Native Fish Abundance Research Articles

Shelter use interactions of invasive lionfish with commercially and ecologically important native invertebrates on Caribbean coral reefs.

Indo-Pacific lionfish have become invasive throughout the western Atlantic. Their predatory effects have been the focus of much research and are suggested to cause declines in native fish abundance and diversity across the invaded range. However, little is known about their non-consumptive effects, or their effects on invertebrates. Lionfish use shelters on the reef, thus there is potential for competition with other shelter-dwelling organisms. We demonstrate similar habitat associations between invasive lionfish, native spiny lobsters (Panulirus argus) and native long-spined sea urchins (Diadema antillarum), indicating the potential for competition. We then used a laboratory experiment to compare activity and shelter use of each species when alone and when lionfish were paired with each native species. Spiny lobsters increased their activity but did not change their shelter use in the presence of a lionfish, whilst long-spined sea urchins changed neither their activity nor shelter use. However, lionfish reduced their shelter use in the presence of spiny lobsters and long-spined sea urchins. This study highlights the importance not only of testing for the non-consumptive effects of invasive species, but also exploring whether native species exert non-consumptive effects on the invasive.

Impact of Chaitén Volcano ashfall on native and exotic fish recovery, recolonization, and abundance

The effects of volcanic disturbance on aquatic communities and their recovery are poorly studied. To fill this gap, we explored the effects on fish communities in rivers in Argentina of the 2008 eruption of Chaitén Volcano in southern Chile (42.8° lat. S). The eruption produced volcanic plumes of ash that persisted in the atmosphere for several months. Borne on westerly winds, deposits of tephra crossed the Andes Mountains, reaching the Atlantic coast (Argentina). We compared the pre- and post-eruption abundances of a native catfish Hatcheria macraei, and two introduced trout from rivers covered by the volcanic plumes (Argentina) using Before-After-Control-Impact analysis to explore fish recovery. Total suspended solids from volcanic ashfall, macroinvertebrate abundance and richness, and species ecological attributes influenced the spatial arrangement of fish in rivers. Twenty-one months after the eruption, Rainbow Trout, Oncorhynchus mykiss, had not returned to pre-eruption abundances in the sampled rivers, and only four rivers had regained pre-eruption species composition, suggesting that disturbance is still ongoing. The abundance of introduced fishes was strongly, negatively correlated with TSS, suggesting that ashfall affected these fish probably by clogging and abrasion of the gills. Fish recolonized previously occupied habitats 4 days to 9 months after the disturbance. Hatcheria macraei was the slowest to recolonize, whereas O. mykiss were the pioneer fish in 4 rivers following the eruption and recolonized all 5 rivers where they were present prior to the eruption. In one river, the catfish and the Brown Trout, Salmo trutta, were still absent 21 months post-eruption, potentially owing to the lack of riparian cover that would have deflected the entry of ash. Rainbow Trout suffered significant declines in abundance, whereas Brown Trout and catfish generally did not, owing to their ecological attributes. Total fish abundance was negatively correlated with ash thickness, but positively related to prey availability.

Use of a novel richness-weighted abundance index of age-0 fishes to identify key features for habitat conservation and restoration

Prioritizing sites for conservation or setting goals for enhancement and restoration projects is often difficult due to limited knowledge about relations between habitat characteristics and faunal assemblages. We tested the utility of a novel richness-weighted abundance (RWA) index as a tool for guiding habitat conservation and restoration for native fishes and compared its utility to established indices of abundance and diversity (i.e., Shannon diversity index, Simpson diversity index, species richness, total catch). Habitat and fishes were sampled in the upper Niagara River during late summer, 2013–2015. We used multivariate adaptive regression splines to model the relation between each index of abundance or diversity of native age-0 fish and aquatic habitat features, and compared R2 values among models to determine the strength of the relationship between each index and aquatic habitat features. Our RWA index had the strongest relation with habitat features (R2 = 0.40) and Shannon and Simpson indices were unrelated to habitat features. We found the best habitats for native fishes (i.e., highest RWA scores) contained substantial submerged aquatic vegetation extending into the water column (>20%), low water velocities (<0.1 m/s), and fine to very fine substrates. Our approach of valuing habitat based on an RWA index allows researchers and practitioners to assess the quality of native fish assemblages and determine which habitat characteristics are associated with supporting those assemblages. This index should be applicable to other ecosystems, and has value for ranking existing sites for conservation and for setting clear goals for enhancement and restoration projects.

