FRIDAY HARBOR — In the grasslands on south San Juan Island, several patches of bright yellow flowers are fenced off from the rest of the landscape.

The flowering plants are considered weeds by many, but to the island marble butterfly, they're imperative to the species' survival. This landscape is the only place the shrinking island marble butterfly population is known to remain.

"The populations have constricted pretty dramatically to the point that this is the only home of this butterfly on the Earth," Ted Thomas of the U.S. Fish & Wildlife Service said while walking through the American Camp portion of San Juan Island National Historical Park.

For about 15 years, various groups have fought for the butterfly to receive federal Endangered Species Act protection. On April 4, the U.S. Fish & Wildlife Service deemed the butterfly a candidate species.

That means the species qualifies for protection, but the agency does not have the resources to complete the listing process, which can cost hundreds of thousands of dollars, according to a notice in the Federal Register.

Naming the island marble butterfly a candidate species is not good enough for some. 

"I was very surprised by their decision," said Scott Hoffman Black of the Xerces Society for Invertebrate Conservation, which has twice sought protection for the butterfly. "There is really one secure population left of this animal on the planet. It is much more endangered than many species that are listed."

Thomas has been the Fish & Wildlife Service's primary scientist working with the island marble butterfly since 2005. 

Although the white butterfly with green marbled wings has gained more attention in recent years, he said its population has continued to decline. 

San Juan Preservation Trust Stewardship Manager Kathleen Foley said it is also a concern that all the known butterflies are in one location. 

"That obviously presents a tremendous risk if they're all in one place. If something catastrophic were to happen out there we could lose them all," she said.

The San Juan Preservation Trust, in partnership with the San Juan County Land Bank, has worked closely with government staff to build new habitat for the butterfly, including some at American Camp.

The National Park Service is also rearing the butterfly in captivity. Eggs and adults from that program may be moved to new pockets of habitat as early as next year, Foley said. 

A marbled mystery

Since the island marble butterfly was found on San Juan Island 18 years ago, many have sought to unravel the mysteries that surround it. 

In 1998, a state biologist found a white and green butterfly he could not identify during a survey on San Juan Island. The butterflies had previously been found on islands in Canada, but disappeared in the early 1900s and had been presumed extinct. 

"It's kind of a mystery how they wound up on San Juan Island," National Park Service biologist Jenny Shrum said.

Researchers have since surveyed the island, documenting island marble butterfly sightings and the habitat the species uses.

As a graduate student, butterfly expert Amy Lambert spent many summers chasing the butterfly around American Camp.

"I would literally run across the landscape after the butterfly so that I would know where it was going," she said.

Lambert also spent those summers painstakingly scouting out eggs in the grasslands and watching caterpillars emerge and grow. Those caterpillars will eventually become island marble butterflies after spending months in cocoons.

Lambert said during her graduate work between 2002 and 2008 she tracked the development of 1,617 island marble butterflies.

She found that the island marble is intricately tied to a few varieties of mustard plants, most notably the nonnative field mustard. 

Adult butterflies scout out the mustard plants when laying their eggs, tying the fate of the next generation to a weed that is at risk of being eaten by other animals.

When caterpillars hatch from the eggs, the plants are their resting place and first source of food, according to the state Department of Fish & Wildlife. 

"One of the biggest threats for the island marble butterfly is that deer will come in and they want to eat the same plants the butterflies need to lay their eggs on," Thomas said.

Protecting a species

Because of the threat posed by deer, the greatest challenge for the island marble butterfly is the survival of its young, according to those working with the butterflies. 

As a result of Lambert's work, patches of habitat rich with yellow field mustard plants have been fenced off at American Camp to keep deer and wandering park visitors from damaging the plants.

Ann Potter, Fish & Wildlife insect specialist, credits researchers such as Lambert and San Juan Island resident Susan Vernon with helping direct conservation efforts by gathering information about the butterfly's biology and life history.

