FROG

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land. Now they’re back – and thriv­ing. This is the first year of doc­u­mented breeding by the frogs in Yosemite since adult red­leggeds started to be rein­tro­duced here in 2017.

“They’re happy here,” said Schuyler Green­leaf, projects di­rec­tor for Yosemite Con­ser­vancy, in Cook’s Meadow near Yosemite Falls.

Her or­ga­ni­za­tion, a phil­an­thropic part­ner of Yosemite, has con­trib­uted $570,000 from donors over the past three years to protect aquatic species in the park. The frog pro­grams re­ceived $130,000 from the con­ser­vancy in 2019.

Around 200 adult frogs were re­leased in sev­eral Yosemite Valley sites last week, in­clud­ing Cook’s, El Cap and Lei­dig mead­ows. An­other 500 have been re­leased since 2017. All are mi­crochipped. Thou­sands of frog eggs and tad­poles have also been re­leased.

WHY DO CAL­I­FOR­NIA RED-LEGGED FROGS MAT­TER?

The Cal­i­for­nia red­legged frog was made fa­mous by au­thor Mark Twain, who took no­tice of this strik­ing am­phib­ian, painted in colors of red, gold, black and green, in his short story, “The Celebrated Jump­ing Frog of Calav­eras County.” But be­yond their fine frog looks and im­por­tant role in any ecosys­tem, frogs help people, too.

“They are a sen­tinel, both of land, air and wa­ter qual­ity,” Grasso said. “So if wa­ter qual­ity is poor, frogs tend not to do well. And since they have a bi­lat­eral – a wa­ter and land life stage – you can actually look for in­di­ca­tors on land that might not be healthy, and that can be a lot of in­di­ca­tors re­lated to habi­tat. So I used to often jok­ingly say to people, ‘It’s the frogs now, but you could be next.’”

Frogs are more sen­si­tive to any con­tam­i­nants in wa­ter, which they ab­sorb and can lead to death. Grasso com­pared frogs to ca­naries that coal min­ers used to bring un­der­ground to watch for deadly lev­els of con­tam­i­nants.

“Frogs are that same sen­tinel,” he said. “If they’re not doing well and we don’t really un­der­stand why, it’s kind of a red flag that we should in­ves­ti­gate that.”

Other work is be­ing done to bring back two other at-risk am­phib­ians: the Sierra Ne­vada yel­low-legged frog, found at higher el­e­va­tions, and the Yosemite toad.

FROGS WITH MICROCHIPS, RA­DIO TRANSMITTERS

All of the adult red­legged frogs re­leased in Yosemite have been im­planted with an 8-mil­lime­ter mi­crochip, sim­i­lar to what’s done for many pets. The microchips con­tain data about the frogs that re­searchers can scan if found in the wild.

In June, an­other 275 frogs will be re­leased in Yosemite. Seventy-five of them will be fit­ted with bat­tery-pow­ered ra­dio transmitters for the first time, se­cured with small beaded chains like a belt or neck­lace. The transmitters al­low re­searchers to track the frogs from a quar­ter mile away and will be re­moved in De­cem­ber, Grasso said.

These are help­ful tools for re­searchers since the red-leggeds are largely noc­tur­nal and prone to hid­ing. They’re also hard to hear since vo­cal­iza­tion oc­curs un­der­wa­ter, and the sea­son for mat­ing calls usu­ally only lasts from March to April. Grasso de­scribes the sound like some­one rub­bing a bal­loon.

GROWN FROM EGGS, TAD­POLES IN SAN FRAN­CISCO

The San Fran­cisco Zo­o­log­i­cal So­ci­ety and Yosemite Na­tional Park Con­ser­va­tion and Re­cov­ery Fa­cil­ity, opened in San Fran­cisco in 2016, reared the frogs. Jessie Bushell, di­rec­tor of con­ser­va­tion for San Fran­cisco Zoo and Gar­dens, said staff had min­i­mal in­ter­ac­tions with them to en­sure the frogs are still afraid of people and preda­tors in the wild.

The frog eggs were gath­ered from pri­vate prop­erty in Gar­den Valley north­east of Sacra­mento. Grasso started look­ing there af­ter a red-legged frog was found nearby in El­do­rado Na­tional For­est by co­work­ers be­fore he started work­ing in Yosemite.

Only a small per­cent­age of eggs were taken, and shouldn’t impact the Gar­den Valley pop­u­la­tion, re­searchers said.

It’s hard to know ex­actly how many have sur­vived in Yosemite, or how the deadly am­phib­ian fun­gus – be­lieved to have been brought to the area from Africa or Korea – will con­tinue to impact them. But Grasso takes heart see­ing they’re healthy enough to breed. Red-leggeds with­out microchips were also found in Yosemite Valley’s Mir­ror Lake, sug­gest­ing tad­poles re­leased there in 2016 sur­vived.

Grasso has seen 20 red-legged egg masses in Yosemite Valley this year, which could mean around 50,000 tad­poles – al­though only about 1% to 3% of tad­poles typ­i­cally sur­vive in the wild. Many more egg masses are be­lieved to ex­ist.

