Comparison of Taxon‐Specific and Taxon‐Generic Risk Screening Tools to Identify Potentially Invasive Non‐native Fishes in the River Neretva Catchment (Bosnia and Herzegovina and Croatia)

The Freshwater Fish Invasiveness Screening Kit (FISK) v2 and Aquatic Species Invasiveness Screening Kit (AS‐ISK) risk identification screening tools were used to assess the invasiveness potential of 24 non‐native (NNS) freshwater fish species in the River Neretva catchment (Bosnia and Herzegovina and Croatia), a risk assessment (RA) area that is an important Mediterranean hotspot for fish endemism. The two assessors assigned similar scores for the invasiveness potential of the NN fishes, and both screening tools successfully distinguished invasive from non‐invasive species. Mean calibrated threshold scores were 10.25 for FISK and 10.00 for AS‐ISK, with the latter increasing to 12.62 when questions that assess the likely impact of predicted future climate conditions on the RA were taken into consideration. These relatively low threshold values are characteristic of areas with an elevated number of translocated species and suggest that NN fishes pose a considerable threat to native species and ecosystems. FISK ranked 50.0–62.6% of the species as being of ‘high risk’ compared with 58.4–59.3% using AS‐ISK. The highest scores (‘very high risk’) were attributed to gibel carp Carassius gibelio (Bloch, 1782) and pikeperch Sander lucioperca (Linnaeus, 1758). The generic screening tool for aquatic species (AS‐ISK) provided similar risk rankings to its predecessor, FISK, as regards invasiveness potential. For this reason, it is likely to be an effective tool for evaluating the potential invasion risk of NNS freshwater fishes for other RA areas in the Balkans. Copyright © 2017 John Wiley & Sons, Ltd.     

The effects of impoundment and non‐native species on a river food web in Mexico's central plateau

Habitat modifications, non‐native species and other anthropogenic impacts have restructured fish communities in lotic ecosystems of central Mexico. Conservation of native fishes requires understanding of food web changes resulting from the introduction of non‐native species, flow alteration and other human impacts. Using δ¹³C and δ¹⁵N analysis of fishes and invertebrates we investigated the effects of non‐native species, and reservoirs on food webs of the Laja river ecosystem (Guanajuato, central Mexico). We estimated trophic position (TP), relative trophic niche and food web dispersion at 11 reservoir, river and tailwater sites. Reservoirs and non‐native fishes modified food webs in the Laja. Food web dispersion was greater in reservoir than in tailwater and river sites. Reservoir food webs had the greatest range of δ¹³C values, indicating a more diverse resource base compared to rivers. δ¹³C values increased with distance downstream from reservoirs, suggesting declining subsidies of river food webs by reservoir productivity. Stable isotopes revealed potential effects of non‐native fishes on native fishes via predation or competition. Non‐native Micropterus salmoides were top predators in the system. Non‐natives Cyprinus carpio, Oreochromis mossambicus and Carassius auratus exhibited lowest TP in the Laja but overlapped significantly with most native species, indicating potential for resource competition. Native Chirostoma jordani was the only species with a significantly different trophic niche from all other fish. Many rivers in central Mexico share similar anthropogenic impacts and similar biotas, such that food web patterns described here are likely indicative of other river systems in central Mexico. Copyright © 2008 John Wiley & Sons, Ltd.     

Status and impacts of non‐native freshwater fish on fisheries biodiversity and biogeography in Kenya: A management perspective

The introduction and spread of non‐native fish species in Kenyan inland freshwater systems are affecting the integrity of Kenya's aquatic biodiversity and ecosystems. The present study investigated the existing knowledge of non‐native fishes in Kenyan inland freshwater systems and their consequential implications regarding fisheries management. A total of 29 non‐native fish species have been introduced to Kenyan inland freshwater systems, with 20 of these being alien fish species and nine extralimital. These introductions have increased the fish faunal compositional similarity of inland drainage systems by 4.1% to a current similarity of 26.9%, compared to a historical similarity of 22.8%. Documented impacts of this situation include displacements, predation, competition, hybridization, habitat modification and disease transmission, all of which have had negative impacts on the status and management of Kenyan freshwater fisheries. The present study addresses the taxonomic bias created by existing studies on non‐native fishes focusing on individual species, by providing more information on the status of other non‐native species about which information is limited and whose status is uncertain. The present study presents information that can be used in management efforts to control invasions and mitigate their negative impacts.     

Selective use and spatial distribution of native and non‐native fish in wetland habitats

Wetland habitats are crucial for many fish species as spawning, feeding or nursery areas, but the major factors that govern their use by fish are poorly identified. In the present study, we aim to investigate the selective use and the spatial distribution of native and non‐native fish species in different types of wetland habitats (grasslands and reed beds) in a large freshwater marsh (North Western France). The selective use was measured by comparing the community that uses wetland habitats to the total community of the marsh (sampled in the permanent aquatic habitats (canals) during the low water period). The spatial distribution was studied by analyzing the presence probability of fish in wetland habitats as a function of the distance from adjacent canals. All sampled wetland habitats were occupied by fish, and the fish community in wetland habitats was dominated by three native (Abramis brama, Scardinius erythrophthalmus and Anguilla anguilla) and three non‐native (Ameiurus melas, Gambusia holbrooki and Lepomis gibbosus) species. Species richness and total fish abundance differed between canals and wetland habitats as a consequence of a variable propensity to use wetland habitats by native (avoidance and preference) and non‐native (no preference) species. Non‐native species were also more abundant in reed beds than in grassland while no differences were observed for native species. Universally, the presence probability of fish always decreased in wetland habitats as the distance from the canals increased and only a narrow area, close to canals (50–80 m), was well used by fish. However, non‐native fish species used over greater distances in reed beds than in grasslands while no differences were observed for native species. Variable interpretations related to species tolerance, reproductive guilds or diet are proposed to understand the mechanisms that might explain the widespread success of non‐native species in this spatially varying environment. Copyright © 2008 John Wiley & Sons, Ltd.     

