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

Ben Ewing shows off a large White Catfish that turned up in an electrofishing survey of Clear Lake.


Recovering the rare and threatened Clear Lake Hitch has been a priority for Environmental Scientist Ben Ewing.


Backpack electrofishing Deer Creek in Nevada County 2018.


Recycled Christmas trees provide warmwater fish habitat at New Hogan Lake in Calaveras County.


Away from work, Ben Ewing's 1967 Chevy Camaro occupies much of his time and attention.

Ben Ewing is an environmental scientist for CDFW's North Central Region. Based out of the region headquarters office in Rancho Cordova, Sacramento County, Ben serves as the district fisheries biologist for Alpine, Amador, Calaveras and Lake counties.

Born and raised in Santa Barbara, Ben holds a Bachelor's degree in wildlife management from Humboldt State University. He first joined CDFW as a volunteer staffing a hunter-angler check station at Camp Roberts on the Central Coast and was later hired as a scientific aid in 2004. Ben worked as a scientific aid in three CDFW regions – the North Central Region, the Marine Region and the Central Region – before landing a permanent position with CDFW in 2007 as a reservoir fisheries biologist in Riverside County. He rejoined CDFW's North Central Region in his current capacity in 2012.

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

When I am out in the field, I may be doing a boat-based electrofishing survey, backpack electrofishing, frog surveys, snorkel surveys, public outreach, warmwater fish habitat work or gill net surveys. All these surveys are used to gather information on the specific fishery we are working on.

I spend most of my spring working with the Clear Lake hitch up in Lake County. It's a threatened species under the California Endangered Species Act. In the summer and fall, I am doing a lot of backcountry work in the Sierra Nevada mountains.

I get to spend a lot of time in beautiful country and simultaneously try to improve the recreational fishery as well as try and save listed species such as the Clear Lake hitch, Lahontan cutthroat trout, and Paiute cutthroat trout.

What are some of your biggest challenges?

One of the greatest challenges is trying to recover the Clear Lake hitch in order to de-list it under the California Endangered Species Act. Getting money for a minnow is a lot harder than for a salmonid. It only grows to about 11 or 12 inches as an adult. No one eats it, no one fishes for it, so it's pretty much at the bottom of the priority list.

But it's native to the Clear Lake watershed. It's an indicator species that speaks directly to the water quality problems at Clear Lake – agricultural runoff, water diversions, drought. If we can improve the health of the watershed and bring back the Clear Lake hitch, Clear Lake will benefit, the local economy will benefit, the whole community will benefit.

What's one thing you'd like the public to know about the fisheries or fishing in the counties you work in?

That CDFW's North Central Region – and, really, the entire state of California – has an unbelievable amount of diversity of fisheries. California has world class trout, bass, salmon and other ocean fishing all in one state. We have high mountain lakes, the ocean, the Delta, the rivers. Californians are very fortunate to have so many fishing options. Clear Lake was recently voted the No. 1 bass fishing lake in the entire nation by Bassmaster Magazine.

Speaking of Clear Lake, how much active fisheries management really goes on there?

We monitor it by electrofishing regularly every spring and try to get out there every fall as well. It is usually a collaboration between CDFW's Fisheries Branch and our North Central Region. I've put fish habitat into Clear Lake so shore anglers will have better access to the fish. During the drought, we received complaints from the bass tournament organizers that the average weight of the bass was going down. Fisheries Branch and Region staff then went out to gather weights of bass to compare them to data collected in previous surveys to see if there was a significant decrease in average weights. We believe the drought may have impacted not only the bass, but the rest of the fish species in Clear Lake. Clear Lake is shallow and it loses a lot of surface acres in a drought, which negatively impacts water quality, food resources, and fish habitat. The record drought from 2015-2017 really hit the fishery hard.

How has COVID-19 changed the way you do your job?

It has limited what type of field work I can do due to the proximity issues. I had to cancel my Clear Lake Hitch work halfway into the season this spring, which was a bummer. We also are limited to specific field surveys that don't put us into close proximity of others. I can still get out into the field, but I am much more limited. As of right now we aren't allowed to do any boat-based surveys or backpack electrofishing (due to COVID-19 and physical distancing requirements). Those activities are typically how I do my usual field sampling.

Is there a particular CDFW project you worked on that you're especially proud of?

I take a lot of pride in trying to recover the dwindling Clear Lake hitch. The fish was listed in 2014, and I think it would be a great success story for our region and the department to be able to remove this fish from listing. It would be the first inland fish species successfully removed from the list if we could pull it off.

I take a lot of pride in acquiring black bass for the display tank at the annual International Sportsmen's Expo in Sacramento every January. We electrofish the Delta just prior to the expo and then release the fish back into the Delta once the expo is over. Year in and year out, the department supplies the biggest bass on the ISE tour. It's great to show off these big, beautiful bass to the public and what they can find just down the road in the Delta. I also think the ISE show is a great way to interact with our constituents and the public and share my passion for the outdoors and fishing with them.

Away from work, where are we likely to find you?

At the drag strip racing my 1967 Chevy Camaro, fishing in the backcountry or out on my ski boat somewhere.

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

Prior to joining the department, I worked at an auto shop changing tires as well as working as a mobile carpet cleaner. Having those jobs motivated me to get a better education so that I would end up with a career that I love. I feel very fortunate to work for the department and have a job that I love.

CDFW Photos

Shoshone pupfish habitat in the Amargosa River.