WHAT HAP­PENED TO THE AMER­I­CAN BULL­FROGS?

One of the red-leggeds’ greatest foes, the Amer­i­can bull­frog, was de­clared erad­i­cated in Yosemite Valley by 2014.

About 1,000 adult Amer­i­can bull­frogs were killed in Yosemite over a 10-year pe­riod, Grasso said.

Yosemite got se­ri­ous with fund­ing this erad­i­ca­tion ef­fort in the 2000s, Grasso said, af­ter a chief of wildlife didn’t like the un­nat­u­ral sound­scape cre­ated by the bull­frogs, be­lieved to have been in­tro­duced in Yosemite Valley in the early 1950s.

Wa­ter sam­ples still show Amer­i­can bull­frog DNA in Yosemite but park re­searchers haven’t seen them for four years, Grasso said. Any bull­frogs that may still ex­ist are no longer con­sid­ered a se­ri­ous threat.

The red-leggeds’ de­cline through­out Cal­i­for­nia also was caused by wet­land habi­tats be­ing dam­aged and de­pleted of wa­ter, and the frogs be­ing killed for food in the 19th and 20th cen­turies. Amer­i­can bull­frogs were then brought in for food – the “nail in the cof­fin,” Grasso said. Rac­coons also have been for­mi­da­ble preda­tors.

Grasso said the bull­frogs in Yosemite were killed us­ing the most hu­mane meth­ods pos­si­ble. A light is shined in a bull­frog’s eyes, caus­ing it to freeze. A bull­frog is then picked up and its belly rubbed with Ora­jel, which puts it to sleep and can stop its heart, Grasso said. A sharp ob­ject is then used to cut the bull­frog at the base of its skull, he said.

IN­VA­SIVE SPECIES MAN­AGE­MENT

Why erad­i­cate in­va­sive, non-na­tive species?

“I think there are fair ar­gu­ments that are tran­spir­ing about where you do this type of work and where you don’t,” Grasso said. “Ob­vi­ously in a na­tional park, you know the land is go­ing to be set aside in per­pe­tu­ity, that it makes a lot of sense to do it here.”

He said ecol­o­gists are now strug­gling with this ques­tion: “How do you value one species over an­other and de­cide which species we are go­ing to erad­i­cate for the ben­e­fit of an­other?”

Erad­i­cat­ing bull­frogs is much dif­fer­ent from Grasso’s child­hood, when he did bull­frog rescue op­er­a­tions, scoop­ing them up from dry­ing ponds with his ball cap and mov­ing them to a nearby river.

“We have an in­va­sive tur­tle, the red-eared slider, not in the park but ad­ja­cent, and I can’t even do that work,” he said.

Grasso said the rein­tro­duc­tion of na­tive Western pond tur­tles in Yosemite has stopped for now. He said tur­tles in­volved in that new pro­gram were sent back to a San Fran­cisco zoo fa­cil­ity while more re­search is con­ducted.

Other non-na­tive an­i­mals and plants have been killed in Yosemite, in­clud­ing some species of fish in the High Sierra. But erad­i­cat­ing an in­va­sive species is not al­ways a goal.

The non-na­tive cray­fish, for ex­am­ple, is now a major food source for the na­tive, re­cently-returned river ot­ters in Yosemite, Grasso said. (The ot­ters also eat red-legged frogs.) Eco­log­i­cal work can cre­ate un­in­tended con­se­quences, he said, and de­cid­ing what to do next takes a lot of fore­thought and re­search.

RE­TURN­ING HOME TO THE SIERRA NE­VADA

Yosemite’s ex­per­tise erad­i­cat­ing bull­frogs is be­ing shared with other re­gions through a new col­lab­o­ra­tive of re­searchers.

Grasso hopes the work be­ing done will help re­store red-leggeds in other ar­eas of Cal­i­for­nia where they’ve dis­ap­peared. The frogs’ historic range has been greatly di­min­ished. The frogs are doing bet­ter on the Coast Ranges than in the Sierra.

“The sig­nif­i­cance is, if we can get the frogs es­tab­lished in Yosemite Valley,” Grasso said, “hope­fully we can use this as a pinch point to start re­leas­ing in other known historic lo­cal­i­ties, not only in Mari­posa County, but Tuolumne County, and in Fresno County.”

U.S Fish and Wildlife Ser­vice, Cal­i­for­nia Depart­ment of Fish and Wildlife, and Na­tureBridge are other part­ners in this project.

“Pro­tect­ing vul­ner­a­ble species like red-legged frogs main­tains the park’s bio­di­ver­sity as na­ture en­vi­sioned,” said Yosemite Con­ser­vancy Pres­i­dent Frank Dean.

ERIC PAUL ZAMORA [email protected]­nobee.com

San Fran­cisco Zoo con­ser­va­tion su­per­vi­sors Jarred Wil­lis, left, and Rochelle Stiles, right, hold frogs as microchips are scanned be­fore be­ing re­leased in Cook’s Meadow at Yosemite Na­tional Park on May 3.

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