A weekly programme featuring a mix of sound-rich stories about science, the environment and medical research, recorded around New Zealand in laboratories and in the field. Our Changing World is broadcast nationwide on Thursday nights on Radio New Zealand National, during Nights with Bryan Crump. It is preceded in this recording by a news and sports bulletin, and weather forecast. In today's programme:
21:06
Uga or Coconut Crab Hunting in Niue
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Uga or coconut crab are hunted in large numbers in Niue but to conserve them the Niuean Government has placed an indefinite ban on their export
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By Justin Gregory
Niueans love the taste of uga, or coconut crab, and the very large, land-living arthropods are hunted across the island. They are also sent in large numbers to Niueans living in New Zealand and Australia – such large numbers that the Niuean Government has placed an indefinite ban on their export.
Brendan Pasisi is the director of Agriculture, Forestry and Fisheries in Niue. He says the introduction of x-ray machines at Niue International Airport has made it possible to accurately count the number of uga being taken out of the country by people wanting to take a tasty treat to offshore friends and family.
Around 10,000 uga left Niue last year in the luggage of locals and tourists. Brendan Pasisi says there are good indicators that this export has had a sizeable impact upon the stock of uga on Niue.
It’s clear that catching larger uga is getting harder and harder, people are having to go further and further into new areas (to catch them). It rings some alarm bells that we need to pay more attention to this.
Coconut crabs reach sexual maturity at around five years of age and can live for up to 60 years, achieving their full size only after the age of 40. Once adult, the crabs only predators are other crabs, dogs, wild pigs and human beings.
Beveridge, or Bev, Mokalei takes tourists on regular uga hunting expeditions on his family land on the south west coast of Niue. He agrees that the number being sent offshore needs to be curbed and says large uga are rarer than before. Bev believes that Niueans naturally limit their take and says that most uga hunting now only happens on special occasions. And it is still possible to find a really big one.
Like Brendan Pasisi, Bev says that hunters need to head further inland and deeper into the bush to find uga but he puts some of the blame for this on the impact of Cyclone Heta in 2004. Niue took the full brunt of this category 5 tropical cyclone and Bev says that vegetation on the coast that normally sheltered the uga was blown away. The crabs were forced to go further inland to find cover.
There are no plans to lift the ban on uga exports any time soon. Brendan Pasisi admits that there was an initial resistance by locals but claims that has been overcome by education about the importance of preserving this famous and very large species of crab.
It’s an iconic species. People come here, they want to go catch one, whether they let it go or not. It means you can get some really good benefits out of maintaining the resource and using it on the island. It’s just unfortunate for our friends and relatives who live abroad. We invite them to come back and enjoy it over here.
Watch a video of uga
Topics: environment
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Tags: Niue, uga, coconut crab, export, hunt
Duration: 12'05"
21:20
Short-tailed Bats and a Conservation Dilemma
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Short-tailed bats are vulnerable to predation by rats - but what is the risk to the bats from toxins being used to protect them from the rats?
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By Alison Ballance
“Introduced predators and competitors have been identified as factors in the decline of New Zealand bat species, so we know that without control of those mammal pests the bats will decline.”
Gillian Dennis, Massey University
Lesser short-tailed bats, or pekapeka-tou-poto, are one of just two endemic bat species found in New Zealand. They’re very vulnerable to predation by rats, so the Department of Conservation (DoC) uses poison bait to manage the rodent problem. However, six years ago then-DoC ranger Gillian Dennis found herself facing a quandary: what about the risk to the bats from the toxins that are meant to protect them from predation? Gillian began a PhD at Massey University to look at the issue, and she tells Alison Ballance that it has been a slow process teasing out the details of this conservation conundrum. However, using a combination of Gillian’s research and on-going monitoring by its own staff, the Department of Conservation has concluded that the benefit to the bats in Pureora Forest from using poison baits to minimise the threat of predation by rats far outweighs the small risk to the bats.
To protect breeding birds and bats by knocking back rat numbers, DoC regularly uses first-generation anti-coagulant poisons, such as diphacinone and pindone, which act to disrupt the blood clotting mechanisms of vertebrates. Standard practice is that the toxin is delivered in hard cereal-based baits that are placed on the ground in bait stations throughout the forest.
It had been suspected that New Zealand bats might be susceptible to toxins but only a single bat had ever been found dead, during the 1980s on the West Coast, next to a cyanide bait used to kill possums.
