The Washington Post - USA (2022-05-17)

E2 EZ EE THE WASHINGTON POST.TUESDAY, MAY 17 , 2022

SCIENCE NEWS

BY WILL DUNHAM

The most comprehensive genetic assessment to date of the vaquita, the world’s rarest marine mammal, is offering a glimmer of hope that this small tropical porpoise native to Mexico’s Gulf of California may avoid extinction despite its population dwindling to about 10. Researchers said this month that genome data from 20 vaquitas showed that while the species possesses low genetic diversity — differences in the DNA among the various individuals — the number of potentially harmful mutations that could endanger its survival through inbreeding was quite low. The vaquita, first described by scientists in 1958 and now deemed critically endangered, is the smallest cetacean, the group including whales, dolphins and porpoises, reaching about 5 feet long and 120 pounds. Its torpedo- shaped body is gray on the top and white on the underside with a dark ring around the eyes. Computational simulations performed by the researchers to predict extinction risk showed that vaquitas, whose population has fallen more than 99 percent since the outset of the 20th century because of human activities, have a high chance of rebounding if fishing gillnets are eliminated from their habitat. Gillnets, large curtains of netting that hang in the water, are used to catch fish and shrimp but have killed many vaquitas that get entangled and drown. “Our key findings are that the vaquita is not doomed to extinction by genetics, as some have begun to assume,” said UCLA ecology and evolutionary biology doc- toral student Christopher Kyriaz- is, co-lead author of the study published in the journal Science. “These findings are important because they provide hope for a species that is at the brink of extinction, one that many are now giving up on.” A particular threat is gillnet poaching of an endangered fish called the totoaba. Totoaba swim bladders, purported to be a fertili- ty enhancer, are prized in China. “Dried totoaba swim bladders are traded on the black market in China for traditional medicinal purposes, and fetch a higher price than cocaine,” said study co-author Phillip Morin, a research ge- neticist at the National Oceanic

and Atmospheric Administra- tion’s Southwest Fisheries Science Center. Vaquitas, still actively repro- ducing despite their small numbers, inhabit the northern Gulf of California, also called the Sea of Cortez, between mainland Mexico and the Baja peninsula. “Gillnet fishing in the vaquita’s habitat has been banned, but the ban has not been enforced and vaquitas continue to perish in nets,” said study co-lead author Jacqueline Robinson, a postdoc- toral researcher at the University of California at San Francisco’s Institute for Human Genetics. The first population estimate, conducted in 1997, found there were approximately 570 vaquitas. The population has since declined by up to about 50 percent annual- ly. The researchers gauged the genetic health of the species, which diverged evolutionarily from its closest relatives about 2.5 million years ago, by examining samples from 20 individuals obtained between 1985 and 2017, mostly ar- chived from vaquitas that had died. One worry with such a small population is that inevitable mat- ing among closely related individuals could increase deleterious mutations harmful to species survival. The genome data indicated that the vaquita population already was relatively small — about 5,000 individuals — for hundreds of thousands of years before the crash caused by human activities, making low genetic diversity a natural feature of the species. It also showed there has been relatively little inbreeding among vaquitas and few harmful reces- sive mutations that may lead to congenital deformities when inbreeding that could imperil species survival — lower than 11 other cetacean species assessed, including the blue whale. One cetacean species already appears to have been driven to extinction by humans in recent decades: the baiji, or Chinese river dolphin. “Because of its shy nature, there is very little known about the vaquita,” Robinson said. “The species is in danger of going extinct before we will even fully know what we are losing, and there is no replacing it once it’s gone.” — Reuters

Genome study offers hope for vaquita, a small and endangered porpoise in Mexico’s waters

