tim Doherty

Feral cats are estimated to eat tens of millions of native animals each night in Australia. But what kinds of wildlife are they eating? In research published today in the Journal of Biogeography, my colleagues and I show that cats kill hundreds of different kinds of animals, including at least 16 species considered globally threatened.

Feral cats are a serious threat to wildlife globally, contributing to the extinction of numerous birds, mammals and reptiles worldwide. In Australia, cats have been implicated in the extinction of at least 20 mammal species and sub-species, including the lesser bilby and desert bandicoot.

Cats are widespread across the country, so it’s likely that their diet varies according to the local environment and fauna community – which might be affected by many factors, such as the amount of rainfall that an area receives or the native plant life.

Knowing what cats eat can help us decide how best to manage them.

Feline feast

What we found supports earlier research – the feral cat is an opportunistic predator – a generalist carnivore that eats a wide range of wildlife across Australia.

A feral cat degustation.
Tim Doherty, Author provided

Feral cats help themselves to a phenomenal number of species in Australia – 400 different vertebrates. This includes 123 bird species, 157 reptiles, 58 marsupials, 27 rodents, 21 frogs and nine exotic medium- and large-sized mammals. This is more than double the 179 species of animals that cats have been recorded eating on other islands worldwide.

However, this list only includes those species that have been recorded in diet studies, so it’s likely that there are many other species of native animals that cats kill and eat, that we just don’t know about yet.

Feral cats also eat many threatened species in Australia, and have been implicated in the decline of many species including the bilby, numbat, and western ground parrot.

We found that cats kill at least 16 globally threatened species and 12 others classed as near-threatened. This include mammals like the critically endangered mountain pygmy-possum and the brush-tailed bettong (woylie); the endangered northern quoll; as well as the critically endangered Christmas Island whiptail-skink and the vulnerable malleefowl.

Feral cats prey on the endangered northern quoll.
University of Technology Sydney/AAP

Desert desserts

What feral cats eat varies depending on where they are.

In our study, cats ate rodents most often in Australia’s tropical north. They ate medium-sized mammals, such as possums and bandicoots, most frequently in the south-east of the country. Still, cats ate rodents three times more often than other small, carnivorous mammals known as dasyurids (like dunnarts for example).

Cats also ate many mammals from a group that has suffered severe declines and extinctions over the past 200 years. These are known as “critical weight range” mammals, and weigh between 0.35 and 5.5 kilograms. Unfortunately, these mammals make suitable sized prey for many predatory species such as the feral cat and the introduced red fox.

What cats eat also depends on the amount of rainfall an area receives. Cats fed on reptiles most frequently in the central deserts, where rainfall is lowest. These deserts are also the most reptile-rich part of Australia (and the world).

Cats commonly feed on another widespread pest species: rabbits. Where cats ate fewer rabbits, the frequency of small mammals (rodents and dasyurids) in their diet increased. In Australia’s tropical north where rabbits are mostly absent, cats ate the highest frequency of rodents and dasyurids of anywhere in the country.

Rabbits are a major food source for feral cats.
Eddy Van 3000, CC BY-SA

This has important implications for how we manage pest animals. If rabbits are culled from an area, but cats aren’t controlled at the same time, then cats might switch prey and eat more small native mammals.

Past experience tells us how these programs can go awry. For example, when feral cats were eradicated from Macquarie Island in 2000, rabbit numbers exploded because the cats had kept the rabbits in check. Rabbits caused severe damage to the island’s native vegetation before being eradicated themselves in 2014. This suggests that a multi-species approach should be adopted for pest animal control.

Cat control

Large-scale control of feral cats is very difficult, particularly on the mainland, although some programs have been successful on islands. The use of poison baits can reduce cat density, but even low levels of cat predation can exterminate threatened mammal populations, such as when cats killed at least seven bilbies reintroduced outside the Arid Recovery reserve in South Australia.

Predator-free islands and fenced reserves on the mainland are the most effective short-term protection for our threatened mammals. However, fences that exclude predators are very expensive to build, and they require constant monitoring, maintenance and funding.

Non-lethal methods have traditionally been overlooked in the fight against invasive predators, such as the feral cat. However, new research suggests that smart fire and grazing management can help preserve the natural shelters that provide native animals with refuge from predators.

Reducing the impact of feral cats on our native animals is a challenging endeavour, but it is essential in the fight to conserve our unique fauna.

The ConversationThis article was originally published on The Conversation. (Reblogged by permission). Read the original article.

Leave a comment

Filed under Reblogs