We examined use of channel modifying structures (CMS; e.g., engineered rock dikes, channel sandbars) and their associated smaller spatial-scale habitats (SSH) on lower Missouri River, USA, by speckled chub (Macrhybopsis aestivalis), sicklefin chub (M. meeki) and sturgeon chub (M. gelida) from June through October, 2006 to identify important habitat characteristics that could aid conservation. We sampled chubs primarily in six CMS types: L-dikes, wing-dikes, kicker dikes, rootless dikes, channel sandbars and bank-lines. Ninety-three per cent of chubs were collected from L-dikes, wing-dikes and channel sandbars. Unidentifiable Macrhybopsis chubs (UHY) were less than 35-mm TL, were collected early in the sampling season and were most associated with L-dikes where mean bottom current velocity was slow (0.07 m/s). Chubs large enough to be identified to species were associated with large channel sandbars where mean bottom current velocity was faster (0.34 m/s). Chubs from wing-dikes were more abundant in shallow water (<1.2 m deep) adjacent to bars than in deeper (>1.2 m deep), open-water areas ( p ¼ 0.007). Month accounted for 54% and CMS with SSH 18% of explained variation in chub species distribution and abundance. Our results demonstrate that CMS in the contemporary lower Missouri River channel provide multiple habitats for multiple life-stages of Macrhybopsis chubs (e.g., nursery and post-nursery habitats). L-and wing-dikes may provide surrogate nursery habitats for chubs where in-channel slow-velocity areas were lost after river channelization. Managing CMS to address life history stages and an ecologically appropriate proportion and distribution of dike to channel sandbar habitats may be critical for conservation of native Macrhybopsis chubs in lower

We compared variability in catch per unit effort (CPUE) and size structure of shovelnose sturgeon Scaphirhynchus platorynchus collected in 2003 and 2004 with stationary winter gill nets, drifted trammel nets, hoop nets, and otter trawls in the Lower Missouri River, USA to determine the most precise types of gear to collect all sizes of sturgeon so that refinements of longterm monitoring protocols can be made. A total of 1947 net sets or trawls collected 8743 shovelnose sturgeon, with 67% of the fish collected during winter gill netting (16% of total samples). Mean coefficient of variation (CV) among all months for juvenile (age 3 and younger; <250 mm fork length) sturgeon was highest for gill nets and lowest for otter trawls (P = 0.0008). Mean CV of subadult and adult shovelnose sturgeon ( ‡250 mm) was highest in hoop nets compared to other gear types (P = 0.0002). All gear and mesh sizes collected the most common sizes of shovelnose sturgeon (500-600 mm), but only otter trawls and trammel nets collected fish <150 mm. The higher precision of winter gill nets and summer otter trawls led to fewer samples needed to detect changes in CPUE as compared to hoop and trammel nets. Sampling only with types of gear that do not collect younger shovelnose sturgeon may hinder management decisions that rely on recruitment trends to determine the effects of management actions (e.g. channel modifications).

White bass (-w) and walleye (m *) coexist in several of the large glacial lakes in eastern South Dakota. We collected age-0 white bass and walleye in Lake Poinsett monthly from July through September of 1996 to assess the extent of diet overlap using Schoener's index (Cw). Age-0 white bass increased from a mean length of 5 1 mm in July to 13 1 mm in September, while walleyes grew from 79 to 134 mm during the same period. Both species initially fed on zooplankton in July; however, diets diverged in later samples. Age-0 white bass primarily consumed zooplankton through September; prey fishes constituted a progressively greater proportion (by number) of age-0 walleye diets. Benthic macroinvertebrates did not make up a substantial portion of the diet for either fish species. Thus, diet overlap between age-0 white bass and age-0 walleye was initially high in July (Cq = 69), but declined through September (Cw = 36).

Objective The ichthyofaunal diversity of the Great Basin is incompletely characterized, with the Wall Canyon Sucker Catostomus sp. being one potential species. The Wall Canyon Sucker is limited in distribution to the Wall Canyon drainage of Surprise Valley, Washoe County, Nevada, USA. It was first documented and collected by C. L. Hubbs and R. R. Miller in 1934, and no species description has been published to date. Nonetheless, the Wall Canyon Sucker has been treated as a species and has appeared in various contexts within and outside of the scientific literature as such. Methods We conducted phylogenetic analyses and the first population genetics study of this putative species using genome‐wide sampling obtained through restriction site‐associated DNA sequencing to assess the Wall Canyon Sucker's relationships and population genetic characteristics. Result We found the Wall Canyon Sucker to be sister to the Warner Sucker C. warnerensis with high support and a median divergence time of 2.12 million years. Population genetic analyses supported that the Wall Canyon Sucker is a single genetic population with a high degree of isolation. Principal components and admixture analyses did not indicate recent admixture of the Wall Canyon Sucker with the Warner Sucker. Substantial differences in allele frequencies between the Wall Canyon and Warner suckers were apparent (genetic differentiation index FST = 0.15–0.21). Nucleotide diversity in the Wall Canyon Sucker was the lowest of all observations, and Tajima's D was greater than zero (D = 1.96), indicating population contraction and a lack of rare alleles, congruent with the desiccation of Lake Surprise and the persistence of the fish in a very restricted recent range. We undertook species delimitation with publicly available mitochondrial gene sequence data and found that a species‐level designation of the Wall Canyon Sucker is appropriate in that framework as well. Conclusion The results of this study are consistent with recognition of the Wall Canyon Sucker as a species; however, it still requires a formal taxonomic description.