SCIENCE SCAN

BY ERIN BLAKEMORE

Whale sharks live up to their name — the largest fishes in the sea, they can weigh up to 1,500 pounds, be longer than 45 feet and live for up to 130 years. But the creatures are no match for industrial ships — and a new study suggests modern shipping is killing far more of the endangered species than previously thought. In a study published in the journal PNAS, an international group of scholars sounds the alarm for whale sharks. Al- though they are found in every ocean, Rhincodon typus are largely found in tropical waters. They like to swim near the surface of the sea — and their numbers have been falling. The study, which lays out the results of a global tracking proj- ect, explains why. Using satellite-linked tags, the team tracked movements of 348 whale sharks. Then they matched the data with informa- tion about the movements of the kinds of ships capable of killing the massive animals. More than 90 percent of the whale activity overlapped with busy shipping corridors. There’s no reporting require- ment for vessels that strike whale sharks, but the researchers were able to pinpoint hot spots for the animals. The tags were designed to pop off animals that had re- mained at a constant ocean depth for a long period of time — a signal that the animal was lying dead on the seafloor. After ruling

transmitters with technical issues out, the researchers learned that the tags popped off most often in busy shipping areas. “We propose that ship strikes may have been responsible for a substantial proportion of these [transmitter tag pop-offs] but were undetected or unreported by vessels,” they write. “Incredibly, some of the tags recording depth as well as loca- tion showed whale sharks mov- ing into shipping lanes and then sinking slowly to the seafloor hundreds of meters below, which is the ‘smoking gun’ of a lethal ship strike,” David Sims, a Uni- versity of Southampton marine ecology professor and co-author, said in a news release. “It is sad to think that many deaths of these incredible animals have occurred globally due to ships without us even knowing to take preventative measures.” It is unclear how many whale sharks are in the world’s oceans, but the population is thought to have declined about 50 percent in the past century. The animals are an important part of the marine food web. Ship speed limits and collision reporting requirements could help, the authors write. Although local conservation laws cover whale sharks in parts of their range, they are not covered by any international laws.

MARINE BIOLOGY

Global shipping trade kills more endangered whale sharks than experts previously thought

Global collision-risk hotspots of marine traffic and the world’s largest fish, the whale shark PNAS

BY KASHA PATEL

Since signing the Paris climate agree-
ment in 2015, nations around the world
have focused on one climate goal: limit-
ing global warming to 1.5 degrees Celsius
(2.7 degrees Fahrenheit) above preindus-
trial levels this century. B ut as greenhouse
gas emissions from fossil fuel burning
have continued to increase, a new report
from the World Meteorological Organiza-
tion shows global temperatures could
temporarily hit that threshold within the
next five years.
The WMO stated last week there is a 50
percent chance that the annual global
temperature will hit this mark by 2026.
The probability is only increasing with
time. In 2015, the chance of temporarily
observing 1.5 degrees Celsius of warming
was zero, underscoring the rapid pace of
human-caused climate change.
“A single year of exceedance above
1.5°C does not mean we have breached the
iconic threshold of the Paris agreement,
but it does reveal that we are edging ever
closer to a situation where 1.5°C could be
exceeded for an extended period,” Leon
Hermanson, a researcher at Britain’s Met
Office who led the report, said in a news
release.
The projection was calculated by cli-
mate scientists across the world and uses
“the best prediction systems from leading
climate centers,” Hermanson said, but
some scientists are wary of the prediction.
“Initialized decadal predictions (such
as used here) don’t have a great track
record (yet),” Gavin Schmidt, a climate
scientist at NASA, wrote in an email.
“While I’m happy that research continues
the regional predictions are not to be
taken too seriously.”

