The years of 2011 and 2012 offered a singular alternative to check flathead catfish diets within the Center Missouri River.

This text initially appeared within the Might 2022 concern of In-Fisherman.

River Connections: Flathead Diets at Excessive Flows

Rivers are dynamic, going by means of intervals of flood and drought extremes, creating distinctive challenges to river catfish anglers. As floods increase rivers into new habitats and droughts constrict the channel, lowering area, fish additionally should acclimate to new circumstances, whether or not it’s shifting places to areas with ultimate present and depth, or to areas with considerable meals sources, or each. Anglers adapt by adjusting fishing places relying on the place it’s doable to fish and the place they predict catfish are situated within the variable surroundings.

One facet of catfish response is how flooding and drought extremes have an effect on their weight loss plan. The years of 2011 and 2012 offered a singular alternative to check flathead catfish diets within the Center Missouri River. File flooding in 2011 had the river overflowing into its floodplain, whereas drought in 2012 had confined the river into its channel all 12 months. College of Nebraska researchers seized this chance to see how diets of flathead catfish differed between flood and drought throughout these two years.*

The researchers sampled flathead catfish utilizing electrofishing throughout July, August, and September of each years, and meals have been flushed from stomachs earlier than all flatheads have been launched alive. A wide range of weight loss plan objects have been present in stomachs together with invertebrates resembling mayflies, dragonflies, and different bugs and crayfish; unidentified fish species together with catfish and freshwater drum, and on uncommon occurrences bass, sturgeon, paddlefish, and customary carp; and a frog and snapping turtle.


Flatheads sampled in 2011, the flood 12 months, had stomachs that have been extra full, and fish have been in higher physique situation in comparison with flatheads sampled in 2012, the drought 12 months. The share of flatheads with empty stomachs additionally was much less through the flood 12 months. A considerable change within the measurement at which flatheads switched from consuming invertebrates to fish was additionally noticed between years. Within the flood 12 months, flatheads switched to consuming fish at 8 inches, whereas within the drought 12 months the swap occurred at about 14 inches. Within the flood 12 months, there was a larger abundance of age-0 fishes within the river general, the researchers report, which may have resulted in elevated encounter charges between flatheads and prey fishes, probably inflicting the swap to a fish weight loss plan at a smaller measurement. Motion of flatheads and prey fishes into the floodplain to hunt refuge from excessive water additionally may have elevated encounter charges.

Variations in weight loss plan construction between flood and drought years occurred in flatheads consuming invertebrates however not in flatheads consuming fish. In different phrases, the sorts of invertebrates eaten have been completely different between years, however the sorts of fish species eaten weren’t. The drought 12 months introduced a lower within the variety of invertebrates within the weight loss plan, which based on the researchers might mirror common declines in macroinvertebrate variety in rivers in low-water years. The researchers conclude that the examine offered proof as to how hydrological circumstances can have an effect on prey consumption and fish weight loss plan, and that in regulated rivers, organisms reply to floodplain connectivity.

—Dr. Rob Neumann

*Hogberg, N. P., and M. A. Pegg. 2016. Flathead catfish Polydictis olivaris weight loss plan composition throughout excessive circulation occasions in a big river. J. Freshwat. Ecol. 31:431-441.

Fish Administration: The place Do Walleyes Go?

Native primarily to the Higher Midwest, walleyes are generally launched into reservoirs inside and out of doors their native vary to supply leisure fisheries. Whereas walleyes can thrive in reservoirs, pure replica is commonly restricted and common stockings are required to take care of wholesome fisheries.

Apart from angler harvest, walleyes are misplaced from populations by means of pure mortality. Reservoirs, nonetheless, are distinctive as a result of walleyes will also be completely misplaced from the inhabitants on account of escapement—the lack of fish over spillways or by means of water-control buildings. Whereas walleye escapement could be important, the way it contributes to fish loss relative to reap and pure mortality just isn’t as clear.

A dam spillway.
A bodily barrier on Large Creek Reservoir spillway was put in in 2012 to scale back escapement of walleyes and muskies.

We measured walleye harvest, pure mortality, and escapement in two Iowa reservoirs—Large Creek and Brushy Creek—to raised perceive the importance of those components in regulating populations. We additionally evaluated the effectiveness of a bodily barrier on Large Creek spillway that was put in in 2012 to scale back walleye and muskie escapement. Walleyes have been implanted with radio tags in each reservoirs starting in October 2016 and tracked to observe their places by means of Might 2019. Anglers have been additionally requested to report tagged walleyes that they caught.

No walleyes escaped from Large Creek Reservoir, the place the fish barrier was put in on the spillway. Walleye escapement at Brushy Creek (no fish barrier) was larger throughout increased lake ranges throughout April; annual escapement ranged from 22 to 47 %. Walleye harvest was increased from April by means of July in comparison with the remainder of the 12 months, with annual harvest starting from 13 to 27 %. Walleye pure mortality was positively associated to water temperature and was estimated at 36 to 38 % yearly. Outcomes of our examine counsel massive numbers of walleyes could be misplaced from reservoirs by way of escapement over spillways, which could be important in sustaining reservoir walleye populations, and that bodily boundaries could be efficient for lowering escapement.

—Robert Weber and Dr. Michael J. Weber, Iowa State College

*Weber, R, and M. J. Weber. 2021. Results of harvest, motion, and escapement on reservoir walleye populations. N. Am. J. Fish. Mgmt. 41:775-790.

Discipline Notes: No Boundaries for Bull Trout

Bull trout, one of many lesser recognized species of char, are native to northwestern North America from Alaska to northern California. They inhabit Arctic waters, Pacific coastal areas, and Missouri River drainages in mountain and coastal streams. This species (Salvelinus confluentus) reveals 4 completely different life-history methods: a non-migratory or resident type; a riverine type; populations that stay in lakes however transfer to tributaries to spawn; and anadromous varieties that feed in marine waters and ascend rivers to spawn.

A man wading in a river, looking down at a bull trout in his hands.
Dr. Tom Quinn, the writer’s brother, is an enormous fan of bull trout fishing.

All populations are listed as Threatened underneath the Endangered Species Act, on account of habitat degradation and fragmentation, dam building, water high quality issues, and introduction of non-native species. However they’re considerable in some waters the place they supply wonderful catch-and-release fishing. Adults eat quite a lot of fish species and readily strike flies, spinners, and spoons. They typically vary from 18 to 24 inches, although the all-tackle document is 31 kilos 15 ounces and fish over 10 kilos are often caught.

State and federal fishery businesses have monitored bull trout populations, and biologists with Idaho Energy Company lately carried out a tagging examine. One fish marked within the Hells Canyon stretch of the Snake River in Idaho has demonstrated the wandering nature of this species. After tagging in 2018 at 12 inches, it was recaptured close by a 12 months later, having grown to 16.5 inches.

In Might, it turned up in northeast Oregon’s Imnaha River, a tributary of the Snake River. In July, it traveled greater than 186 miles to spawn in a small mountain stream within the Salmon River watershed of central Idaho. The next winter, it was again residence in Hells Canyon, however made its migratory journey to Oregon once more the next spring. Contemplating that bull trout might stay greater than 12 years, it’s more likely to proceed its interstate travels.

—Steve Quinn

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