Featured Scientist

Isaac Chellman recording data on a recaptured Sierra Nevada yellow-legged frog in Bucks Lake Wilderness, Plumas County.


Isaac Chellman releasing a zoo-reared Sierra Nevada yellow-legged frog in Desolation Wilderness, El Dorado County.


Isaac Chellman holding a mountain gartersnake in Desolation Wilderness, El Dorado County.


Isaac Chellman looking for Sierra Nevada yellow-legged frogs in Desolation Wilderness, El Dorado County.

Isaac Chellman is an environmental scientist in CDFW’s North Central Region, which includes much of the northern Sierra Nevada and Sacramento Valley. Isaac has worked for CDFW since 2017, leading the region’s High Mountain Lakes (HML) project.

Isaac is originally from the east coast, where he earned a bachelor’s degree in Wildlife and Fisheries Biology (’02) and later a master’s in Aquatic Ecology and Watershed Science (’11) from the University of Vermont. Following undergrad, Isaac worked for the U.S. Geological Service Amphibian Research and Monitoring Initiative at the Patuxent Wildlife Research Center in Maryland, and later for the USGS Brown Treesnake Project on Guam and the Northern Mariana Islands. In 2007, he was hired by the USGS for backcountry amphibian monitoring in Yosemite National Park. After that, Isaac worked for the Western Riverside County Biological Monitoring Program. After taking a few years off for grad school, Isaac returned to Guam as a crew leader for the Ecology of Bird Loss Project, a multi-island ecological study focused on the secondary ecological effects of native forest bird loss caused by invasive brown treesnakes. He also spent five years as the crew supervisor for the Aquatic Ecosystems Program at Sequoia and Kings Canyon National Parks, before coming to work for CDFW.

Who or what inspired you to pursue a career as an Environmental Scientist?

I’ve been captivated with the outdoors for as long as I can remember. Growing up in rural New Hampshire, I was usually outside, often in wetlands. I became really interested in amphibians (frogs, in particular), and that love of ectothermic critters stuck. My dad and aunt are probably my two biggest influences in helping foster an appreciation for the natural world. Dad would often take my brother and me out on hunting and fishing trips, both locally and further afield. My aunt was the head of the New Hampshire Fish and Game Department’s moose project for many years, until retiring a couple years ago. She was a big inspiration for me, and she definitely supported my pursuit of a wildlife career as I was planning to enter college.

What type of work do you do as a CDFW environmental scientist?

As part of the HML project, the seasonal field crew and I visit aquatic habitats all over the northern Sierra Nevada, monitoring the status and trends of frog populations, assessing fisheries and working to help conserve threatened and endangered species, in particular. Most of the specific projects I work on — which tend to be federally funded through section 6 of the Endangered Species Act, State Wildlife Grants or similar sources — focus on monitoring the various Sierra Nevada yellow-legged frog (Rana sierrae) populations in the region, and carrying out actions to help recover the species.

Part of that work involves targeted removal of introduced trout, which prey on R. sierrae in locations where the species overlap. Trout are a major contributor to declines of R. sierrae and Southern Mountain yellow-legged frogs (Rana muscosa). Introduced trout, including brook trout (native to the eastern U.S. and Canada) and rainbow trout (native to the west coast, but not originally found in many areas of the Sierra Nevada), were originally stocked into high mountain lakes beginning in the latter half of the 19th century. Other species of trout are native to parts of the Sierra Nevada (including Lahontan cutthroat trout, Paiute cutthroat trout, Little Kern golden trout, Kern River rainbow trout and golden trout). However, prior to the mid-1800s, most of the remote, high elevation lakes and streams did not contain any fish, which had been precluded by glaciation and natural barriers to upstream fish movement. During my time with CDFW, we have removed introduced trout from a few specific locations that contain small populations of R. sierrae nearby. In those places, R. sierrae have often been relegated to smaller, fishless waterbodies, since the frogs can’t effectively reproduce in areas occupied by trout. We use mechanical methods (gill nets in lakes and backpack electrofishing units in streams) to catch the fish, the carcasses of which are then sunk to the deeper portions of lake bottoms, where they break down and return nutrients into the ecosystem. Once the fish are removed, the habitat is again available for the frogs to reproduce without the threat of being suppressed by predators with which they did not evolve.

