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Fisheries Research Highlights
Fisheries research is the foundation of smarter, more efficient and effective fisheries management. The DNR’s Fisheries Research Program focuses on evaluating existing fisheries management practices, innovating new techniques, and advancing the science and technology used to improve fishing in Iowa’s lakes, rivers, and ponds. This focus helps the Fisheries Bureau ensure that fishing license dollars are spent wisely and as efficiently as possible.
DNR’s Fisheries Research Program accomplishes all this with a relatively small group of highly skilled fisheries scientists. Seven research stations are located across the state. Each has a particular field of investigation. Five teams focus on fisheries in a specific Iowa water resource: natural lakes, reservoirs, small impoundments, interior streams, and the Mississippi River. The other two teams improve fish culture practices used in DNR fish hatcheries and investigate new ways to use technology to get information and data from fisheries managers to Iowa anglers.
122 252nd Ave, Spirit Lake, IA 51360, 712-336-1840 Jonathan Meerbeek ; Daniel Vogeler
The Natural Lakes Research team provides high quality and relevant research information to fisheries management and hatchery programs to enhance fisheries resources in Iowa’s natural lakes.
Iowa’s muskellunge stocking program began in 1960 with the stocking of 40 fingerlings in two natural lakes. The goal was to help anglers catch trophy-sized fish without leaving Iowa. The need for research evaluating the survival of stocked muskellunge raised on different feeds and stocked at different times of the year increased as muskellunge breeding techniques advanced. Finding the most efficient stocking strategies would reduce production costs and provide desired muskellunge populations that would meet the needs of anglers and hatchery production.
Starting in 1991, all muskellunge fingerlings stocked into Spirit and West Okoboji Lakes in Northwest Iowa were marked with freeze brands to identify the type and year they were stocked. Adult muskellunge were caught with gillnets each spring and examined for brands, individually marked with a fish tag, and released into the same lake they were caught. Stocked muskellunge survival was estimated from recaptures of branded and individually marked fish. In most years, none of the pellet-raised fall stocked fingerlings survived. Minnow-raised muskellunge fingerlings survived much better than pellet-raised fish, most likely because of their larger size (10-13 inches), better camouflage markings, and better health. This research also found that minnow-fed yearlings stocked in the spring survived much better than those stocked in the fall. Further evaluation showed that the survival of spring-stocked yearlings that were started on pellets and finished on minnows was as good as their minnow-raised counterparts and cost less to produce.
Since 2003, only muskellunge yearlings that were started on pellets and finished on minnows have been stocked in Iowa and population numbers have increased greatly. Yet, muskellunge population goals were not always met for all lakes. Loss of muskellunge into connected waterways during high flow events has added to some of the changes in population abundance. Further research found that the survival of spring-stocked yearlings to age-4 varied largely among years (8.3-52.6%) and limited adult population abundance. Using this information, a model was developed to predict adult densities at various stocking rates and times. More (24-33%) fish and frequent (yearly) stockings of spring yearling muskellunge are needed to meet management goals in Iowa’s lakes.
Changes to stocking rates and frequencies were made in Spirit Lake and the Okoboji Lakes in 2014 to improve adult muskellunge populations. In addition, all yearling muskellunge stocked in natural lakes since 2010 have been tagged before stocking to identify additional factors (fish length, condition, etc.) that may affect muskellunge survival. In 2015, this information was used to develop a plan for managing muskellunge in Iowa’s natural lakes.
Future research for this project will focus on understanding and improving stocking success of spring yearlings. For example, in 2016 and 2017, a subset of yearling muskellunge stocked into Spirit Lake were tagged with radio transmitters to help estimate post-stocking survival. Early results from this study suggest that yearling muskellunge survival to 100 days was 65% and was related to size at time of stocking, with larger fish surviving at a higher rate. Using this information, yearling muskellunge stocked in 2018 and 2019 will be required to be at least 13 inches before stocking and additional radio telemetry will be conducted to evaluate their post-stocking survival.
Shallow lakes in Iowa are known as “tweener” lakes because they are too shallow to always be good lakes and too deep to always be good marshes. Shallow lakes in Iowa can be in one of two conditions; turbid or clear water state. Lakes in the turbid water state have very dirty water, little to no aquatic vegetation, limited emergent vegetation, a sparse fishery dominated by carp and bullheads, and limited waterfowl production. Many of these lakes can also be in a clear water state with clear water, lots of aquatic vegetation, shallow bays covered with emergent vegetation, a desirable fishery dominated by sport fish species, and good waterfowl production.
In the past, many “tweener” lakes needed long drought periods to remove common carp and let emergent vegetation reestablish to shift back to the clear water state. The lack of large drought periods has caused many “tweener” lakes to stay in the turbid state for several decades. During this period, some shallow lakes were managed by applying pesticides and restocking with desired sport fish; little attention was given to aquatic macrophyte growth or long-term rough fish management and eventually these lakes shifted back to the turbid water state.
A similar renovation project at Lost Island Lake started in 2008 that did not include lake drawdowns or chemicals to eliminate the fish; however used alternative techniques such as incentive-based commercial removal of carp, installing fish barriers to prevent carp from reaching spawning areas, enhanced predator stocking, and targeted watershed improvements to renovate the fishery and improve water quality. Since 2008, about 800,000 pounds of carp were removed from Lost Island Lake and carp population estimates dropped from 136,718 fish in 2008 to 5,789 fish in 2016. Concurrently, significant improvements in water quality and angling were observed in Lost Island Lake. Due to the success of this project, in 2017, additional shallow natural lakes were identified that could benefit from a similar carp reduction strategy. Center Lake, Five Island Lake, Silver Lake (Dickinson County), Storm Lake, and North/South Twin lakes were selected and pre-renovation carp population estimates were conducted at Center Lake and North/South Twin lakes. Pre-renovation carp population estimates are important so that population benchmarks can be established that may guide a commercial fishing incentive program.
Continued monitoring of carp population and incentive-based commercial carp harvest will be important tools to guide future management and research in all of these lakes. In addition, carp barriers, stocking regimes, and watershed projects will be identified that may help improve the fishery. The findings from the suite of shallow lakes studied will be compiled and management tools that can be used to shift and maintain shallow lakes in a clear water state will be identified.
Natural reproduction of walleye in Iowa’s natural lakes is very limited. Annual stockings of fry and fingerlings are needed to sustain these fisheries. Consistent survival of stocked fry and fingerling walleye is key to increase walleye numbers in many Iowa’s natural lakes. These lakes often have high walleye harvest deaths, so stocking alone would not produce the walleye numbers needed to meet management goals. A combination of improved stocking survival and proper harvest regulations is needed to increase walleye populations. Since hatchery costs are dependent on the size of fish produced, most research in Iowa has focused on evaluating the survival of fall stocked walleye fingerlings. Several years of research examining age-0 and age-1 walleye electrofishing catch rates and population numbers concluded that large (at least 7 inches) walleye fingerlings are needed to meet adult walleye population goals.
Iowa’s walleye culture program has focused on developing production techniques that produce the largest walleye fingerlings. Many natural lakes are stocked in the fall with 9-10 inch walleye. Current research is evaluating large walleye fingerlings survival; early findings suggest that large fingerlings can provide valuable additions to walleye populations. Since walleye fry are the most important driving force for strong walleye year classes, research is also being done to evaluate the survival of fry stocked near shore directly from distribution tanks and those stocked away from shore via bags. Recaptures of marked age-0 walleye in the fall has shown that in some years, fry stocked offshore contribute better to the fall age-0 walleye population than those stocked near shore. In addition to stocking survival, managers also use harvest regulations to improve adult walleye abundance, size structure, and growth rates.