Effect of Microhabitat Structure on the Distribution of an Endangered Fish, Coreoperca kawamebari (Temminck &amp; Schlegel, 1843) in the Geum River, South Korea

Macrophytes play a major role in the structuring of aquatic environments and may influence the distribution and feeding habits of fish species. We explored the microhabitat characteristics influencing the spatial distribution of newly discovered Coreoperca kawamebari (Temminck &amp; Schlegel, 1843) in the upstream reaches of the Geum River. Out of 21 study sites, C. kawamebari was found in 10 sites, and its abundance was strongly positively correlated with “vegetated” microhabitats, especially those covered by elodeids (e.g., Ceratophyllum demersum). The utilization of elodeids by the piscivores fish, C. kawamebari, may limit the abundance of other native fishes, and stable isotope analysis also showed that C. kawamebari is likely to consume other fish species. However, the influence of other fish species on C. kawamebari is assumed to be small, considering that C. kawamebari is a latent predator. Although the abundance of other fish was low within the preferred microhabitat of C. kawamebari, other species were abundant in each site where C. kawamebari was dominant. From this finding, we conclude that the successful settlement of C. kawamebari in the upper section of the Geum River can be attributed to their habitat preferences. Although the elodeids favored by C. kawamebari generally have difficulty developing in the upstream section, the habitat creation by humans has contributed to the stable settlement of new fish species.

Effects of Multiple Nonnative Fish on an Imperiled Cyprinid, Hornyhead Chub

AbstractNonnative fish can have substantial negative effects on the abundance and distribution of native fishes through predation and competition. Nonnative predators are of particular interest because they represent novel threats to native prey species that are not adapted to their presence. Prey species with limited distributions or population sizes may be particularly vulnerable to the effects of nonnative predators. In the Laramie River, four nonnative predators—Brown TroutSalmo trutta, Rainbow TroutOncorhynchus mykiss, Brook TroutSalvelinus fontinalis,and Smallmouth BassMicropterus dolomieuare present along with a state‐imperiled population of Hornyhead ChubNocomis biguttatus. The abundance of Hornyhead Chub has declined with increasing abundance of nonnative predators, with the probability of occurrence of Hornyhead Chub dropping drastically when Smallmouth Bass were present. All four nonnative species preyed on native cyprinids, but Smallmouth Bass relied most heavily on fish as a prey item. Isotopic niche overlap occurred between Hornyhead Chub and all of the nonnative predator species. Our results demonstrate that nonnative predators have the potential to negatively affect the abundance and distribution of Hornyhead Chub through the mechanisms of predation and competition, and predator identity is important in determining the extent of effects. Smallmouth Bass are a greater concern than nonnative salmonids because of their more piscivorous behavior, and their recent upstream expansion may be limiting the downstream distribution of Hornyhead Chub in the Laramie River.

The influence of natural flow and temperature and introduced brown trout on the temporal variation in native fish abundance in a “reference” stream

Understanding what drives variation in fish abundance at reference sites provides perspective for assessing the effects of human alterations to river flow and land use. We examined temporal variation in fish community abundance in a headwater tributary of a large river in the upper South Island (New Zealand) over 10 years. We were interested in the influence of natural flow variation and temperature on native fish abundance within the context of potential competition/predation pressure from juvenile introduced trout. Results from biannual sampling highlighted the dominating influence of floods on fish population dynamics, overriding biotic effects. We found no evidence for adverse effects of trout on native fish, and flow-related habitat performed more poorly in explaining variation in fish abundance than low- and median-flow statistics. Differences in temporal variation in abundance between species were largely consistent with life histories that provide resistance and (or) resilience to flood flows and relative insensitivity to low flows. Long-term data (≥10 years) are needed for detecting meaningful trends and quantifying the effects of human activities on fish community abundance.

