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.

Montalvo collecting samples at an oil spill in the Huntington Beach channel


Quagga mussels found in Lake Mead


New Zealand mudsnails found at the Lower Feather River


Montalvo working a spill in the Oakland Harbor

Environmental Scientist Angie Montalvo is the aquatic invasive species (AIS) regional coordinator for CDFW’s North Central Region. Her job is to ensure that invasive species – including quagga and zebra mussels, snails, crabs, clams, fish and aquatic plants – don’t find their way into bodies of water in the region.

Montalvo graduated from the University of California, Davis, with degrees in biological sciences and behavioral psychology. In 1996, she was hired as a scientific aid in CDFW’s Aquatic Bioassessment Laboratory. She was hired as a full-time scientist in 1998 and spent about 15 years working for CDFW’s Office of Spill Prevention and Response (OSPR) on issues involving statewide pollution response, natural resource damage assessment and biological monitoring for macroinvertebrates. Through her work at OSPR she got to know the North Central Region, which helped earn her a promotion in 2013 as the region’s lead AIS coordinator.

What inspired you to become a scientist?

I’ve always been interested in the environment and being outdoors, and I wanted to see positive change for the environment. I always envisioned myself doing a great deal of field work because I enjoy it immensely, and I wanted to be a voice for the natural resources in our state. I developed my interest in AIS while at the Aquatic Bioassessment Lab and while working for OSPR. At OSPR, the focal point was protecting the state’s natural resources from damages due to various pollutants. My current job is somewhat similar, but I am protecting our natural resources from the impacts of introduced AIS.

Tell us more about your role at CDFW?

My work is focused on aquatic biology, mostly dealing with inland, freshwater issues. Currently, there are no waters infested with quagga or zebra mussels within my region, so my focus is on prevention and monitoring. I conduct a lot of monitoring of waterbodies where the risk of introduction and establishment for quagga and zebra mussels falls within the moderate to high range or is unknown. I typically conduct field sampling three to four days per week between late March through November, depending on weather conditions. I monitor for other invasive species as well, including the New Zealand mudsnail, Asian clam and invasive aquatic plants such as hydrilla and Eurasian watermilfoil. Asian clams were introduced into California roughly 40 years ago and have spread from low elevation to high elevation waters. New Zealand mudsnails were introduced into California’s streams about 20 years ago and continue to spread throughout the state.

Another important part of my job is the inspection of watercraft that have entered California from other states. It’s common for people to purchase boats from out of state that have been launched in infested waterbodies. Watercraft entering California are checked while coming across state lines at a California Department of Food and Agriculture inspection station. Food and Ag staff will contact me if they quarantine a watercraft for invasive mussels or other AIS, and I will then reach out to the owner to arrange for an inspection.

Depending on the size of the watercraft, it can take anywhere from 30 minutes to several hours to complete a thorough inspection. I can usually identify quagga and zebra mussels visually. However, if I anticipate a difficult inspection — for example, a houseboat with a lot of small components to search — I reach out to our wildlife officers and their mussel detection dogs. These K9s are trained to detect by scent and can find things that I might not see. I’ve worked with the mussel detection K9s at least half a dozen times and it has worked out very well.

Decontamination of vessels involves using a high-pressure hot washer that can reach water temperatures of more than 160 degrees. I usually conduct follow-up inspections as well. Watercraft aren’t released until there are no remnants of quagga/zebra mussels or other AIS observed.

Why is it important to monitor for aquatic invasive species?

Unfortunately, once you have an infestation – for example, of quagga mussels – you can never eradicate them from a waterbody. They change the water quality and infrastructure of the ecosystem. The infestation results in a build-up or layers of mussels in the ecosystem, which can deplete the water body of nutrients and cause clogging and filtering issues. Not only do invasives alter the ecosystem, but they can affect fisheries, water delivery and recreational opportunities. Trying to address these issues after an infestation can cost many millions of dollars. Prevention, monitoring and education are crucial.