In 2007, a protected slot limit of 17-22 inches (1 fish over 22 inches, daily bag of 3 fish) was implemented on the Iowa Great Lakes and Storm Lake. The minimum length limit of 14 inches was kept on Clear Lake. Angler surveys have been done each year on most of these natural lakes to document changes in walleye harvest and release rates before and after the regulation change. Information about adult walleye numbers, size structure and growth rates were collected from spring broodstock gillnetting and recaptures of tagged walleye. There was a large increase in walleye harvest in Spirit Lake and the Okoboji Lakes right after the length limit change, largely because of a very large 2001 walleye year class that became vulnerable to harvest with the regulation change. At the same time, adult walleye broodstock numbers increased greatly in these lakes due to reduced competition among adult walleye and better growth rates. By 2013, walleye harvest rates had dropped a lot, but adult densities remained high, thus reducing walleye stocking survival through predation.
Walleye populations have varied widely in Clear and Storm lakes, but were more a result of variable stocking success than angler harvest rates. Further research monitoring broodstock densities, life history features of the broodstock populations, and stocking success with creel surveys, mark and recapture tagging, and age and growth analysis is needed to understand the impacts of harvest regulations and stocking strategies changes. Findings from this research will guide walleye management decisions and strategies for Iowa’s natural lakes and will be included in the 2018 comprehensive management plan.
Yellow Bass are not a native fish species to Iowa’s natural lakes. They were unintentionally stocked in Clear Lake in the 1920s during Mississippi River fish rescue operations and were first reported in Clear Lake in 1932. Two other natural lakes in Iowa (North/South Twin and Black Hawk lakes) were later found to have non-native Yellow Bass populations in the 1950s and 1980s. Yellow Bass population densities in natural lakes fluctuate widely and have resulted in stunted populations. In Iowa’s small impoundments, Yellow Bass often overpopulate and stunt, causing negative effects to the entire fishery that are difficult to overcome with traditional management practices.
Recently, new Yellow Bass populations have been discovered in several of Iowa’s natural lakes. In 2005, Yellow Bass were found in East Okoboji and currently are one of the most abundant fish species caught and harvested. Yellow Bass were discovered in Lost Island Lake in 2008 and now are the most abundant fish caught by anglers and by DNR sampling. Although the exact method of transport is unknown, it is not uncommon for illegal introductions of fish to succeed, resulting in declines of important game fish. Since many of Iowa’s shallow lakes have simple fish communities that are dependent on fluctuations in Yellow Perch reproductive cycles, lulls in fishing success often occur.
With recent improvements in Yellow Bass angler catch rates and size structure in several of Iowa’s larger natural lakes (i.e., Clear Lake, Okoboji Lakes, and Lost Island Lake), the rate of illegal introduction into other natural lake systems has greatly increased. For example, since 2013, new Yellow Bass populations have been found in five more natural lakes in Iowa. Concurrently, the Minnesota Department of Natural Resources has identified new populations of Yellow Bass in two of southern Minnesota’s shallow lakes within the last five years. Yellow Bass introductions are occurring at an alarming rate and thus the need to understand, evaluate, and communicate the potential impacts of these introductions is warranted.
Although Yellow Bass have occurred in natural lakes in Iowa since the 1930s, relatively little is known about their impacts to existing fish communities in shallow natural lakes. Work completed in 2017 for this study focused on evaluating the distribution of Yellow Bass in shallow natural lakes. Of the 32 lakes sampled, 12 had previous or newly established Yellow Bass populations. In lakes identified as having Yellow Bass populations, calcified structures were taken from a subsample of fish for age and growth analysis. Yellow Bass growth in newly established natural lakes was extremely fast (average length of 9.7 inches at age-4) compared to established lakes (average length of 6.7 inches at age-4).
This study will seek to thoroughly examine changes in fish community structure both before and after Yellow Bass introductions by examining catch rates and diet overlap of popular sport fish and Yellow Bass. Understanding effects of introduced predators on existing fish communities is crucial for determining management strategies that will improve fishing.
24143 Hwy 52, Bellevue, IA 52031, 563-872-4978
Ryan Hupfeld; Gene Jones; Royce Bowman
The Mississippi River team conducts research to answer critical questions to help our Fish Management Teams and partners manage the fisheries and habitat of the Mississippi River in Iowa.
Walleye and sauger support popular and important fisheries on the Upper Mississippi River bordering Iowa. Walleye continually rank high in angler catch and harvest in summer pool wide and winter tailwater angler surveys. Saugers are the majority of fish caught and harvested at tailwaters fisheries from October – March. This study was started because of concerns with high sauger death rates, highly variable reproduction in walleye, and the desire to maintain and improve these important fisheries.
Concerns with deep water post-release hooking deaths of sauger led to a study completed in 2012. Sauger were caught from the tailwaters of Guttenberg and Bellevue and held in a deep-water net pen to measure 72-hour death rates. Overall, hooking deaths was 18 %, but rates increased with depth. Death rates were 7 % for sauger caught from depths of 20-29 feet, 17 % from 30-39 feet, 25 % from 40-49 feet, and 41 % from 50 feet or greater. Sauger length was also found to be related to depth. Larger saugers were caught on average at shallower depths than small sauger. Tailwater anglers can use this information to decide where they should fish. Fishing in deep water yields small sauger; a large proportion of released fish will likely die. Fishing in shallower water yields larger fish and a greater proportion of released fish will survive.
Walleye reproduction on the Upper Mississippi River is highly variable with boom and bust years. Increasing and stabilizing reproduction would improve the consistency of the fishery. Seventy percent of walleye eggs come from 20-27 inch fish. Protecting this size class to increase the number of eggs in the system may improve future reproduction. In 2004, a 20-27 inch release slot limit was started from Lock and Dam 11 in Dubuque to the Missouri border. Evaluation of the walleye slot limit has shown an increase of 20-27 inch walleyes in pools where the regulation is in effect (Pool 13) versus pools without the regulation (Pool 11). While proportional stock density (% fish > 10” that are > 15”) was high at both Pools 10 and 13 (74 and 95 respectively), the percent of walleye over 20 inches was only 12 in Pool 10 compared to 47 in Pool 13.
Night electrofishing is done each October in the tailwaters of Pools 11 and 13 to measure walleye and sauger year class strength. Surveys in 2016 showed weak walleye and sauger year classes at Bellevue (Pool 13) and Guttenberg (Pool 11), however high water levels during sampling likely negatively affected catch rates. There are good numbers of 14-inch and larger sauger available, so anglers should have good success in the tailwaters this winter and spring. Walleye in the large 2015 year class should grow over 15 inches this summer and offer excellent walleye fishing. Future work on this project will study the effects of the slot limit on walleye reproduction.
Northern pike provide an important recreational fishery for Upper Mississippi River (UMR) anglers, consistently being one of the top ten species caught in Pools 11 and 13. Despite their popularity, there is limited information on northern pike populations in Iowa’s stretch of the Mississippi River. Angler expectations for UMR northern pike vary greatly because anglers target this species for many reasons. Some anglers target pike because of their trophy potential, while others are more consumption oriented. For many anglers, northern pike are a non-target species that they appreciate for the uniqueness they offer to their angling experience. This study was started in 2010 to provide information on northern pike population dynamics, angler opinions, and habitat availability in the UMR to help manage this fishery for diverse anglers.