A review of the ecological effects of European Common Reed (Phragmites australis) on fishes and fish habitat in North America

The invasive European Common Reed (Phragmites australis), first established in North America in the early 1900’s, is now a dominant emergent aquatic plant in many coastal and inland wetlands. A review of the literature was conducted to evaluate the extent of ecological impacts on fishes and their habitat, such as changes in the composition and abundance of native fishes and wetland plants, and alterations to water availability and substrate. The review indicated that a reduction in the abundance of native fishes was common (54.54% of studies), as were impacts to fish habitat (e.g., 54.54% of studies documented a change in wetland plant composition). Many studies were conducted in the eastern and northern United States, which showed that the abundance of juvenile and larval fishes was significantly lower in marshes dominated by P. australis, relative to those dominated by native plant species (Spartina alterniflora); however, changes to wetland plant abundance and composition, water availability, water temperature, nutrient cycling, substrate, reproduction and spawning, genetics of native fishes, and general food web effects were also observed. These results indicate that P. australis poses numerous ecological impacts to the structure and function of wetland habitats, with implications for the ongoing productivity of aquatic ecosystems.

Fish diversity in the cascade of reservoirs along the Paranapanema River, southeast Brazil

ABSTRACT The Paranapanema River is a major tributary of the upper Paraná river basin. Eleven hydropower dams regulate its main course, but no study has investigated fish diversity in these impoundments at the basin-scale. The present study investigated spatial patterns of richness, composition, and abundance of native (non-migratory and migratory) and non-native fishes in the cascade of reservoirs along the Paranapanema River. The study is based on data collected from 34 independent studies conducted in nine reservoirs (47 samples). The compilation recorded 161 species, being 111 native (14 migratory) and 50 non-native. Total richness ranged between 56 and 112 species/reservoir, with a mean of 72 (49.9 non-migratory, 8.1 migratory and 14 non-native). The number of non-migratory species showed no spatial trend along the cascade system, but migratory and non-native richness increased toward downstream reaches. We also observed spatial variation in species composition along the cascade system, but some non-native fishes were widely distributed. Migratory fishes showed low relative abundance (usually &lt; 10%), while non-native species were common and more abundant, especially in reservoirs downstream. Our results revealed a high diversity of fishes in the cascade of impoundments, but indicated that migratory fishes are rare, while non-native species are common or dominant.

CONTEMPORARY STRUCTURE AND DYNAMICS OF FISH COMMUNITIES IN THE COASTAL ZONE OF SOUTHWESTERN CRIMEA, EXAMPLE OF KAZACH’YA BAY

The results of long-term ichthyological research in one of the largest bays on the southwestern coast of the Crimea, Kazach’ya Bay, are presented. The fish fauna includes 83 species belonging to 59 genera in 41 families, and according to this parameter it ranks top among bays of Sevastopol. The ecological and faunal composition of the fish population is analyzed. Marine fishes dominate in terms of diversity, contributing about 90 % to the total number of species, while the rest are relict Ponto-Caspian migratory and brackish-water species. During the study period, the invasion of 8 alien East atlantic and Mediterranean species and one intentional introduction of a Far East endemic (so-iuy mullet) into the azov-Black Sea drainage basin were monitored. The abundance of the alien species has increased noticeably, possibly owing to a rise in water temperature. The bulk of the fish fauna in Kazach’ya Bay is resident fish belonging to the demersal ecological group. The importance of the bay as spawning grounds and feeding grounds for fish of various ecological groups is emphasized. among the species registered in the bay, 48 are objects of commercial or amateur fishing, 9 species are included in the Red Data Book of the City of Sevastopol. Data on the spatial distribution, habitat preferences and species diversity of the five ichthyocenes of the bay are reported. It is concluded that the diversity of the fish fauna of the south-western coastal zone of the Crimean Peninsula is continuing to grow due to ‘mediterranization’, but at the same time there is a decrease in the abundance of native Ponto-Caspian migratory and brackish-water fish, and this process is typical for the Black Sea at large. It is proposed to set up nature protection areas in the waters of Kazach’ya Bay.