Other projects I work on include translocations and reintroductions of R. sierrae into remote, fishless lakes on public lands within the known range of the frogs. For example, in Desolation Wilderness, my colleagues and I have undertaken several frog translocations, using one of the more robust R. sierrae populations in the northern Sierra Nevada as the source, and moving some of the adult frogs to a fishless lake basin about two miles away. The recipient lake basin likely had R. sierrae in the relatively recent past, but the area had been stocked with brook trout for many years, and the frogs were no longer present. However, the fish died out in the absence of stocking, so we began a project in 2018 to reintroduce the frogs. So far, that effort has been really successful.

All the adult frogs we release are individually marked with passive integrated transponder (PIT) tags, which are tiny (8 mm long) inert microchips encased in glass, which we insert under the frog’s skin to give each individual a permanent, unique identifying code that we can detect using a handheld scanner. We closely monitor the newly translocated population: surveys involve catching every adult frog we find, scanning and recording their PIT tag, and collecting morphological measurements. Those measurements have revealed that the recaptured frogs have been growing quickly and appear to be very healthy.

All of this work, and more, is part of an Interagency Conservation Strategy for mountain yellow-legged frogs in the Sierra Nevada. The strategy was developed over several years by a dedicated team of biologists, managers and administrators with CDFW, the U.S. Fish and Wildlife Service, U.S. Forest Service, National Park Service, U.S. Geological Survey, university-affiliated researchers and several California zoos.

What types of invasive species do you encounter?

The main invasive species connection to the HML work is a fungal pathogen, often associated with aquatic environments, known as amphibian chytrid fungus (Batrachochytrium dendrobatidis), or just “Bd” for short. Bd causes an amphibian-specific disease known as chytridiomycosis, which has been a major contributor to amphibian declines (particularly in frogs). The disease has been linked to many frog extinctions all over the world. The exact origin of Bd, and all the ways in which it spreads, is not fully understood, but the current prevailing theory is that Bd was likely introduced to North America at least a century ago, and Bd later spread up into the Sierra Nevada, possibly around the 1960s or 1970s.

Bd is currently present throughout most of the Sierra Nevada. Scientists have detected the pathogen in many different species, but some frog species are more susceptible than others to developing chytridiomycosis. For example, American bullfrogs (Lithobates [Rana] catesbeianus), which are native to the eastern and central U.S. but invasive in California, are a known host for Bd. However, the pathogen doesn’t seem to affect bullfrogs very much, particularly when compared with many other frog species. There is a lot of concern that bullfrogs may act as a vector for spreading the disease to more susceptible native species in California, like Foothill yellow-legged frogs (Rana boylii), and lower elevation populations of montane ranid frogs, including Cascades frogs (Rana cascadae), R. sierrae and R. muscosa). There are also native species that appear to be less susceptible to Bd-induced mortality (and could, therefore, also be potential reservoir hosts for Bd), particularly chorus frogs (Hyliola [Pseudacris] spp.), which are often known simply as “treefrogs” in our area. Although many native species are highly susceptible to Bd, not all populations have the same outcome when the pathogen arrives. Some populations are able to persist, and even thrive, despite the presence of Bd, whereas others become extirpated (that is, the population in that particular area dies out). Investigating why there can be such differences in outcomes from Bd infection in various populations, even within the same species, is one of the biggest areas of scientific research surrounding the pathogen.

Although Bd is now fairly ubiquitous in California, there is still concern about moving the pathogen around, in part because there are many different genetic strains of Bd that have been recently identified in the Sierra Nevada. Since we roam all over the Sierra Nevada to study native California amphibians, my crew and I decontaminate all gear that came into contact with the aquatic environment, including shoes and socks, nets and sampling equipment. These efforts also help greatly reduce the chance we’ll move any other high elevation aquatic invasive species (AIS) or pathogens around, including things like Ranaviruses (another group of microorganisms that can affect frogs). Additionally, if we’re ever working in lower elevations areas that may have other AIS present, such as New Zealand mudsnails and quagga/zebra mussels, we also freeze our gear overnight after use, in addition to the other decontamination procedures.

What do you love about your job?

It probably won’t be a shock to know that I love the field work. Being able to study native amphibian populations throughout the mountains and foothills of the Sierra Nevada is incredible, and I don’t take that opportunity for granted. Knowing that I’m doing work that directly benefits native species, while doing so in some of the most beautiful landscapes in the country, is hard to beat. I also work with great people, and being able to collaborate with others toward common conservation goals is something I love about the job.