While northern pike are found throughout the Mississippi River in Iowa, sampling and angler surveys show that their abundance and angler success decreases as you move downriver with the best fishing in Pools 9-14. Over three quarters of anglers surveyed at boat ramps in these pools reported catching northern pike compared to 15% from downstream pools. The percent of anglers that reported catching northern pike also decreased as you move downriver with 43% reporting harvest in Pools 9-11, 25% from Pools 12-14, and 3% from Pools 16-19.
To gain insight into northern pike seasonal habitat use, radio transmitters were implanted in 60 fish in Norwegian, Methodist, and Bussey lakes in Pool 10 and Crooked Slough and South Sabula Lake in Pool 13. In winter, northern pike used similar habitat (no flow, adequate oxygen, and 2-6 feet deep) as bluegill, crappie, and largemouth bass. In shallow backwaters, northern pike were very skittish under the ice and would swim away from noise. Radio tagged pike regularly avoided large groups of panfish anglers on a lake. Winter pike anglers should minimize noise and place tip-ups 50+ yards away from activity on the ice.
During open water, northern pike stay in backwater lakes or side channels in four feet deep or less with many pike found near vegetation beds. Cold water seeps, springs, and streams are known to gather northern pike during hot summer months when water temperatures can exceed 90° F. These areas are popular with anglers and offer excellent seasonal fishing opportunities; the importance of these areas to pike populations is unknown and being further studied. Results from telemetry work can be used to design and plan future backwater habitat projects and results from other parts of this study will be used to help fisheries biologists manage and improve the northern pike fishery on the UMR. This project is scheduled to be completed in 2017.
Shovelnose sturgeon support popular recreational fisheries on the Mississippi River and major tributaries such as the Des Moines, Iowa, Cedar, Skunk, and Maquoketa Rivers. These tributary fisheries usually coincide with spawning migrations of adult fish in April through June. Larger tributaries like the Des Moines and Cedar Rivers likely have resident populations that support year round fishing. Previous tagging and sampling efforts in the Des Moines and Cedar Rivers has documented movement between these tributaries and the Mississippi River in excess of 100 miles and commercial harvest of tributary tagged fish. The dynamics between tributary and main stem populations is poorly understood at this time.
River managers are worried that inadequate commercial regulations and increased harvest on the Mississippi River may adversely affect tributary recreational fisheries. Shovelnose sturgeon are long-lived, slow-growing fish that do not spawn each year, making them vulnerable to overharvest. Shovelnose sturgeon populations in Iowa beyond the Mississippi River have been studied little and basic population demographic information necessary for proper management of these fisheries is needed. The Des Moines River has recently had a series of summer sturgeon kills related to low flows and high water temperatures (>90° F), with estimates of dead fish in the tens of thousands, increasing the need to study these fisheries.
This five-year study was started in 2014 to determine best sampling procedures for shovelnose sturgeon, study sturgeon movement by tagging fish, and study sturgeon population dynamics (size structure, age, growth, and spawning periodicity) in the Mississippi River and its tributaries. This information will help biologists manage and improve this fishery.
Fish telemetry has provided proof that the availability of overwintering habitat is a limiting factor for centrarchid (e.g., bluegill, crappie sp. and largemouth bass) populations in the Upper Mississippi River (UMR). Centrarchids traveled long distances (> 3 miles) to reach suitable overwintering backwater areas with low current speeds, water depth > 1 m, water temperatures 1-3° C warmer than the main channel, and adequate dissolved oxygen levels. Lock and dam construction in the 1930’s greatly increased the total aquatic area of the UMR and provided deep backwater areas favorable to centrarchid populations; however, sediment deposition in backwaters has reduced the quantity of deep-water lentic habitats. As the post-impoundment UMR ages and backwater sedimentation continues, abundance of centrarchids will likely decline unless management actions are taken.
The Iowa Department of Natural Resources works collaboratively as part of the partnership of state and federal agencies that make up the Upper Mississippi River Restoration - Environmental Management Program. Many Habitat Rehabilitation and Enhancement Projects (HREP) are designed to increase sportfish populations important to Iowa anglers. Multiple HREPs have specifically focused on mitigating effects of backwater sedimentation through sediment dredging, restoration of aquatic connections between backwater and channel areas, and installing control structures that let oxygen-rich channel water enter into backwaters areas during periods of hypoxia. Research has documented positive effects of HREPs on centrarchid populations in backwater habitat and identified habitat variables (e.g., dissolved oxygen, velocity, and depth) critical to centrarchids.
Despite our understanding of the benefits of overwintering HREPs, many questions remain. For example, we do not know how many or at what interval overwintering areas are needed in a pool to keep centrarchid populations healthy. Information is lacking on the best size of an overwintering backwater and the amount of flow needed to maintain a fishery without adversely effecting fish use. This study, started in 2014, will help us gain a greater understanding of these questions and lead to improved efficiency and success of future overwintering habitat project design and placement.
57744 Lewis Road, Lewis, IA 51544-5103, 712-769-2587 Lewis Bruce
Man-made lakes research provides fishery managers the tools they need to manage small public lakes for anglers.
The Iowa DNR strives to provide the best fishing possible using a blend of good water quality, balanced fish populations, and good angler access. Aquatic plants play a part in each of these aspects.
The Lake Restoration Program is improving water quality and fishing on many of our lakes. Underwater plants often grow well in these restored lakes that do not have common carp, grass carp or muddy water. Plant growth provides habitat for fish of all sizes. However, too many plants affect anglers and other recreational users and can cause fish population problems. Gaining control of too many plants is never easy, quick, or without cost.
This project began in 2007 to help lake managers manage plants and thereby improve fishing in Iowa lakes. DNR fishery managers and researchers statewide use the Best Management Practices manual for aquatic plants developed during this project to guide sampling, provide control and improve lake plant populations.
Plants must be identified before they can be controlled. On-line aquatic plant ID guides were developed to assist both natural resource professionals and pond owners.
We have compared vegetation maps made with special fish-finders to sampling done with rakes at points across the entire lake. Each sampling technique has its benefits and provides helpful information about lake plant growth. Both of these sampling methods are being used to provide baseline information before zebra mussel numbers increase in the Iowa Great Lakes, and rake sampling is being used to find aquatic plant growth trends in lakes that have been through the Lake Restoration Program.
Lotus, a type of water lily that floats on and stands above the water’s surface, can spread to waters up to 15 feet deep and become a barrier to anglers and boaters. Ongoing herbicide control is needed to keep these plants from causing trouble in man-made lakes. An extended drawdown at the Mt. Ayr marsh will let biologists document the effectiveness of this technique to control Lotus and improve angler access.
At Cold Springs Lake near Atlantic, before 2014, growths of native underwater plants occasionally stopped people from using the lake. Because this lake does not have a large watershed that drains into it, a black dye has been applied in the spring of 2014, 2015 and 2016 to find the lowest amount needed to control plants. When applied at the right amount, this dye has worked well to reduce plant abundance through the summer months. Plans are to continue using dye at this lake and other similar lakes.
Though many lakes have an abundance of plants, when there are only one or two kinds, invasive species can become established more easily. Too many plants with the same growth form may also keep anglers from fishing and make control more difficult. For these reasons several kinds of plants were planted into lakes around the state to increase plant diversity and hopefully limit a single species from taking over the system. Efforts to increase plant diversity have been most successful at Red Haw Lake near Chariton and Lake Anita east of Atlantic. The water lilies at these lakes have done very well and other species, though less noticeable, are beginning to spread.
