Featured Scientist

Moccasin Creek Hatchery Manager Justin Kroeze


Kroeze and his daughters during a fish planting outing

Nestled in the foothills of Tuolumne County, about an hour west of Yosemite, Moccasin Creek Hatchery raises several species of trout to stock in lakes and streams in half a dozen counties. CDFW Fish Hatchery Manager Justin Kroeze is responsible for overseeing Moccasin Creek Hatchery’s operations and supervising the facility’s nine employees.

Kroeze was introduced to the hatchery business at a young age by his stepfather Jim Groh, a longtime CDFW employee who retired as a senior hatchery supervisor. Groh worked at the San Joaquin Hatchery, Kern River Hatchery and Moccasin Hatchery. And his dad, Fred Groh, worked at the Kern River Hatchery, San Joaquin Hatchery, Mokelumne River Hatchery and Feather River Hatchery.

Kroeze started volunteering at hatcheries in 2003, and two years later he landed his first job with CDFW as a fish and wildlife technician at Moccasin Creek Hatchery.

Moccasin Creek Hatchery has recently faced challenges as a wildfire in late August almost forced the evacuation of staff and their families who live in state housing on hatchery property. Moccasin is also currently raising fish to help stock waters in the eastern Sierra following a bacterial outbreak in July that affected 3.2 million fish at three CDFW hatchery facilities.

What was it like getting the evacuation order due to the fire in August? 

The fire started about a mile-and-a-half from the hatchery. Seven families live in state housing at the hatchery, including my wife and two kids. We all got an evacuation order due to limited firefighting resources, so we all packed up our belongings and were ready to evacuate. My youngest was very upset. But we did not end up having to leave. We’ve experienced fires nearby before, and the wind tends to travel up the canyon which is away from us. We were pretty sure we were safe, but we packed up and got ready to go just in case.

One of the most challenging aspects of the evacuation order was that my wife and family needed me, but simultaneously I was coordinating with the other employees that live on the property to make sure their families and animals had a place to go. 

Moccasin is currently helping fill the gaps for several hatcheries in the eastern Sierra that lost fish due to a bacterial outbreak. Has helping those hatcheries been a rewarding experience? 

It has definitely been a rewarding experience. The state hatchery system has to work together to provide the best opportunities to anglers. When Moccasin was hit with a flood in 2018, the Fish Springs Hatchery gave us fish to help us restart. Now we have the opportunity to provide fish for their restart. It all comes around. Running a single hatchery is a big enough challenge as it is. If we don’t help each other it would be even more difficult.

What memories do you have growing up around hatcheries?

I have fond memories of going on fish plants 30 years ago with some of the crew members that used to work at Moccasin Creek Hatchery. I grew up living at Moccasin Hatchery in the state hatchery housing. My dad was a fish hatchery manager at the time and my mom was the office technician. I’m now raising my daughters in one of the hatchery houses I lived in as a kid.

Where does Moccasin Creek Hatchery typically stock fish? How is this year different?

Moccasin stocks Tuolumne, Mariposa, Merced, Stanislaus, Alpine, Calaveras, Alameda, Contra Costa, Mono, Inyo, Fresno, Madera and Sierra counties. Roughly 50 percent of the fish we stock go into our local county of Tuolumne.

This year we’ll be doing our normal catchable rainbow trout plants, but we won’t be doing golden trout air plants due to COVID-19.

Fish hatcheries play an important role in CDFW’s efforts to stock fish throughout the state, but how they work is a mystery to much of the general public. What would you say are the biggest misconceptions about hatcheries?

I think there’s a misconception that trout hatcheries are funded from tax revenue. Our trout hatcheries typically do not receive money from the general fund. We’re funded directly from fishing license sales. When people buy a fishing license, a percentage of that license fee is actually contributing to growing fish and putting fish in the water so people have the opportunity to catch them.
We also get people stopping by the hatchery wanting to buy fish directly from us. We don’t do that. We stock public waters and give people the opportunity to catch fish.

What’s the key to raising healthy fish?