The translocation project I mentioned is one of the more recent work projects that I’ve found gratifying. That project has been a group effort, involving other biologists who have laid the groundwork, including conceptualizing the project and securing the initial funding, and other staff who have helped in the field, including many seasonal scientific aids and partner biologists with Eldorado National Forest. It has been rewarding to recapture many of the frogs we have released and see that they appear to be doing very well, and it has been particularly exciting to see new frogs entering the population. Seeing some initial successes like this is motivating and gives me hope that our projects, along with other great work by colleagues working throughout the Sierra Nevada, can help recover the species.

One other thing I really like about the projects we undertake is that they are relatively low cost, particularly given the benefits we can see. Monitoring, translocations and mechanical fish removal projects are pretty cheap when it comes to conservation work. We can do these projects using small crews, composed mostly of seasonal staff, with limited resources in relatively short periods of time.

What advice would you have for a young scientist wanting to do what you do?

If you’re thinking about pursuing this kind of work, it’s important that you feel fairly confident you’ll truly enjoy it, whatever your specific interest may be. If you are pursuing what you love to do, any potential challenges will be more endurable. In terms of practical needs, it’s important to obtain a baseline education in this type of work, particularly to meet the minimum qualifications many jobs require. It doesn’t need to be wildlife or fisheries biology, specifically, but the degree should have a related focus (for example, degrees in general biology, conservation biology, environmental science/studies, molecular ecology, genetics, zoology, etc.), and that degree could be from a local community college or elsewhere, depending on your desires and resources. With that as a baseline, if you have the ability, I highly recommend applying to all sorts of seasonal field jobs, and try working for different agencies/organizations, on different projects, and with different species, to see what you enjoy the most. It can be a long road of working for low pay and living in austere conditions, but it can also be a lot of fun, and rewarding life experience.

Another big piece of advice I have is to be persistent: do not give up, particularly when it comes to applying for those seasonal jobs. When you’re just starting out and trying to gain experience, it can take many applications before you get interviewed, let alone be offered a job. However, perseverance is huge, and you will eventually be able to land a job in your field, if you keep at it.

Photos courtesy of Isaac Chellman.

Sara Holm is an environmental scientist with the Wildlife Management Program in CDFW’s North Central Region. Based in Colfax, she is the unit wildlife biologist for Placer and Nevada counties. Her work includes a multi-agency wildlife-crossing project, collared mule deer studies, coordinating the region’s upland game bird hunts, land acquisition and management and many resource assessment projects and surveys. She works primarily with deer, bear, dove, pheasant and turkey but dabbles with lions, elk and bighorn sheep. Critical aspects of her work include responding to wildlife conflicts and providing technical expertise to hunters and the public.

Sara earned a Bachelor of Science degree in Wildlife Management from Humboldt State University in 1999 and started her career two days later as a scientific aide with CDFW. She has worked in the North Central Region for 17 years. She also recently became a hunter education instructor.

What led you into a career as a wildlife biologist?

I credit my family for introducing me to wildlife. The first vacations I can remember were camping, fishing and visiting national parks like Yosemite, Glacier and Yellowstone. There is nothing as exciting as a bear jam (a traffic jam caused by tourists stopping their cars on the side of the road to view bears) in Yellowstone, or that quick flash of a trout taking your fly.

When I was young, I knew I wanted to work outside but all I could envision was being a park ranger. I took a forestry class in junior college but realized that was not quite right for me. My biology professor told me about Humboldt State University and CDFW, so I volunteered with CDFW’s Wildlife Investigations Lab. That is when I realized I could be a wildlife biologist and that I wanted to work for CDFW. It was all fascinating work, whether I was pulling a bear tooth at the front counter, feeding a lion in the pens or responding to a deer stuck in a fence.

I am inspired by the resources and by the chance to make a difference with science. It always made me proud to know I worked for the wildlife as well as the hunters (and anglers). When I complete a great project that I know will help wildlife, or validate a deer tag and talk to another happy outdoor enthusiast, I know that I am in the right place.

What is a typical day like for you at work?

One of the things I like best about my job is that it is never typical! On an office day I may start out answering nuisance wildlife calls, doing paperwork, checking on our collared deer locations or catching up on data entry -- but I could get a call that takes me into the field, to help an injured animal or check damage caused by a bear or lion. When I know I will be in the field the day usually starts early and could take me anywhere in my unit, or throughout the region to help on a colleague’s project.

