Patterns and predictors of fish dispersal in rivers

Quantifying fish dispersal and identifying its general predictors is key for understanding temporal patterns in population dynamics, emigration and immigration, meta‐community dynamics, many ecological processes and predicting recovery time or population responses to environmental changes. This is the first comprehensive quantitative meta‐analysis of heterogeneous freshwater fish movement, aiming to determine mobile and stationary shares of fish communities, their dispersal distances and key predictors of dispersal patterns. By reviewing and analysing 160 empirical data sets from 71 studies covering 62 fishes in streams, it goes beyond previous studies of salmonids’ heterogeneous movement. Based on fitted leptokurtic dispersal kernels, the movement distances of (i) a stationary component (σ_stat) and (ii) a mobile component (σ_mob) as well as the (iii) share of each component (p) were calculated. The median movement distance of the stationary and mobile component of a fish population was 36.4 and 361.7 m, respectively. The share of the stationary individuals was high (median = 66.6%), but unrelated to movement distance. Single and multiple linear regressions as well as mixed‐effects models revealed movement distances positively related to fish length, aspect ratio of the caudal fin, stream size and duration of the study. Furthermore, movement distance differed between taxonomic families. The quantitative parameters of heterogeneous fish movement provided are prerequisite to estimate time lags in fish response to river rehabilitation, temporal patterns in species dispersal, and minimum effective size of potential founder populations for species conservation and stock recovery based on minimum numbers of specimen to disperse.     

Genetic estimates of population structure and dispersal in a benthic stream fish

Abstract–  Comparing genetic and demographic estimates of dispersal in freshwater fish can improve understanding of movement distributions and population connectivity. Here we examined genetic variation among mottled sculpin (Cottus bairdi) in the Nantahala River (North Carolina, USA) to compare genetic estimates of dispersal with estimates derived from mark–recapture studies of individual movement. Microsatellite‐based analysis of gene flow revealed evidence of strong isolation by distance among locations spanning only 5.6 km and limited dispersal among clusters of sites separated by swift cascades. Estimates of between‐cluster contemporary dispersal rates derived from Bayesian assignment tests ranged from 1% to 6%, with most movement occurring among adjacent clusters in a downstream direction. Evidence of a long‐term net immigration asymmetry and decreasing genetic diversity from downstream to upstream locations indicates that historical patterns of stream colonisation contrast with contemporary dispersal patterns. Our findings are largely consistent with predictions from individual movement patterns but suggest that long moves (>500 m) are more frequent, and maximum dispersal distances are greater than what has been reported from mark–recapture studies. The discrepancy may reflect spatial limitations of mark–recapture methods or temporal variation in dispersal in individuals and populations.     

Population ecology and seasonal demography of the endangered grotto sculpin (Cottus specus)

Subterranean fishes are understudied worldwide and often at risk before their populations are discovered and described. The nature of karst systems limits the applicability of ecological paradigms and hinders our ability to identify and preserve endemic fauna. Aquatic karst taxa in particular are subject to environmental threats that increase in severity over time. Once a population or species is recognised as distinct, it is imperative we gain understanding of its biology to inform effective resource management and mitigate risk factors. The grotto sculpin (Cottus specus) is endemic to Perry County, Missouri, U.S. caves and was formally described and listed as endangered under the U.S. Endangered Species Act in 2013. We used mark–recapture methods to quantify population densities and estimate population sizes in two caves and two corresponding spring branches. Size structure varied among habitats and seasons. Spring branches were dominated by juveniles year‐round with peak young‐of‐year (YOY) densities in May. Adult densities in both macrohabitats decreased in winter, possibly due to recruitment or seasonal stress, and were lower at spring branches compared to caves and declined further during late winter which may be indicative of cave spawning. YOY were captured variably underground with peak densities in summer. The ecology of grotto sculpin appears to be more complex than has been reported previously for subterranean fishes. Variable patterns of demography requiring multiple contiguous habitats are unique for cave species and support the recently substantiated suggestion that subterranean systems are not as simple or disconnected as once thought.     