Mercury is a toxic, long-lasting and widespread pollutant. People are exposed to mercury mainly through eating fish. It is the one pollutant most likely to contaminate fish from Iowa waters.
Though this element occurs naturally, man-made sources of mercury have increased concentrations in the environment locally and worldwide, mainly through energy-related sources (e.g. coal-fired power plants). Once in the aquatic environment, mercury can be changed into methyl-mercury; the form that living things can absorb. The amount of this mercury in aquatic organisms can increase far above background levels by concentrating when moving up food chains. Anglers are advised of the presence of mercury in sport fish on a lake-by-lake or stream-reach basis (see the Fish Tissue Monitoring in Iowa webpage or the Iowa Fishing Regulations for current advisories).
Though mercury contamination in Iowa fish was not a widespread concern, the Iowa DNR started a proactive statewide research project in 2013 to develop guidelines to help Iowa anglers and residents make informed choices on what kinds and sizes of fish to eat from Iowa waters.
DNR biologists and Iowa State University researchers are sampling the smallest to the largest sizes of 17 different fish species (largemouth and smallmouth bass, walleye, sauger, northern pike, yellow perch, black and white crappie, bluegill, channel and flathead catfish, white and yellow bass, hybrid striped bass, freshwater drum and rainbow, brown and brook trout) from lakes and rivers across Iowa. Muscle tissue from these fish was analyzed for mercury. Comparisons of mercury level to fish species, length, weight, age, sex and place of capture will be completed to find science-supported trends that are useful to anglers and others eating fish caught in Iowa. Results to date show that in most of the fish that are kept to eat there is so little mercury that it cannot be detected (e.g. yellow perch, crappie, bluegill, trout, yellow bass). Predator fish, like largemouth and smallmouth bass, muskie, northern pike and walleye have shown the highest concentrations of mercury. However, levels above our 1-meal-per-week consumption advisory are usually found for only a small portion of the largest and oldest of these fish. This study should be completed in 2017.
Management biologists use many tools to evaluate fish populations throughout Iowa. Two commonly used tools are fish age and growth. These evaluation methods can tell a story about the life of a single fish or the whole population. Each fish species has many bones that can be used to collect age and growth information. For example, spines are the best structure to estimate the age of Channel Catfish, but inner ear stones are best for estimating Bluegill age. Regardless of the type of structure used, each lays down a visible ring during times of slow growth. Count these rings, formed during the winter, to get the age of that fish. This way is similar to how trees are aged, the number of rings represents the age and the distance between the rings show fast or slow growth. Slow growing fish have rings close together and fast growing fish have more space between rings.
Knowing the age and how fast or slow fish grow in a body of water is important to managers. A manager that estimates the age of several Largemouth Bass from a lake and finds the oldest fish is only four and the total length is 15 inches could have a problem with too many fish being taken from the lake. If growth is slow there may be a limited food supply or a “stunted” population caused by too many fish in the water body.
Before managers decide to change length limits on a lake or stock more predator fish, they must make sure their age-estimation data is correct and exact. ”Known-age structure libraries” can be created to test age estimation methods to ensure methods are correct and estimated ages are accurate.
Verifying ages of structures collected around the state and training people to read these structures was the catalyst for this project. Bluegill, ChannelCatfish, LargemouthBass, and RedearSunfish were stocked into four small lakes in 2011. These fish were marked to tell them apart from other age classes in the population. Over the past six years, 293 fish have been collected from these lakes. Structures from the fish will be verified as marked known-age fish and added to the statewide age and growth database. Scales, spines and inner ear stones were removed from the Bluegill, Largemouth Bass and Redear Sunfish, only the spine and inner ear stones were removed from Channel Catfish.
The lake mapping study started in 2012 has completed all of the data collection requirements. Lake bathymetry data was analyzed and processed for all 135 Significant Public owned lakes (SPOLs); 42 have been selected for more analysis with sportfish survey data. PDF maps and an interactive fishing atlas were created for management biologists and anglers. Management biologists can use these maps to plan management activities, e.g. placing fish attracting structures in the lake and herbicide treatments to open up fishing access. Anglers can use these two tools to plan a trip or find fish attracting structures while on the water. Boat, shore, and ice anglers can access these free tools on the Iowa DNR Fishing webpages.
15053 Hatchery Place, Moravia, IA 52571, 641-647-2406 Alan Johnson; Randy Esser
The Fish Culture Research team evaluates potential solutions to problems hatchery staff face through carefully designed experiments. Culture research increases the efficiency and productivity of DNR hatcheries through research.
Effective disease management and treatment at Iowa fish hatcheries is essential in raising quality fish for Iowa fisheries. Diseases can lead to fish mortality and reduce growth rates. In 2006, the Iowa DNR initiated a new project to dedicate more attention to obtaining approved hatchery drugs. Efforts will focus on improving prevention and management of Ich, a commonly occurring disease effecting our walleye production.
The Rathbun Fish Hatchery uses raw lake water that has not been disinfected in the tanks used to grow-out walleye. Since the water has not been disinfected, Ich infestations are common. Preventative treatments with formalin were used in the past to manage infestations. Formalin treatments are very effective, but increase the cost of walleye production. Beginning in 2009, research was conducted in production tanks to evaluate the reduced use of preventative treatment and the impact on Ich infection and the amount of formalin applied. A nine-hour formalin treatment every other day when Ich is first detected at less than 15 Ich cells per arch then daily treatments when more than 15 cells are detected is the most effective and economical treatment plan tested.
In 2014 a continuous 24-hour formalin treatment at 30 to 40 ppm was compared to the standard treatment tested in 2009. When 15 or more Ich cells were detected, continuous treatment began and continued until fish were resampled 4 to 7 days later and no Ich cells were observed. This treatment plan eliminated Ich infestations in seven days or less and compared to the standard treatment that was applied for two or more weeks. However, the final cost and amount of formalin applied between treatment plans was similar.
This research established a monitoring and treatment system used by hatchery staff to apply formalin judiciously resulting in cost savings and production of healthy fish. This study continues to garner knowledge to help hatchery staff reduce the cost of producing large walleye fingerlings.
Currently, all of Iowa’s large walleye are produced in a tandem pond to tank culture method where fry are stocked in ponds and grown on natural prey items, then converted to dry feed and grown to eight inches. Raising fry on dry feeds in tanks without first starting in a pond has been evaluated at the Rathbun Fish Culture Research Facility; however, the success of these techniques needed to be tested in production-scale tanks. Culture methods and tank designs may need changes before hatchery staff use this technology.
In 2016, we compared phase I fry production in 275-L tanks using Mississippi River brood stock sources and fed fry pelleted feed at 5-minute and 10-minute intervals until 38 days after hatch. All tanks of fry, regardless of strain, had ongoing deaths from cannibalism, either attempted or successful, because feed rates did not meet the appetite of fast growing fry. River source fry fed at 5-minute intervals survived at a rate of 53.8% while fry fed at 10-minute intervals had a 64.0% survival rate. This difference in survival was significant. The final size of fry was similar at 40 mm and 0.60 g. All river source fry were freeze branded to identify them in a comparison of pond rearing and tank rearing walleye fingerlings as part of another fisheries research study.
The training of pond fingerlings to eat commercial feed had been a challenge to production of eight-inch fingerlings until 2006. However, in the past five years hatchery staff observed poor survival during the feed training time which was believed to be from an unknown change in the Walleye Grower 9206 diet. In 2016, we compared survival and growth of pond-reared walleye trained to eat Otohime feed and then converted to WG 9206, BioVita, BioPro2, or Gemma Silk feeds. Fish fed BioVita had a survival rate of 76% while fish fed the other diets had a survival rate of 60.2% to 76.3%, but the difference was not significant. Final length of fish fed BioPro2 and BioVita was much greater than that of fish fed Walleye Grower 9206 and Gemma Silk.
