Ecology

“Here in Norway, red foxes (Vulpes vulpes) are all over the place. But Arctic foxes (Vulpes lagopus) — the fluffy white cousins of red foxes — survive only high up in the mountains, and meeting one is a really rare occurrence.Researchers estimated that, in 2000, just 40 to 60 Arctic foxes remained in Norway and Sweden. A combination of factors probably explains why the population has collapsed since the start of the twentieth century. For example, fur hunting occurred until the 1930s, and reductions in the numbers of lemmings — a crucial prey animal for the foxes — have also had an impact. Moreover, Arctic foxes live in a fragmented mountain habitat, and the construction of roads has increased the risk of the animals being killed as they disperse from one area to another.Steps taken by the Norwegian Institute for Nature Research are starting to turn things around. These include supplementary feeding of the wild population and running a captive breeding station. Now there are an estimated 560 Arctic foxes across Norway, Sweden and Finland.We have 15 foxes at our captive breeding station near Oppdal in Norway’s Trøndelag county. In this photo, I’m crouching down helping a colleague to transfer a pup from a trap into a handling bag for a health check. We try not to handle them more than we have to, and we prepare them as much as possible for life in the wild. As cute as they are, they are not tame. The 464 young foxes we’ve released since 2006 have done really well. They’ve survived and bred in the wild.At this point, we’ve progressed from trying to save the Arctic fox from extinction in Scandinavia to working on getting its population to be sufficiently large and genetically diverse to sustain itself. We’ve still got a way to go, however, before we can say the species is saved.” More

A periodic cicada in Illinois, where two broods are emerging this month at once.Credit: AJ Mast for Nature

As spring turns to summer in the United States, warming conditions have started to summon enormous numbers of red-eyed periodical cicadas out of their holes in the soil across the east of the country. This year sees an exceptionally rare joint emergence of two cicada broods: one that surfaces every 13 years and another with a 17-year cycle. They last emerged together in 1803, when Thomas Jefferson was US president. This year, billions or even trillions of cicadas from these two broods — each including multiple species of the genus Magicicada — are expected to swarm forests, fields and urban neighbourhoods.To answer readers’ cicada questions, Nature sought help from three researchers. Katie Dana is an entomologist affiliated with the Illinois Natural History Survey at the University of Illinois at Urbana-Champaign. John Lill is an insect ecologist at George Washington University in Washington DC. Fatima Husain is a cognitive neuroscientist at the University of Illinois at Urbana-Champaign. Their answers have been edited for length and clarity.Why do periodical cicadas have red eyes?JL: We’re not really sure. We do know that cicadas’ eyes turn red in the winter before [the insects] come out. The whole coloration pattern in periodical cicadas is very bright: red eyes, black and orange wings. They’re quite different from the annual cicadas, which are green and black, and more camouflaged. It’s a bit of an enigma why the periodical ones are so brightly coloured, given that it just makes them more obvious to predators. There are no associated defences with being brightly coloured — it kind of flies in the face of what we know about bright coloration in a lot of other animals, where usually it’s some kind of signal for toxicity. There also exist mutants with brown, orange, golden or even blue eyes. People hunt for blue-eyed ones; it’s like trying to find a four-leaf clover.

Entomologist Katie Dana collects cicadas in Monticello, Illinois.Credit: AJ Mast for Nature