Seasonal abundance and movement of the invasive round goby (Neogobius melanostomus) on rocky substrate in the Duluth–Superior Harbor of Lake Superior

Abstract – Despite its small size [adult: 60–130 mm, total length (TL)] and limited home range, the round goby (Neogobius melanostomus) has quickly become established throughout the Laurentian Great Lakes. Little information is available, however, on the natural dispersal pattern of this species. This capture–mark–recapture study utilised alphanumeric tags subcutaneously inserted into round gobies (n = 1228) along a 550‐m stretch of the Duluth–Superior Harbor shoreline to observe their movement over a 13‐month period. Recaptured round gobies (n = 415) exhibited highly leptokurtic movement distributions, and movement events were not correlated with fish size, gender or month. Our work indicates that round gobies >50 mm (TL) generally occupy an area less than the minimum sampling interval (25 m); however, occasional movement up to 50 m per day could facilitate range expansion in the Laurentian Great Lakes.     

Variability in movement dynamics of topminnow (Fundulus notatus and F. olivaceus) populations

Abstract – Movement and dispersal patterns are key biological processes across a range of organisational levels. The Fundulus notatus species complex includes several species with similar ecological niches that exhibit broadly overlapping ranges. We conducted a mark–recapture study on two of the most widely distributed members of this species complex to improve our understanding of their movement and habitat use. A population of F. notatus was studied between June and August of 2008 and 2009 in Cahokia Creek, a small tributary of the Mississippi River in Illinois, along with a parallel study of Fundulus olivaceus between May and July of 2009 in Big Creek, a tributary of the Pascagoula River in Mississippi. Fish were recaptured approximately weekly, and habitat variables were measured. Estimated daily movement rates varied significantly both between locations and between years. Fundulus olivaceus in Big Creek moved <1 m per day, while F. notatus in Cahokia Creek in 2009 moved nearly 23 m per day. The distribution of movements was strongly leptokurtic in all three data sets. Differences in movement rates were attributed to significant differences in population size and habitat characteristics. Our data did not support the hypothesis that populations consist of distinct mobile and resident components. Instead, individual fish went through periods of little or no movement followed by extensive movement (consistent with the home range shift model of fish movement). We discuss the implications these results have for contact zone dynamics between these two species.     

Movement of three stream‐resident balitoroid loaches and a goby in a Hong Kong hillstream

We undertook a mark–recapture study of three pool‐dwelling balitoroid loaches and a nonmigratory goby in a Hong Kong hillstream, which extended over a 35‐week period. The target species were Pseudogastromyzon myersi and Liniparhomaloptera disparis (Balitoridae), Schistura fasciolata (Nemacheilidae) and Rhinogobius duospilus (Gobiidae). Recapture rates of tagged individuals were high (58% overall), especially for the abundant R. duospilus (70% of 412 tagged) and P. myersi (57% of 762 tagged). At the end of the study, most recaptured individuals (78% of gobies, 62% of P. myersi, 42% of L. disparis and 67% of S. fasciolata) were within the pools where they had been released. Of those that had moved elsewhere, maximum displacements ranged from 46 m (R. duospilus) to 101 m (P. myersi), giving rise to a strongly leptokurtic distribution of movement distances. Mean displacements after 35 weeks ranged from only 2.9 m (R. duospilus) to 10.0 m (L. disparis). The sedentary behaviour of these species was more marked than most other small benthic fishes, although our study excluded the breeding period and wet season when high flows might have stimulated movement. Among the mobile P. myersi individuals, most travelled upstream, whereas mobile gobies tended to move downstream. Juveniles of P. myersi and R. duospilus, as well as large adult P. myersi, were especially sedentary, while mobile adult P. myersi that travelled further showed smaller growth increments. The highly sedentary habits of all four fishes suggest that they may exert persistent local top‐down control of benthic communities within pools in Hong Kong streams.     

