Channel Catfish Reproductive Traits in the Lower Platte River, Nebraska, USA

Reproductive traits including fecundity, egg diameter, and condition of freshwater fishes influence offspring survival and abundance and may provide insight regarding timing of reproduction (Winemiller and Rose 1992, Johnston and Leggett 2002). Fish size (i.e., length or weight) may influence the number of eggs produced by an individual female (i.e., fecundity; Michaletz 1998). Larger individuals may, thus, disproportionately contribute to year-classes through increased fecundity if egg and larval survival is similar or greater than those from smaller reproductive females (Gwinn et al. 2015). Likewise, maternal fish size may influence egg diameter and offspring survival, whereby larger egg diameters are associated with greater parental care and increased egg quality (Sargent et al. 1987). Variation in egg diameter within and between individuals in a population may also indicate phenotypic plasticity in reproductive timing. For instance, intra-individual variation in egg diameter may indicate protracted spawning behavior (Pope et al. 1996). Inter-individual variation in egg diameter may indicate differences in sexual maturity and provide insight regarding timing of spawning (Hamel et al. 2015). Understanding relationships between fish size and reproductive traits is important for managing exploited fish populations where relaxed fishing regulations stemming from inaccurate reproductive information may lead to unintended consequences, including over-fishing and reduced population sustainability (Gwinn et al. 2015, Barneche et al. 2018)

Channel Catfish Reproductive Traits in the Lower Platte River, Nebraska, USA

Reproductive traits including fecundity, egg diameter, and condition of freshwater fishes influence offspring survival and abundance and may provide insight regarding timing of reproduction (Winemiller and Rose 1992, Johnston and Leggett 2002). Fish size (i.e., length or weight) may influence the number of eggs produced by an individual female (i.e., fecundity; Michaletz 1998). Larger individuals may, thus, disproportionately contribute to year-classes through increased fecundity if egg and larval survival is similar or greater than those from smaller reproductive females (Gwinn et al. 2015). Likewise, maternal fish size may influence egg diameter and offspring survival, whereby larger egg diameters are associated with greater parental care and increased egg quality (Sargent et al. 1987). Variation in egg diameter within and between individuals in a population may also indicate phenotypic plasticity in reproductive timing. For instance, intra-individual variation in egg diameter may indicate protracted spawning behavior (Pope et al. 1996). Inter-individual variation in egg diameter may indicate differences in sexual maturity and provide insight regarding timing of spawning (Hamel et al. 2015). Understanding relationships between fish size and reproductive traits is important for managing exploited fish populations where relaxed fishing regulations stemming from inaccurate reproductive information may lead to unintended consequences, including over-fishing and reduced population sustainability (Gwinn et al. 2015, Barneche et al. 2018)

Trout Responses to Stocking Rates and River Discharge within a Southeastern U.S. Hydropeaking Tailwater

Freshwater fish populations often exist in systems characterized by novel ecological processes resulting from human alteration. Salmonid populations embedded within coldwater sections of warmwater rivers are spatially constrained by habitat availability. Tailwater fish contend with fluctuating river discharges and density-dependent processes associated with fish stocking and exploitation. Salmonid populations sustained through stocking versus natural reproduction may respond differently to changes in hydrologic patterns (e.g., hydropeaking) as well as declines in fish abundance. We assessed differences between stocked (Rainbow Trout Oncorhynchus mykiss) and naturalized (Brown Trout Salmo trutta) trout populations in Greers Ferry tailwater, Arkansas, regarding (1) spatial and temporal patterns of mean length, electrofishing catch rates, and relative condition following reduced number of stocked Rainbow Trout and (2) evidence that hydrologic characteristics and fish stocking intensity influenced relative condition. A 56% reduction in Rainbow Trout stocking did not result in systemwide change in mean length or relative abundance for Rainbow Trout or Brown Trout over the 16-year study period. Hydrologic variability, where river discharge spanned both reduced and elevated levels, positively influenced condition of both Rainbow Trout and Brown Trout. Assessment of survival of stocked Rainbow Trout may aid in further refining the timing and amount of stocking needed to sustain the population at a desired abundance. Further, assessing the influence of stocking fewer but perhaps larger (in terms of mean length) fish to meet management goals may be warranted. The persistent differences in relative abundance among river sections can inform management actions directed at Brown Trout, including harvest regulations. Such regulations may aid in reaching desired management goals, including abundance and mean length targets not observed after reduced stocking

