Assessment of Smallmouth Bass Populations in Iowa Interior Rivers

Smallmouth bass Micropterus dolomieu are a popular sport fish throughout North America and occupy an important ecological role as top predators in aquatic systems. Despite the importance of smallmouth bass, knowledge of their population structure and dynamics in Iowa interior rivers is limited. The objective of this study was to describe population dynamics (e.g., relative abundance, size and age structure, growth, mortality) of smallmouth bass in six Iowa rivers. Smallmouth bass were sampled from the Upper Iowa, Maquoketa, and Wapsipinicon rivers in northeast Iowa and the Des Moines, Iowa, and South Skunk rivers in central Iowa using electrofishing during the fall of 2005. Scales were removed for age and growth estimation. Dorsal spines were removed from fish greater than 350 mm for comparison with scales. Relative abundance, size structure, condition, age structure, growth, and mortality varied among populations. For instance, proportional size distribution varied from 26 to 73 relative weight (Wr) varied from 83 to 102, and total annual mortality of age-2 and older fish varied from 23 to 62% among populations. Smallmouth bass in the Maquoketa and South Skunk rivers generally had the fastest growth rates, while smallmouth bass in the Iowa and Wapsipinicon rivers exhibited the slowest growth. This study provides information that contributes to our knowledge of smallmouth bass ecology, and will be useful for guiding management decisions and making regional and national comparisons

Age Estimation of Burbot Using Pectoral Fin Rays, Branchiostegal Rays and Otoliths

Throughout much of its native distribution, burbot (Lota lota) is a species of conservation concern.  Understanding dynamic rate functions is critical for the effective management of sensitive burbot populations, which necessitates accurate and precise age estimates.  Managing sensitive burbot populations requires an accurate and precise non-lethal alternative.  In an effort to identify a non-lethal ageing structure, we compared the precision of age estimates obtained from otoliths, pectoral fin rays, dorsal fin rays and branchiostegal rays from 208 burbot collected from the Green River drainage, Wyoming.  Additionally, we compared the accuracy of age estimates from pectoral fin rays, dorsal fin rays and branchiostegal rays to those of otoliths.  Dorsal fin rays were immediately deemed a poor ageing structure and removed from further analysis.  Age-bias plots of consensus ages derived from branchiostegal rays and pectoral fin rays were appreciably different from those obtained from otoliths.  Exact agreement between readers and reader confidence was highest for otoliths and lowest for branchiostegal rays.  Age-bias plots indicated that age estimates obtained from branchiostegal rays and pectoral fin rays were substantially different from age estimates obtained from otoliths.  Our results indicate that otoliths provide the most precise age estimates for burbot

DIET OF JUVENILE BURBOT AND INSIGHT INTO GAPE LIMITATION

Throughout much of their distribution, Burbot (Lota lota ) populations are declining or have been extirpated.  Burbot in the Kootenai River, Idaho represent one such imperiled population.  In an effort to restore Burbot in the Kootenai River, managers have turned to conservation aquaculture.  However, no appreciable increase in natural recruitment has been observed in the system.  The lack of natural recruitment is believed to be partly due to a deficiency of high-quality prey.  As a result, we sought to i) describe the diet of juvenile Burbot, ii) evaluate the influence of Burbot mouth gape on diet and iii) estimate prey availability at release locations.  Burbot were stocked into two earthen ponds at the Boundary Creek Wildlife Management Area (BCWMA) and sampled weekly to evaluate diet.  Zooplankton were sampled weekly from each pond and from release locations of hatchery-reared Burbot (i.e., Kootenai River, Goat River, Boundary Creek, Deep Creek) to quantify prey availability.  Over the course of the study (~3 months), Burbot primarily fed on Cyclopoida.  Burbot never appeared to be gape limited and exhibited little variability in the size of zooplankton ingested.  Zooplankton densities at stocking locations were relatively low in comparison to BCWMA ponds.  Low zooplankton densities at release sites indicate that alternative management actions may need to be considered to enhance Burbot recruitment in the Kootenai River drainage

Spatial and Temporal Distribution and Habitat Selection of Native Yellowstone Cutthroat Trout and Nonnative Utah Chub

Henrys Lake, Idaho, is a renowned trophy trout fishery that faces an uncertain future following the establishment of Utah Chub (UTC) Gila atraria. Utah Chub were first documented in the lake in 1993 and have become abundant over the past two decades. Little is known about the ecology of UTC, but they typically have negative effects on salmonids in systems where they have been introduced. We sought to fill knowledge gaps in UTC ecology and provide insight on potential interactions with Yellowstone Cutthroat Trout (YCT) Oncorhynchus clarkii bouvieri. Ninety-four YCT and 95 UTC were radio-tagged in spring 2019 and 2020 to better understand potential interactions between YCT and UTC in Henrys Lake. Fish were located via mobile tracking and fixed receivers from June to December 2019 and 2020. In June of both years, YCT and UTC were concentrated in nearshore habitats. As water temperatures increased, UTC were documented in deeper water (mean ± SD = 3.6 ± 1.4 m) and YCT became more concentrated in areas with cold water (e.g., mouths of tributaries, in-lake springs). In July and August, large congregations of UTC were observed. Yellowstone Cutthroat Trout were detected in tributaries from June to August, but no UTC were detected in the tributaries. By late fall (November–December), YCT were located along the shoreline and UTC were detected in the middle of the lake. Both YCT and UTC were observed in areas with dense vegetation. Macrophytes likely provided a food source for UTC and cover from predators for both species. Locations of YCT were negatively related to warm water temperatures, whereas UTC were positively associated with warm water temperatures. Results from this research fill knowledge gaps in UTC and YCT interactions as well as provide valuable insight on the ecology of UTC and adfluvial Cutthroat Trout populations. Furthermore, distribution patterns and habitat selectivity of YCT and UTC in Henrys Lake can be used to inform management decisions for fishery improvement and YCT conservation

