Recent accomplishments of CDFW's scientific community
Banded black brant feeding on eelgrass
Volunteer John Roser in the field at Morro Bay
Flock of black brant in flight above Morro Bay
Black brant in Morro Bay
John Roser began hearing the stories shortly after he moved to Los Osos, San Luis Obispo County, on the shores of Morro Bay in the mid-1990s.
Longtime birders, waterfowl hunters, biologists and other coastal residents were all saying the same thing: It seemed fewer black brant were showing up on the bay each winter.
The coastal sea goose is a cultural icon of the area, the signature species of the Morro Bay Winter Bird Festival and a temporary visitor welcomed by locals as the geese arrive each fall from their summer breeding grounds in the Arctic. When the geese are present in big numbers, you can hear their cacophony almost anywhere on the bay from November through April or until the warm environs of Baja California lure the birds farther south on their migration.
Roser, who holds a degree in biology from Cal Poly San Luis Obispo and spent 25 years as an environmental educator, set out to see if the old-timers’ stories were true. For the past 21 years, he has provided CDFW and brant biologists throughout the Pacific Flyway with their most credible and reliable source of data on wintering brant in Morro Bay.<
“I’m retired, and I wanted to take on a volunteer project that would make a difference in this community,” Roser said of his motivation. “I wanted to create a Morro Bay specific data set significant enough that it would be valuable in brant studies and research across the Pacific Flyway.”
Roser’s retirement project has led him on a brant-like odyssey.
He banded brant one summer in Alaska, worked in Humboldt Bay with leading brant researcher Jeff Black and his Humboldt State University graduate students, and traveled to Baja California to help biologists read bands on birds at the extreme end of their southern range. Much of Roser’s winter observations take place at CDFW’s Morro Bay Wildlife Area.
“John is our go-to guy on the ground in Morro Bay for sure,” said Melanie Weaver, the head of CDFW’s Waterfowl Program. “We only have two employees in our program, myself included, so we depend on regional staff and volunteers like John to help compile survey data. John is part of the local community, he cares, and he is close to the resource.”
The data Roser supplies are incorporated into CDFW’s Mid-winter Waterfowl Survey, which is used to set hunting regulations for the following waterfowl season.
What attracts brant to Morro Bay is the same thing that prompts the birds to stop at other coastal bays along their southward migration: eelgrass. The underwater seagrass grows in shallow marine environments and is the birds’ primary food source.
Roser’s initial research in 1997 confirmed the reports he was hearing: The wintering brant population in Morro Bay had declined significantly and corresponded with a crash in eelgrass acreage in the bay.
While CDFW surveys from the 1930s through 1960s documented Morro Bay’s wintering brant population as high as 11,800 birds, Roser’s first survey in 1997 recorded a population high of fewer than 700 birds.
The eelgrass crash in the mid-1990s was temporary and well-understood, caused by an influx of sediment from a fire-ravaged landscape, a deluge of freshwater from a rainy year and warming El Nino ocean conditions. As environmental conditions normalized in subsequent years, the eelgrass rebounded, and the brant returned. Roser counted a population high of 4,600 birds in Morro Bay in 2001.
The story since then, as told in Roser’s annual reports to CDFW, is of another dramatic crash in eelgrass acreage in Morro Bay and a corresponding drop in the numbers of brant wintering there. Unlike the eelgrass crash of the mid-1990s, the latest decline has been more persistent and perplexing.
Biologists measure Morro Bay’s eelgrass acreage each year. Eelgrass spanned 344 acres as recently as 2007 but had dwindled to just 14 acres by 2017. Not surprisingly, Roser’s 2016-17 brant survey recorded a population high of just 319 birds and a low of 43. Roser’s brant-use-day metric has fallen by 90 percent since the nearly 500,000 brant use days he recorded in 2001. In the past five years, brant use days have measured around 50,000 a year. Money from the purchase of the California duck stamp-validation, required to hunt waterfowl in California, is funding research into the eelgrass decline along with restoration efforts.
In addition to fewer numbers of brant frequenting Morro Bay, Roser has noticed behavioral changes in the birds that still show up. Increasingly, the brant are foraging on secondary food sources that include salt marsh vegetation and green algae species such as sea lettuce with eelgrass in short supply.
Roser takes some solace that the overall Pacific Flyway brant population is holding steady if not increasing, estimated between 130,000 to 165,000 birds. Roser says waterfowl biologists are seeing flyway-wide changes in brant behavior that they suspect may be linked to climate change.
Fewer brant are migrating to Mexico for the winter. More are remaining in Alaska and their northern range throughout the year as warming Arctic conditions require fewer calorie demands and less ice exposes more eelgrass. Ten years ago, less than 10 percent of the population wintered in Alaska. By 2017, almost 40 percent of the Pacific Flyway population spent the winter there.