Michael Mann, a climate scientist at Penn State, said that while global temperature readings may temporarily spike to the 1.5 degree Celsius threshold in the next several years, the real concern occurs when it is surpassed over a p eriod of many years. “When we talk about the need to avoid 1.5 degrees Celsius global warming in a climate change context, we’re talking about the long-term trend, not the values for individual years,” he told Inside Cli- mate News. Hitting 1.5 degrees Celsius for an extended period may not be far off. The U.N. Intergovernmental Panel on Climate Change concluded last month that the world could blow past the key target within eight years. The assessment of 278 top climate experts wrote that while con- certed action could avert this scenario, it “cannot be achieved through incremental change.” Staying under the threshold, the panel concluded, would involve a coordinated push to expand renewable energy pro- duction, revamp transportation net- works, extract carbon from the air and redesign how cities are built and farming is done. Scientists have long warned about the dangers of 1.5 degrees Celsius of warming on people and the environment. Extreme heat events are more likely to take place and break previous records by large mar- gins, as seen in the Pacific Northwest in June. Hurricanes will unleash more dam- age, intensifying more rapidly and un- leashing more rainfall in a warmer climate. Coral reefs as well as a number of animals species could vanish. Glaciers will continue to melt, raising global sea levels and flooding communities.

Even if the world does not hit 1.5 degrees Celsius in the next five years, the report said it is “very likely” (a 93 percent chance) that it will post its warmest year on record by 2026, knocking off 2016 from the top ranking. The next five years prob- ably will also be warmer on average than the past five years, which have been some of the hottest on record. Natural weather patterns will play a key role in determining when annual global temperatures spike to a record level. For instance, the development of a powerful El Niño event, associated with warm waters in the tropical Pacific, helped fuel record temperatures in 2016. The planet’s temperature then shot up to its second-highest level in 2019 following a weaker El Niño. But La Niña, the cyclical cooling of ocean waters in the tropical Pacific, has put the brakes on warming since then. After El Niño faded and La Niña developed in 2020 and 2021, temperatures plateaued. Those two years ranked as the second- (tied with 2019) and sixth-warmest on record, according to the National Oceanic and Atmospheric Administra- tion (NOAA). With the possibility of La Niña extend- ing into a third straight year, NOAA says there’s only about a 40 percent chance 2022 finishes among the warmest five years on record, but it’s “virtually certain” it will still rank in the top 10. “We are very likely to exceed 1.5ºC in the next decade or so but it doesn’t neces- sarily mean that we are committed to this in the long term — or that working to reduce further change is not worthwhile,” Schmidt wrote in an email.

Jason Samenow contributed to this report.

Threatening climate threshold looms

CAPITAL WEATHER GANG

HANNIBAL HANSCHKE/REUTERS

An aerial view of Greenland’s melting Sermeq glacier last September.

ISTOCK A whale shark near Isla Mujeres, Mexico.

BY JANET MCCONNAUGHEY

Stinky but handsome and
widely popular landscape trees
have spawned aggressive invad-
ers, creating thickets that over-
whelm native plants and sport
nasty four-inch spikes.
Bradford pears and 24 other
ornamental trees were developed
from Callery pears — a species
brought to America a century ago
to save ravaged pear orchards.
Now, their invasive descendants
have been reported in more than
30 states.
“Worse than murder hornets!”
was the tongue-in-cheek title of a
U.S. Department of Agriculture
webinar in 2020 about Callery
pears, including the two dozen
thornless ornamental varieties
sold since the 1960s.
“They’re a real menace,” said
Jerrod Carlisle, who discovered
that four trees in his yard and one
at a neighbor’s had spawned
thousands on 50 acres he was
turning from cropland to woods
in Otwell, a community of about
400 in southern Indiana.
Indiana is among 12 Midwest-
ern and western states that have
reported invasions, although
most are in the South and North-
east.
Until 2015, Carlisle rented his
field to a farmer. Then he enrolled
it in a USDA crop reduction pro-
gram that paid for planting
29,000 trees as wildlife habitat.
Carlisle realized the spiky flow-
ering pears were a problem in

