Fragmentation and drying ratchet down Great Plains stream fish diversity

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Using occupancy models to assess the effectiveness of underwater cameras to detect rare stream fishes

1. Many conservation efforts for freshwater fishes have been undertaken; however, continuing the monitoring of both the distribution and the abundance of species to determine the effectiveness of these actions can be difficult. As species increase in rarity, they are more difficult to detect in the field, making inferences on occupancy less reliable.
2. Conventional sampling methods, such as electrofishing and seining, require the physical handling of rare fishes, which may cause stress and mortality and, consequently, compromise conservation goals and limit monitoring programmes. Non‐invasive surveillance methods, including underwater video, are playing an increasingly important role.
3. In this study, occupancy models were used to estimate the detection probability of underwater cameras as an alternative to the conventional sampling methods for rare stream fishes. Redside dace (Clinostomus elongatus), a small minnow listed as Endangered, was used as a model organism for rarity. A total of 69 historical redside dace sites were sampled using three sampling methods to determine the effect of gear type on detecting and identifying the habitat preferences of this rare minnow.
4. On average, using multiple underwater cameras is as effective at detecting a rare minnow as conventional sampling methods (backpack electrofisher and seine) and causes no harm.
5. The detection probability of both underwater cameras and backpack electrofishing were adversely affected by turbidity, whereas seining was positively affected by stream velocity. The probability of occupancy of redside dace is driven by open channels and sediment size, and this provides a strong basis for informing stream restoration projects.
6. The use of multiple underwater cameras over conventional sampling methods is recommended when sampling for rare and endangered minnows in systems with low turbidity.

     

Antipredator responses of two native stream fishes to an introduced predator: does similarity in morphology predict similarity in behavioural response?

Abstract –  Antipredator defences in prey species are moulded largely by predation. One general expectation is that an organism's size, shape or morphology determines the optimal set of corresponding behavioural antipredator responses. We test the hypothesis that species with similar morphology and ecology exhibit similar antipredator responses by quantifying and comparing avoidance and escape responses of two similar species, leatherside chub and redside shiner. We also examine how antipredator responses of these two species translate into mortality using experimental stream enclosures. In the presence of brown trout, redside shiner increased activity level, responded to a simulated attack sooner, quicker and had a more manoeuvrable escape than leatherside chub. Predation by brown trout decreased survival of both species, but caused higher levels of mortality in leatherside chub compared with redside shiner. Similar morphology and ecology of these two prey species does not correspond to similarity in avoidance and escape responses, and this difference has consequences for the long-term survival of these species in the presence of introduced brown trout.     

In‐stream structure alters density‐dependent fish effects in stream ecosystems

The independent effects of in‐stream structure (ISS) and fish foraging on stream properties have been well documented, but few studies have explored the interactive effects of ISS and fishes on streams. Herein, we tested the independent and interactive effects of ISS and a generalist fish (Blacktail shiner, Cyprinella venusta) on suspended organic matter (SOM), benthic algae, invertebrate density and fish growth using experimental mesocosms. We found that Blacktail shiner foraging affected all of the ecosystem properties; however, in some cases, the fish effects differed between mesocosms with and without ISS. Specifically, mesocosms with ISS provided greater surface area for invertebrate colonisation and enhanced food resources for Blacktail shiner. As a result, benthic foraging by Blacktail shiner was reduced in these mesocosms. The reduced benthic foraging in turn enhanced benthic algae and benthic invertebrates via a bottom‐up, nutrient excretion pathway. The ISS‐dependent effects of fish on these stream properties, however, were only evident at low and intermediate fish densities (1 and 2 fish·m^?2 respectively). This was likely because at the highest fish density (4 fish·m^?2) intense fish foraging overrode any mediating effects of ISS. Furthermore, fish growth decreased with fish density because of intraspecific competition, but this negative effect on growth was reduced in mesocosms with ISS because of the increased forage base. However, the positive effect on fish growth was weak and only marginally significant. Our data suggest that fish‐mediated effects on streams are context dependent, changing with microhabitat availability (e.g. ISS) and density of the fish population.     

Reproductive biology of whitespotted bamboo shark Chiloscyllium plagiosum in northern waters off Taiwan

ABSTRACT:   In total, 491 whitespotted bamboo sharks were collected from northern Taiwanese waters from February 2002 to February 2003. The sex ratio of the specimens was 0.65, total length (TL) ranged from 35.3–85 cm, and weight ranged 124–2580 g. The mean size at first maturity was estimated to be 64.9 and 65.6 cm TL for females and males, respectively, based on the relationship between mature percentage and TL. The ovulation season was estimated as March to May based on gonadosomatic index (GSI) variations and captive observation. The monthly changes in GSI of males suggested that the mating season was from December to January. The inconsistency between mating and ovulation seasons suggested that females have sperm storage and delayed fertilization. One or two eggs were deposited every 6 or 7 days on average. Deposition of eggs extended for 2 months, and fecundity was 8 ± 3.8 eggs. Thirteen of 48 eggs deposited in 2003 were hatched and the hatching rate was 0.27. The hatching period was 107 ± 9.3 days with accumulated water temperature ranging from 2372–2835°C.     