Diets and tank shape were compared in a growout study in the research facility. All fish were graded for uniformity before phase III tank stocking. Three round tanks and rectangular tanks were fed BioOregon diets (BioOlympic followed by BioTrout) and three round tanks and rectangular tanks were fed WG 9206. Death rate was much lower in rectangular tanks (2.4%) compared to round tanks (10.0 to 12.2%). Death was caused by Columnaris disease that infected eroded caudal fins of fish in round tanks. Caudal fin condition was scored on a scale of 0 to 3 with three being an intact tail with lower scores progressively more eroded. The lowest caudal fin score at the end of the study was in round tanks fed the BioOregon diets. Death due to caudal fin erosion was not seen in raceways. Fish fed WG 9206 in round tanks were significantly longer and heavier than fish in the other tank shape and diet combinations. More research is needed to determine the dietary link to higher rates of caudal fin erosion in walleye.
Iowa DNR staff gets hybrid striped bass fry from other states to improve fisheries and culture methods to offer Iowa anglers more opportunities. However, the supply of fry is limited and raising pond fingerlings has been inconsistent and below expectations. This study will examine concerns of moving fry and fish production techniques to develop a management plan to raise hybrid striped bass in plastic-lined (Rathbun Fish Culture Research Facility) and earthen (Mt. Ayr Fish Hatchery) ponds. The plan will include best management practices for: 1) moving fry, 2) timing of first stocking, 3) recommended stocking densities, 4) pond fertilization treatments, and 5) water quality management. In 2016, current best management practices were compared in earthen ponds at the Mt Ayr Hatchery. Production performance of Sunshine Bass fed once daily by hand or four times daily by feeder was compared in plastic-lined ponds at Rathbun Fish Culture Research Facility (Rathbun) with similar best management practices.
Sunshine bass fry were stocked at a rate of 140,000 fry/acre at Rathbun. Ponds 1, 4, and 5 at Mt Ayr were stocked on 10 May with Sunshine Bass from Keo Fish Farms at a rate of 248,306 fry/acre counted by volumetric method. An error in fry estimates in the stocking barrel resulted in those ponds being stocked with 77% more fry than the standard 140,000 fry/acre stocking rate. Ponds 2 and 3 were stocked on May 11 with Palmetto Bass fry at a rate of 144,927 fry/acre. A mixed fertilization treatment of alfalfa and soybean meal was used to increase pond productivity throughout the culture period in ponds that were not fed fish feed. In ponds that were fed fish feed, fertilization was stopped after day 14 when feeding began.
Survival rate at the Mt Ayr Hatchery was excellent with one pond having a survival rate of 29% and the other four ponds with survival rates between 42% and 95%. Feeding ponds at Mount Ayr resulted in larger fish size compared to ponds that were only fertilized. The higher stocking rate of ponds resulted in 889,331 fingerlings harvested, the highest hybrid striped bass fingerling production to date at the Mt Ayr Hatchery.
Harvest at Rathbun was delayed to allow for a 35-day period of offering pelleted feeds so that any trend in growth or survival between feeding methods would become apparent. Feeding rates were increased from the initial feeding rate of 8 lbs/acre to 16 lbs/acre during the last week of feeding. Survival ranged from 40.7% to 58.0% among all ponds. Ponds fed by hand had a survival rate of 57.1% while those ponds of fish fed by automatic feeder had 47.3% survival which was not a significant statistical difference. Mean length was similar between feeding methods but the variation in length was significantly greater for ponds of fish fed by automatic feeder four times daily compared to ponds of fish fed once daily by hand. This finding suggests that fish size varies more which leads to cannibalism and reduced production with four daily feedings using an automatic feeder.
Production plans for 2017 include evaluating the best management practices at the Mt Ayr Fish Hatchery with pond feeding to increase fish size. Rathbun Fish Culture Research staff will evaluate the relationship of feeding methods and fish performance to produce a better product for stocking into Iowa’s fisheries.
The Iowa Department of Natural Resources produces over 200,000, 6 to 9-inch walleyes each year intensively on formulated diets at the Rathbun Fish Hatchery (RFH) or Spirit Lake Fish Hatchery. Both hatcheries use surface water sources to produce these fish in culture systems that only use water once before being discharged. The surface water sources may carry viral, bacterial, and protozoan pathogens which can cause fish deaths. Additionally, surface water sources for both hatcheries are threatened by aquatic invasive species such as zebra mussels. Disinfection systems to stop the spread of pathogens could be expensive using current culture systems. Though surface water sources at both hatcheries are plentiful, water quality and the presence of undesirable organisms are challenges to fish production. One fish pathogen, Ichthyophthirius multifilis, costs $25,000 to $35,000 each year to control during walleye growout at RFH.
One solution to these problems may be use of recirculating aquaculture system (RAS) technology which uses a small amount of makeup water to replace water lost during waste processing. When compared to our traditional culture systems, which replaces 100% of its tank water every one to two hours, the RAS may replace only 5 to 10% of its water each day. To continually reuse water while raising fish at high densities requires special components to remove waste products. These components are: 1) self-cleaning circular fish tanks; 2) microscreen filter for solids removal; 3) water pumps; 4) biofilter for ammonia and nitrite removal; 5) CO2 stripping column; 6) oxygen and ozone contactor; and 7) ultraviolet disinfection unit for reduction of bacterial counts.
The use of RAS for sport fish production is a new trend among state agencies. Egg incubation to food size fish production in RAS has been well documented for many food fish species like trout and salmon. However, few studies have evaluated RAS for walleye production. A pilot-scale RAS was built at the Rathbun Fish Culture Research Facility in 2014-15 with the goal of testing walleye and other sport-fish production in this technology. Fish performance, system performance, and economics information gained will help the IDNR develop these systems for production scale use.
In July 2016, feed trained walleye fingerlings were stocked into three culture tanks in the RAS to test grow-out performance to the nine-inch fall fingerling size. After four weeks in the system, the caudal fins of some walleye became eroded and those fish later died. Fish samples were sent for diagnosis and a Flavobacterium species of bacteria was found on the caudal fin. The condition of caudal fins was scored on a scale of 0 to 3 with three being a complete tail with lower scores reflecting increasingly worse conditions of tail erosion. At the end of the study, 38% of walleye had a score of 3 and 62% had a score of 0 to 2. Final survival rate was 78% and fish were 8.1 inches long and shorter than fish produced at RFH because of the disease issue. Future research should evaluate disease treatments to stop bacterial fin erosion (e.g. hydrogen peroxide).
Walleye fingerling growout occupied the RAS for about three months, leaving enough time to disinfect the system, repopulate the biofilter, and restock the system with cold-water species to culture overwinter. Walleye were harvested in October, the system was disinfected, and rainbow trout were restocked in December. The RAS was restocked with eight-inch rainbow trout from Manchester Fish Hatchery that were grown to a catchable size (11 inches) and stocked into urban fisheries in Ottumwa and Davenport, Iowa.
This project will determine how many fish can be produced in a RAS during summer and winter production seasons, using species that grow better at summer and winter temperatures that reduce the need to heat or cool water out of season. In the end, a more efficient production system will be developed to enhance fisheries for Iowa anglers.