River-Wide Habitat Availability for Fish Habitat Guilds: Implications for In-Stream Flow Protection

The variation in river discharge alters habitat heterogeneity with implications for the distribution of fish species with different habitat requirements. Assessments of habitat availability following changes in river discharge are difficult to apply at broad spatial scales and with relevance to multiple species. We used a MesoHABSIM modeling approach to quantify river-wide changes in habitat availability for five fish habitat guilds under three river discharge levels along the Niobrara River, NE, USA.We used a time-series of river discharge (1958–2010) to create uniform continuous under-threshold habitat duration curves that identified habitat conditions that may result in periods of stress for fish communities along the Niobrara River. Habitat availability for each fish habitat guild was dependent on river discharge and location along the river. Habitat availability for fish habitat guilds ranged from 5% to 49% of the total channel area suggesting habitat availability may, at times, be limited. We provide river discharge guidelines for bioperiods that limit the frequency and duration of stressful habitat conditions. Understanding interactions between river discharge and habitat availability through time and at river-wide scales may aid in managing for ecological integrity by including protection of river discharge variability to support multiple fish habitat guilds

Aquatic habitat changes within the channelized and impounded Arkansas River, Arkansas, USA

River-wide changes in morphologic character following channelization and impoundment alter the occurrence and distribution of surface water and available habitats for aquatic organisms. Quantifying patterns of creation, redistribution or disappearance of habitats at river-wide and decadal spatiotemporal scales can promote understanding regarding trajectories of different habitat types following alteration and prospects of direct habitat enhancement projects within altered alluvial rivers. Newly available remote-sensing tools and databases may improve detection of river-wide changes in habitat through time. We used a combination of remote-sensing data and generalized linear models to assess changes in surface water coverage from 1984 to 2015 among aquatic habitats of 496 km of the Arkansas River within Arkansas, USA. Changes through time in surface area of permanent and episodically inundated areas — and thus the availability of aquatic habitat — were variable along the river. Overall, the river lost a total 2.1% of permanent and 12.1% of episodic water surface area. The general trend of loss of off-main-channel habitat and increased coverage of permanent water along main-channel habitats may indicate a long-term transition (i.e. ramp-type disturbance) within areas of the Arkansas River where backwaters are transitioning to terrestrial environments, and habitat heterogeneity in the main channel is decreasing. As such, a decadal-scale change of channel form and backwater habitats may be the dominant pattern with limited regeneration of diverse habitat types. Understanding changes to permanent and episodic water availability may aid predictions regarding ecological effects of channelization and impoundments, including both increases and decreases in riverine productivity, biotic diversity and population abundances through space and time. Water resource managers and biologists can use information regarding river-wide changes in habitat availability obtained through remote sensing data to direct river management practices, including dredging and side-channel construction, and to assess ecological responses to such changes

Tag Type and Location-Dependent Retention Impart Varied Levels of Bias on Mark–Recapture Parameter Estimates