When he cut or mowed
them, new sprouts popped up.
Trees sprayed with herbicide re-
grew leaves. Cutting off bark in a
circle around the trunk kills most
trees. Not these.
He and his 17-year-old son have
cut down an estimated 1,400 Call-

ery pears, applying herbicide to the stumps. But he figures there are about 1,000 more to go. Without regular maintenance, fields near seed-producing trees can be covered with sprouts within a couple of years, said James “J.T.” Vogt, a scientist at the Forest Service’s Southern Research Sta- tion in Athens, Ga. “If you mow it, it sprouts and you get a thicket,” he said. “If you burn it, it sprouts, too.” Seedlings only a few months old bear spurs that can punch through tractor tires, said David R. Coyle, an assistant professor in Clemson University’s Depart- ment of Forestry and Environ- mental Conservation. The stench wafting from the tree’s billows of white blossoms has been compared to perfume gone wrong, rotting fish, chlorine and a cheese sandwich left in a car for a week. The trunks branch off in deep Vs, so after 15 to 20 years they tend to break in storms. But Frank N. Meyer, an agricul- tural explorer who brought 2,500 species of plants including his namesake Meyer lemon to the USDA in the early 1900 s, called the Callery pear wonderful, not- ing that it survived drought and poor soil. At the time, a fungus called fire blight was devastating U.S. pear orchards, University of Cincinna- ti researchers Theresa M. Culley and Nicole A. Hardiman wrote in a 2007 BioScience article about the plant’s U.S. history. And, just as researchers had hoped, grafting edible pears onto Callery roots produced blight-resistant fruit trees. In 1952, USDA workers noticed a spikeless mutant growing among Callery pears started from

seed. By grafting its cuttings onto roots of other Callery pears, they cloned an ornamental line they named Bradford pears. That variety was commercially available by 1962 , Culley and Hardiman wrote. Other seedlings grew into 24 more ornamental varieties. All are so pretty, hardy and insect-resistant that they were planted nationwide. Bradford and other Callery ornamentals are the third most common trees of 132 species planted along New York City streets — more than 58,000 out of 650,000 as of 2015, the most recent count, said Dan Kastanis, city parks department spokes- man. But the city is no longer planting them, Kastanis said. Neither is Newport News, Va., which got rid of its Bradford pears in 2005. South Carolina, Ohio and cities, including South Bend, Ind., have banned or are banning all com- mercial varieties of Callery pears. Some states, including Mis- souri and Alabama, are asking homeowners and landowners to stop planting them or to cut exist- ing ones down and apply herbicide to the stumps. Several, such as North Carolina, offer free native trees to landowners who provide photos proving they have cut down Callery pears on their prop- erty. For the USDA, which ordered Meyer to send Callery pear seeds from China, the nasty spurs and marble-sized, inedible fruit were irrelevant. What mattered was that the plant was resistant to fire blight. Genetically identical pears don’t produce seed, so botanists figured the cloned varieties were safe for ornamental use.

In 1971, the USDA even put out a brochure about their care, tout- ing them as trees that bloom several times from spring through fall, thrive in many cli- mates and soils, and don’t attract plant pests. Now, the USDA describes Call- ery pears as near ubiquitous and has been studying the best way to kill them. Their adaptability is one rea- son they’re so invasive. And their bug-resistant waxy leaves mean insect-eating birds don’t come near them. “They’re kind of a food desert for a bird,” said Coyle, who leads Clemson’s annual “Bradford pear bounty,” providing native sap- lings to landowners who have felled their Callery ornamentals. It turned out that, although trees of the same variety cannot produce seeds with each other, two different varieties within a pollinator’s range can produce fruit that squishes on sidewalks and feeds starlings and robins, which spread the seeds widely. In addition, the root stock can send up sprouts. If those aren’t regularly pruned to prevent them from blossoming, they can cross- pollinate with the grafted-on tree to produce fertile seed, Culley said. “A wild population can potentially originate from a single land- scaping tree that someone plants in their yard,” she said in an email. Carlisle, the Indiana landown- er, says he is finally getting ahead of his invasion because native trees planted for reforestation, especially six oak species, are casting enough shade to inhibit Callery seedlings. “I truly believe I’m in eradica- tion mode now,” he said. — Associated Press

Invasive Callery pear trees called ‘a real menace’

The Washington Post - USA (2022-05-17)

Get our desktop app

Company

Features

Documentation

Resources