The Thermal Regime and Species Composition of Fish and Invertebrates in Kelly Warm Spring, Grand Teton National Park, Wyoming

Abstract. We evaluated the thermal regime and relative abundance of native and nonnative fish and invertebrates within Kelly Warm Spring and Savage Ditch, Grand Teton National Park, Wyoming. Water temperatures within the system remained relatively warm year-round with mean temperatures >20 °C near the spring source and >5 °C approximately 2 km downstream of the source. A total of 7 nonnative species were collected: Convict/Zebra Cichlid (Cichlasoma nigrofasciatum), Green Swordtail (Xiphophorus hellerii), Tadpole Madtom (Noturus gyrinus), Guppy (Poecilia reticulata), Goldfish (Carassius auratus), red-rimmed melania snail (Melanoides tuberculata), and American bullfrog tadpoles (Lithobates catesbeianus). Nonnative fish (Zebra Cichlids and Green Swordtails), red-rimmed melania snails, and bullfrog tadpoles dominated the upper 2 km of the system. Abundance estimates of the Zebra Cichlid exceeded 12,000 fish/km immediately downstream of the spring source. Relative abundance of native species increased moving d...

Invasive level of the exotic species Neopomacentrus cyanomos (Bleeker, 1856) (Pomacentridae) within the ichthyofauna associated to Orbicella spp. (Scleractinia: Merullinidae) in the Enmedio reef, Lobos-Tuxpan Reef system

Biological monitoring is important for assessing the invasive level of alien species. Therefore, in the present work, the abundance of the exotic fish Neopomacentrus cyanomos was estimated with respect to the native ichthyofauna of the Enmedio reef, Veracruz. Five sampling sites were established on the leeward slope, a reef zone characterized by massive corals; in each place, the richness and abundance of native and exotic fishes were estimated in colonies of Orbicella annularis and Orbicella faveolata. The estimated community attributes were specific wealth, abundance, equitability index, and true diversity. To detect significant differences or similarities in the fish community structure, multivariate techniques were applied: similarity and ordering analysis. A total of 39 species of native fish and two exotic species were recorded: Neopomacentrus cyanomos and Pterois volitans. The most abundant species were Halichoeres burekae and Chromis multilineata, which constituted 89% of the total abundance. In contrast, Neopomacentrus cyanomos presented small populations &lt;15 ind/coral and was common in O. faveolata. In the O. faveolata corals, 39 taxa were found and in O. annularis 35; however, fish abundance was higher in colonies of O. annularis than in O. faveolata. The ichthyofauna was characterized by the dominance of zooplanktophagous fishes; equitable and true diversity were higher in areas with greater coral cover and decreased at places where sand and coral pavements prevail. The ichthyofauna was similar in composition and abundance in O. annularis and O. faveolata as well as between the sampling sites. The small populations of N. cyanomos suggest that it is not a competitive species to the native ichthyofauna; however, it is necessary to continue monitoring in order to assess changes in abundance. In addition, it is imperative to investigate the status of invasion in the other reefs of Veracruz.

Water guns affect abundance and behavior of bigheaded carp and native fish differently

Water guns have shown the potential to repel nuisance aquatic organisms. This study examines the effects of exposure to a 1966.4 cm3 seismic water gun array (two guns) on the abundance and behavior of Bighead Carp Hypophthalmichthys nobilis, Silver Carp H. molitrix (collectively referred to as bigheaded carp) and native fishes (e.g., Smallmouth Buffalo Ictiobus bubalus). Water guns were deployed in a channel that connects the Illinois River to backwater quarry pits that contained a large transient population of bigheaded carp. To evaluate the effect of water guns, mobile side-looking split-beam hydroacoustic surveys were conducted before, during and between replicated water gun firing periods. Water guns did not affect abundance of bigheaded carp, but abundance of native fish detected during the firing treatment was 43 and 34% lower than the control and water guns off treatments, respectively. The proximity of bigheaded carp to the water gun array was similar between the water guns on and water guns off treatments. In contrast, the closest detected native fish were detected farther from the water guns during the water guns on treatment (mean ± SE, 32.38 ± 3.32 m) than during the water guns off treatment (15.04 ± 1.59 m). The water gun array had a greater impact on native fish species than on bigheaded carp. Caution should be taken to the extrapolation of these results to other fish species and to fish exposed to water guns in different environments (e.g., reduced shoreline interaction) or exposure to a larger array of water guns, or for use of water guns for purposes other than a barrier.

