Scientific American - USA (2022-02)

ADVANCES

14 Scientific American, February 2022

make up 97 percent of New Zealand’s land

area). Native life surrounded by fence or

sea is rebounding. And in 2016 the prime

minister announced a first-of-its-kind

nationwide goal: Predator-Free 2050.

The initiative aims to remove rats,

stoats and possums from all New Zea-

land’s 600-plus islands by that year. “Those

three animal predators are basically just

eating our native wildlife out from under

us,” says program director Brent Beaven.

Killing stoats and possums might star-

tle some nature lovers, but University of

Auckland ecologist James Russell

describes the situation as an ecological

trolley problem: “If we choose not to kill

the mammals,” he says, “we’re essentially

choosing to let the birds die.”

Russell describes the initiative as a

broad social movement. “It’s not some-

thing that the government proposed,” he

says. “The government adopted some-

thing for which there was a groundswell

already.” In Predator-Free 2050, the gov-

ernment coordinates actions by universi-

ties, nonprofits, wildlife sanctuaries, habi-

tat-rehabilitation programs, and people

with traps in their backyards. These

groups are removing the predators while

developing better-targeted poisons,

restoring native plant life, reintroducing

native species and inventing new ways to

keep predators out.

Predator-Free 2050 also relies on M ̄aori

tribes, says Tame Malcom, who works for

the environmental nonprofit group Te Tira

Whakam ̄ataki: they have been trapping

rats for centuries, and M ̄aori partnership

has increased the program’s effectiveness

and reduced costs. “Our language is prov-

ing almost vital to ecological restoration

efforts,” Malcolm adds, “because the

names of places give a clue about what the

place used to be like.” The location name

Paek ̄ak ̄a, for example, comes from “hori-

zon” and a type of parrot, indicating the

place was once rich with that species.

For everyone focused on eradication,

the basic blueprint is the same: choose an

island or sanctuary, intensively kill invasive

animals, then monitor to make sure they

stay away. But reality, of course, is more

complex. Massey University conservation

biologist Doug Armstrong, who heads

the Oceania section of the International

Union for Conservation of Nature’s rein-

troduction specialist group, notes that not

all native species take off quickly once an

area has been cleared. Learning and

catering to struggling species’ habitat

needs will take time. And with their com-

petition so helpfully removed, mice can

balloon in number as they feast on native

lizards and frogs.

Then there is cost. “Our standard

eradication practices at the moment are

$600 to $1,000 [NZD] a hectare, and we

just can’t sustain that as a country,” Bea-

ven says. Program leaders hope technol-

ogy will help. Last year biologists finished

sequencing all target species’ genomes,

which could lead to targeted baits or

gene-editing approaches akin to recent

mosquito-control projects elsewhere.

(New Zealanders, many of whom worked

to ban genetically modified organisms in

the early 2000s, are still debating whether

to pursue gene editing.) Engineers are

developing traps that identify species by

their footsteps, and researchers are build-

ing drones to distribute bait and monitor

large areas for reinfestation. The country’s

innovations are already rippling outward:

Armstrong says the bulk of international

invasive species eradication efforts have

New Zealanders somewhere at the helm.

But as researchers tackle the chal-

lenges of clearing invasive predators from

an entire country, some ecologists ques-

tion the initiative’s premise, even for some-

where as geographically isolated as New

Zealand. Wayne Linklater, an environmen-

tal scientist at Sacramento State Univer-

sity, suggests fully removing invasive pred-

ators is unattainable. Instead he advo-

cates for mitigation, such as protected

breeding zones or a network of sanctuar-

ies to conserve threatened species more

effectively. Such tactics have met with

success in Australia and South Africa.

Beaven, however, sees those

approaches as stopgaps requiring con-

stant human involvement. Eradication,

he says, lets native flora and fauna truly

thrive. That’s what program fieldworker

Scott Sambell would like to see. A few

times a year Sambell uses a rat-sniffing

dog to monitor islands that have previ-

ously been cleared. His circuit includes

some places that, like Maria Island/Rua-

puke, have been pest-free for five decades.

“You get into these areas, and you feel like

a stranger,” he says. “This is the birds’

domain. And it’s awesome. ” — Katie Peek

ANIMAL BEHAVIOR

Shark Feels

Fish species around the world

deliberately rub against sharks

Lacey Williams was using a drone to follow

a great white shark in South Africa’s Pletten-

berg Bay when a school of leerfish began

actively pursuing the predator—and then

started rubbing their bodies against its tail

as though it were an exfoliating pumice

stone. “We were just really gobsmacked,”

says Williams, a marine biology graduate

student at the University of Miami.

Numerous past studies have confirmed

that a whole host of marine organisms,

including sharks themselves, chafe on sand

and rocks—presumably to remove parasites

and bacteria. But even though there were

anecdotal reports of other fish chafing on

sharks’ sandpapery skin, no one had ever

undertaken a formal study of the behavior.

Williams and fellow graduate student

Alexandra Anstett compiled all the records

they could uncover of such chafing—includ-

ing drone footage, photographs, diver video

feeds and anecdotal reports. They found

47 incidents involving eight different shark

species being chafed by 12 species of fish

and one species of shark (the last being silky

sharks seen rubbing against a whale shark).

These examples spanned 13 locations in three

O P T I C S

Out of Sight

Holographic camera tech can

reconstruct hidden objects

A new imaging technique might one day
help physicians peer into human tissue and
behind bones, let mechanics inspect moving
machinery such as airplane turbines for tiny
defects, or enable automated vehicles to see
through dense fog or around blind corners.
A study detailed in Nature Communications
shows how the process, called synthetic
wavelength holography, can capture de-
tailed and nearly instant snapshots of objects
hidden from view.
Light scatters when it bounces around a
corner or travels through a cloudy material,
says Atul Ingle, an electrical engineer at
Portland State University who was not in-
https://www.scientificamerican.com/article/ volved in the study. To see what lies on the
behind-new-zealands-wild-plan-to-purge-all-pests1/