Can periodical cicadas see in colour?JL: They do see colour. But their eyes are basically non-functional when they’re underground. They’re not investing a lot of energy in making the sort of proteins associated with vision when they’re not needed. And so there’s some dramatic, abrupt developmental switch that happens, that probably coincides with the eye colour changing to red. They now need to be able to use their eyes in a new habitat, which is above ground.Can the two cicada broods interbreed?KD: We know that they can interbreed when introduced to each other in the lab, but it remains to be seen if it actually happens in a wild setting.Do cicadas compete to be heard?JL: Cicadas get together in all-male groups called choruses, and usually in a given tree. Cicadas of a particular species congregate together, put on a big show, and the females are hanging out around the periphery, judging the quality of potential mates. So that’s the reason it’s so loud, but I don’t know the degree to which they’re competing to be heard. They’re obviously trying to distinguish themselves among an already loud group, for the females. And the females are judging something about the quality of the call. But I think the loudness is probably correlated with how vigorous that male is, and might indicate [for a female] good genes to pass on to her offspring, so that she can, in turn, have loud-calling sons that would pass on those genes.
Why locusts congregate in billion-strong swarms — and how to stop them
Can the incessant din of cicadas cause people to develop conditions such as temporary psychosis?FH: I highly doubt that the loud noise of the cicadas causes temporary psychosis. At least, I have not heard of any such cases. People do have hypersensitivity to loud sounds and may find the cicada noises bothersome. Some may find that the noise exacerbates their tinnitus. But for some others, the cicada noise can actually mask their tinnitus.If cicada males buzz to attract females, is it possible that females of one species will be attracted to males of the other species?KD: Noise absolutely brings female cicadas. If you run a lawnmower these days, all the cicadas will flock to you. But once they get closer to each other, there’s a call-and-response that’s more species-specific. The other thing is that in insects, we often talk about lock and key: the male [reproductive organ] is the key and the female [reproductive organ] is the lock, and they have to fit together perfectly. That’s how a lot of insect species make sure they’re mating with the right species.Do any insects thrive on periodical feasts of cicadas?JL: The cicada killer [Sphecius speciosus] is one of the largest native, stinging wasps that we have in this area [the eastern United States]. But the wasps don’t really start foraging until after the periodical cicadas are mostly gone. They mostly feed on the larger, green annual cicadas [family Cicadidae] that come out later in the year. The wasps capture cicadas and paralyse them with their venom and then bring them back to a pre-dug nest in the ground, where they lay an egg upon them. And the cicada serves as live meat for the developing wasp larva that will feed underground on the hapless cicada that gets eaten alive by the wasp larva. More

The emergence is in full swing. Periodical cicadas (Magicicada) are crawling out of the ground in vast numbers — in their trillions, maybe — across swathes of the southeastern and midwestern United States. And researchers, many of whom usually study other insects, are dropping everything to race to sites where they’ve popped up, eager to collect samples and observe the ecological spectacle.“There’s an awful lot that we don’t know” about these insects that spend most of their lives about 60 centimetres underground “in a little mud hole in the dirt”, says Martha Weiss, an entomologist at Georgetown University in Washington DC.This year’s emergence also ups the ante for researchers. Two particular broods — groups of multiple cicada species with the same life cycle appearing above ground in the same year — will sync up for the first time in 221 years. That means the last time they saw daylight together was when the United States was being led by its third president, Thomas Jefferson. Brood XIX, also known as the Great Southern Brood, has been emerging for the past few weeks after 13 years underground, and the more northerly brood XIII has just started popping up after 17 years.Separate territoriesGeographically, the two broods don’t overlap much, although “they come really close together” in central Illinois, near the city of Springfield, says Chris Simon, an evolutionary biologist and entomologist at the University of Connecticut in Storrs. Brood XIX spans the largest area of any known cicada brood, from Maryland to Georgia in the southeast and from Iowa to Oklahoma in the Midwest. Brood XIII, meanwhile, covers northern Illinois, including Chicago.But there is a possible contact zone, and some scientists are flocking to it. Katie Dana, an entomologist affiliated with the Illinois Natural History Survey at the University of Illinois Urbana-Champaign, is hoping to investigate how the two broods might interact and how their mating songs differ. Normally, the pitch of these songs is one way to distinguish between the multiple, visually similar, cicada species that make up a single brood.