闽南-台湾浅滩渔场六种主要中上层鱼类的生化组成检测分析

检测了闽南 -台湾浅滩渔场六种主要中上层鱼类 (蓝圆、金色小沙丁鱼、鲐鱼、颌圆、竹鱼、羽鳃鲐 )鱼肌的生化组成 ,蛋白质含量为 16 .94%～ 18.77% ,脂肪含量为 2 0 .12 %～ 2 5 .15 %。随鱼体体长的增加 ,脂肪含量增长。鱼肌脂肪含量与繁殖活动存在密切相关的季节变动。鱼肌中均含 17种氨基酸 ,必需氨基酸占总氨基酸的 45 .2 5 %～ 49.39% ,极性氨基酸占 42 .82 %～ 45 .16 % ,非极性氨基酸占 39.2 4%～ 41.5 9% ,鲜味氨基酸占 42 .5 6 %～ 46 .0 2 %。     

Spatial and temporal distribution of fish in a small lowland stream

Abstract  The fish fauna and habitat characteristics in five reaches of a small lowland stream were studied through the summer and winter of one year. All species densities, except Atlantic salmon, Salmo salar L., were correlated with either instream or outstream cover, reaffirming the importance of cover to maintain the local abundance of fish populations. There were significant differences between reaches in the density of all the fish species studied, with the exception of the larger size group of dace. Leuciscus leuciscus (L.), and between sampling times for salmon, dace and eel, Anguilla anguilla (L.). There were significant differences between reaches for all the measured habitat variables apart from instream cover, and between sampling times for velocity. instream cover, and substrate particle size, but not depth, width:depth ratio and outstream cover. The implications of these variations for fish stock assessment and predictive fish habitat models such as PHABSIM and habitat suitability indices are discussed.     

Influences of local habitat and stream spatial position on fish assemblages in a dammed watershed,the Qingyi Stream,China

Abstract – Identifying the underlying mechanisms that explain the spatial variation in stream fish assemblages is crucial for the protection of species diversity. The influences of local habitat and stream spatial position on fish assemblages were examined from first‐order through third‐order streams within a dammed watershed, the Qingyi Stream, China. Based on linear regression models, the most important environmental variables influencing fish species richness were water temperature and wetted width, but stream spatial position variables were less important. Using canonical correspondence analysis, five environmental variables were identified to significantly influence fish assemblages, including three habitats (elevation, substrate and water depth) and two spatial variables (C‐link and Link). Our results suggest that, in a heavily dammed watershed, by blocking the migration routes of fishes, dams weaken the influence of stream spatial position on fish species richness. However, fish species compositions are significantly influenced by both local habitat environment and stream spatial position, which is perhaps owing to the distribution of fish species according to ecological requirements not related to spatial processes.     

Density dependence of herbivorous central stoneroller Campostoma anomalum in stream mesocosms

Herbivorous fish can have strong effects on stream ecosystem function by consuming primary producers and excreting limiting nutrients, but it is unclear whether they are resource limited. Thus, understanding factors regulating abundance of these fish might help predict ecosystem function. We used stream mesocosms to test whether populations of central stoneroller Campostoma anomalum exhibit density dependence across a range of typical densities and resource abundance found in Great Plains streams. We predicted that incrementally increasing stocking biomass from 3·7 to 24·9 g·m^?2 would reduce standing stocks of resources resulting in lower growth of stocked fish. Fish growth (over 41 days) was compared to initial stocking biomass and primary production as well as standing stocks of algae and invertebrates using regression analysis. Mean growth of individuals was negatively associated with stocking biomass ( = 0·55; P = 0·02), as predicted. Contrary to our prediction, increases in fish biomass led to increased primary productivity ( = 0·31, P = 0·07), but resulted in no relationship among algal filament lengths ( = 0·00; P = 0·34), algal biomass ( = 0·12; P = 0·19) or invertebrate biomass ( = 0·03; P = 0·30). Thus, density dependence occurred without an apparent reduction in food resources. We hypothesised that stoneroller growth was possibly limited by competition for high‐quality algae or invertebrates, or behavioural interactions causing interference competition.     