Morphological divergence of the threatened Rocky Mountain sculpin (Cottus sp.) is driven by biogeography and flow regime: Implications for mitigating altered flow regime to freshwater fishes

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Declines in deepwater sculpin Myoxocephalus thompsonii energy density associated with the disappearance of Diporeia spp. in lakes Huron and Michigan

Pothoven SA, Hondorp DW, Nalepa TF. Declines in deepwater sculpin Myoxocephalus thompsonii energy density associated with the disappearance of Diporeia spp. in lakes Huron and Michigan.
Ecology of Freshwater Fish 2011: 20: 14–22. Published 2010. This article is a US Government work and is in the public domain in the USA. Abstract – The deepwater sculpin Myoxocephalus thompsonii is a glacial relict in the Laurentian Great Lakes that primarily consumes two glacial relict crustaceans, Mysis relicta and Diporeia spp. Deepwater sculpin were collected in Lake Michigan off Little Sable Point (in 2001) and Muskegon, Michigan (in 2001 and 2009), and in Lake Huron off Harbor Beach, Michigan (in 2007) for energy density and diet analyses. These sites and years represented differences in available prey. In Lake Michigan, energy densities of deepwater sculpin in 2001 were similar to those reported in 1969–1971. In contrast, energy content declined at least 26% at Muskegon between 2001 and 2009. Overall, energy density was 31–34% higher at a site with abundant Diporeia spp. compared with two sites without Diporeia spp. Deepwater sculpin diets consisted primarily of M. relicta at all sites, but included 10–17% (dry mass) Diporeia spp. at sites where this crustacean was still abundant. Food biomass in stomachs was higher at sites with abundant Diporeia spp. than at those without Diporeia spp. Deepwater sculpin energy density and food biomass in stomachs were similar between two sites without Diporeia spp. despite differences in abundance of remaining prey, M. relicta. Declines in deepwater sculpin energy density suggest the potential for further effects on other species and changes in the flow of energy through the food web of the Great Lakes.     

Extensive dispersal of Roanoke logperch (Percina rex) inferred from genetic marker data

The dispersal ecology of most stream fishes is poorly characterised, complicating conservation efforts for these species. We used microsatellite DNA marker data to characterise dispersal patterns and effective population size (N_e) for a population of Roanoke logperch Percina rex, an endangered darter (Percidae). Juveniles and candidate parents were sampled for 2 years at sites throughout the Roanoke River watershed. Dispersal was inferred via genetic assignment tests (ATs), pedigree reconstruction (PR) and estimation of lifetime dispersal distance under a genetic isolation‐by‐distance model. Estimates of N_e varied from 105 to 1218 individuals, depending on the estimation method. Based on PR, polygamy was frequent in parents of both sexes, with individuals spawning with an average of 2.4 mates. The sample contained 61 half‐sibling pairs, but only one parent–offspring pair and no full‐sib pairs, which limited our ability to discriminate natal dispersal of juveniles from breeding dispersal of their parents between spawning events. Nonetheless, all methods indicated extensive dispersal. The AT indicated unrestricted dispersal among sites ≤15 km apart, while siblings inferred by the PR were captured an average of 14 km and up to 55 km apart. Model‐based estimates of median lifetime dispersal distance (6–24 km, depending on assumptions) bracketed AT and PR estimates, indicating that widely dispersed individuals do, on average, contribute to gene flow. Extensive dispersal of P. rex suggests that darters and other small benthic stream fishes may be unexpectedly mobile. Monitoring and management activities for such populations should encompass entire watersheds to fully capture population dynamics.     

Movement patterns of southern redbelly dace,Chrosomus erythrogaster,in a headwater reach of an Ozark stream

Previous research on fish movement has focused primarily on recreationally important fishes in perennial streams; however, fewer studies have examined movement patterns of small‐bodied fishes in intermittent streams where abiotic and biotic conditions can be extreme compared with perennial systems. Using mark–recapture, we examined movement patterns of southern redbelly dace, Chrosomus erythrogaster, in an intermittent Ozark stream having both permanently connected and temporally isolated sections. Juvenile (60–88%) and adult (55–83%) residency rates were not significantly different for any mark–recapture sample, and movement was primarily within a section for both groups. Ontogenetic differences were detected for kurtosis, distance moved and population spread, with adults exhibiting greater variability in movement, moving more often and further. When considering only adults, there was a significantly higher number of individuals that exhibited intermovement from isolated sections compared with connected sections. In addition, a higher proportion of adults exhibiting intermovement moved to connected stream sections in May and July compared to January and March. Dace exhibited upstream bias in July, with 76% of emigrates moving to an upstream connected section. Although there were no statistically significant associations between the proportion of intermovers from connected and isolated sections and measured water quality and habitat variables, noteworthy trends were observed, and these trends were always stronger for connected sections. Understanding the factors that influence population dynamics in headwater streams is important for the survival and persistence of stream fish populations, especially considering the anticipated expansion of intermittent headwater streams as a result of future climatic changes.     