What has been your biggest career accomplishment so far?

I’ve worked on major oil spill incidents like Cosco Busan, the BP Gulf spill and others, which have all been major accomplishments and unique experiences.

Currently, the major accomplishment is there are no waters infested with quagga or zebra mussels within my region. I attribute this success to CDFW’s dedication to practicing the best sampling methodologies, continuing to improve and standardize its statewide program and having a great public outreach and education program.

We’ve had good success with outreach. For example, we have a campaign called “Clean, Drain and Dry” to get boaters up to speed on what they can do to prevent the spread of invasive mussels and other AIS. We strongly encourage boaters to clean, drain and dry their motorized and non-motorized boats and any equipment that comes in contact with a waterbody. We try to make sure boaters are aware that that their boats can be subject to screening or inspections prior to launching at a waterbody. Based on feedback and what I’ve seen, the outreach does translate. Boaters are more familiar with invasives and following proactive steps to preventing the spread of AIS.

In addition to your work with AIS, you also serve as the lead environmental responder when there’s an inland pollution incident. What does that entail?

As part of the region’s Inland Pollution Response Support team, I respond to discharge incidents from sources like wastewater treatment plants, asphalt or cement contamination, vegetable oil and wine waste. When there is a discharge or spill incident, I typically work with wildlife officers and other agencies in an incident command setting. I collect samples to assess the extent of the impact. For example, with a sediment incident, I determine the volume of sediment within the waterbody, extent of injury to the biological and physical habitats. If the containment is chlorine, I collect field water samples to determine the percent chlorine level. My role as a spill responder is not directly connected to my work with AIS, but if I am out responding to a spill, then I will document any non-native species.

What advice do you have for young people who are considering careers in science or natural resources?

I would say follow your passion and do what you enjoy. It can be difficult to get a job in environmental science or in the field of aquatic biology, so be proactive and start volunteering early. Applying for a position as a scientific aid is very helpful and don’t be afraid to move around to different departments or groups to get a sense of what you enjoy and learn valuable field experience.

CDFW Photos. Top Photo: Environmental Scientist Angie Montalvo conducting an aquatic invasive species survey at a reservoir near Lake Tahoe

Media Contact:
Ken Paglia, CDFW Communications, (916) 322-8958
 

Josh Bush is an environmental scientist with the Wildlife Management Program in CDFW’s North Central Region. Based in West Sacramento, he is the unit wildlife biologist for Colusa, Lake and Yolo counties. His work includes a multi-herd tule elk project, collared mule deer studies, coordinating the region’s land acquisitions, management of CDFW lands, and numerous resource assessment projects and surveys. He works primarily with elk, deer, bear, dove, pheasant, quail and turkey but dabbles with lions, bank swallows and Swainson’s hawks. His responsibilities include responding to human-wildlife conflicts and providing technical expertise to hunters and the public.

Josh earned a Bachelor of Science degree in Wildlife, Fish and Conservation Biology, with an emphasis in Wildlife Management, from the University of California, Davis in 2007. He started his CDFW career as a scientific aide in 2005, and worked his way up started his current position in 2011.

Who or what inspired you to become a scientist?

I have always been inspired by my dad, Mark Bush; my fondest memories are the many hunting and fishing trips we enjoyed together. My dad taught me everything he knew about wildlife, biology and the outdoors. He was a constant backstop for all my questions and never discouraged my asking them. After a long day in the field, I would come home and grab my taxonomy book to ID any animal we did not recognize. Those early trips evolved into an obsession with wildlife and progressed into a need to understand interactions between species and the role each played in the environment.

It was much later in college and after I arrived at CDFW that I learned that, you can apply science to the outdoors to help understand and ultimately help manage and create more of the wildlife that we all enjoy seeing. I strive to do this every day.

What is a typical work day like for you?

