The Strategy and Science Behind Fish Stocking
Why fisheries experts stock certain species and sizes of fish in public water.

Stocking Trout

“Why did you stock that species of fish in that water?” is one of the most common questions I get as a fisheries professional. That question is usually followed by “And, why did you stock the fish at that size?”

While the answer to each of these questions can be tied to specific situations, there are some general reasons why biologists choose to stock certain species and sizes of fish.

Providing fish and fun

Rainbow trout are a favorite catch for many anglers. We stock them in Utah’s community ponds in the spring and fall.

The most common reason to stock a fish in a river, lake or reservoir is to provide anglers with a recreational fishing opportunity.

Stocking rainbow trout in waters across Utah is a good example of recreational fish stocking. Rainbow trout are stocked solely to provide a great fishing experience for anglers.

Rainbow trout are very adaptable. They can be stocked everywhere from high-mountain lakes and streams to valley reservoirs — and even into the fisheries in our towns and cities. Other fish stocked for recreational reasons include brook trout, Arctic grayling, walleye and channel catfish.

Munching other fish

Our biologists are always happy to find chunky wipers during survey work — it means they’ve been eating the prey fish we’re trying to control.
In addition to providing a recreational opportunity, some fish are stocked for more scientific reasons — to serve as management tools. This means the stocked fish have a job to do. Often, that job is to consume (and thereby manage) overabundant forage fish, such as Utah chub or golden shiner.

Bear Lake cutthroat trout are a great example of a predator fish. We’ve stocked them in Strawberry, Scofield and Lost Creek reservoirs to feast on populations of Utah chub, a fish species that would get out of control without a predator to keep them in check.

Wipers — a hybrid cross between a striped bass and a white bass — are another predator we often use to control prey fish. Wipers prevent the overpopulation of prey species in Minersville, Newcastle and Scofield reservoirs.

In each case, these fish have a job to do first, but there’s a major upside to having them in these waters: they reach large sizes, providing anglers with a chance to catch a trophy fish.

Helping fish in need

There are other species of fish in Utah, particularly fish that are native to the state (i.e., in Utah when European settlers arrived), which need stocking to boost or maintain their populations until conditions improve.

In most cases, populations of these fish have decreased as a result of changes humans have made to the fish’s environment. Stocking them helps maintain or enhance populations while biologists work with partners to find and address the factors leading to the population decline.

This can be a slow process, but there are recent indications it’s working. For example, in recent years, the U.S. Fish and Wildlife Service has recommended that two fish — June sucker in Utah Lake and razorback sucker in the Colorado River — be downlisted from endangered to threatened on the federal Endangered Species list.

This move to downlist is only possible because populations of both species are improving. More work still needs to be done, but raising and stocking these fish is one of the key factors in the progress they’re making toward recovery.

Stocking fish at the right size

The fish that fisheries managers stock typically fall into one of three categories: fry, fingerlings or catchables.

Supplemental stocking has helped Utah’s razorback sucker population.
Fry are newly hatched fish that are just a few days old. Fingerlings are months older than fry, and — just like the name implies — are about the size of your finger, typically 3 to 6 inches long.

Catchables are even bigger. They get their name because they’ve already reached a size anglers want to catch.

Choosing which size to stock often comes down to giving anglers the most bang for their buck.

It takes personnel time and money to raise fish. In fact, because fish put on more weight for every inch they grow, every additional inch a fish grows makes it more expensive to raise.

Stocking fish at the smallest size necessary to achieve management goals saves a lot of money. With that in mind, fisheries managers frequently conduct comparisons of different sizes of fish to see which size provides anglers with the greatest return.

These tiger muskie fingerlings were stocked in Scofield Reservoir in 2017. Today, any surviving adult fish could be more than 3 feet long!
Being cost conscious allows us to stretch our funding farther and maximize the number and variety of fish we can stock for anglers.

Using research to improve efficiency

Most of the rainbow trout stocked in Utah enter the water as either large fingerlings or catchables. If we stocked rainbows at a smaller size, we could put even more into Utah’s waters, but the vast majority of these smaller rainbows wouldn’t survive.

We’ve learned through studies that for every dollar spent to raise them in a hatchery, anglers catch larger rainbow trout, at a higher rate, than they would if we stocked the fish at a smaller size. Therefore, it’s more cost effective to raise rainbow trout to a larger size before stocking them.

In contrast, other species — such as kokanee salmon, splake, tiger trout, wiper and tiger muskie — perform well when stocked as small fingerlings. Stocking them at a smaller size saves money that would otherwise be spent feeding and maintaining hatchery space for the fish as they continued growing.

Some fish, such as walleye, are stocked as fry. We stock these fish by the thousands — and even the millions. Despite being about the length of your fingernail and the width of a pinhead, walleye stocked as fry are a major contributor to some of Utah’s fisheries. Willard Bay Reservoir is a good example.