There are several aspects of the biology of short-tailed bats that might make them especially vulnerable to ground-based poisons. They are opportunistic feeders with a broad eclectic diet, eating everything from insects to fruit and nectar and pollen, such as that from parasitic Dactylanthus flowers, which they help pollinate. They also spend a lot of time foraging on the ground, and are regarded as the most terrestrial of all bat species. They are able to tightly furl their wing membranes out of the way, to ensure they won’t get damaged, and they run around on the ground at night as well as flying.
Gillian also points out that in South America diphacinone is used to control vampire bats, which carry rabies and are considered a health threat. The vampire bats are very sensitive to the toxin and just a small amount is toxic; it’s thought that short-tailed bats could also be as sensitive.
Then, in 2009, Gillian found a number of dead bats next to a roost tree in Pureora Forest, and post-mortems revealed the presence of anti-coagulant toxin in their bodies. DoC immediately stopped rat baiting and the deaths stopped. However, not controlling the rat populations is a conservation conundrum, as bats do much better when there are no rats around.
Gillian says that the story of the greater short-tailed bat highlights the vulnerability of our bat species to rodents. By the early 1960s this species had already been wiped out on mainland New Zealand, most likely due to predation by rats as well as loss of habitat. It survived only on rat-free Great South Cape Island near Stewart Island. When rats were accidentally introduced to the island the bat and two species of endemic native birds were made extinct.
One of the prime questions facing Gillian was do the bats eat the baits directly or are they getting it indirectly through eating insects, such as weta, that have consumed small amounts of bait? She investigated this question firstly with a colony of captive bats at Auckland Zoo, seeing if they approached or ate non-toxic baits. Then she looked at wild bats, filming at non-toxic baits to see what animals, if any, approached or ate the baits. The bats showed almost no interest in the baits and never ate them, but Gillian recorded numbers of weta and other invertebrates – which bats eat – eating the bait. The conclusion was that secondary poisoning rather than direct poisoning is affecting the bats.
The rat control operation carried out at Puroera in the year the bats died used diphacinone presented as a paste, nailed to trees in biodegradable plastic bags. This is not the usual method of presenting toxin, and it was thought it may have resulted in bats or insects having more access than usual to the bait. So the following year the Department of Conservation followed the survival of a well-studied population of short-tailed bats during a more standard rat control operation in Fiordland. The toxin pindone was made up into hard cereal pellets that were contained in bait stations. There was a very high survivorship of bats that year in Fiordland so the following year DoC decided to use the same baiting regime at Pureora.
Gillian was still concerned, however, as earlier research had showed that invertebrates do eat hard cereal baits. So it was still possible for bats to be consuming small quantities of toxin that might not kill them but might still be affecting their health.
To see if these sub-lethal effects were occurring Gillian measured a number of factors in the Pureora bats. Anti-coagulants prolong blood clotting time, so she measured pro-thrombin time which is an early indicator of anti-coagulant poisoning. She assessed the body condition of the bats, and gave them a visual check for bleeding and anaemia. She was particularly interested in pregnant females, as the toxin can cause abortions or birth deformities. As a comparison she also collected all this information from the Fiordland bat population in a year when no rat control was being carried out. While she didn’t find any measurable health effects, tests on bat guano showed that the bats were still ingesting small doses of toxin.
"For now the use of poisons is the best option we have for broad-scale rodent control in native forest,” says Gillian. “And while this might present a risk to bats, we can minimise that risk by delivering baits in bait stations when pest control is done within bat habitat. Other studies that have been done with bats comparing survival in years where there has been pest control to years when there hasn’t been pest control, have shown that bats definitely benefit from having rodent control.”
DoC continues to use poison to control rat populations and closely monitors the survival of the Pureora Forest bat population.
There are three recognised subspecies of short-tailed bats, and a number of distinct populations that are found from Northland right down to Codfish Island/Whenua Hou near Stewart Island. The sub-species each have a different threat status, with the central North island sub-species, which includes the Pureora Forest bats, is listed as ‘At risk – declining’. The southern lesser short-tailed bat is classified as Nationally Endangered while the northern lesser short-tailed bat is in the threat category of Nationally Vulnerable.