The key to raising healthy fish at our facility is having clean, cold water and low densities, meaning we make sure the fish aren’t too crowded. Genetics is also a huge component. Maintaining diverse genetics within our state’s brood programs results in healthier fish. If you’re starting a brood program from wild fish, it’s critical to have what we call a good spawning matrix. CDFW geneticists look at the genetics of each individual fish and cross the two fish that are going to create the most diverse genetics.

What’s the biggest challenge to raising healthy fish?

In the past, it was getting quality fish feed, but in recent years our feed manufacturers have gotten really good at putting out a high-quality product. The newer feeds are very palatable, easily digested and packed with ample vitamins, fats and proteins which aid in the fishes’ growth. Because the feed that’s manufactured these days is a lot more efficient than what we used to have, we’re producing healthier fish with less feed than we used to.

Staying ahead of fish diseases within the hatchery can be challenging. It takes close daily observation of each group of fish and working with our state’s Fish Health Lab when we notice any abnormal behavior from the fish or signs of disease.

What skills do you need to work at a hatchery?

You can take classes on fish culture, but for the most part our employees learn right here at the hatchery. Since we can teach fish culture, we like to hire employees who have a diverse skillset, including mechanical abilities. A lot of our employees have carpentry, electrical and welding skills. There’s a lot of science to raising fish, especially in the last 10 years with the new advances in fish culture techniques. But a science degree is not a requirement for working at the hatchery, especially for our entry level classifications.

Do fish have different personalities?

Yes, they definitely do. There’s a big difference in personality between the domesticated rainbow stock that we have here vs. trying to raise non-domesticated strains of trout. The domestic rainbow trout swim right up to you because they’re used to being hand fed. Brown trout swim away from you, which makes them less efficient because they’re swimming away from a food source. So domestic fish are easier to raise and grow because they’re more efficient eaters. Non-domesticated strains of trout can get used to you after a certain amount of hand feeding.

For several years our hatchery raised Lahontan cutthroat trout, which is a genetically distinct native species. They were escape artists. If one fish found an opening in a tank cover, then a bunch of them would find it. I haven’t seen that behavior from other types of fish.

What would you like the public to know about hatcheries?

First, it takes time to grow fish. The eggs we’re hatching right now won’t be stocked as fish until nearly two years from now. Second, our goal is to produce as many fish as possible and to give the fishing community the greatest opportunity to catch them. Sometimes due to budget constraints and other environmental factors there’s only so much we can do, but we want anglers to know we’re committed to providing as many angling opportunities as we can.

CDFW Photos

Laureen Thompson conducting a salt marsh harvest mouse survey in the Suisun marsh.


Thompson and a UC Davis graduate student putting a radio collar on a salt marsh harvest mouse.


Plant survey at the Suisun marsh.

When people ask Laureen Thompson what she does for a living, she often tells them she’s a “glorified mouse trapper.” If you get her talking more, she’ll tell you she’s an environmental scientist who works in the Suisun Marsh in Solano County. Much of her work involves the endangered salt marsh harvest mouse. Her duties also include managing CDFW’s role in monitoring compliance of permits for outside agencies and preservation agreements that protect the marsh and its wildlife. Thompson graduated from University of California, Davis, with a bachelor’s degree in wildlife biology. She was hired by CDFW in 1993.

What sparked your interest in wildlife conservation?

When I was a kid, my grandparents were very involved in the Associated Sportsmen of California. They interacted with the California Fish and Game Commission, wrote letters and commented on laws and regulations. I used to go out in the field with them. At the time, I didn’t realize how much they were influencing me. All through school I kept moving toward wildlife conservation. I didn’t know exactly what I wanted to do, but I kept following what I liked.

How did you become involved with the salt marsh harvest mouse?

I started out my career as a waterfowl biologist, and I heard of the position in the Suisun Marsh where an endangered mouse was potentially being affected by duck club owners managing facilities for waterfowl. I had the impression that the mouse was not being negatively impacted by the way duck clubs were managed for wildlife. We started surveying for the mouse the way it had always been done: putting traps in areas of short pickleweed plants. But when we didn’t catch anything, we started trapping in tall vegetation – really tall, almost to the point where it resembled an apartment complex to a mouse. We started catching a lot of the endangered mice, and we soon realized that the marsh likely has the highest numbers anywhere in the mouse’s range. We were able to hire some really good scientific aids and received several grants. We started doing radio telemetry studies, putting tiny radio collars on mice, as well as studies looking into mouse numbers in tidal wetlands vs. diked wetlands, and we were able to show that the mouse population is equal or greater in diked wetlands in certain times of the year. Now we’re looking at genetics and genetic diversity – not just in Suisun but in the mouse’s entire range from the bay area to Lower Sherman Island Wildlife Area and into the Bay-Delta.