A study conducted at Willard Bay found stocking only 500,000 walleye fry each year created measurable increases in the already existing walleye population in the reservoir. In fact, during two years of the three-year study, walleye stocked in the reservoir as fry made up a larger portion of each new year class of fish than those produced by natural reproduction.

Stocking walleye fry may not be successful in every water, but you can bet fisheries managers will try stocking fry first before considering stocking larger walleye, simply because anglers are receiving more for their money by stocking smaller fish.

Understanding the strategy

So, there you have it. The next time you’re looking at fish stocking reports or reading a news story about a fish that’s been stocked somewhere in Utah — or reeling in a stocked fish — you’ll have a better idea why that fish was stocked in a particular location, at a particular size.

Chris Penne

Chris Penne is the regional aquatic manager in the DWR’s Ogden office. As a self-described fish-head, he loves managing fish on the job and then catching them in his spare time.

SEEING YOUNG WILDLIFE ALONE? IF YOU CARE…LEAVE THEM THERE

SOCIAL CIRCLE, Ga. (April 5, 2021) – In the spring, it is not unusual to see young wildlife that appear to be alone. Before you attempt to help – remember that it is best to leave wildlife where you find them, according to the Georgia Department of Natural Resources’ Wildlife Resources Division (WRD).

“When you take wildlife out of their environment and bring them into your home, it often takes away that animal’s ability to then survive in the wild, where they belong,” explains Kaitlin Goode, program manager of the Georgia WRD Urban Wildlife Program.  “In most instances, there is an adult animal a short distance away – even though you may not be able to see it.  Adult animals, such as deer, spend most of the day away from their young to reduce the risk of a predator finding the young animal.”

The best thing people can do when they see a young animal is to leave it exactly as they found it for at least 24 hours. If the animal is still there after this time period, reach out to the local WRD office for guidance (https://georgiawildlife.com/about/contact).

Young wildlife demand a great deal of care and have specific nutritional requirements. If they are not cared for properly, they will not be releasable or retain the ability to survive on their own. Persons not licensed and trained in wildlife rehabilitation should not attempt to care for wildlife.  In fact, Georgia law prohibits the possession of most wildlife without a permit.

For more information, visit www.georgiawildlife.com and click on “Living With Wildlife” or contact the local Wildlife Resources Division office (https://georgiawildlife.com/about/contact).

Hayley Rutger, Mote Marine Labs

from The Fishing WireMote’s Dr. Jim Locascio holds a juvenile snook from a Sarasota County canal. Credit: Dr. Nate Brennan/Mote Marine Laboratory

Dozens of fish species — including common snook and largemouth bass — use certain parts of the upper Phillippi Creek system, according to the first fish survey of this urbanized network of canals, retention ponds and wetlands in Sarasota County, Florida.

The survey — led by Mote Marine Laboratory and funded by Sarasota Bay Estuary Program (SBEP) — found the highest numbers and diversity of fishes around upper creek areas mimicking natural habitat: curving canals or ponds with wetland vegetation and sections of slower-moving water. Less naturalistic canals, with shorelines straightened for optimum drainage, generally hosted fewer fish of fewer species.

Urban waterways can lose ecosystem value — for example, ability to support economically important sport fish — due to pollution, altered water flow and loss of natural habitat. Scientists around the nation are investigating how to help these waterways better serve wildlife, ecosystems and communities. Phillippi Creek drains approximately 60 square miles (145 square kilometers) of Sarasota County land, with downstream waterways richer in natural habitat and upstream waterways bearing a clearer human fingerprint: more straightened, channelized canals, sediment traps and retention ponds.

“We want to understand how to balance the role of these waterways between stormwater management and ecosystem function,” said Mote staff scientist Dr. Jim Locascio. “Can upper Phillippi Creek be enhanced to benefit fish without sacrificing its performance as a drainage system? That’s what we hope our survey results will lead into. First we needed to learn how the system is functioning and understand whether some creek areas are more productive in supporting fish.”

“Typical stormwater drainage systems were designed to transport excess water directly from residential areas to the sea; this concentrates flow through a narrow area,” said Mote Staff Scientist Dr. Nate Brennan, who was also involved in the project. “Such systems can experience flash-flooding as well as very reduced flow, and they can transport nutrient-laden sediment downstream, all of which affects how many species can survive in the canals themselves and in downstream ecosystems such as estuaries and seagrass flats. However, slower and more consistently flowing waterways can be refuges with higher diversity of prey animals as well as high-value, predatory fish such as snook and largemouth bass. Upper Phillppi Creek is dominated by straightened canals, but it also includes good refuge areas and sites with potential to create more; that really interests us.”

