The plains topminnow Fundulus sciadicus appears to be experiencing reductions in geographic range and local abundance, which has led to regional protection throughout its native range. Conservation of this species may require introductions to reestablish populations at known historic locations. Therefore, a pond was constructed during September 2007 to house a refuge population of plains topminnow in Nebraska. A total of 123 plains topminnow were stocked into the pond in two stocking events during 2008. Plains topminnow populations were sampled throughout 2008 and mark–recapture population estimates were conducted after reproductive events during 2009 and 2010 resulting in estimates of 9,844 ± 1,698 (mean ± SD) and 3,974 ± 452 plains topminnow, respectively. Mean fish weight was used as an estimate of pond biomass, which was 28.4 kg/ha in 2009 and 44.9 kg/ha in 2010. Reproduction was first observed in 2008 and in each following year, and a strong year-class was produced in 2009, which suggested there were factors that limited reproduction in the other 2 years. Extensive culture may be an effective way to rear plains topminnow and related species. However, more research is needed to determine factors that affect year-class strength and production.Received April 25, 2011; accepted February 8, 2012
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[Show abstract][Hide abstract] ABSTRACT: Movement behaviors attributed to spawning, dispersal, or altered habitat availability are essential to the ecology of many lotic fishes and, although considerable research has described movements of sport fish, little is known about the movement patterns of nongame species. Streams and rivers, wherein plains topminnow Fundulus sciadicus are prevalent, occur in a nonequilibrium state in which habitat patches are sporadically created and lost due to hydrologic variability. This results in regular extirpation and need for recolonization of many plains fishes, including plains topminnow. Species persistence, therefore, is dependent on tolerances to fluctuating habitat conditions and life-history traits that allow dispersal over large areas. To better understand the regional distribution of plains topminnow, we monitored large-scale dispersal patterns and habitat use of two introduced populations in Nebraska. In 2011 and 2012, plains topminnow were marked using visible implanted elastomer (VIE) marks and released at the center of two 3000-m study reaches. Populations were sampled monthly from April to November in 2011 and April through September in 2012 to describe movement patterns and habitat use. Plains topminnow were highly mobile, consistently associated with select habitat features, and the estimated individual home range exceeded standard sampling reach distances by nearly four times. The movement of plains topminnow occurred at greater rates and to distances further than known for similar species. These large-scale movements likely help maintain connectivity among populations within stream drainages and facilitate recolonization of regularly extirpated habitat patches. In this context, species movement may be critical to the maintenance and potential recovery of populations of this and other rare lotic fishes.
[Show abstract][Hide abstract] ABSTRACT: The establishment of nonnative species and subsequent replacement of native species is among the greatest threats to freshwater biodiversity worldwide. However, little is known of the effects that invasive species have on individual species and specific mechanisms by which species displacement occurs. The expansion of western mosquitofish Gambusia affinis beyond its native range has commonly been thought to cause shifts in species assemblages throughout the United States. Although plains topminnow Fundulus sciadicus populations have declined as the range of western mosquitofish in Nebraska has expanded, long-term coexistence of mosquitofish with the closely related northern plains killifish Fundulus kansae has been observed within the same systems. To investigate the potential mechanisms by which differential displacement of the native topminnow species may have occurred, biotic interactions and spatial distribution of both conspecific and heterospecific groups of plains topminnow, plains killifish, and western mosquitofish were quantified in microcosms for three life stages (larval, juvenile, and adult). Interactions between adult western mosquitofish and the native species were complex and dependent upon life stage, but collectively suggested that populations of both plains topminnow and plains killifish are vulnerable to mosquitofish establishment. Detrimental effects towards fundulid species were primarily mediated through predation of larvae and aggressive interactions directed towards juvenile life stages which caused significant mortality. In addition, simultaneous alterations of behavior, as quantified by activity patterns and microhabitat use, were apparent in both native species in response to western mosquitofish presence. Because similar impacts of western mosquitofish were observed for plains killifish and plains topminnow, the persistence of plains killifish in areas occupied by western mosquitofish may be linked to species attributes not assessed in the current analysis. Subtle differences in microhabitat selection between the topminnow species and adult western mosquitofish could potentially explain observed differential displacement in the environment. These results have augmented our understanding of the impacts that western mosquitofish has on the at-risk plains topminnow, and have further elucidated the potential mechanisms for impact via competitive interactions.