The Ecological and Conservation Status of The Guadalquivir River Basin (s Spain) Through The Application Of A Fish-based Multimetric Index

An index of biotic integrity (IBI) based on fish health, population age-structure, abundance and community richness of native and alien fish, originally developed for the Júcar basin (E Spain) (IBI-J), was adapted and validated here for another Mediterranean basin– the Guadalquivir (IBI-G). Until now, no one fish-based IBI − sensitive, useful in a large geographical context, simple and easily applied −has been employed in species-poor Mediterranean basins. Various attempts to develop such an index have generally failed to achieve all these objectives. In this paper, the applicability of the index was enhanced through several modifications to the metrics used in the original IBI-J, and a new version of the index was also developed which included an additional metric recommended by the author of the IBI-J. In the IBI-G each of the five metrics that make up the IBI (percentage of individuals with anomalies, age structure of native fish population, relative native fish density, loss of native species and alien fish pressure) were validated and adjusted to the specificities of a typical Mediterranean fish community. Both, IBI-J and IBI-G, are robust and coherent assessment tools, highly sensitive to the main pressure gradients observed in the study area, as demonstrated by its correlation with many pressure indicators (biotic and habitat indexes, habitat variables and physico-chemical parameters). It points to the real possibility of extending the same methodology to similar basins for the purposes of monitoring, management and ecological assessment, especially in contexts relating to the Water Framework Directive (WFD). In addition, this new index does not need undisturbed reference sites, a completely unreal requisite in Mediterranean basins, where there is a general scarcity of pristine sites to be used as reference conditions. The results of this study highlight the usefulness of IBI-J/IBI-G as a powerful biomonitoring tool, especially in application of the WFD.

Predicted Native Fish Response, Potential Rewards and Risks from Flow Alteration in a New Mexico Arid Mountain Stream

AbstractWater and natural resource managers are concerned with evaluating how fish habitat and populations may respond to water diversions and small‐scale flow augmentations. We used two‐dimensional hydraulic models, habitat suitability curves and an individual‐based population viability model to assess whether flow augmentations of about 0.28–0.57 m3/s would create suitable habitat for federally listed native fish loach minnow Rhinichthys cobitis and spikedace Meda fulgida in a reach of the Gila River, New Mexico, and then examined how fish population viability may change under a variety of colonization and extinction scenarios. These simulations help to inform water management decisions in a reach of the Gila River where river diversions currently exist and new diversions and augmentations are being proposed. Our results suggest that the flow augmentations evaluated will result in small changes (on average across life stages, −0.22% to 4.06%) in suitable habitat for loach minnow and spikedace depending on augmentation scenario and fish life stage. While these percent changes are small, they would result in a reduction in the dewatering of the river channel in a river reach where native fish abundance is thought to be low. Actual native fish responses to these habitat changes are unknown; however, these flow augmentations could potentially allow these native species to re‐colonize this river segment from upstream or downstream sources increasing species distribution and likely population viability. Maintaining viable populations of native fish in this river reach is dependent on complex factors including persistence of suitable habitat for multiple life stages, connectivity with other populations and minimizing risk of invasion from non‐native species. We recommend that these predictions from the habitat and population models be tested and verified in an adaptive management framework linking modelling, experimental management, monitoring and reassessment to inform water management decisions in the Gila River. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Tropical fish community does not recover 45years after predator introduction.