Vernon, who has been working with the island marble butterfly for more than a decade, said she is impressed with the collaboration between local, state and federal agencies to study and protect it.

"It has been a great privilege to have worked so closely with this rare gem of a butterfly almost from the beginning and to watch the story unfold with the diligent efforts of so many talented and dedicated folks," she said.

After first encountering the butterfly while walking at American Camp in 2000, Vernon went on to lead the development of a captive rearing program to further the research and preservation of the butterfly species.

"It is a beautiful little butterfly worthy of our time, attention and support," she said. "It represents yet another strand of the web of life that connects us all. It matters."

The National Park Service — in partnership with state and federal wildlife agencies — is continuing the captive rearing work spearheaded by Vernon in 2010.

"We thought it might be necessary to develop methods of captive rearing because there were so few of the butterflies left and there were some situations where we would know there were eggs or caterpillars (that wouldn't survive)," Potter said.

The partner agencies gather eggs and caterpillars from at-risk areas such as exposed mustard plants that may entice grazing deer. 

The captive rearing program has helped ensure the survival of more island marble butterflies, which are released from the program each spring.

"We're doing this not because we need more information, but because we're worried about where the population is headed," said Shrum with the National Park Service.

An awareness issue

Even with the efforts to help the island marble butterfly population, few know about the butterflies and their plight.

"The general population doesn't have knowledge of what it (the butterfly) is or that it's so imperiled," Foley said.

Following the species' rediscovery in 1998, the state wildlife agency surveyed the San Juan Islands for the butterfly. During that time, the butterfly was noted in several locations on San Juan and Lopez islands, Fish & Wildlife's Potter said. 

Then the species started to disappear.

"Fast forward to today ... and we think from the surveys that we've done that they only persist in one area of San Juan Island," Potter said. "In the process of that monitoring, we watched populations blink out."

The U.S. Fish & Wildlife Service acknowledged the population's decline in its April 4 finding.

During surveys in 2006, four of the five populations of the butterfly that were found were outside of American Camp, according to the agency's notice. By 2015, surveyors were unable to find signs of the butterfly at any of those sites outside of American Camp.

The number of butterflies seen by surveyors has also declined, decreasing from 270 in 2004 to 63 in 2008, according to the notice.

The hope is that the captive rearing program will help bolster the population and ensure the butterfly remains a part of the island ecosystem.

"I think it's really important for people to know we have these endemic species. It's another reflection of what makes a place special and unique," Potter said.

Many working with the butterfly said preserving the species is important for maintaining biodiversity, which means allowing a variety of plant and animal life to thrive in a given environment.

Foley said all species should be protected, no matter their size.

"When we start getting cavalier about anything going extinct, no matter how charismatic or big it is, then we're in trouble," Foley said. 

Seeking federal protection

Efforts to secure Endangered Species Act protection for the island marble butterfly began in 2002 when the Xerces Society for Invertebrate Conservation petitioned the Fish & Wildlife Service, asking for the butterfly to be recognized as an endangered species. 

In response to that petition, the federal agency deemed the butterfly a species of concern, which means while the population may be in need of conservation there is not enough evidence to support designating it as threatened or endangered, according to the agency website.

Xerces again petitioned the Fish & Wildlife Service in 2012 to list the butterfly as endangered. That petition resulted in the federal agency's recent classification of the butterfly as a candidate species.

Foley and Thomas say being termed a candidate species is a step in the right direction for the protection of the butterfly.

"Being a candidate species means people are paying attention to it and all federal agencies should treat it as if it's on the endangered species list," Thomas said.

If the butterfly does become recognized as a threatened or endangered species, its habitat would be protected by a set of Endangered Species Act regulations.

— Reporter Kimberly Cauvel: 360-416-2199, kcauvel@skagitpublishing.com, Twitter: @Kimberly_SVH, Facebook.com/bykimberlycauvel

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