“This bird is tied to Morro Bay, our culture and our identity,” Roser said. “A robust wintering brant population needs abundant eelgrass beds. Eelgrass needs a healthy bay and watershed. Our actions as stewards of Morro Bay really do reverberate across the globe.”
CDFW photos: courtesy of John Roser
Top photo: Pair of black brant on Morro Bay
It does not take a leap of faith to believe that CDFW scientists have gained the upper hand in bolstering the population of yellow-legged frogs in the High Sierra.
Over the past three decades, Sierra Nevada yellow-legged frogs have become imperiled in California due to the two-pronged impact of introduced (non-native) trout and chytridiomycosis, a disease that is affecting amphibians worldwide.
Past introduction of non-native fish, including rainbow trout and golden trout, to benefit sport fishing in the High Sierra took a heavy toll on the species. High-elevation lakes where these frogs once flourished were largely fishless until fish stocking came into vogue. As the years passed, scientists determined that these introduced fish were depopulating the frogs by competing for food sources (primarily insects) and by predation (trout ate both adult frogs and their tadpoles). Chytridiomycosis, which affects many frog species, also impaired the ability of the Sierra Nevada yellow-legged frog’s skin to exchange vital nutrients, which often leads to death.
As a result, Sierra Nevada yellow-legged frogs are believed to have vanished from approximately 92 percent of their historical habitat, and halting and reversing that decline has become an important goal of CDFW, as well as other state and federal entities.
“This is an animal that only lives in the Sierra Nevada,” said Sarah Mussulman, a CDFW senior environmental scientist. “It is one of our unique California species that lives in high-elevation areas, and as an amphibian it serves as an important link between the terrestrial and aquatic ecosystems. This link is especially critical in the low nutrient, granitic basins of the High Sierra, where frogs and tadpoles consume insects and algae and are themselves consumed by a variety of snakes, birds and mammals.”
CDFW recently completed two projects as part of its ongoing efforts to reverse the population decline of Sierra Nevada yellow-legged frogs.
The efforts took place at two sites: Highland Lake and Clyde Lake, located approximately seven miles apart on the Rubicon River in the Desolation Wilderness area of El Dorado County. The projects were completed with federal grant funds earmarked for the recovery of endangered and threatened species (the species is listed as threatened by the State of California and as endangered by the U.S. Fish and Wildlife Service).
Highland Lake, along with its outlet, an unnamed stream, and two small adjacent ponds, supported a small population of rainbow trout when the project began in 2012. Trout abundance had declined in the absence of stocking in recent years but sufficient natural reproduction occurred in the inlet to Highland Lake to sustain the population. CDFW began using gill nets to remove rainbow trout -- the descendants of fish planted in the lake by CDFW from 1935 to 2000 -- in 2012, in partnership with Eldorado National Forest personnel.
During a frog-monitoring survey at Highland Lake in 2016, approximately 800 adult frogs were observed, as compared to a 2003 survey in which only a few tadpoles were observed. Because the frogs have consistently survived in this area despite the presence of chytridiomycosis, scientists believe they have a good chance at persisting in the area for a long time.
“Highland really had a population explosion over the past five years and can be counted as one of the most successful projects of this type ever undertaken,” Mussulman said.
The project at Clyde Lake was smaller and had somewhat different factors.
Golden trout, which frequently have the same negative impacts on Sierra Nevada yellow-legged frogs as rainbow trout, including predation and competition for food sources, were planted by CDFW at Clyde Lake from 1932 through 2000.
Once stocking was halted, the golden trout proved less resilient then the rainbow trout at Highland Lake, due to habitat factors.
“Clyde Lake sits in a north-facing granite bowl bordered by 1,000-foot cliffs, and no flowing streams enter the lake,” explained Mussulman. “There was no spawning habitat, which is likely why golden trout did not persist there after stocking was halted.”
The stream flowing out of Clyde Lake and four nearby ponds did support a small population of golden trout after plants were halted. The fish in the stream and ponds, which are self-sustaining populations, are precluded from moving from the stream into Clyde Lake by a fabricated dam. In 2013, frogs and a few tadpoles were observed in the stream alongside fish, and CDFW began removing the fish from the stream with gill nets to provide additional habitat for the frogs.
Nine years of monitoring data collected by CDFW scientists indicate that the area’s Sierra Nevada yellow-legged frog population, while small, is slowly increasing. Surveyors observed more than 120 frogs in 2016, compared to a low of six observed in 2005. Moreover, in 2016, for the first time, dozens of tadpoles were observed in the newly fish-free lower reaches of the stream.
“It is great to see these populations recovering,” Mussulman said. “It is a great privilege doing this work that helps keep these frogs on the landscape.”
CDFW photos: Highland Lake in the Desolation Wilderness, and a Sierra Nevada yellow-legged frog
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