22693 205th Ave, Manchester, IA 52057, 563-927-3276 Greg Gelwicks; Greg Simmons; Megan Thul
The Interior Rivers and Streams team gather and share information needed to better manage Iowa’s stream and river fishery resources and maintain and improve fishing opportunities for Iowa anglers.
Stream habitat is a key factor influencing the health of stream fish populations. Iowa’s river and stream fish resources have been greatly impacted by habitat degradation. Concerned with the continued degradation of river and stream habitats and fisheries, Iowa resource managers are interested in using stream rehabilitation practices to effectively improve these resources. This study began in 2010 to evaluate Iowa river and stream rehabilitation practices and develop management guidelines to improve river and stream habitat as well as fishing opportunities for Iowa anglers.
The first project being evaluated is the modification of the Vernon Springs Dam on the Turkey River at Cresco. The dam was converted into a series of rock arch rapids in late July 2010 to address safety and fish passage concerns. Pre-construction fish community and habitat sampling was done at three sites above the dam and two sites below. Over 3,900 game and non-game fish were marked below the dam to monitor fish movement over the new structure. Fish community and habitat sampling was also done at three sites on the Volga River to serve as control sites for the three upstream sites on the Turkey River. Post-construction sampling upstream of the project found 16 Black Redhorse, 11 Golden Redhorse, 3 Walleye, and 1 Northern Hog Sucker that moved upstream over the structure. Smallmouth bass and Black Redhorse were sampled post-construction above the dam at sites on the Turkey River and N. Branch Turkey River where they were not found pre-construction.
Pre-project fish and habitat data were collected in 2012 and 2013 for a dam removal on the Shell Rock River in Rockford. The dam was removed in the winter of 2014 and two years of post-project sampling have been completed. Golden Redhorse and Northern Hog Sucker were collected for the first time at sites above the dam in 2014, and increasing numbers of these species were found upstream in 2015. Channel Catfish numbers also increased at sites above the former dam.
A whitewater park and habitat improvement project was completed in spring 2015 at the site of the Marion Street Dam on the Maquoketa River in Manchester. Pre-project fish and habitat sampling was done at sites upstream and downstream of the dam in 2012-2014. Over 6,600 fish of 18 species were marked downstream of the dam to monitor fish movement over the new structures. Sampling in 2015 and 2016 found 234 marked fish representing 9 species that had moved upstream over the structures. Continued monitoring of these projects and investigations of additional stream rehabilitation projects will help guide future decisions and lead to improved methods, designs, and sharing of resources to improve Iowa’s river and stream fisheries.
Interest in modifying and removing aging, low head dams on Iowa’s interior rivers has increased over the past several years. This interest is driven by safety/liability concerns, deterioration of existing dams, and a desire to increase river recreation opportunities. Areas below dams are often popular fishing spots. A common concern is that dam removal or modification projects will negatively impact angling, particularly below the dam. The impact of dam removal or modification on angling has not been studied in Iowa and little information is available from other states.
A whitewater park and habitat improvement project was completed in spring 2015 at the site of the Marion Street Dam on the Maquoketa River in Manchester. The dam was removed and six structures were built to create whitewater features while also letting fish to pass upstream. The project is expected to improve angler access and fish habitat at the site. A roving angler survey was started in April 2012 to collect pre-project data on angler use, catch, and harvest on the Maquoketa River upstream and downstream of the dam. Anglers were surveyed in April-October for three years before, and will be surveyed for three years after construction. During 2012-2014, total angler participation ranged from 4,232 to 6,797 angler hours per year. Smallmouth Bass, Common Carp, Walleye, Bluegill, Crappie, Suckers, and Channel Catfish were caught most often during this period. The second year of post-project monitoring began in April 2016. In 2016, total angler participation was 3,770 angler hours per year, and Smallmouth Bass, Walleye, Bluegill, and Suckers were caught most often.
Measuring the impacts of a dam modification or removal project in Iowa will provide information to help managers address angler concerns with future projects. This information may also help identify project features which benefit anglers that can be incorporated into future projects.
Evaluation of Interior River Fingerling Walleye Stocking Strategies
Walleye fingerling stocking has greatly increased Iowa’s interior river Walleye populations over the last 20 years. This has created an increasingly popular fishery that has brought Walleye fishing opportunities close to home for many Iowa anglers. The success of this program has also increased demand for two inch long, Mississippi River strain Walleye fingerlings. Limited hatchery space has made it difficult to consistently produce enough fingerlings of the size and genetic strain requested for the program. Providing information needed to more efficiently use our limited hatchery production capacity, and exploring the potential of other fish culture systems to meet the demands of the river Walleye program is the focus of this study.
Available pond culture space has been a limiting factor for producing Mississippi River strain fingerling Walleye to stock in interior rivers. Recent research at the Rathbun Fish Culture Research Facility has shown promising results raising Walleye fingerlings using an alternative method, intensive fry culture. Intensively reared walleye fry are stocked into recirculating tanks and trained to eat formulated feed from day 1 post-hatch, instead of stocking them into ponds where they eat zooplankton (extensive culture). Evaluating the relative contribution of intensively reared fingerlings to interior river Walleye fisheries will determine if this production method could help further improve river Walleye fisheries.
Study sites were selected on four Iowa rivers to evaluate the contribution of intensively reared Walleye fingerlings to interior river Walleye populations. Extensively reared fingerlings were marked, hauled, and stocked alongside intensively reared fingerlings to serve as a control. Walleye fingerlings produced by this culture method are known to survive and contribute to river Walleye fisheries if river conditions are favorable. Intensively cultured Walleye fingerlings were marked with a circle freeze brand, and extensively cultured fish were marked with a bar brand. Over 61,000 marked intensively and extensively cultured walleye fingerlings were stocked in the Wapsipinicon, Maquoketa, Shell Rock and Cedar rivers in June 2016. Study sites were sampled during late-September and October to determine survival and growth of walleye fingerlings. This process will be repeated for several years. The results will help guide Walleye fingerling production and stocking methods to provide the greatest benefits for sustaining and improving Walleye fisheries in Iowa rivers.
14360 255th St, Boone, IA50036, 515-204-8021 Jeff Kopaska
Technology and Data Management provides computer-oriented technical help to field personnel by developing, modifying, installing and maintaining a statewide database and other software and hardware for fisheries applications, software and hardware training, and updating and maintaining systems. Technology and Data Management strives to make information about fish, fishing, and fisheries more available and easily accessible to the public.
Technology and data management efforts are used to make information easily available to the public and help fisheries staff be more efficient and effective in their work. Fisheries staff collect information, such as fish numbers and sizes in lakes and rivers or numbers of fish stocked. This information is stored and analyzed in many data systems that the public can view online. To make all this work, the technology and data management team creates and modifies data systems, trains staff in their use, and regularly updates the computer systems that provide information to anglers and the public.
This work is important because the internet is the tool agencies use to share information with the public. More than 40% of Iowa anglers visit the Iowa DNR web site often. It is necessary to continuously improve the web site and the information it provides to keep current with new technologies.
Activities associated with this work have been started to develop, modify and maintain databases which store large fisheries data sets. Interpretation of these data provides the basis for making effective management decisions. Products of this work include the following:
The DNR Fisheries Bureau is funded only by the sale of fishing and hunting licenses and equipment. Continued license sales are critical to provide the funding needed to manage Iowa fisheries. After years of simply selling fishing licenses, the DNR began a partnership with the Recreational Boating and Fishing Foundation (RBFF) in 2005 to assess fishing promotional efforts. These efforts were started in response to declining or fluctuating fishing license sales. Fishing promotional campaigns have varied from localized efforts to statewide and from specific target populations to all anglers. Using new strategies to sell more fishing licenses makes financial resources available to maintain and improve fishery resources.