Observations on the Distribution and Status of Western Sand Darter, Spotted Gar, and Skipjack Herring in Iowa Rivers

This paper describes new records of western sand darter (Ammocrypta clara), spotted gar (Lepisosteus oculatus), and skipjack herring (Alosa chrysochloris) in Iowa\u27s interior rivers. A western sand darter was collected from the Cedar River, Benton County, in 2007. Western sand darters are occasionally collected from the upper Mississippi River (UMR), but have not been sampled in interior rivers since 1958. Two spotted gar were collected from the Des Moines River, Polk and Wapello counties, in 2007. Two spotted gar were sampled from the UMR in 2000, but no spotted gar have been previously recorded from Iowa\u27s interior rivers. A skipjack herring was sampled from the Des Moines River, Wapello County, in 2007. Skipjack herring are occasionally sampled in the UMR and the middle Missouri River, but have not been recorded beyond the lower extremes of Iowa\u27s interior rivers since the early 1900s. All three species are listed as species of greatest conservation need in Iowa

Diet of Burbot and Implications for Sampling

Burbot (Lota lota) are an apex piscivore that were illegally introduced to the Green River drainage, Wyoming, raising concerns for the conservation and management of fishes throughout the basin.  However, relatively little is known about the diet of non-native burbot.  The objectives of this research were to characterize diet composition of burbot and identify differences in diet composition as a function of sampling gear.  Diet composition was characterized using frequency of occurrence, percent by number, and percent by weight to identify the importance of each prey type to burbot.  Diet composition was compared across gears to identify the relationship between gear and diet.  Fishes were present in the stomach contents of nearly all burbot sampled and composed 62–100 percent of the stomach contents of burbot greater than 300 mm.  Prey diversity was greatest in diets of burbot sampled with small-mesh hoop nets.  Results from the current study provide important information on the diet of non-native burbot and highlight the potential influence of gear on diet studies

Informing Management of Henrys Lake, Idaho, using an Integrated Catch-at-Age Model

Henrys Lake, Idaho, supports a popular fishery for Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri and Yellowstone Cutthroat Trout × Rainbow Trout O. mykiss hybrids. A majority of the adult population of fish in Henrys Lake are of hatchery origin that were stocked as fingerlings. The fishery is closed to angling during the late winter and spring months, but fisheries managers are considering opening the fishery year-round with catch-and-release- only regulations or with a two-fish bag limit during the extended season. However, there is concern that the proposed management actions may negatively affect the current fishery. Therefore, we developed an integrated catch-atage model to estimate population parameters for trout in Henrys Lake and used a simulation model to evaluate alternative management actions. Results of this study suggest that catch and release of both Yellowstone Cutthroat Trout and hybrids would increase and that abundance of trout in the spring (i.e., the start of the traditional season) would decrease under both proposed bag limits. Losses in abundance can be mitigated by stocking additional fish as long as no more than approximately 1,520,000 Yellowstone Cutthroat Trout are stocked annually. If catch-and-release-only regulations are implemented during the newly proposed season, total harvest is expected to decrease compared to the current fishery due to additional catch-and-release mortality. Ultimately, managers will need to prioritize harvest or catch-and-release opportunity, both of which provide additional utility to anglers, when choosing how to proceed with bag limit regulations

Nutrient Restoration of a Large, Impounded, Ultra-Oligotrophic Western River to Recover Declining Native Fishes

Declines in many fish populations in large, western rivers have been primarily attributed to the anthropogenic reduction of nutrient inputs and subsequent impacts to the food web. The largest known river fertilization program was implemented starting in 2005 on the Kootenai River in northern Idaho to restore resident fisheries. Annual electrofishing surveys were conducted at multiple sites in Idaho and Montana before and during nutrient addition to evaluate assemblage and population-level responses. Although few responses in fish assemblage structure were observed, the addition of liquid ammonium polyphosphate fertilizer (3 μg/L) to the Kootenai River increased fish abundance and biomass over the 20-km stretch of river downstream of the treatment site. Increases were most notable in Largescale Suckers Catostomus macrocheilus, Mountain Whitefish Prosopium williamsoni, and Rainbow Trout Oncorhynchus mykiss populations, although increases in catch and biomass were detected for nearly all fish species. The Kootenai River is approximately 30 times larger in discharge than other rivers that have been experimentally fertilized and provides compelling evidence that the mitigation of nutrient declines in rivers of similar size can result in positive influences on the fish populations where primary and secondary production are limiting growth, survival, and recruitment. However, results from our study also highlight the importance of completing evaluations across varying levels of biological organization (e.g., assemblage and population) and over biologically relevant timeframes