Predation on native sculpin by exotic brown trout exceeds that by native cutthroat trout within a mountain watershed (Logan,UT, USA)

We explored potential negative effects of exotic brown trout (Salmo trutta) on native sculpin (Cottus sp.) on the Logan River, Utah, USA by (i) examining factors most strongly correlated with sculpin abundance (e.g., abiotic conditions or piscivory?), (ii) contrasting the extent of brown trout predation on sculpin with that by native cutthroat trout (Oncorhynchus clarkii utah) and (iii) estimating the number of sculpin consumed by brown trout along an elevational gradient using bioenergetics. Abundance of sculpin across reaches showed a strong (r ≥ 0.40) and significant (P < 0.05) correlation with physical variables describing width (positive) and gradient (negative), but not with abundance of piscivorous brown trout or cutthroat trout. In mainstem reaches containing sculpin, we found fish in 0% of age‐1, 10% of age‐2 and 33% of age‐3 and older brown trout diets. Approximately 81% of fish consumed by brown trout were sculpin. Despite a similar length–gape relationship for native cutthroat trout, we found only two fish (one sculpin and one unknown) in the diets of native cutthroat trout similar in size to age‐3 brown trout. Based on bioenergetics, we estimate that an average large (> 260 mm) brown trout consumes as many as 34 sculpin per year. Nevertheless, results suggest that sculpin abundance in this system is controlled by abiotic factors and not brown trout predation. Additional research is needed to better understand how piscivory influences brown trout invasion success, including in‐stream experiments exploring trophic dynamics and interactions between brown trout and native prey under different environmental conditions.     

Lack of genetic population structure of slimy sculpin in a large,fragmented lake

Most of what is known about sculpin population structure comes from research in streams; however, slimy sculpins are also a common benthic species in deep lakes. In streams, sculpins are considered to be a relatively inactive species, moving only small distances, and characteristically have high levels of genetic structure. We examined population genetic structure of slimy sculpin (Cottus cognatus) across multiple barriers and over distances up to 227 km in Lake Champlain (USA, Canada) and Lake Ontario (USA, Canada) to determine whether lake populations of sculpin are also highly structured. We predicted that slimy sculpin populations in Lake Champlain would be structured by six causeways as well as by distance, Lake Ontario populations would be structured only by distance, and differences between the lakes would be large relative to within‐lake differences. We examined microsatellite variation among 200 slimy sculpins from Lake Champlain and 48 slimy sculpins from Lake Ontario to evaluate patterns of population connectivity and structure. There was no indication of population substructuring within either lake but sculpin were genetically distinct between lakes. We conclude that there is a single, panmictic population of sculpin present in Lake Champlain and another potentially panmictic population in Lake Ontario, with no indication of genetic isolation by distance. Our results contrast with data from sculpin in streams, suggesting distance and habitat fragmentation exert little influence on population connectivity of benthic fish in lakes.     

Evaluation of ageing accuracy with complementary non‐lethal methods for slow‐growing,northern populations of shoal bass

In the upper Chattahoochee River basin, where some populations of shoal bass, Micropterus cataractae Williams & Burgess, are imperilled, age and growth data are lacking. Age and growth of shoal bass in this basin were assessed with non‐lethal means using scales and mark–recapture. Mark–recapture data allowed for estimation of accuracy and determination of effects of any scale‐based inaccuracies on growth models. Scale‐based age estimates were accurate for 57% of the samples, and errors of 1 to 3 years included equal numbers of over‐ and underestimates of age. von Bertalanffy growth models based on scale ages were similar to those based on mark–recapture ages for ages 3–8 but noticeably divergent for younger and older fish. Scales provided estimates of longevity up to 12 years of age, and growth models produced from mark–recapture suggest scale ages underestimated age, especially for older fish. These populations of shoal bass live longer and grow slower than other populations, suggesting regional management strategies may be needed.     