One way to distinguish between species of cicada is to collect specimens, freeze them and later sequence their DNA.Credit: AJ Mast for Nature

It could also be a way to distinguish between broods XIX and XIII. They, too, are closely related and look the same, Dana says, making interbreeding possible but really challenging to study in the field.So Dana is now observing their interactions and collecting as many samples as possible, then flash-freezing them for storage. This will allow her and her colleagues to sequence the insects’ DNA later, to help them to distinguish between the broods.“There are gonna be so many graduate-student projects that we’ll have in our freezer after this year,” says Dana, who enthusiastically signs her e-mails “Dr. Ci-Katie-Dae”.Telling the time undergroundOne of the big questions that researchers will seek to answer during this emergence is, how do cicadas keep track of time?When they are above ground, periodical cicadas have a loud and frenzied mating season, after which the females lay eggs in small slits in tree branches. Once the eggs hatch weeks later, the white nymphs fall to the ground like snowflakes, burrow down into the soil and stay there, sucking sap from tree roots for nutrition. They survive and grow like this for a long time — usually prime-numbered stretches of years. The cicadas somehow know to emerge in a particular year once the soil warms up to a balmy 18°C.

Periodical cicadas typically have red eyes, black bodies and orange-tinted wings.Credit: AJ Mast for Nature

Researchers think that having prime-numbered reproduction cycles puts the cicadas conveniently out of sync with the life cycles of various predators that might stalk them. Emerging all at once, in vast numbers, also means that at least some members of a particular brood will survive to have offspring for the next reproduction cycle.But how exactly the insects work out whether 13 or 17 years have passed underground is a mystery. Certainly, they can clock seasonal changes in the trees they feed on, but that can’t be the whole story, Simon says. She suspects that epigenetics — chemical modifications of DNA that control how various genes are expressed — wind the insects’ internal clocks. Specifically, she thinks methyl groups (carbon atoms with three hydrogens attached) are involved. Like Dana, Simon will be collecting samples this year to test her hypothesis.A terrifying fungusAlthough the prime-number trick seems to help cicadas evade predators, it hasn’t fooled a certain parasite. Massospora cicadina fungus infects 13- and 17-year cicadas as they crawl out of the ground, eating through their abdomens and replacing their tissue with plugs of spores. Psychoactive chemicals released by the spores turn the infected cicadas into ‘zombies’, driving them to mate manically to pass spores on to others.
Do insects have an inner life? Animal consciousness needs a rethink
The spores remain dormant in soil for periods matching the prime-numbered cicada cycles, and become activated during an emergence year. But researchers have questions about how this works.Has the fungus evolved its own internal way of tracking 13- and 17-year cycles to keep up with the cicadas? Or is it simply activated by chemical cues released by cicada nymphs as they are about to emerge? To find out, Sierra Raglin, a soil microbial ecologist at the University of Illinois Urbana-Champaign, will locate and collect infected cicadas this year, as well as look for spores in the nearby soil. The soil and its microbiome haven’t been studied much in this context, Raglin says.Cicada emergences are a bolt out of the blue for people and wildlife alike. “Swarms of shrimp-like nymphs crawl out of the ground and cover the trees and the car tyres and the mailboxes,” says Weiss, along with “the legs of passers-by”. Weiss studied her first cicada emergence in 2004; she is now in Illinois to record how brood XIII affects the surrounding ecosystem, including animals such as birds and ants. Piles of cicada carcasses, left behind after the mating is over, offer a feast. This time around, Weiss plans to use ant colonies as an indicator of how nature reacts to this bounty, by studying their foraging patterns and interspecies relationships before, during and after the emergence.“It’s a new experiment every single time,” she says. More

RESEARCH BRIEFINGS
29 May 2024

The genomes of all eight living species of baobab tree (Adansonia sp.) reveal the group’s origin and diversification history. Ecological analyses were incorporated to characterize the baobabs’ past population dynamics and were used to propose protection measures for these iconic species, including the reassessment of their conservation status and the close monitoring of several of Madagascar’s baobab species. More

.readcube-buybox { display: none !important;}
Sea urchins enable complex reef ecosystems to thrive by eating algae that would otherwise smother corals. But that delicate natural balance is under threat in the Red Sea and Western Indian Ocean.