Pureora Forest is also home to New Zealand’s second bat species, the long-tailed bat. In the South Island this species is classified as ‘Threatened: Nationally Critical’, while in the North Island its threat risk is ‘Threatened: Nationally Vulnerable.’ Long-tailed bats are considered to be less at risk of poisoning during rodent control operations because they forage on insects on the wing, and they generally forage above the canopy or along forest edges. Gillian says that although long-tailed bats would be less likely to eat invertebrates that had fed on baits laid on or near the ground, further investigation is needed to properly assess the chances of these bats being exposed to poisons.
Topics: science, environment
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Tags: mammals, native bats, short-tailed bats, rodents, rats, conservation, toxins, bats
21:36
A Neutrino Map of the Universe
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University of Canterbury physicist Jenni Adams explains how high-energy neutrinos could help track the origins of cosmic rays.
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By Veronika Meduna Veronika.Meduna@radionz.co.nz
Cosmic rays have energies more than a million times greater than anything achievable by man-made particle accelerators.
They bombard the Earth’s atmosphere all the time, but just where exactly they come from remains a mystery. However, scientists are hopeful that neutrinos may one day help them solve the puzzle.
Cosmic rays are mostly made up of protons, the charged particles in the nuclei of atoms. Because of their charge, the rays’ path through the universe is twisted by magnetic fields, and by the time they enter the Earth’s atmosphere, there’s no way of tracing them back to their origins.
But where ever cosmic rays are generated, there are also high-energy neutrinos.
As their name suggests, neutrinos are neutral or without a charge. They therefore travel through space unimpeded - and University of Canterbury physicist Jenni Adams is now capturing these elusive particles in the hope that they’ll point her back to the birthplace of cosmic rays.
Humankind is trying our very hardest to see how energetic can we accelerate particles so we can see what happens, whereas million times more energetic particles are just being thrown into our atmosphere from somewhere in the universe. So we would like to know where in the universe [something] is accelerating these particles, what has such a huge energy source that it can produce these particles.
Neutrinos are elementary particles, just like electrons and quarks, which means that they can’t be broken down into anything smaller. They have a very tiny mass and no charge.
In our most immediate galactic neighbourhood, the sun is the most prolific producer of neutrinos. They are also emitted during radioactive decay, such as in the centre of our planet or in our bodies, where we each produce about 340 million neutrinos each day.
Right now there’s a billion, or a thousand million, neutrinos passing through every square centimetre of your body every second, without you knowing anything about it.
Whatever their source, they usually travel through the universe unbothered by anything else. Thanks to Ernest Rutherford, we know that atoms are mostly empty space, with the nucleus making up 99.9 per cent of the mass but taking up only a trillionth of the volume.
“And that’s the way a neutrino sees the world,” says Jenni Adams. “Neutrinos have no charge so the only way we can detect them is when they smash into a nucleus, which happens very rarely.”
At that rare moment, the collision produces charged particles that still carry the energy and direction of the neutrino, and they produce light. Over the years, physicists have gone to extreme lengths in their chase of the neutrino, trying to detect the light from neutrino crashes by using large bodies of water, such as Lake Baikal, as detectors.
The largest neutrino detector today is buried deep in the ice at the South Pole. The IceCube detector stretches over a cubic kilometre of ice, studded with watermelon-sized light detectors – and it is here that Jenni Adams and colleagues from Germany and the USA recently detected the first evidence for high-energy cosmic neutrinos.
“Solar neutrino produce just a tiny amount of light. High-energy neutrinos produce much brighter light and we have a condition that eight light detectors must light up at the same time before we can be sure that it was a cosmic neutrino.”
IceCube detects about 100,000 neutrinos per year, but most of them were produced in our own atmosphere when cosmic rays interact with other particles. The high-energy neutrinos the team detected in 2013 clearly came from outside our solar system, and Jenni Adams is keen to see more of them.
Neutrinos are really unique in giving us a view of the universe that’s not possible in any other way. They are messengers, or a tool, and we are looking at a neutrino image of the high-energy universe.
The team recently received a Marsden grant to focus on reconstructing the direction of cosmic neutrinos as a way of investigating the origin and acceleration of nature’s highest-energy particles. You can watch her recent TEDxChristchurch talk below.
Topics: science
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Tags: astronomy, neutrinos, cosmic rays, Antarctica, South Pole, IceCube project, neutrino detector
21:46
How Do Rock Pool Fish Cheat Death?