Radio and television advertising, live events, movie theater advertising, magazines, letters, postcards and emails have been used to promote fishing to potential license buyers. An evaluation of fishing promotion efforts from 2005 to 2013 showed that lift (or increase in license sales associated with the marketing approaches) ranged from 0.1% to 4.6%. License sales patterns show that weather and economic conditions may strongly influence fishing license sales.
The results from these analyses support recommendations and suggestions for future fishing promotional efforts and highlight the uncertainty of major drivers of license purchase rates. Results from these assessments include:
Future assessment activities will continue to look at promotional efforts, as well as community fishing opportunities like the urban trout stocking program. The DNR is also starting an aggressive Recruitment, Retention, and Reactivation (R3) program for hunters and anglers, in partnership with sporting goods vendors and local conservation groups. The research done thus far, and building better partnerships, should provide more and better fishing opportunities and fishing locations closer to home for more Iowans.
In 2016, the Iowa Department of Natural Resources (DNR) conducted a comprehensive mail and online survey to evaluate the trout fishing activities and preferences of anglers fishing for trout. The Iowa DNR conducts this survey about every five years; similar surveys were conducted by telephone in 1975, 1980, 1986, 1991, 1996 and 2001, by mail in 2006, and by mail and online in 2011. A total of 3,605 angler surveys were completed, equaling 7.7% of the 46,604 anglers who purchased trout fees in 2016. Mean age of all trout anglers was 43.8 years, which is similar to what was observed in 2011.
Licensed trout anglers spent an estimated 489,455 days trout fishing in Iowa and made 720,611 trips to individual trout fisheries in 2016. Total annual angler trips were determined for each catchable, special, urban winter pond, and put-and-grow trout fishery in Iowa. North Bear (21% of trout anglers), South Bear (17% of trout anglers), Trout Run (13% of trout anglers) and Bloody Run (12% of trout anglers) were the top four most heavily used fisheries. Put-and-grow streams had the least angling use and ranked the lowest including Turner (94th), Monastery Creek (91st) and White Pine Hollow (88th). Streams with the highest number of angler trips per mile of stream open to public fishing were Baileys Ford (30,836 trips), Trout Run (Winneshiek County) (21,450 trips), Joy Springs (14,804 trips), Richmond Springs (13,808 trips), Turkey River (13,210 trips) and Twin Springs (13,048 trips).
The average trout angler spent 11 days fishing Iowa’s trout waters. Overall, trout fishing activity days, angler trips, and mean days and trips per angler were at or above 2011 levels and comparable to previous years. The percent of anglers fishing and total trips taken to special urban trout fisheries have increased significantly since 2001. Fishing pressure on the urban winter trout fisheries in 2016 increased to 99,444 trips from 70,202 in 2011, 48,868 in 2006 and 12,920 in 2001. Trips to urban winter trout fisheries increased to 13.8% of all trout angler trips in 2016 from 12% in 2011 and 9% in 2006. The number of urban fisheries available expanded to 8 locations in 2006 and 17 in 2011 and 2016. Heritage Pond, Prairie Park Pond, Terry Trueblood Lake and Ada Hayden Lake ranked the highest in estimated angler trips to winter urban trout fisheries. Thirty percent of trout anglers purchased a trout fee specifically for an urban trout fishery.
Angler satisfaction with the trout program was ranked at 8 on a scale of 1 to 10, exactly the same as the 2011 survey. Angler responses to questions about the published stocking schedule broke down in a geographic pattern. Anglers from northeast Iowa’s trout zone and non-resident trout anglers were least likely to check the announced stocking schedule (39%), while anglers in areas with only winter stocking were most likely to check the stocking schedule (58%). Anglers who do check the stocking schedule generally use this information to fish the stocked water body (72%-84%). Most anglers are satisfied with the current amount of announced stockings (59%-67%). Anglers from the trout zone are more likely to avoid streams that were recently stocked than other resident anglers. While the majority of anglers prefer that the stocking calendar remain the same, anglers from the trout zone prefer fewer announced trout stockings. This information, combined with the budgetary issues of maintaining a rigid stocking schedule, could be used to justify reducing the number of announced trout stockings on northeast Iowa streams.
24570 US Hwy 34, Chariton, IA 50049, 641-774-2958 Rebecca Krogman; Mark Richardson ; Savannah Fernholz
The Large Reservoir Research Team works with fisheries managers to identify and resolve issues affecting the fishery resources of large reservoirs. Large reservoirs provide many recreational opportunities throughout Iowa and include some of the state’s most popular fishing and boating destinations, such as Lake Red Rock, Rathbun Lake, the Creston area lake chain, and many others. Ongoing research projects ensure that Iowa’s reservoirs are managed with the best available science.
Walleye are a very popular game fish in Iowa, despite a low rate of natural reproduction in most waters. Natural reproduction is especially low in artificial lakes (reservoirs), so Iowa DNR hatcheries supplement walleye populations with yearly stockings. Our management goal is usually a target population density of walleye in each lake.
Smarter StockingPast research at Rathbun Lake showed that stocking both fingerlings and fry produces more consistent year-classes of adult walleye, meeting our fishery management goals better than stocking only fry. Study results have been inconsistent in identifying which size of fingerling or stocking location is best. Fingerling walleye cost more to produce than fry and limited availability may cause small or irregular fingerling stockings in some reservoirs. Better ways to share the stocking of advanced (>6 inches) fingerlings, 2-inch fingerlings, and fry are being studied to maximize the number of reservoirs that meet our walleye management goals.
This research project started in 2011 at Big Creek Lake, when the Iowa DNR stocked 3,000 walleye fry/acre and five 8-inch fingerlings/acre into the reservoir. The fingerlings received a unique brand (like a tattoo) on their side each year to identify which year-class they were from. Their survival from year to year was tracked by electrofishing each fall and identifying the age and origin (fry versus fingerling) of each fish. In addition to this aggressive stocking method, a physical fish barrier was installed on the Big Creek Lake spillway in 2012. This helped to bring the Walleye population up to almost 6 adult Walleye/acre. Stocking has been reduced to let the existing Walleye grow. We learned that fry stocking was 17 times more cost effective than stocking advanced fingerlings. However, advanced fingerling Walleye have much higher survival rates and make up a large part of the Big Creek Lake population, so it is important to stock them when and where fry do not survive.
Big Creek Lake’s walleye stocking success and popularity led to the expansion of this study to six other reservoirs in 2014: Lake Manawa, Lake Macbride, Lake Icaria, Little River Lake, Pleasant Creek Lake, and Twelve Mile Lake. These waters will be stocked for years with fry and fingerlings to better determine when each stocking size should be used. The study is also working to find an effective sampling method for estimating fry stocking success before fingerling stocking; waters where fry did not “take” could then be prioritized in fingerling stocking allocations.
Reducing Escapement Keeping strong walleye populations in reservoirs is a challenge because of fish escaping downstream often through the spillway during spring flooding. After passing over the dam, escaped walleyes cannot move back up into the reservoir. This has been seen at Big Creek Lake and Rathbun Lake, when tagged fish stocked into the reservoir were caught by anglers in the river below, and likely happens at many reservoirs across Iowa. Fish escaping reduces the success of stocking and drains a reservoir’s walleye population over time.