The work can be hard if you are putting in 14-hour days trying to collar deer and you do not see a single animal, or you come out of the field to 20 messages on your phone, but I would do most of it for free because it is so fun. I have collared tons of deer, put bear cubs out in dens, flown many helicopter surveys, captured bighorn sheep and had many great adventures, but all of the work I do is made better by my fellow biologists. They are a second family to me and we have fun together, whether we are at a meeting or around the campfire. I think everyone should love their job but I am lucky to love the people I work with.

What is your favorite species to interact with or study?

I have a hard time choosing and I am always looking to work with something new. I love seeing fuzzy quail babies in the summer and flushing blue grouse out in the woods but I am more of a mammal person. I mostly work with mule deer and they are more fascinating than they look. Ground darting is anything but routine, as each captured animal is different. It is so exciting to get collar data back and see how and where they moved.

What aspect of working in the Sierra Nevada foothills is unique?

The foothills are interesting, especially considering my unit covers the foothills all the way over the crest of the Sierra to the Tahoe Basin (the elephant in this room is actually a bear!). The most complex part of this area is that there are many people living in urban environments that are actually in rural settings. Communities and pets, including livestock, actually create habitat in areas that are not ideal for wildlife. A pond in the middle of a small town attracts too many geese or maybe invites beavers that then flood roads. Rose bushes attract deer, which draw in lions. People want to raise chickens and then bears walk past homes and across busy roads to eat them. Sometimes I evaluate human-wildlife conflict in a busy city like Auburn, and other times I have to drive an hour out a dirt road for a similar issue.

What is the most rewarding project that you’ve worked on for CDFW?

I am the most proud of my work with the Highway 89 Stewardship Team. Our inter-agency team has built three wildlife crossings with fencing and wildlife jump-outs (which allow animals an exit point if they are within a fence) that are allowing animals to get across the road safely, connecting their habitat and making it safer for drivers. We have mentored other teams and run a successful program for students to teach others about the problems roads cause and the available solutions. These crossings will be in place long after I am gone, so it is a legacy that I can leave on the landscape.

If you had free reign and unlimited funding, what scientific project would you most like to do?

I believe we are currently doing projects that are good science and important for our agency but we could always do them better. I completed a project to evaluate the feasibility of reintroducing desert bighorn sheep to the North Central Region. With enough time, money, and legwork we may be able to clear out the livestock and make it happen. I would love to release some collared animals back in the Truckee River Canyon, spend my days monitoring them and witness their successful return to the area.

Is there a preconception about scientists you would like to dispel?

I guess I would dispel any lasting notions that science is only for men. I work with several other “lady bios” and I am proud of how we operate and the skills that we have. Sometimes when you are talking to the public, they will misconceive what you know or can do just because you are a female. After providing technical assistance I’ve been asked how long I’ve done this job as if to validate my credibility, or I’ve had questions automatically directed at male counterparts even though it’s my area and I’m the one who can answer the question.

Any advice for people considering careers in science or natural resources?

Be persistent and open to opportunity where it is available. We tend not to leave our jobs, so you may have to put in time and wait for something permanent to open up, but you can find a natural resource job in unexpected places like airports or land trusts. Volunteering and meeting people are how I got in. I would advise people to work hard for what they want because this is the best job!

Vicky Monroe is an environmental scientist with the Wildlife Management Branch in CDFW’s Central Region. Based in Bakersfield, she is the unit wildlife biologist for Kern County. Her work has included resource assessment surveys of deer, elk, pronghorn, upland game birds and San Joaquin kit foxes by vehicle, fixed-wing airplane and helicopter. She has captured black bears, elk and kit foxes and assisted with deer captures. Other critical aspects of her work include addressing the human-dimensions of wildlife management and wildlife conflicts, providing technical expertise and assistance and educating the public.

Vicky earned a Bachelor of Science degree in Psychology with an emphasis in Animal Behavior and a Minor in Biology from Colorado State University. She also earned a Master’s degree in Zoology from James Cook University in Queensland, Australia and is currently pursuing a graduate certificate in Environmental Conflict Resolution and Collaboration from George Mason University in Virginia.

What is a typical day like for you at work?

That depends on the time of year. During the spring, summer and fall, I have a steadily increasing volume of resource assessments, wildlife conflicts, phone calls, emails, meetings, office work, field responses, and sometimes extensive travel throughout the county. Kern County, at 8,100 square miles, is larger than many states. When I am in the field, the diversity of calls that I may respond to never ceases to amaze and thrill me.