Since the 1980s, Sarasota County has significantly enhanced its measures to prevent floods and enhance water quality, most commonly using wet ponds. Ponds help delay the discharge of runoff, capture sediments and protect downstream ecosystems. County officials and Mote scientists each want to know whether further enhancements will help support fisheries.

Based on discussions with Sarasota County and SBEP staff, Mote scientists surveyed fish and select invertebrates (such as shrimp) at about 70 sites – most along upper Phillippi Creek, north of Bahia Vista Street and east of Beneva Road, and one downstream from this junction: Red Bug Slough preserve. Sites represented three habitat types: canals with generally straightened shorelines maintained to drain storm water; secondary stage canals with more bent shorelines, restored wetland areas, a natural preserve and sediment traps; and retention ponds known as the Celery Fields.From left: Mote scientists Dr. Jim Locascio, Dr. Nate Brennan, and Greer Babbe use a seine net to survey for fish in Sarasota County’s stormwater canal system. Credit Conor Goulding/Mote Marine Laboratory.

“Canals are a common feature around Florida and around the world, which means the results of this study could be far reaching,” said John Ryan, Environmental Manager for Sarasota County’s Stormwater Environmental Utility. “Nature friendly drainage designs could add value to the lives of a great many people who live on the world’s coasts.”

During March-May and September-November 2016, Mote scientists and interns used purse seine nets to catch, identify, count and release fish and invertebrates, measuring a sample of them. The scientists documented temperature, salinity, dissolved oxygen and the presence or absence of vegetation.

In all, the researchers counted 36,136 fishes and invertebrates in 37 scientific groups. Overall, the most abundant species were the native eastern mosquitofish (scientific name: Gambusia holbrooki), which were 46.5 percent of all animals counted. Also abundant were non-native tilapia (Oreochromis spp., 13.3 percent), native  grass shrimp (Palaemonetes spp., 11.5 percent), and native sailfin molly (Poecilia latipinna, 9.2 percent). Native blue killifish (Lucania goodei), native least killifish (Heterandria formosa), and native Seminole killifish (Fundulus seminolis) were semi-abundant.

The highest biodiversity sites — with the most species and the most evenly distributed numbers of animals in each species — were secondary stage canal habitats. Their complex curves, vegetation and flow patterns can mimic natural habitat. Less biodiversity was found at retention pond sites, followed by the least naturalistic sites: canals.

Common snook (Centropomus undecimalis) — a favorite Florida sport fish — were found at 15 sampling sites in seven areas. Among those areas, 61.6 percent of snook were in secondary stage canal habitats, especially two sediment traps. All snook were juveniles that had completed their larval, or baby, stage within the past two years.

“Of the juvenile snook we found, a notable number were in sediment traps, which are used to keep sediment from moving downstream but also appear to mimic the natural systems where the snook larvae settle and become juvenile fish,” Locascio said. “In wild tidal creeks, snook may settle in terminal ponds with reduced flow. Sediment traps may be creating similar habitat as a byproduct. However, we need to better understand how the snook are affected during maintenance, when the sediments are removed. This is one good opportunity for follow-up research.”

Largemouth bass (Micropterus salmoides) juveniles and/or adults were found at 30 sites in eight areas, with 69.2 percent in secondary stage canal habitats.

According to Mote’s report, “…secondary stage canal habitat which included preserves, sediment traps and restored wetlands were most important for snook and largemouth bass and maintained the highest levels of diversity.”

“Some engineered habitats are mimicking natural habitats and functioning as recruitment areas for these fish in upper Phillippi Creek,” Locascio said. “That is a very positive finding, and there is more that could be done if additional areas can be enhanced and then monitored through future surveys.”

Locascio continued: “Some fish-friendly enhancements might even save money; for instance, say you have an area that’s difficult and costly to manage. Why not use that as a habitat restoration site, ultimately improving conditions for fish and decreasing maintenance costs such as removing vegetation?”

Other recommendations from this report include:

• Build fish-friendly features resembling the current sediment traps but varying in design to enhance their appeal to snook and bass. Then follow up with a monitoring program and fish-tagging studies to determine which designs help support fish.
• Find even more options for fish-friendly upgrades at multiple scales along Phillippi Creek by applying the current results to a mathematical model published by others in 2015. If the model applies to Phillippi Creek fish habitat, it could provide a wealth of additional ideas for fish-friendly, waterway management. 
• Make better use of non-native tilapia, which are abundant in the Celery Fields retention ponds but may not travel far due to weirs that limit water flow. It the weirs could periodically release a pulse of water — and tilapia — safely and strategically, those tilapia may provide additional food to native, predatory fish downstream.

“The next steps are exciting,” added Brennan, “because they can involve eco-engineering where we consider stormwater management goals but add components like ecosystem health and societal benefits.  Places like stormwater canals that are often hidden from society can actually be transformed into attractive, productive urban ecosystems that improve property value and natural productivity.”