Access options

/* style specs start */
style{display:none!important}.LiveAreaSection-193358632 *{align-content:stretch;align-items:stretch;align-self:auto;animation-delay:0s;animation-direction:normal;animation-duration:0s;animation-fill-mode:none;animation-iteration-count:1;animation-name:none;animation-play-state:running;animation-timing-function:ease;azimuth:center;backface-visibility:visible;background-attachment:scroll;background-blend-mode:normal;background-clip:borderBox;background-color:transparent;background-image:none;background-origin:paddingBox;background-position:0 0;background-repeat:repeat;background-size:auto auto;block-size:auto;border-block-end-color:currentcolor;border-block-end-style:none;border-block-end-width:medium;border-block-start-color:currentcolor;border-block-start-style:none;border-block-start-width:medium;border-bottom-color:currentcolor;border-bottom-left-radius:0;border-bottom-right-radius:0;border-bottom-style:none;border-bottom-width:medium;border-collapse:separate;border-image-outset:0s;border-image-repeat:stretch;border-image-slice:100%;border-image-source:none;border-image-width:1;border-inline-end-color:currentcolor;border-inline-end-style:none;border-inline-end-width:medium;border-inline-start-color:currentcolor;border-inline-start-style:none;border-inline-start-width:medium;border-left-color:currentcolor;border-left-style:none;border-left-width:medium;border-right-color:currentcolor;border-right-style:none;border-right-width:medium;border-spacing:0;border-top-color:currentcolor;border-top-left-radius:0;border-top-right-radius:0;border-top-style:none;border-top-width:medium;bottom:auto;box-decoration-break:slice;box-shadow:none;box-sizing:border-box;break-after:auto;break-before:auto;break-inside:auto;caption-side:top;caret-color:auto;clear:none;clip:auto;clip-path:none;color:initial;column-count:auto;column-fill:balance;column-gap:normal;column-rule-color:currentcolor;column-rule-style:none;column-rule-width:medium;column-span:none;column-width:auto;content:normal;counter-increment:none;counter-reset:none;cursor:auto;display:inline;empty-cells:show;filter:none;flex-basis:auto;flex-direction:row;flex-grow:0;flex-shrink:1;flex-wrap:nowrap;float:none;font-family:initial;font-feature-settings:normal;font-kerning:auto;font-language-override:normal;font-size:medium;font-size-adjust:none;font-stretch:normal;font-style:normal;font-synthesis:weight style;font-variant:normal;font-variant-alternates:normal;font-variant-caps:normal;font-variant-east-asian:normal;font-variant-ligatures:normal;font-variant-numeric:normal;font-variant-position:normal;font-weight:400;grid-auto-columns:auto;grid-auto-flow:row;grid-auto-rows:auto;grid-column-end:auto;grid-column-gap:0;grid-column-start:auto;grid-row-end:auto;grid-row-gap:0;grid-row-start:auto;grid-template-areas:none;grid-template-columns:none;grid-template-rows:none;height:auto;hyphens:manual;image-orientation:0deg;image-rendering:auto;image-resolution:1dppx;ime-mode:auto;inline-size:auto;isolation:auto;justify-content:flexStart;left:auto;letter-spacing:normal;line-break:auto;line-height:normal;list-style-image:none;list-style-position:outside;list-style-type:disc;margin-block-end:0;margin-block-start:0;margin-bottom:0;margin-inline-end:0;margin-inline-start:0;margin-left:0;margin-right:0;margin-top:0;mask-clip:borderBox;mask-composite:add;mask-image:none;mask-mode:matchSource;mask-origin:borderBox;mask-position:0 0;mask-repeat:repeat;mask-size:auto;mask-type:luminance;max-height:none;max-width:none;min-block-size:0;min-height:0;min-inline-size:0;min-width:0;mix-blend-mode:normal;object-fit:fill;object-position:50% 50%;offset-block-end:auto;offset-block-start:auto;offset-inline-end:auto;offset-inline-start:auto;opacity:1;order:0;orphans:2;outline-color:initial;outline-offset:0;outline-style:none;outline-width:medium;overflow:visible;overflow-wrap:normal;overflow-x:visible;overflow-y:visible;padding-block-end:0;padding-block-start:0;padding-bottom:0;padding-inline-end:0;padding-inline-start:0;padding-left:0;padding-right:0;padding-top:0;page-break-after:auto;page-break-before:auto;page-break-inside:auto;perspective:none;perspective-origin:50% 