Population parameter estimates from mark–recapture studies are dependent on individuals retaining marks or tags. Therefore, tag retention estimates are needed for different tag types and anatomical tagging locations. Few studies have empirically quantified the bias from tag retention on fish population parameters that are derived from mark–recapture studies. We examined differences in retention between T-bar anchor tags and PIT tags as well as among four anatomical locations for PIT tags in Brown Trout Salmo trutta in a tailwater fishery in Arkansas, USA. We also estimated the relative bias of tag type and PIT tag location on apparent survival estimates from Cormack–Jolly–-Seber models. Tag retention for the anchor tags was 15.1% lower than that for the PIT tags after 1 year and 46.1% lower after 4 years. Greater PIT tag retention resulted in less biased estimates of apparent survival for PIT tags (average −7.1%) than for anchor tags (average −37.8%). However, PIT tags that were placed in different anatomical locations had varying retention rates, so the degree of relative bias that was associated with their apparent survival estimates also varied. Inserting the PIT tags in the cheek or dorsal musculature provided the greatest retention for Brown Trout and may provide the least biased apparent survival estimates from future mark–recapture studies

Assessment of a channel catfish population in a large open river system

Estimates of dynamic rate functions for riverine channel catfish, Ictalurus punctatus (Rafinesque), populations are limited. The open nature and inherent difficulty in sampling riverine environments and the propensity for dispersal of channel catfish impede estimation of population variables. However, contemporary population models (i.e. robust design models) can incorporate the open nature of these systems. The purpose of this study was to determine channel catfish population abundance, survival and size structure and to characterize growth in the lower Platte River, Nebraska, USA. Annual survival estimates of adult channel catfish were 13%–49%, and channel catfish abundance estimates ranged from 8,281 to 24,261 fish within a 10-km sampling reach. Channel catfish were predominantly (90%

The Global Status of Freshwater Fish Age Validation Studies and a Prioritization Framework for Further Research

Age information derived from calcified structures is commonly used to estimate recruitment, growth, and mortality for fish populations. Validation of daily or annual marks on age structures is often assumed, presumably due to a lack of general knowledge concerning the status of age validation studies. Therefore, the current status of freshwater fish age validation studies was summarized to show where additional effort is needed, and increase the accessibility of validation studies to researchers. In total, 1351 original peer-reviewed articles were reviewed from freshwater systems that studied age in fish. Periodicity and age validation studies were found for 88 freshwater species comprising 21 fish families. The number of age validation studies has increased over the last 30 years following previous calls for more research; however, few species have validated structures spanning all life stages. In addition, few fishes of conservation concern have validated ageing structures. A prioritization framework, using a combination of eight characteristics, is offered to direct future age validation studies and close the validation information gap. Additional study, using the offered prioritization framework, and increased availability of published studies that incorporate uncertainty when presenting research results dealing with age information are needed

Can translocated native fishes retain their trophic niche when confronted with a resident invasive?

Diet interactions between native and non-native fishes may influence the establishment of native species within their historical range (i.e., reintroduction). Therefore, we illustrated the food web structure of and followed the transition of the federally endangered humpback chub Gila cypha into a novel food web following translocation and determined the potential for a non-native species, rainbow trout Oncorhynchus mykiss, to influence translocation success. Humpback chub and rainbow trout used resources high in the food web and assimilated similar proportions of native fishes, suggesting non-native rainbow trout may occupy an ecological role similar to humpback chub. Subsequently, humpback chub may be well suited to colonise tributaries because of their ability to consume resources high in the food web. Additionally, diet partitioning may occur between all members of the fish community as indicated by separation in trophic niche space and little trophic overlap; although all species, particularly bluehead sucker Catostomus discobolus, used a broad range of food resources. Rainbow trout stomach content analysis corroborated stable isotope analysis and suggested rainbow trout diet consisted of aquatic and terrestrial macroinvertebrates, while larger rainbow trout (\u3e120 mm total length) consumed a greater proportion of fish (incidence of piscivory = 5.3%). Trophic interactions may reveal an underutilized niche space or biotic resistance to the establishment of translocated native fishes. Continued translocation of humpback chub into tributaries appears to be one option for conservation. However, successful establishment of humpback chub may depend on continued removal of non-native trout, increasing availability of diet sources at higher trophic levels