In one week in my first year, I provided field responses from the Mojave to Maricopa, agricultural to oil fields, and throughout the Sierra Nevada and Transverse mountain ranges. I responded to calls regarding an injured condor, human-black bear conflicts, mountain lion depredation, urban kit foxes and desert tortoises, and conducted an elk calf capture. I also work closely with our wildlife officers, Natural Resources Volunteer Program participants, non-governmental organizations and local, state and federal government staff.

My relative slow season lasts about two to three months each winter. During that time I respond to emails and phone calls from the public, work to better organize file documents and reports and update data files. It is a good time to strategically assess wildlife management and conservation priorities, provide outreach to stakeholders and maintain and strengthen working relationships.

What is the most rewarding project that you’ve worked on for CDFW?

One of the most challenging, rewarding and unexpected “projects” that I’ve worked on for CDFW occurred my first year (2014) managing Kern County, and it was not so much a project as a call to action! Kern was experiencing an unprecedented increase in reported black bear activity, sightings, depredation and wildlife conflicts due in part to extreme drought. Some of us jokingly called it “Bearmageddon” and it certainly made for an intense year or two. Department wildlife officers and I captured and relocated numerous bears from Bakersfield and other areas. My two most unusual field responses were for multiple bears wandering into Bakersfield city limits in a single 12-hour period, and the night capture of a sow and cub stuck in a solar panel facility in Boron.

Providing increased public information, community outreach, media response and “Bear Aware” public meetings were a critical component of our strategy to mitigate human-wildlife conflicts and to educate and serve the public. CDFW’s Office of Communications, Education and Outreach staff was instrumental in supporting this effort. It was rewarding to collaborate so effectively to transform human-bear conflicts into an opportunity to empower residents with greater knowledge about wildlife, our department’s mission and values, responsible stewardship and co-existence.

What is most challenging about working with wildlife?

Probably the knowledge of the profound responsibility we have to each animal with which we come into contact. With each field response or capture effort, we become stewards of that individual animal. Its life is literally in our hands and it is difficult knowing that we cannot control every condition in the field. Whether capturing black bears in the desert, kit foxes in the city, elk in an enclosure or deer in the mountains, the focus, intensity and level of preparation remain the same. As biologists, we are armed with the expertise and experience to respond where others may not. That responsibility is not to be taken lightly. Another major challenge is balancing people’s expectations about when a field response, intervention or capture effort is necessary versus inappropriate.

What is the most challenging aspect of your career as an environmental scientist?

Trying “to do it all” in a 40-hour work week. As a unit wildlife biologist, I am on the front line and often in the public eye. It can be challenging to address everything that comes my way in the order and manner in which I would like to address things. Another challenging aspect is serving members of the public through education and outreach in a manner that empowers them to co-exist with wildlife, drives science-based management and conservation and balances the expectations people may have about how wildlife “should” act or behave.

If you had free reign and unlimited funding, what scientific project would you most like to do?

There are almost too many areas of scientific interest, management and conservation to narrow the scope. Kern County has the most diverse range of habitats of any county in the state; it is a remarkable place. I would love to conduct a study to assess genetics, disease, predation, fecundity (reproductive rates and success) and recruitment (fawn survival) of migratory and resident deer herds. I would love to conduct a study to assess genetics, survival, mortality and disease impacts on mountain lions and black bears. A study on the abundance, fecundity, and mortality of lesser studied species or species of special concern in Kern, such as fishers, would also be valuable. In particular, conducting a study to further assess genetics, disease impacts and mortality of the urban kit fox population in Bakersfield would be incredible. Really, I would love to do it all… I guess I would need a whole stable of research scientists on my team!

Any advice for people considering careers in science or natural resources?

Be bold, be serious, be focused, and never lose faith that you can end up exactly where you were meant to be with a career in science or natural resources. Serving as a professional scientist (such as a wildlife biologist) is a true calling, and the path is not always direct or clear. Do not limit yourself -- be open to pursuing different opportunities and unique experiences and never stop trying to gain new skills, diversify your skill set and cultivate deeper expertise. Remember that a college degree is critical and an advanced degree is valuable, although not vital. And finally, taking initiative is non-negotiable. Do not be passive. Show a willingness to acquire experience (either paid or volunteer) as readily as you attain your education, rather than waiting to graduate with a degree and then hoping to find career-relevant work. Building a career is a lifetime process, a journey, and no one can start it for you except you.