50%;pointer-events:auto;position:static;quotes:initial;resize:none;right:auto;ruby-align:spaceAround;ruby-merge:separate;ruby-position:over;scroll-behavior:auto;scroll-snap-coordinate:none;scroll-snap-destination:0 0;scroll-snap-points-x:none;scroll-snap-points-y:none;scroll-snap-type:none;shape-image-threshold:0;shape-margin:0;shape-outside:none;tab-size:8;table-layout:auto;text-align:initial;text-align-last:auto;text-combine-upright:none;text-decoration-color:currentcolor;text-decoration-line:none;text-decoration-style:solid;text-emphasis-color:currentcolor;text-emphasis-position:over right;text-emphasis-style:none;text-indent:0;text-justify:auto;text-orientation:mixed;text-overflow:clip;text-rendering:auto;text-shadow:none;text-transform:none;text-underline-position:auto;top:auto;touch-action:auto;transform:none;transform-box:borderBox;transform-origin:50% 50%0;transform-style:flat;transition-delay:0s;transition-duration:0s;transition-property:all;transition-timing-function:ease;vertical-align:baseline;visibility:visible;white-space:normal;widows:2;width:auto;will-change:auto;word-break:normal;word-spacing:normal;word-wrap:normal;writing-mode:horizontalTb;z-index:auto;-webkit-appearance:none;-moz-appearance:none;-ms-appearance:none;appearance:none;margin:0}.LiveAreaSection-193358632{width:100%}.LiveAreaSection-193358632 .login-option-buybox{display:block;width:100%;font-size:17px;line-height:30px;color:#222;padding-top:30px;font-family:Harding,Palatino,serif}.LiveAreaSection-193358632 .additional-access-options{display:block;font-weight:700;font-size:17px;line-height:30px;color:#222;font-family:Harding,Palatino,serif}.LiveAreaSection-193358632 .additional-login >li:not(:first-child)::before{transform:translateY(-50%);content:””;height:1rem;position:absolute;top:50%;left:0;border-left:2px solid #999}.LiveAreaSection-193358632 .additional-login >li:not(:first-child){padding-left:10px}.LiveAreaSection-193358632 .additional-login >li{display:inline-block;position:relative;vertical-align:middle;padding-right:10px}.BuyBoxSection-683559780{display:flex;flex-wrap:wrap;flex:1;flex-direction:row-reverse;margin:-30px -15px 0}.BuyBoxSection-683559780 .box-inner{width:100%;height:100%;padding:30px 5px;display:flex;flex-direction:column;justify-content:space-between}.BuyBoxSection-683559780 p{margin:0}.BuyBoxSection-683559780 .readcube-buybox{background-color:#f3f3f3;flex-shrink:1;flex-grow:1;flex-basis:255px;background-clip:content-box;padding:0 15px;margin-top:30px}.BuyBoxSection-683559780 .subscribe-buybox{background-color:#f3f3f3;flex-shrink:1;flex-grow:4;flex-basis:300px;background-clip:content-box;padding:0 15px;margin-top:30px}.BuyBoxSection-683559780 .subscribe-buybox-nature-plus{background-color:#f3f3f3;flex-shrink:1;flex-grow:4;flex-basis:100%;background-clip:content-box;padding:0 15px;margin-top:30px}.BuyBoxSection-683559780 .title-readcube,.BuyBoxSection-683559780 .title-buybox{display:block;margin:0;margin-right:10%;margin-left:10%;font-size:24px;line-height:32px;color:#222;text-align:center;font-family:Harding,Palatino,serif}.BuyBoxSection-683559780 .title-asia-buybox{display:block;margin:0;margin-right:5%;margin-left:5%;font-size:24px;line-height:32px;color:#222;text-align:center;font-family:Harding,Palatino,serif}.BuyBoxSection-683559780 .asia-link{color:#069;cursor:pointer;text-decoration:none;font-size:1.05em;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;line-height:1.05em6}.BuyBoxSection-683559780 .access-readcube{display:block;margin:0;margin-right:10%;margin-left:10%;font-size:14px;color:#222;padding-top:10px;text-align:center;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;line-height:20px}.BuyBoxSection-683559780 ul{margin:0}.BuyBoxSection-683559780 .link-usp{display:list-item;margin:0;margin-left:20px;padding-top:6px;list-style-position:inside}.BuyBoxSection-683559780 .link-usp span{font-size:14px;color:#222;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;line-height:20px}.BuyBoxSection-683559780 .access-asia-buybox{display:block;margin:0;margin-right:5%;margin-left:5%;font-size:14px;color:#222;padding-top:10px;text-align:center;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;line-height:20px}.BuyBoxSection-683559780 .access-buybox{display:block;margin:0;margin-right:10%;margin-left:10%;font-size:14px;color:#222;opacity:.8px;padding-top:10px;text-align:center;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;line-height:20px}.BuyBoxSection-683559780 .price-buybox{display:block;font-size:30px;color:#222;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;padding-top:30px;text-align:center}.BuyBoxSection-683559780 .price-buybox-to{display:block;font-size:30px;color:#222;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;text-align:center}.BuyBoxSection-683559780 .price-info-text{font-size:16px;padding-right:10px;color:#222;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif}.BuyBoxSection-683559780 .price-value{font-size:30px;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif}.BuyBoxSection-683559780 .price-per-period{font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif}.BuyBoxSection-683559780 .price-from{font-size:14px;padding-right:10px;color:#222;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;line-height:20px}.BuyBoxSection-683559780 .issue-buybox{display:block;font-size:13px;text-align:center;color:#222;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;line-height:19px}.BuyBoxSection-683559780 .no-price-buybox{display:block;font-size:13px;line-height:18px;text-align:center;padding-right:10%;padding-left:10%;padding-bottom:20px;padding-top:30px;color:#222;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif}.BuyBoxSection-683559780 .vat-buybox{display:block;margin-top:5px;margin-right:20%;margin-left:20%;font-size:11px;color:#222;padding-top:10px;padding-bottom:15px;text-align:center;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;line-height:17px}.BuyBoxSection-683559780 .tax-buybox{display:block;width:100%;color:#222;padding:20px 16px;text-align:center;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;line-height:NaNpx}.BuyBoxSection-683559780 .button-container{display:flex;padding-right:20px;padding-left:20px;justify-content:center}.BuyBoxSection-683559780 .button-container >*{flex:1px}.BuyBoxSection-683559780 .button-container >a:hover,.Button-505204839:hover,.Button-1078489254:hover,.Button-2496381730:hover{text-decoration:none}.BuyBoxSection-683559780 .btn-secondary{background:#fff}.BuyBoxSection-683559780 .button-asia{background:#069;border:1px solid #069;border-radius:0;cursor:pointer;display:block;padding:9px;outline:0;text-align:center;text-decoration:none;min-width:80px;margin-top:75px}.BuyBoxSection-683559780 .button-label-asia,.ButtonLabel-3869432492,.ButtonLabel-3296148077,.ButtonLabel-1651148777{display:block;color:#fff;font-size:17px;line-height:20px;font-family:-apple-system,BlinkMacSystemFont,”Segoe UI”,Roboto,Oxygen-Sans,Ubuntu,Cantarell,”Helvetica Neue”,sans-serif;text-align:center;text-decoration:none;cursor:pointer}.Button-505204839,.Button-1078489254,.Button-2496381730{background:#069;border:1px solid #069;border-radius:0;cursor:pointer;display:block;padding:9px;outline:0;text-align:center;text-decoration:none;min-width:80px;max-width:320px;margin-top:20px}.Button-505204839 .btn-secondary-label,.Button-1078489254 .btn-secondary-label,.Button-2496381730 .btn-secondary-label{color:#069}
/* style specs end */Access Nature and 54 other Nature Portfolio journalsGet Nature+, our best-value online-access subscription$29.99 / 30 dayscancel any timeSubscribe to this journalReceive 51 print issues and online access$199.00 per yearonly $3.90 per issueRent or buy this articlePrices vary by article typefrom$1.95to$39.95Prices may be subject to local taxes which are calculated during checkout