Shoshone pupfish from the Amargosa River.


Nick in the Amargosa River following green sunfish removal.

CDFW environmental scientist Nick Buckmaster works as a biologist in the Heritage and Wild Trout program. Based in Bishop (in the northern part of Inyo County), he’s far from where he grew up in San Diego County, but he couldn’t be closer to what he loves: California’s natural resources.

As a member of the team managing heritage and wild trout, Nick helps protect and restore native trout and habitats through field studies and data analysis. He initially joined CDFW six years ago to work in habitat conservation, moving over to his current assignment about a year ago. He’s a graduate of UC Davis with Bachelor’s degrees in Wildlife Fisheries Conservation and Geology. His Master’s degree is in Ecology.

Tell us about your current assignment – what to you do?

I’m the heritage and wild trout biologist for Inyo and Mono counties; which is really about managing the Eastern Sierra fisheries in a sustainable fashion. Rather than relying on stocking, we work to manage the populations to ensure good fishing into the future. That allows me to work on two different threatened trout species that occur out here – Lahontan cutthroat trout and Paiute cutthroat trout – as well as manage some of the most iconic trout fisheries anywhere in California, if not the United States. On a day-to-day basis, I could be anywhere from 11,000 feet up in the High Sierra, to the desert streams of the Owens River Valley. It’s a pretty sweet setup. When I got the job offer to come out here, I didn’t think twice. I packed up and lived out of my car for a couple of weeks, until I found a place to rent.

So you’re checking on the health of a fish in a particular body of water to make sure it’s doing well, and that tells you other fish in that area are doing well?

Fisheries monitoring can include a number of things. A lot of it can be quick reconnaissance assessments -- looking at population structure and relative weight of the fish. From there you can drill down into habitat specifics and stream production. What’s the stream temperature, are your pools deep enough, is there enough food for the fish to grow, are they growing fast enough, are they reaching the size we want? Are there other potential stressors, like drought, flood or upstream water diversions?

How did you come to decide on ecology – and fisheries, specifically – as a profession?

I grew up in a small town (Descanso) playing in the mountains and hills every day, hunting and fishing. When I took biology in high school, there was a brief section on ecology, where we talked about lakes and how the various fisheries are supported, and I was a huge fisherman when I was younger, and it just clicked. All of a sudden, fishing became a science for me. Science was something I was already passionate about. I always loved the outdoors, ecology and nature.

How do you balance the need to preserve our resources in their natural state, and the idea that we can or should take action to assist species?

One of the things I did previously out there was work a lot with pupfish in lower elevation areas. Those are species that only persist because of human intervention. The Owens pupfish was rescued by a fish and game biologist from extinction in 1969 – if he hadn’t put them in a bucket, they would have blanked out. At the end of the day, conservation always requires some measure of management.

In 1910, humans brought largemouth bass into the Owens Basin. That drove the Owens pupfish to the brink of extinction. If humans hadn’t also stepped in and removed the bass, the Owens pupfish would have been wiped out. There was a similar situation with cutthroat trout in the Walker Basin (Kern County), where a lot of the habitat had been impacted by logging in the late 1920s. The habitat still hasn’t recovered, so it’s up to us as a management agency to go in and try to take that ecosystem-based approach to restore the stream and the fishery.

Almost every habitat I’ve encountered out here has been so profoundly impacted by humans … it’s not necessarily a question of whether to intervene, but how to intervene in the most appropriate way.

Is there a particular project you’ve worked on in which you saw the results and realized you made a difference?

Last August we had green sunfish invade the Shoshone Springs on the other side of Death Valley. Springs in the desert are a lot like islands in the ocean. They’re the only habitats like them for tens or hundreds of miles. In this case, Shoshone Springs has an endemic pupfish called the Shoshone pupfish. All pupfish, at least in the desert southwest, are highly susceptible to non-native predation. These non-native predators can eliminate a pupfish population in less than six months in some cases. So in early August, we had the non-native green sunfish show up in the only known habitat for Shoshone pupfish. They had washed down from Crystal Reservoir in Nevada during a heavy rain season – typically it’s a dry riverbed. Another employee and I went out and worked in 110 degree weather, for two weeks, to remove the sunfish from the pupfish habitat. Within the course of just two weeks, we removed what can only be described as an existential threat to the Shoshone pupfish. Those efforts secured the species going forward. At the end, I don’t think I’ve ever felt more satisfied with my job.

If you had an unlimited budget and unlimited time, what project would you like to tackle?

I’d probably try to restore cutthroat trout in the Walker Basin. It’s one of the most distinct cutthroat trout on the face of the planet. They’ve been in that basin for millions of years. They’re very rare at this time, but if left to their own devices they get really large. They’re fantastic fish to catch – they’re just beautiful. I would probably put them back. We all love catching big cutthroat trout at Pyramid Lake (Nevada), and I’d like to see that in Eastern Sierra. A project like that would fit with my passions of conservation, native fish management and recreation.

Can you describe a typical day of work?

Today I’m working from home on a couple of reports involving analysis of fish population data. On a field day, I would be hiking into the high country or back country to conduct some level of fisheries assessment. Office days involve typical tasks like answering emails, data analysis or writing summary reports. To be honest, I really like the balance that I have. While it’s critical to do field work in order to collect the information necessary to make decisions as natural resources agency, it’s also important to answer emails and maintain relationships with the public, co-workers and management. If you collect all the data in the world, and don’t share it, you might as well not have collected it at all.

CDFW Photos