The only thing that is typical about my day it that is it is always unpredictable. I work mostly in my three counties but my job takes me all over the 17-county North Central Region. It’s a healthy balance of about 65 percent field work and 35 percent desk work. Field days are often 14-16 hours long with lots of overnights and varied tasks including setting camera traps, rescuing injured wildlife, visiting potential land acquisitions, running survey transects and capturing and collaring study animals. You could find me one day near Clear Lake tracking elk and then the next day in Lake Tahoe darting deer. Public phone calls and answering emails are a big and necessary part of the job. I like to start and end each week by clearing the phones and answering any emails that fieldwork prevented me from getting to. It is especially rewarding talking to hunters who are excited to get try their luck.

What is most challenging about working with wildlife?

The most challenging things are the hours that wildlife keep. I enjoy sleeping at night but wildlife can make that difficult. While I am still up early and out late to do portions of my job, science is evolving and remote cameras and satellite collars have made getting some normal shut-eye a little more possible.

What is your favorite species to interact with or study?

I have a soft spot for all animals but mule deer fascinate me – they are so hardy and able to live out their lives in some incredibly rough environments. There is nothing better than darting a mule deer, watching its migration via satellite and then picking up the collar after it is released. It is especially rewarding when you see an ear-tagged deer you collared years prior, knowing that it is still out there doing its thing.

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

I am currently working on it. I am the lead on a tule elk project in partnership with UC Davis and the Rocky Mountain Elk Foundation. The project uses both collars and a non-invasive capture/recapture process that features DNA extracted from elk droppings to determine population levels, among other things, in the herds occupying Lake and Colusa counties. We just started year two of a four-year project but it is already the most rewarding and difficult thing I have worked on. This is the first project I have led and, while it is tough managing all aspects, it is rewarding to see the early results and to work with such dedicated people.

We are currently tracking 38 collared elk via satellite and just completed the first year of fecal-DNA collection, which had myself and UC Davis Ph.D. student Tom Batter hiking the interior Coast Range in 100 degree plus heat picking up elk poop. While not the most glamorous work, it is certainly rewarding!

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

California’s Mediterranean climate is characterized by cold, wet winters, which can result in flooding, and hot dry summers, which can result in fires. My dream is to implement large-scale infrastructure projects that work with the climate-related ecology of California. Specifically, I would like to implement riparian setbacks and large wildland burn units as well as study and document the response from wildlife and the benefit to California. Last winter’s rainfall and flooding, as well as the unfortunate large-scale fires that followed, make these projects all the more important.

The Central Valley has lost a large majority of its riparian habitat since European contact. Riparian setbacks are a truly multi-benefit project. Setbacks could benefit flood control by slowing, sinking and spreading out water. They would also increase habitat for native wildlife and increase recreational opportunities for all. An excellent test case in benefit to recreation and wildlife is the Sacramento River. Above Colusa, the river is dynamic -- it meanders with gravel bars, cut banks and oxbows that are teeming with wildlife diversity. Downstream from Colusa the river is channelized with less habitat, wildlife, recreational opportunities and wildlife diversity.

Wildfire is a part of California, as years of suppression created unhealthy forests with high fuel loads, which lead to high intensity large-scale wildfires. These fires can be detrimental to urban areas, wildlife and wildlife habitat. Wildland burn units – large rotating wildland areas that are burned periodically on a rotational basis – can restore some of these native areas, increase the value to wildlife, habitat heterogeneity and fire safety at the wildland/urban interface.

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

My advice is to embrace everything about your potential career. Show up early, leave late, volunteer, network, be available for the jobs others do not want to do. If you are a hunter, get to know the little fuzzy creatures or little brown birds you would normally overlook. If you do not hunt or fish, grab a fishing rod or take a hunter’s safety class and sign up for a CDFW-sponsored hunt. Be well-rounded and let your passion for the job be visible.

CDFW photos of Josh Bush