Additional access options:

doi: https://doi.org/10.1038/d41586-024-01400-1

References

Subjects

Conservation biology More

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain
the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in
Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles
and JavaScript. More

A tank of captive-bred Chinese sturgeons about to be released to the Yangtze River.Credit: Xiao Yijiu/Xinhua via Alamy

Five fish species, including the iconic Chinese sturgeon, have gone extinct, or will soon be extinct, because of dams on the Yangtze River in China, according to a paper released on 10 May in Science Advances1. The findings have reignited a long-running debate among Chinese scientists about the best way to rescue the species in the Yangtze, with some saying that the analysis is flawed.The Yangtze River is a mighty 6,300-kilometre-long waterway and a global biodiversity hotspot that runs through 11 Chinese provinces. But over the past 50 years, six major hydropower dams and more than 24,000 smaller hydropower stations have been built in the river’s main stream and branches — with even more on the drawing board.The dams were built to help generate electricity, provide flood protection and make the river easier to navigate. But dams can block migratory fishes and damage their habitat. To mitigate the effects of the dams, fish-rescue programmes have been in place in various forms since 1982, when the first dam was being constructed.Huang Zhenli, the deputy engineer-in-chief at the China Institute of Water Resources and Hydropower Research in Beijing, and his colleague Li Haiying developed an analytical tool that models the impact of the Yangtze River dams on its fish populations.They focused on five iconic species: the Chinese sturgeon (Acipenser sinensis), the Yangtze sturgeon (Acipenser dabryanus), the Chinese paddlefish (Psephurus gladius), the Chinese sucker (Myxocyprinus asiaticus) and the largemouth bronze gudgeon (Coreius guichenoti).By the time of the analysis, the paddlefish was already extinct. The Yangtze sturgeons are being kept alive only through captive-breeding programmes. The Chinese sturgeon is critically endangered. The International Union for Conservation of Nature lists the sucker as vulnerable, and the gudgeon as endangered.The researchers’ modelling found that all five species will be entirely extinct or extinct in the wild by 2030.David Dudgeon, a retired freshwater ecologist at the University of Hong Kong, says that the study is helpful in identifying the effect of the dams on the five species, particularly the understudied Chinese sucker. “There is nothing much that surprises me about the conclusions of the study,” he says. “It is good to see a well-integrated investigation of these five species.”However, not all researchers are convinced by the study. Wei Qiwei, a conservation researcher at the Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, in Wuhan, says that the authors’ work “deserves to be encouraged”, but disagrees with their conclusions.Wei — who co-authored a 2020 paper2 that declared the Chinese paddlefish extinct — says the predictions that all species will be extinct or near extinct in by 2030 can’t be relied on because the parameters in the analysis are uncertain and difficult to quantify.Xie Ping, a freshwater ecologist at the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences in Wuhan, agrees that it might be too soon to draw definitive conclusions from the models’ findings. “More needs to be done to cover more fish species in more geographic regions, so as to validate the effectiveness of the models and to optimize their parameters,” Xie says.‘Six misjudgements’The authors blame the dams, and the lack of specialized passageways for migratory fish to bypass the dams — known as fish-ladders — for the five species’ collapse.“To prevent more migratory fishes from going extinct in China, [its] dam-related fish-rescue programmes must undergo fundamental changes,” Huang says.As fish numbers continued to decline from the 1980s onwards, China stepped up its efforts to safeguard the ecology and environment of the Yangtze.In 2021, it commenced a ten-year fishing ban and increased its restocking of the river with young, captive-bred fish.