Dispersal and tributary immigration by juvenile coho salmon contribute to spatial expansion during colonisation

Anadromous fishes are frequently restricted by artificial barriers to movement such as dams and culverts, so measuring dispersal helps identify sites where improved connectivity could promote range expansion and population viability. We used a combination of DNA‐based parentage analysis and mark–recapture techniques to evaluate dispersal by juvenile coho salmon (Oncorhynchus kisutch) in a population in the initial stages of colonisation following installation of fish passage structures at a previously impassable dam on the Cedar River, WA, USA. The spatial distribution of individuals within maternal families revealed that dispersal was common. Among the offspring of radio‐tagged mothers, 28% were collected outside the spawning reach and dispersed up to 6.3 km (median = 1.5 km). Most juveniles captured in a tributary (Rock Creek, where few adults spawned) had immigrated from the Cedar River and represented many different families. Juvenile dispersal therefore provided a secondary phase of spatial expansion following initial colonisation by adults. Consistent with the condition‐dependent dispersal hypothesis, juveniles that dispersed farther upstream in the tributary were larger than fish collected near the tributary mouth. Overall, the results demonstrated widespread dispersal in a system with low coho salmon densities, and this might increase the rate of population growth if it reduces the effects of local density dependence. By implication, juveniles can take advantage of rearing habitats reconnected through barrier removal, even when such areas are located several kilometres from adult breeding grounds.     

Geographic variation in host fish use and larval metamorphosis for the endangered dwarf wedgemussel

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Water diversion reduces abundance and survival of two Mediterranean cyprinids

Water flow is a fundamental characteristic required for the ecological integrity of stream ecosystems. However, populations of many freshwater fishes in the Mediterranean region are threatened by man‐induced drought due to water diversion. Mark‐recapture methodology is an effective tool for estimating fish abundance and survival probability, but it has been seldom used with Mediterranean freshwater fish. We tagged over 2,400 individuals of two threatened cyprinids (Mediterranean barbel Barbus meridionalis and Catalan chub Squalius laietanus) inhabiting an Iberian stream affected by water diversion, and used mark‐recapture methods to evaluate the effects of flow, temperature and depth on their apparent survival and abundance at hydrologically altered and perennial reaches. Based on estimates over the summer drying season, survival of Mediterranean barbel was more than six times higher in an upstream reach with permanent flow than a middle reach impacted by water diversion. Water depth was the most important habitat feature accounting for differences in survival, with both barbel and chub exhibiting higher survival and abundance at permanent sites farther downstream where flow had been restored and in an unaltered tributary. Our results show clear negative impacts of water diversion on fish populations. Both species, but particularly barbel, have life‐cycle characteristics that may allow populations to recover quickly if natural streamflow was restored by conserving water and reducing water diversion.     

Assessing large-scale movement of an endangered fish: Dispersal of stocked age-0 pallid sturgeon in the lower Missouri River

1. Large-scale movement of fishes is a challenge for conservation and management in rivers, especially when individuals can cross jurisdictional boundaries.
2. Assessing large-scale movement is particularly difficult during early life stages, especially when endangered species are involved. After hatching, free embryos of the federally endangered pallid sturgeon (Scaphirhynchus albus) drift long distances during development. Following the transition to exogenous feeding, individuals may continue to move downstream, resulting in a potential two-step migration.
3. Tagged age-0 pallid sturgeon were stocked into the lower Missouri River, which provided an opportunity to assess pallid sturgeon dispersal as well as the hypothesized two-step migration. From July 2018 to April 2021, 79 individuals were captured, with most dispersing 200–800 km downstream from the stocking location.
4. The observed dispersal of pallid sturgeon supports the two-step downstream migration hypothesis. This migration may lead to dispersal into the Mississippi River, which highlights the need for expanded monitoring into the Mississippi River for an effective evaluation of pallid sturgeon recovery actions. This study also reinforces the importance of inter-jurisdictional management and collaboration to better account for the large-scale movement of river fishes.