Reproductive biology of the dolphin fish Corphaena hippurus on the east coast of Taiwan

ABSTRACT: The dolphin fish, Corphaena hippurus Linnaeus, is one of the most important migratory fishes on the east coast of Taiwan. Present results are based on an investigation of 1439 specimens caught using long-line and driftnet, and set net collected monthly between September 1996 and September 1997. The sex ratio of female to male and female combined was 65%, demonstrating a female predominance. Oocytes became mature and transparent when they attained 1.0 mm in diameter. The total number of oocytes per ovary was estimated to range from 2.78 × 10⁵ to 23.48 × 10>⁵, but batch fecundity was noticeably lower than the total number of ovarian eggs, ranging 5.3–32.7% (average 30.1%), and the relative fecundity ranging 10–344/g bodyweight (mean 111/g bodyweight). Minimum body size at sexual maturity was estimated to be 51 cm for both sexes. Dolphin fish spawned throughout the year with reproductive activity peaking in February to March. It is suggested that the dolphin fish has an extended spawning season, during which it lays eggs almost continuously.     

Longitudinal segregation of Astyanax janeiroensis in Rio Ubatiba: a Neotropical stream of south‐east Brazil

Abstract – In this study, we explored patterns of size and abundance of Astyanax janeiroensis in Rio Ubatiba (Rio de Janeiro, south‐east Brazil) in relation to reproduction. A. janeiroensis broadcast their eggs in the water column throughout the year. Samples at seven sites conducted every second month from July 1994 to August 1995 revealed a predominance of larger adult specimens upstream and immature juveniles downstream. We hypothesize that upstream movements of adult individuals is a response to drifting of eggs and larvae.     

Ecology of stream fish: insights gained from an individual-based approach to juvenile Atlantic salmon

Abstract – Using data from an ongoing study of juvenile Atlantic salmon growth and survival in tributaries of the Connecticut River, USA, we compare standard population-level approaches to those focusing on individuals. We highlight the potential benefits of resampling individually tagged stream fish as compared to standard approaches. Specifically we focus on growth, survival, movements and population estimation. The advantages of estimating sizes and growth rates from individual size trajectories include obtaining growth histories and the ability to perform retrospective analysis of the consequences of different life-history strategies. An example might be the patterns of growth leading to either early maturity or migration. Resampling known individuals is the only way we know to chart both short-term and long-term movements and to assign growth and mortality consequences to such movements. Finally, individual-level data permit robust estimation of survival and density/abundance using methods such as Cormack/Jolly-Seber. The results indicate that population estimates were about 10% lower using individual data than using population data, that survival from sample to sample was typically >90%, that the majority of recaptured fish did not move during the summer, that growth was rapid during spring and most fish lost mass during the summer and that growth trajectories for maturing and non-maturing fish showed substantially different patterns. An individual-based approach to stream fish ecology provides the opportunity to explore the mechanisms responsible for population-level patterns but comes at the cost of significant field effort. Tradeoffs between increased data resolution and the effort required to obtain the data must be considered before undertaking individual-based field studies of stream fishes. ^NOTE     

Effects of current and future climates on the growth dynamics and distributions of two riverine fishes

1. To facilitate conservation planning, there is a need for improved confidence in forecasts of climate change impacts on species distributions. Towards that end, there have been calls for the development of process-based models to test hypotheses concerning the mechanisms by which temperature shapes distribution and to corroborate forecasts of correlative models.
2. Models of temperature-dependent growth (TDG) were developed for two Australian riverine blackfishes with disjunct longitudinal distributions: Gadopsis marmoratus (occupies lower, warmer elevations) and Gadopsis bispinosus (occupies higher, cooler elevations). The models were used to (a) predict blackfish monthly and annual growth dynamics under current and future climate scenarios within different elevation bands of their current distribution, and (b) test the hypothesis that, under the current climate, the distributions of each species would be positively correlated with predicted TDG.
3. Increases in mean annual growth were forecast for both species under all warming scenarios, across all elevation bands. Both species currently occupy annual habitat temperatures below those optimal for growth. Under certain warming scenarios, the predicted increases in annual growth belie forecasts of within-year dynamics that may interact with the phenology of blackfish to impair recruitment.
4. There was not a significant positive linear relationship between predicted TDG and observed abundance among river segments for either species. Both species were strongly under-represented where annual growth rates were forecast to be optimal and over-represented where growth rates were forecast to be intermediate.
5. Confidence in forecasts of climate change impacts based on correlative models will increase when those forecasts are consistent with a mechanistic understanding of how specific drivers (e.g. water temperature) affect processes (e.g. growth). This process-based study revealed surprises concerning how future climates may affect fish growth dynamics, showing that although the blackfish distributions are correlated with temperature the temperature-dependent mechanisms underpinning that correlation require further investigation.