What threats does the salt marsh harvest mouse face?

The public is familiar with sea level rise, and how we’re going to lose existing marshes and infrastructure as sea level rises. The marsh is where the mouse lives and they will eventually get flooded out and have no place to go. If we don’t accommodate for sea level rise and keep the marshes expanding and alive, we could lose the mouse. It may not seem like that big of a deal. But the mouse is a key indicator showing the health of the marsh. By losing the marsh, we lose what’s filtering and cleaning the water, which results in loss of habitat for birds, fish and other wildlife species. Diked wetlands are a way to protect the mouse and provide protections for roads and buildings. If we can improve management of diked wetlands, those improvements will also help bird and waterfowl communities.

What would you like the public to know about Suisun marsh?

The main thing I’d like people to know is that public use near the marsh can have a negative impact on the animals that live there. We want everyone to be able to recreate in the marsh and appreciate all it has to offer, but we also want people to follow a few simple rules like keeping your dogs in line and not dumping trash. There’s a lot of wildlife living out there that you don’t ever see. Be mindful. If there’s a trail, stay on the trail. You can end up destroying the marsh if you go deeper into it.

Are there any species of wildlife in the marsh that might surprise people?

There’s a population of western pond turtle, and many snake species including gopher snakes, racers and garter snakes. Additionally, there are numerous bird species, river otters and a large tule elk population.

What’s your favorite part of your job?

Getting out in the field at o’dark-thirty and watching the sunrise. I get to be out in the field five to 20 days per month. My duties allow me to have maintain flexible hours for the most part, so I can be out working before sunrise and after sunset.

What’s the most challenging part of your job?

Sometimes, it’s not having enough time in the day to get things done. Collecting and managing data, answering emails, attending meetings, and report writing. I really do enjoy all aspects of my job.

What advice do you have for people interested in conservation careers?

Get out and volunteer. Find out what you really like to do and don’t like to do. I receive many applications for seasonal staff positions. Too often, applicants have the necessary college education, but have not tried to obtain any conservation-related experience. When people apply for our positions, they should know how to think on their feet and have some basic experience through class fieldwork, seasonal work with an agency, or volunteering. When you volunteer, you get to know your likes and dislikes and increase your networking opportunities. If the people you work with like your work ethic, they may be able to help find job opportunities in the future. Don’t be afraid to ask someone if you can help out. You never know when it could lead to a paying job.

CDFW photos

CDFW Senior Environmental Scientist Jenn Garrison at the American Museum of Natural History in New York City


Jenn Garrison stands next to Milo-Baker Lupine, a rare native plant found only in Mendocino County.


A one-time art major in college, Jenn Garrison occasionally draws pet portraits for friends and fundraisers.


Away from work, Jenn Garrison’s various art interests – ceramics, painting, wall hangings, photography -- keep her busy.

Jennifer Garrison is a senior environmental scientist (specialist) based in Fort Bragg, Mendocino County. She joined CDFW’s Habitat Conservation Planning Branch in Sacramento in 2013 after working more than a decade as a project manager and environmental consultant in the private sector. Jenn moved to Fort Bragg in 2017 to bring her expertise and experience in conservation planning, habitat connectivity, mitigation and regional planning to Mendocino County.

Jenn was born outside of Athens, Ga., and grew up there and in South Carolina. She spent a good portion of her childhood on Folly Beach, S.C., an island town off of Charleston. She holds a bachelor’s degree in physical anthropology from Kent State University in Ohio.

You’re a long way from your childhood roots in the South. To what degree does your upbringing in the South reflect who you are and what you do today?

My parents were rather hands-off and as such raised children who became very independent. I spent much of my childhood exploring the natural world, romping around forests and estuaries with my Labrador retriever. I think my upbringing instilled a sense of curiosity, compassion and a duty to serve and contribute to my community. 

