A Day in the Life of a...

Fisheries Research Biologist

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By Larry D. Hodge

Texas Fish & Game magazine, March 2005

Prentice at work bench with fish and tweezersGone are the days when Texas natural resources were managed by guesswork. (One example of such was the introduction of common carp into the state’s waters around 1900 in an attempt to make up for the over-fishing of native species.) Today’s management decisions are based on science, and research biologists play a vital but largely invisible role in collecting information to guide those decisions.

John Prentice has worked for the Texas Parks and Wildlife Department for better than 30 years. Currently he’s a research biologist stationed at the Heart of the Hills Fisheries Science Center near Kerrville. I caught up with him there while he was taking liver samples from largemouth bass for one of his current projects.

“The project I’m working on today deals with the reintroduction of northern strain largemouth bass into lakes that were stocked with Florida strain bass and are now 100 percent Florida,” John said. “We stock the Florida strain to take advantage of their tendency to grow to trophy size. Northern strain bass, at least during their first few years of life and under some conditions, can be more readily caught. Anglers have different preferences. Some don’t mind waiting for a large bass; others want a high catch rate. We want to be able to provide the mix of opportunities that anglers want. What we don’t know is, can we increase the percent of northerns in a lake after stockings produced a population almost completely composed of Florida bass.”

Four South Texas reservoirs are involved in the study—Calaveras, Coleto Creek, Choke Canyon and Amistad. “Part of the job of a research biologist is to design studies that will provide answers to questions,” John said. “We work with questions from management biologists, from the public, from ourselves. What do we need to know to do things better? What’s the most efficient way to stock fish? What do anglers want to catch? How can we most effectively regulate catch and harvest regulations? It’s all stuff that affects people who fish. We work for the anglers, the people who buy fishing licenses. Our job is to give them the best outdoor experience.”

Setting up and performing such projects involves a variety of tasks, including going to collection sites, dealing with weather and collecting and analyzing data. Biologists first had to determine the genetic makeup of the bass populations in each of the four lakes prior to stocking northern strain bass. Bass were collected by electrofishing. A liver sample was taken from each bass, and these samples were sent to a TPWD lab in San Marcos, where a procedure called electrophoresis was used to determine the genetic makeup. “Before we started, bass populations in all the lakes were virtually 100 percent Florida or a Florida-northern cross,” John explained. “Then we established sites where we would and would not stock northern strain bass, so we could see if the northern strain bass spread. We’ve been stocking northerns for two years now. The results of the first year were that we got a good survival rate and incorporation into the population of the northern strain fish. In Calaveras the fish spread out, but in the other lakes they stayed more in the areas where they were stocked.”

“When we finish, we hope to be able to tell management biologists that yes, there is a way we can manage the fisheries to have the kinds of fish the anglers want,” John said. “Ultimately we could have a fishery that will provide both trophy fish and a higher catch rate.”

Pulling Livers

Fish go on ice as soon as they are collected by electrofishing and are kept frozen until processed. Pulling livers is simple. The fish are thawed just enough for their bellies to be snipped open with a pair of scissors. The fish is bent backward to expose the liver, then curved tweezers are used to grab a small piece of liver—about the size of a small pea—and drop it into a vial coded with the lake name, the location in the lake, date collected and number of that individual fish.

“Lab work is what we do a lot of the time,” John said. “It’s not all running around the lake. But it’s not a bad way to spend a day. Sometimes we have to be outside when it’s cold or pouring down rain.”

Advice for Wannabe Biologists

John had some advice for anyone considering pursuing a career as a research biologist. “Be sure you enjoy being outside no matter what the weather, because enjoying the work is important. Prepare yourself with education and experience. There’s lots of math, statistics and computer science in addition to biology. You also need to be able to communicate what you’ve learned—how to write. Visit as many different places that do this kind of work as you can.

“One of the things that really formed my career was the intern program where I got to work for TPWD during the summer,” John continued. “I learned what the department and the work were like, and they learned what I was like.”

Prentice standing by outdoor pond, wildflowers blooming on bank Working Conditions

John is fortunate to work at one of the prettiest sites TPWD has, and he took me on a tour of the facilities. Heart of the Hills (HOH) is located on a site that was donated to TPWD with the stipulation that it be used to produce fish for stocking into public waters. Although primarily a research facility, it is still a working hatchery that produces Guadalupe bass and acts as a backup to other hatcheries. In 2003, it produced hybrid stripers.

Earthen ponds fed by crystal-clear spring water stairstep down a hillside overlooking Johnson Creek. The soil bottom in the ponds results in more natural conditions than can be found in a large fiberglass tank or plastic-lined pond. Also, since there are matching ponds that are similar, the ponds are ideal for doing experiments in which researchers wish to investigate the impacts of a particular aspect, such as water temperature, while keeping other conditions similar. These experiments need to be done multiple times to verify results. For example, HOH did a study to investigate how many fingerlings get eaten by larger fishes immediately after the fingerlings were stocked into a reservoir. They kept some fingerlings in a cage for one hour before releasing them, released a similar number of fingerlings immediately into the environment and then compare how many were eaten by predators. Fewer stocked fingerlings from the group held in cages were eaten, most likely because they were able to orient themselves to their new environment before they were released.

HOH also has four arrays of outdoor tanks that simulate stream environments, with riffles, pools, and various kinds of substrate. They can do more than one experiment at a time, cutting the time needed to get results. The same can be done in indoor tanks.

Even though the researchers at HOH work behind the scenes and most anglers never know the role they play in keeping Texas fishing great, they remain closely connected to the public. One of the ponds in the hatchery is used for youth fishing events, and biologists can see the ultimate reward for their unsung efforts: a smile on the face of a kid hooked up with a fish. That’s what all the research is really aimed at accomplishing.


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