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Little triplefin fish living in rock pools regularly face not enough or too much oxygen - discovering how they cope could help people suffering from brain hypoxia
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By Alison Ballance
“The changes on a daily basis are absolutely astounding. During the day, temperatures in these rock pools can rocket up to 30° Celsius, whereas normal sea temperatures in the summer are around 21° or 22°. If the rock pools are exposed at night then oxygen levels can plummet to virtually nothing.”
Neill Herbert, University of Auckland
Marine biologists are studying how small fish, known as triplefins, survive low oxygen levels in rock pools. They hope it will provide physiological insights into how human brains cope when starved of oxygen following a stroke or other hypoxic damage. “What can we learn from these fish in order to help prevent hypoxic brain death?” asks Neill.
Neill Herbert and PhD student Tristan McArley from the Institute of Marine Science at the University of Auckland are studying the triplefins at the Leigh Marine Laboratory. The work is part of a collaborative Marsden-funded project into hypoxic brain damage being carried out with Anthony Hickey and Nigel Birch from the School of Biological Sciences and Gillian Renshaw of Griffith University in Australia. “We’re … doing the preliminary work to establish from a whole animal perspective how tough these fish are” says Neill. “My colleagues are looking at the cellular mechanisms and what we might learn from these species that we can adapt [to humans].”
Rock pools are extreme environments. On a sunny day, a rock pool at the top of the shore might be exposed for more than six hours before it is flushed by the incoming tide, and in summer temperatures can quickly climb by eight or more degrees.
At night, oxygen levels in the rock pool drop because “basically everything, including all the algae, is respiring and using up the oxygen” says Tristan.
“So it tends to be the rock pools with lots of algae where oxygen drops really low at night.”
“Effectively these fish are just sat in stagnant water, so it’s a tough environment,” says Neill. “Bear in mind that fish are ectothermic, so at higher temperatures their metabolic rate goes up and they’re churning through oxygen at a faster rate.” This double whammy is of interest as climate change predictions are that water temperatures will go up so the fish will be facing an even greater challenge than they do today.
Although conditions in the rock pools become hypoxic – low in oxygen – at night, the opposite can happen during the day, with the water becoming hyperoxic. “The water is becoming supersaturated with oxygen, above a hundred per cent saturation,” says Tristan “I’ve measured as high as 220 per cent oxygen saturation. And that’s a result of photosynthetic organisms such as algae and plankton photosynthesising and releasing oxygen.” Although not part of their current project Neill says it’s an interesting question as to how the fish cope in hyperoxic conditions as high oxygen levels are considered toxic. And, as well, the fish may have to cope with both extreme hyperoxia and hypoxia within a single day.
Tristan has been putting individual triplefins in small sealed tanks and measuring their physiological responses to different oxygen levels at different temperatures. So far he has measured oxygen consumption using a respirometer, which is an indirect way of measuring metabolic rate. The next stage will involve using a whole body calorimeter to measure the fish metabolism directly. He is comparing five different species – the twister (Bellapiscis medius), the common triplefin (Forsterygion lapillum) and the estuarine triplefin (F. nigripenne) are inter-tidal specialists, while the striped triplefin (F. varium) and mottled triplefin (F. malcolmi) are subtidal species that are usually found between 5-20 metres deep.
Not surprisingly, the inter-tidal species cope much better with low oxygen.
In terms of their ability to survive low oxygen, Neill says that “the Bellapiscis species would be the equivalent of the mountaineering athletes that are climbing Everest … except our fish are doing it without a supplementary oxygen tank.”
Mike Hamlin’s work on training human athletes in hypoxic conditions has previously featured on Our Changing World.
The 2014 Marsden Fund project that this work is part of was awarded in 2014 and is called 'How to avoid brain damage during oxygen deprivation? Intertidal fish provide a unique test model'.
Check out the gallery of triplefin photos (below) from Paul Caiger. Paul is a PhD student at the University of Auckland's Leigh Marine Laboratory, and he is studying triplefins. You can see more of his great photos on Flickr. New Zealand is a centre of diversity for triplefins, with 26 endemic species that are the most abundant of New Zealand’s shallow-water subtidal reef fish.
Listen here to the audio:
Topics: science
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Tags: marine ecosystems, fish, physiology, health, rock pools, triplefins, Marsden Fund
Duration: 15'24"