The Wudongde Hydropower Station on the Jinsha River, an upper stretch of the Yangtze, became operational in 2020 — after the Chinese paddlefish was declared extinct.Credit: CFOTO/Future Publishing via Getty

However, the authors say that it was not enough. They describe “six misjudgements” of these fish-conservation campaigns, including that overfishing is the primary cause of the population declines; and that restocking is a “viable strategy” for mitigating the effects of the dams.Wei and his team lead the scientific research behind the current conservation plan. He says that the dams’ impacts on fishes exist, but “one cannot ignore other factors”, such as overfishing.“I believe if the 10-year fishing ban had been introduced to the Yangtze River 30 years earlier, the Chinese paddlefish would not be extinct. Nor would the Chinese sturgeon, the Yangtze sturgeon and the Chinese sucker get so close to extinction,” Wei notes.As for restocking from captive-bred populations, he describes it as “the most important protection and restoration task” for the Chinese sturgeon and Yangtze sturgeon.A 2023 study led by IHB researchers3 found that a 2017 pilot fishing ban introduced to the Chishui River — an upstream tributary of the Yangtze — was “an effective measure to facilitate fish resources recovery”.Steven Cooke, a biologist specializing in fish ecology and conservation at the Carleton University in Ottawa, says that science-based restocking can work “quite well” in cases such as the white sturgeon (Acipenser transmontanus) in North America. “But if the habitat is degraded and fish can’t complete their life cycles, then stocked fish may not survive,” Cooke says.Dudgeon, meanwhile, regards the paper’s criticism of restocking of the Yangtze as being “well-founded”.“There is absolutely no evidence that sturgeon restocking has enhanced wild populations, despite the release of millions of cultured juveniles … [and] the fact that the practice has continued for many years,” he says.Fishway or highwayXie highlights that, for large and long-lived species such as sturgeons, conservation work is “very hard”.Chinese sturgeons feed and grow near the sea when they are young and migrate more than 3,200 kilometres up the Yangtze to reproduce. “They spent at least 10 to 20 million years adapting to such a cycle,” Xie says, “They cannot adapt to the huge changes caused by humans within these few decades.”Xie says that fish ladders might not be enough to save the sturgeons. “Fish passages in Europe and North America are mainly designed for relatively small-sized fishes, such as salmon. But sturgeons are mostly large and need a lot of space to swim in rivers,” Xie says. “Less than 2% of sturgeons are able to successfully navigate through the fish passages in dams,” he says.Dudgeon says that, even when fish ladders work, the stillness of the water in the dam might not provide adequate cues to guide the fish upstream to complete their migration.On the downstream journey, both adult and juvenile fish have to find a way to navigate the dam, locate the fish ladder and make a safe descent, he adds.
Dam removals: Rivers on the run
Some countries, such as the United States, France and the United Kingdom, have started to dismantle dams to re-establish migration corridors. When removal is not feasible, or fish ladders are ineffective, Xie and his colleagues suggested in a 2023 paper4 that building river-like side channels around hydropower dams is “the best way” to restore sturgeon migration routes and provide alternative habitats. Successful such cases have been observed in Russia, Canada and the United States, they noted.Dudgeon says that, with so many complications, improving the situation for fishes in the Yangtze “will be challenging”. More

“It’s dirty, hot work picking up blue crabs (Callinectes sapidus). They like murky water, and you need special clothing and equipment to wade through the swampy lagoon here in the Palud – Palù ornithological reserve in Pula, Croatia. It was the end of a long day in September last year when this photo was taken, and I was hot and sweaty under that special clothing. And once you find a crab, you have to be careful not to injure yourself picking it up: either on its sharp lateral spine, or from its very strong claws.I catch the crabs because they are an invasive species, and because it’s my job: as well as working as a biotechnologist, I’m a fisher. Blue crabs are native to Chesapeake Bay in the eastern United States, and they probably made their way here on a ship in the early twentieth century.There has been a large population in the Po river estuary for many years — but a combination of factors, including global warming, has seen them spread down the Adriatic coast since 2022.The crabs are a problem because they eat the bivalves, fish and other crabs that make up the diets of many of the endangered seabirds here at the nature reserve — without that vital source of food, these birds will be even more threatened and we’ll face a serious loss of biodiversity.My colleagues and I at the Juraj Dobrila University of Pula are encouraging local people to eat the crabs, which are sold at the markets. We’ve held awareness activities since long before 2022, in anticipation of the explosion of the invasive population. I know more and more people who collect blue crabs for food.We’re losing the battle against climate change: the changes are too fast and we are far too slow to adapt to them. But I hope by better understanding the biological capital we have available here, we can build a better relationship with nature.” More