Predation is considered to be an important factor structuring natural communities. However, it is often difficult to determine how it may influence long-term, broad-scale, diversity patterns, particularly in diverse tropical systems. Biological introductions can provide powerful insight to test the sustained consequences of predation in natural communities, if pre-introduction data are available. Half a century ago, Zaret and Paine demonstrated strong and immediate community-level effects following the introduction of a novel apex predator (peacock bass, Cichla monoculus) into Lake Gatun, Panama. To test for long-term changes associated with this predator introduction, we followed up on their classic study by replicating historical sampling methods and examining changes in the littoral fish community at two sites in Lake Gatun 45years post-introduction. To broaden our inference, we complemented this temporal comparison with a spatial analysis, wherein we compared the fish communities from two lakes with and one lake without peacock bass. Comparisons with historical data revealed that the peacock bass remains the most abundant predator in Lake Gatun. Furthermore, the collapse of the littoral prey community observed immediately following the invasion has been sustained over the past 45years. The mean abundance of native littoral fish is now 96% lower than it was prior to the introduction. Diversity (rarefied species richness) declined by 64% post-introduction, and some native species appear to have been locally extirpated. We observed a similar pattern across invaded and uninvaded lakes: the mean abundance of native fishes was 5-40 times lower in lakes with (Gatun, Alajuela) relative to the lake without peacock bass (Bayano). In particular, small-bodied native fishes (Characidae, Peociliidae), which are common prey of the peacock bass, were more than two orders of magnitude (307 times) less abundant in Gatun and one order of magnitude (28 times) less abundant in Alajuela than in Bayano. However, total native fish diversity did not differ significantly across lakes, suggesting that while many native species have declined in abundance, few have been completely extirpated. Introduced predators can have strong effects on community structure and functional diversity, even in highly diverse tropical communities, and these effects can persist over multiple decades.

Examining gradients in ecosystem novelty: fish assemblage structure in an invaded Everglades canal system

AbstractNovel ecosystems result from a combination of altered historical abiotic regimes and new species assemblages. In freshwater systems, novel environmental conditions often result from large‐scale changes to hydrological connectivity as well as species invasions. Novel environmental conditions may affect the survival of aquatic fauna by altering dispersal patterns and resource fluctuations, and/or may impose physiological constraints on native species evolutionarily adapted to particular environments. Further, novel systems can provide insight into processes driving community structure because re‐sorting or filtering of regional biota is a likely consequence of decoupling from historical conditions. Although several studies document the presence of novel conditions, few examine variation or gradients in novelty. The Florida Everglades is a highly invaded and hydrologically altered system characterized by a large network of canals that compartmentalize the ecosystem and act to both increase and decrease connectivity. Little is known about how canals in this region function as habitat for native and nonnative fishes, the extent to which these canals may function as novel habitats, and how these habitat characteristics may influence distribution, abundance, and assembly patterns. In this study, we examined native and nonnative fish assemblages along a gradient of novelty, defined as the loss of wetland connectivity, influence of the natural hydrological regime, and habitat complexity (well connected to leveed canals). As novelty increased, native species richness and abundance strongly declined and the contribution of nonnatives increased to nearly 50%. Vast differences in community structure across the novelty gradient were strongly influenced by spatial factors and secondarily by hydrological factors, while habitat and abiotic factors were of very low relevance. Natives and nonnatives had opposing responses to key hydrological and habitat characteristics. Abundance of native fishes declined with decreased connectivity to adjacent marshes and canal littoral zone width, while nonnative fishes increased significantly in the most novel canals. Our results suggest that the inherent loss of natural environmental conditions and subsequent replacement by novel ones can lead to extensive changes in fish community structure. Success or failure at maintaining native assemblages will rely heavily on natural resource manager's ability to incorporate natural environmental characteristics with ecosystem restoration.

Declining streamflow induces collapse and replacement of native fish in the American Southwest

Water scarcity is a global threat to freshwater biodiversity, but connecting variation in streamflow to viability of imperiled faunas remains a challenge. Here we combined time‐series modeling techniques on long‐term ecohydrological data to quantify flow–ecology relationships on native and non‐native riverine fish in the American Southwest, and simulate likely fish trajectories and “quasi‐extinction” risks in the near future. Streamflow has been declining conspicuously over the past 30 years in the Colorado and Rio Grande river basins, and year‐to‐year variation in streamflow influences the covariation between native and non‐native fish abundance. Risks of decline are high (&gt;50%) for nearly three‐quarters of the modeled native species, and current trends in streamflow increase quasi‐extinction risk for natives (+8.5%) but reduce this risk for non‐natives (–5.9%). Hydrological changes need to be mitigated if we are to slow down the rapid replacement of native biodiversity with non‐native species in American Southwest rivers.