     

The spectre of past spectral conditions: colour plasticity,crypsis and predation risk in freshwater sculpin from newly deglaciated streams

Whiteley AR, Bergstrom CA, Linderoth T, Tallmon DA. The spectre of past spectral conditions: colour plasticity, crypsis, and predation risk in freshwater sculpin from newly deglaciated streams. Ecology of Freshwater Fish 2011: 20: 80–91. © 2010 John Wiley & Sons A/S Abstract – Coastrange sculpin (Cottus aleuticus) have colonised recently deglaciated streams of Glacier Bay National Park, Alaska, USA, within the last 200 years. Highly cryptic colouration across a marked gradient of stream substrate colours within Glacier Bay could result from physiological (rapid) or morphological (slower) colour change. Laboratory experiments revealed that physiological colour plasticity occurred on the order of minutes, with significant variation in the degree of colour change among individuals and between populations. In contrast, morphological colour plasticity occurred on the order of weeks to months. Experimentally manipulated spectral conditions influenced the magnitude and variance of subsequent physiological colour plasticity. In‐stream predation trials revealed significantly more predation attempts on higher background contrast sculpin models, providing evidence that background colour matching has strong fitness consequences. Colour plasticity with apparent fitness consequences occurs at multiple interacting time scales in coastrange sculpin and may play an important role in the colonisation of recently deglaciated streams.     

Modelling individual variability in growth of bull trout in the Walla Walla River Basin using a hierarchical von Bertalanffy growth model

We examined growth in length of fluvial bull trout (Salvelinus confluentus) in the Walla Walla River Basin, Washington and Oregon. Our objectives were to quantify individual variability in growth; examine growth within and among years, life history forms, life stages and sexes; and estimate von Bertalanffy growth parameters. Individual variability was evaluated by modelling asymptotic length (L_∞) and the growth coefficient (k) as random variables. All models were fit with Bayesian methods and were evaluated for fit by the deviance information criterion. By incorporating individual variability, population‐level estimates of L_∞ and k appeared appropriate and estimated growth trajectories for specific bull trout fit individual observed patterns in growth. Growth trajectories and positive correlation between individual estimates of L_∞ and k suggest that some individuals grow at a faster rate and reach a larger maximum size than other individuals and those differences are maintained throughout life. Selected models suggest that fluvial migrants have higher estimates of L_∞ and k than residents, but there were only slight differences in parameter estimates among migrants from two adjacent spawning populations in the Walla Walla River Basin, as well as between males and females. Growth rates increased for fluvial migrants after subadult emigration. Individual variability in growth is consistent with the life history diversity assumed essential for bull trout population persistence. Quantifying this variability is important for modelling population dynamics and viability to conserve this threatened species.     

Dispersal strategies of juvenile pike (Esox lucius L.): Influences and consequences for body size,somatic growth and trophic position

Individual variability in dispersal strategies, where some individuals disperse and others remain resident, is a common phenomenon across many species. Despite its important ecological consequences, the mechanisms and individual consequences of dispersal remain poorly understood. Here, riverine Northern pike (Esox lucius) juveniles (age 0+ (young-of-the-year) and 1+ years) were used to investigate the influence of body size and trophic position (at capture) on the dispersal from off-channel natal habitats and the subsequent consequences for body sizes, specific growth rate and trophic position (at recapture). Individuals that dispersed into the river (“dispersers”) were not significantly different in body size than those remaining on nursery grounds (“stayers”). For trophic position, 0+ dispersers were of significantly lower trophic position than stayers, but with this not apparent in the 1+ fish. Following dispersal into the river, the dispersers grew significantly faster than stayers and, on recapture, were significantly larger, but with no significant differences in their final trophic positions. Early dispersal into the river was, therefore, not associated with early dietary shifts to piscivory and the attainment of larger body sizes of individuals whilst in their natal habitats, contrary to prediction. These results suggest that despite an increasing risk of mortality for individuals dispersing early from natal areas, there are long-term benefits via elevated growth rates and, potentially, higher fitness. Such early dispersal behaviour could be driven by early competitive displacement.