Let’s say you’re at a party without any scientists or CDFW employees around. How do you explain what you do for a living?

I am CDFW’s conservation planner in Mendocino County. I am here to work with others to pursue conservation, restoration and regional planning opportunities to save the best of what’s left, restore and reconnect habitats and increase the landscape’s permeability for wildlife movement.

What are some of the big challenges facing Mendocino County from your perspective?

Our county is in a period of transition, shifting from traditional industries – timber and fishing – to increased agricultural and tourism-based economies – cannabis, vineyards and eco-tourism. Collaboration and partnerships are and will continue to be essential for Mendocino County’s sustainable future. I am looking to strengthen those relationships and develop new ones through collaborative projects with local government, other agencies, special districts, public and private landowners, developers, universities, nonprofits and the public through engagement and citizen science programs. It’s through this work that I hope we will craft a future that highlights Mendocino County’s biodiversity and champions the sustainability of our industries into the future.

What does a typical day at work look like for you?

Prior to March, I was split between field work, meetings and desk time with an occasional bear tag validation. My portfolio includes a fair bit of work with rare plants and sensitive natural communities, something I wouldn’t have dreamed I’d be ever doing – and it wouldn’t have been possible without the tutelage of my supervisor, Gordon Leppig, our VegCAMP (Vegetation Classification and Mapping Program) staff, and local experts. Hands-on field work, community outreach, and collaborating with CDFW staff in other programs, non-governmental organizations, and private and public landowners are key components of my job. My greatest passion is habitat connectivity, and I’ve become a resource for CDFW scientists around the state for their connectivity questions. Since COVID-19 shelter in place began, my days are far more predictable. Less field time has translated into immense focus on existing and new projects, including a few regional planning efforts. My work involves lots of variability. It’s always interesting and there’s never enough hours in the days.

What are some of the bigger projects you’re working on?

When I moved to Fort Bragg, I became the department’s lead on the Willits Bypass project. In 2013-14, Caltrans built a freeway bypass to route Highway 101 traffic around the community of Willits, which resulted in Caltrans purchasing roughly 2,000 acres of land to the east of Highway 101 as mitigation for impacts to state and federal resources. The Mendocino County Resource Conservation District (RCD) manages the property and CDFW will hold the conservation easement, so we’re partners out there.

It was grazing land for 100 years, but we think about what it might look like in the next 100 years – not just the next 10 years. We’re now looking at how grazing can be used to control invasive plant species and encourage the growth of native plant species. The RCD modified fences to allow wildlife movement across the mitigation lands, which increases habitat connectivity. We’re seeing an uptick in species diversity and abundance. About five years ago, elk came onto the mitigation lands for the first time in decades. Now they are there year-round. We have beavers that have moved in for the first time in 70 years and we have an expanding river otter population as well. They’re doing a lot of free restoration work for us. We hadn’t seen amphibians in those creeks for years but last year we found a larval Pacific giant salamander in one of the creeks. This means at least one species of salamander has begun to breed in the mitigation lands’ creeks. We envision a field research station of sorts out there some day. The RCD has begun public tours and there are endless possibilities for outdoor education and research.

I’ve also been working to protect and preserve the Mendocino Cypress Pygmy Forest, one of the rarest plant ecosystems in the world and working with Caltrans and CDFW’s Native Plant Program staff at headquarters to maintain – and I hope someday recover – the Milo Baker lupine, a native plant that only exists in Mendocino County’s Round Valley.

What advice would you give someone considering a career in natural resources? 

Consider reading David Quammen’s The Song of the Dodo and E.O. Wilson’s Consilience. They’re inspiring. Know that there will be challenging days that test your resolve but keep going. Find mentors and nurture relationships with colleagues. Learn as much as you can from others, apply that knowledge, and build on it. Share your knowledge and think big; consider how your work fits into the broader landscape and how it contributes to sustaining – if not recovering – species diversity and abundance. Make it your goal to keep common species common. Don’t just focus on the listed species. Connect the dots and challenge yourself to see opportunities in every problem.

Tell us something about yourself many people would be surprised to learn.

I entered college as an art major with an emphasis on ceramics and have had many art shows over the years displaying my art, including batik wall hangings and photographs.

CDFW Photos