Fine-scale determinants of conservation value of river reaches in a hotspot of native and non-native species diversity

Global freshwater biodiversity is declining at unprecedented rates while non-native species are expanding. Examining diversity patterns across variable river conditions can help develop better management strategies. However, many indicators can be used to determine the conservartion value of aquatic communities, and little is known of how well they correlate to each other in making diagnostics, including when testing for the efficacy of protected areas. Using an extensive data set (99,700km2, n=530 sites) across protected and unprotected river reaches in 15 catchments of NE Spain, we examine correlations among 20 indicators of conservation value of fish communities, including the benefits they provide to birds and threatened mammals and mussels. Our results showed that total native fish abundance or richness correlated reasonably well with many native indicators. However, the lack of a strong congruence led modelling techniques to identify different river attributes for each indicator of conservation value. Overall, tributaries were identified as native fish refugees, and nutrient pollution, salinization, low water velocity and poor habitat structure as major threats to the native biota. We also found that protected areas offered limited coverage to major components of biodiversity, including rarity, threat and host-parasite relationships, even though values of non-native indicators were notably reduced. In conclusion, restoring natural hydrological regimes and water chemical status is a priority to stem freshwater biodiversity loss in this region. A complementary action can be the protection of tributaries, but more studies examining multiple components of diversity are necessary to fully test their potential as fluvial reserves in Mediterranean climate areas.

Invasive lionfish reduce native fish abundance on a regional scale.

Invasive lionfish pose an unprecedented threat to biodiversity and fisheries throughout Atlantic waters off of the southeastern United States, the Caribbean, and the Gulf of Mexico. Here, we employ a spatially replicated Before-After-Control-Impact analysis with temporal pairing to quantify for the first time the impact of the lionfish invasion on native fish abundance across a broad regional scale and over the entire duration of the lionfish invasion (1990–2014). Our results suggest that 1) lionfish-impacted areas off of the southeastern United States are most prevalent off-shore near the continental shelf-break but are also common near-shore and 2) in impacted areas, lionfish have reduced tomtate (a native forage fish) abundance by 45% since the invasion began. Tomtate served as a model native fish species in our analysis, and as such, it is likely that the lionfish invasion has had similar impacts on other species, some of which may be of economic importance. Barring the development of a control strategy that reverses the lionfish invasion, the abundance of lionfish in the Atlantic, Caribbean, and Gulf of Mexico will likely remain at or above current levels. Consequently, the effect of lionfish on native fish abundance will likely continue for the foreseeable future.

No effect of round goby Neogobius melanostomus colonisation on young-of-the-year fish density or microhabitat use

The round goby Neogobius melanostomus has recently invaded several major freshwater systems in Europe and North America. Despite numerous studies predicting an impact on native fish assemblages, few have attempted to demonstrate it. In this case study, we monitored the effect of N. melanostomus colonisation on abundance and habitat utilisation of both young-of-the-year (YOY) native fish and YOY western tubenose goby Proterorhinus semilunaris in a typical, medium-sized European river. Colonisation by N. melanostomus had no apparent effect on either native fish abundance and species richness or P. semilunaris abundance. Moreover, after colonisation, both native fish and P. semilunaris occupied similar niches (i.e. microhabitats) to those occupied before colonisation. While niche use of YOY N. melanostomus and P. semilunaris overlapped significantly, YOY native fish utilised different habitats from the gobiids. We suggest that N. melanostomus did not compete for resources with YOY fish in our study area due to lack of niche overlap and/or surplus resources. As N. melanostomus rapidly dominated the fish assemblage at our site, we further suggest that utilisation of an empty niche, rather than competitive superiority, was the main factor facilitating its success.