     

Effects of within-patch habitat structure and variation on fish assemblage characteristics in the Bernecei stream, Hungary

Abstract –  Over a 3-year period we examined variability in physical habitat structure and species richness, abundance and assemblage composition of fishes in 13 habitat patches in the Bernecei stream, Hungary. Principal component analysis of habitat structure data from patches elucidated a riffle-run-pool habitat gradient across patches. Temporal habitat variability increased significantly from riffle to pool patches. Fish assemblage characteristics displayed relatively continuous change over the habitat gradient and were relatively stable within patches. Assemblage structure properties (e.g., species richness) displayed different responses to the habitat gradient and to within-patch habitat variability. In general, pool patches had more diverse assemblages and greater within-patch assemblage variability than riffle patches. However, within-patch dynamics were largely determined by the population dynamics of a habitat generalist (i.e., minnow). Broad scale environmental variability (i.e., a catastrophic 100-year flood) also appeared to affect within-patch fish assemblage characteristics. Our results demonstrate that fish assemblage structure is influenced by physical variability (i.e., both floods and spatio-temporal habitat variability) within the Bernecei stream.     

长江重庆段干流与主要支流鱼类分布的比较分析

对长江重庆段干流与8条主要支流的鱼类组成及主要生境进行了调查,并做了对比分析。结果显示:嘉陵江、乌江、綦河、小江、大宁河与长江干流的类似性系数(AFR值)大于80%,为共同区系关系,其中嘉陵江与干流的类似性系数最高。各支流与干流鱼类组成(包括鱼类种类总数、长江上游特有、珍稀、濒危鱼类数)的共有比例各有差异,其中嘉陵江最高,五布河最低。各支流的产卵场数较干流少,但都是以粘性卵产卵场为主,漂流性卵产卵场比例很低。其中,梅溪河没有发现漂流性卵产场,而五布河内漂流性卵产场和粘性卵产场均没有发现。各主要支流洄游通道最长的是小江,为146.5 km,最短的是五布河,仅19 km。河口流量最大的是嘉陵江,为2 100 m~3/s,最小的是五布河,为7.74 m~3/s。综合比较8条支流的鱼类分布情况,嘉陵江是最适宜作为长江重庆段干流替代生境的支流。     

Spatial and temporal variations of two cyprinids in a subtropical mountain reserve – a result of habitat disturbance

Abstract –  We investigated the variations of population of two cyprinids, Varicorhinus alticorpus and Varicorhinus barbatulus , using long-term survey data (1995–2004) in the subtropical island of Taiwan. Fish abundance data showed that at the mainstem stations, V. barbatulus which used to dominate in the higher altitude had declined significantly, while V. alticorpus that used to occupy only the lower altitude had spread upward. However, at the tributaries, trend of the populations of V. barbatulus were not significantly different over time, while populations of V. alticorpus were absent at higher altitude but began to increase at lower altitude. Environmental parameters revealed that sporadic high turbidity was observed at the mainstem stations, but not at the tributaries. Images taken before and after typhoon also showed habitat destruction by debris flow at the mainstem stations. As some models predicted that suitable fish habitats will shrink because of increasing water temperature due to global warming, we showed that fish distribution may be affected by habitat disturbance due to intensified storms sooner than the actual increase of water temperature.     

Diet of the Eurasian otter (Lutra lutra) on the River Gradac,Serbia: Predation in a brown trout‐dominated stream

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Evaluation of single-pass backpack electric fishing for stream fish community monitoring

Abstract  Data from Lake Ontario tributaries were used to evaluate the efficacy of single-pass backpack electric fishing for stream fish monitoring by: testing the relationship between single-pass catch-per-unit-effort (CPUE) and multiple-pass-based population estimates; comparing species richness estimates derived from single-pass and multiple-pass data and assessing the concordance of fish assemblage patterns described using single-pass and multiple-pass data. Significant correlations were calculated between single-pass CPUE and removal-based population estimates for total catch, 15 species, six taxonomic families, five feeding and four reproductive guilds and tolerant/intolerant species. Strong correlations were more commonly associated with the abundance of individual species than other metrics. Capture probability was not affected by stream size or habitat complexity for most measures. Species accumulation curves and significant correlations ( r ² = 0.9) between single-pass and multiple-pass electric fishing indicate that single-pass surveys provide a representative index of species diversity. In addition, within and among-site variation in fish community composition based on single-pass and multiple-pass data were similar.     

Evidence of mutual benefits of nest association among freshwater cyprinids and implications for conservation

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