The Iowa DNR is testing a variety of methods to monitor and prevent more fish from escaping. For example, we can track fish tagged with Passive Integrated Transponders (or “PIT tags”) when they pass by or through a tag reader, which may be installed on a dam spillway. The Iowa DNR is working with the Army Corps of Engineers and Iowa State University to test the effectiveness of a physical barrier installed at Big Creek Lake in 2012 and an electric barrier at Rathbun Lake to be installed soon. An effective barrier that reduces fish escaping will help the Iowa DNR strengthen current walleye populations and improve the success of stocking.
Hybrid striped bass are becoming more popular in Iowa's large reservoirs and urban ponds, but little is known about how to best manage these fish in Iowa. Ongoing culture research may make it cost-effective to raise hybrid striped bass in Iowa hatcheries; previous stocking efforts have been supplied by out-of-state hatcheries. The first hybrid striped bass cross, the "palmetto bass," was the strain of choice for many years. Palmetto bass are produced by fertilizing striped bass eggs with white bass milt. Recently, the reciprocal cross, or "sunshine bass," was stocked in several Iowa reservoirs. Sunshine bass are produced by fertilizing white bass eggs with striped bass milt. Although they look alike as adults, palmetto and sunshine bass may provide different fisheries to Iowa anglers.
The Iowa DNR is evaluating the success of palmetto and sunshine bass in five reservoirs: Easter Lake, Lake Icaria, Badger Creek Lake, West Lake Osceola, and Lake Wapello. Both strains were stocked at fingerling size (usually 2-4 inches) in 2012 and again from 2014-2017 (except for Easter Lake, which is undergoing renovation). Every reservoir is sampled each year to compare each strain's population size and survival rate. So far, more palmetto bass have been collected during sampling (implying better survival), but no difference in size has been seen between the two crosses. Several other factors, in addition to genetic cross, can affect the success of establishing hybrid striped bass fisheries. For example, the size at stocking (fry versus fingerling) can affect survival and expense. Ideal stocking numbers are also unknown at this time.
In 2014, fish from Lake Icaria were also sampled for stable isotope analysis, which can show dietary differences between the two crosses and possible competition or predation with other species. Several other factors, in addition to genetic cross, can affect the success of establishing hybrid striped bass fisheries. For example, the size at stocking (fry versus fingerling) can affect survival and expense. Ideal stocking numbers are also unknown at this time.
Using different sampling methods, including fall gill netting and daytime and nighttime electrofishing, was also evaluated. Different sampling tools can be more or less effective at catching fish and may catch different sizes of fish; more importantly, some are less stressful for the fish and less likely to cause accidental sampling injury. Population dynamics can be measured without affecting the fish population when the best tool is used. Each of the focus reservoirs was sampled with all three sampling methods from 2013-2015, resulting in the selection of fall experimental gill netting as the best sampling method. This is now the statewide standard sampling method for Hybrid Striped Bass in lakes and reservoirs.
The Iowa DNR can more effectively manage hybrid striped bass fisheries with better stocking strategies and population assessments. The goal is to create high-quality trophy hybrid striped bass fisheries for Iowa anglers.
The Iowa DNR has been restoring lakes using a watershed approach since the early 1990s, starting with Lake Ahquabi. The program’s impact increased when Iowa’s legislature approved $8.6 million in yearly funding in 2006. Restored lakes in Iowa usually have strong public support and benefit from increased recreational use. Unfortunately, the new lake effect can wear off quickly, fish populations stabilize, and aquatic vegetation control issues start taking more time and money to manage.
This project was started in 2014 to study which factors, planned and unplanned, lead to the fastest fishery recovery and popularity with anglers, as well as which fishery management strategies work best. Creating or improving habitat, new fish stocking strategies, and adding public access or recreational facilities must be evaluated. For example, although constructed in-lake habitat helps to group fish for anglers, which type of structure is most often used for fishing has not been identified. Knowing this would let managers install the type of structures that anglers use the most
The Iowa DNR uses angler surveys to measure the success of constructed habitat and other pieces of lake restoration. These on-lake surveys can help determine fishing success, angler satisfaction, recreational use and economic impact before and after a restoration. Angler surveys are being done at Easter Lake (major renovations began in 2015), Green Valley Lake (restored in 2009), Twelve Mile Lake (restored in 2006), Three Mile Lake (fishery renovated in 2016), Hickory Grove Lake (scheduled for future restoration), and Thomas Mitchell Pond (dredged in 2011).
As the Lake Restoration program grows and continues to invest in Iowa’s lake and reservoirs, the method of prioritizing and selecting lakes becomes very important. Another focus of this project is to revise and improve the process used to select lakes for restoration. The first list of program priority lakes was based on potential for public benefit, ecological health, and overall project feasibility. These categories are important, but several new or greatly expanded datasets are available that were not before. These datasets include the Iowa Lakes Information System, Iowa Lakes Survey, and improved geographic information from high-resolution photography (LiDAR) and detailed lake mapping. A decision-making model that incorporates data on ecological health (measured by water quality, biological integrity, and habitat quality), potential for public benefit, and project feasibility is being developed.
The Iowa DNR Fisheries Bureau manages fisheries across the state to conserve and improve Iowa’s aquatic resources, including small streams, large rivers, natural lakes, ponds, and reservoirs. Fisheries biologists regularly sample many aquatic systems to identify and monitor fish communities, fish health and growth, and fishery quality. The diversity of aquatic habitats requires a diversity of sampling tools and methods. The Iowa DNR regularly uses electrofishing, gill nets, fyke nets, hoop nets, trawls, traps, and seines to collect fish; each of these have biases such as fish size and species. The design of each tool and method of its use may lead to different data. Effective fisheries management and research rely on the understanding that different sampling methods may result in different data. This is a challenge for fisheries biologists across the country.
Iowa DNR developed standard operating procedures for fisheries sampling in 2012. However, these do not align with newly created North American standards. This can limit collaboration with other agencies and data sharing. Sampling instructions or design may not be adequately detailed, despite evidence that minor differences within a single tool may affect results. For example, Iowa fisheries biologists routinely use modified fyke nets to catch structure-oriented fish species in deep lakes, reservoirs, and large rivers. Differences in design such as trap dimensions, mesh size, funnel size, and number of hoops can change the fish captured and/or retained. Similar issues may affect other sampling tools, but are unknown due to a lack of research. An examination of current sampling methods and possible revisions is needed to ensure data quality and long-term dataset viability.
The modified fyke net was the first tool studied. A survey of modified fyke net dimensions was done in all fifty states during the fall of 2014 and yielded a wide variety of descriptions, all referred to as a “modified fyke net.” Three of these net designs were tested in Lake Ahquabi during September 2015 and compared for their ability to catch and hold fish. Results show that two net designs held more fish than the third design, but may or may not have been different from each other. So, the two designs were tested again for their ability to hold fish in September 2016 at Williamson Pond and West Lake Osceola. Extra catch information was also taken from lakes and reservoirs across the state to help decide if catch rates were different. One net design yielded higher and more reliable catch rates for target fish species and was recommended as the statewide standard for modified fyke nets. Additional netting studies may be conducted for unbaited hoop nets, which could improve fisheries monitoring in shallow natural lakes.
In addition to netting, electrofishing is an essential sampling tool Iowa DNR fisheries biologists use. However, a 2017 review of the DNR’s electrofishing boat fleet revealed many differences in boat configurations. A common difference was boom shape and size, which affect the size of the electrical field created in the water. This could lead to substantial differences in fish catch between boats. Continued review and standardization of electrofishing boats will improve the consistency and safety of electrofishing as a sampling gear.