Fish Assemblage Structure and Habitat Associations in a Large Western River System

Longitudinal gradients of fish assemblage and habitat structure were investigated in the Kootenai River of northern Idaho. A total of 43 500‐m river reaches was sampled repeatedly with several techniques (boat‐mounted electrofishing, hoop nets and benthic trawls) in the summers of 2012 and 2013. Differences in habitat and fish assemblage structure were apparent along the longitudinal gradient of the Kootenai River. Habitat characteristics (e.g. depth, substrate composition and water velocity) were related to fish assemblage structure in three different geomorphic river sections. Upper river sections were characterized by native salmonids (e.g. mountain whitefish Prosopium williamsoni), whereas native cyprinids (peamouth Mylocheilus caurinus, northern pikeminnow Ptychocheilus oregonensis) and non‐native fishes (pumpkinseed Lepomis gibbosus, yellow perch Perca flavescens) were common in the downstream section. Overall, a general pattern of species addition from upstream to downstream sections was discovered and is likely related to increased habitat complexity and additions of non‐native species in downstream sections. Assemblage structure of the upper sections were similar, but were both dissimilar to the lower section of the Kootenai River. Species‐specific hurdle regressions indicated the relationships among habitat characteristics and the predicted probability of occurrence and relative abundance varied by species. Understanding fish assemblage structure in relation to habitat could improve conservation efforts of rare fishes and improve management of coldwater river systems. Copyright © 2015 John Wiley & Sons, Ltd.     

Long‐term Dynamics of Large‐bodied Fishes Assessed from Spatially Intensive Monitoring of a Managed Desert River

Imperilment of native fishes worldwide, and particularly in the American Southwest, has prompted management actions to protect and recover threatened populations. Implementation of management activities, however, often proceeds without clear understandings of ecological interactions between native fishes and other biotic and physical components of the environment. Using data obtained in a 19‐year, intensive monitoring effort across 288 km of the San Juan River in NM and UT, USA, we quantified relationships among large‐bodied fishes and longitudinal environmental gradients, tested for faunal breaks of fishes and habitat structure along the river's course, and assessed the response of fishes to mechanical removal of non‐native fishes and stocking of endangered fishes. Mesohabitat variation was not strongly linked to densities of large‐bodied fishes, but we found strong and temporally consistent longitudinal patterns of native and non‐native fishes: Native fish densities were highest upstream while non‐native fish densities where highest downstream, potentially driven by differential responses to temperature regimes. Two breaks in the longitudinal structure of large‐bodied fishes were identified and were associated with a man‐made barrier and changes in the width of the river's floodplain. While densities of common native fishes were relatively constant during the study, non‐native fish removal apparently reduced densities of one of two targeted species and densities of two endangered fishes increased as a result of stocking hatchery‐reared fish. Results of this study suggest that large‐bodied fishes of the San Juan River are responding to large‐scale longitudinal gradients rather than small‐scale habitat variation and management activities have altered densities of target species with limited responses by other fishes in the system. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of flow on the fish communities of a regulated California river: implications for managing native fishes

We assessed the importance of flow regime to the success of native and non‐native fish species by analysing winter/spring seining data collected from 1987 to 1997 on the resident fish communities of the lower Tuolumne River, California. The data were analysed using regression models to predict the percentage of non‐native fish at a site. The regression models included various combinations of the variables longitudinal location of the site, mean April/May stream discharge in the year of sampling, and mean April/May stream discharge in the previous year. Comparison of the models indicated that the best model included longitudinal location and stream discharge in the previous year. This model is consistent with the hypothesis that flow in the previous year differentially affects reproductive success of native and non‐native species and thus the resulting community sampled in the following winter/spring. A detrended correspondence analysis of percentage abundance species data identified a co‐occurring group of native species and a co‐occurring group of non‐native species with the non‐native red shiner (Cyprinella lutrensis) grouping separately. The differing reproductive strategies of the species were consistent with the hypothesis concerning spawning success. Our results indicate that flow regime is an important determinant of the reproductive success of native and non‐native fish species in regulated rivers. Manipulations of flow regime are a potentially powerful tool for managing native fish species, but should be considered in combination with other restoration efforts and in the context of ecosystem restoration. Copyright © 2002 John Wiley & Sons, Ltd.     

Passage and reproductive activity of fishes in the Igarapava fish ladder,Grande River,Southeastern Brazil

We sampled fishes within the vertical‐slot Igarapava fish ladder (IFL), Grande River, southeastern Brazil, and immediately downstream IFL in 12 field trips from February 2000 to December 2002. A total of 1145 fishes belonging to 13 families and 39 species were captured. The most abundant species captured within the IFL, in order of abundance were: Pimelodus maculatus, Metynnis maculatus, Astyanax altiparanae, Hypostomus spp., Leporinus octofasciatus, Salminus hilarii, Leporinus elongatus, Leporinus friderici, Schizodon nasutus and Prochilodus lineatus. Size distribution of the most abundant fishes captured downstream or within the IFL was similar indicating no constraints to adult fish to ascend the IFL. Except P. maculatus, the number of migratory species captured in the IFL and downstream the IFL were very low. Some of the so‐called sedentary species were collected in the IFL indicating that they possess an innate behaviour to migrate. Juveniles of P. lineatus and P. maculatus were captured ascending the IFL implying a dispersal behaviour. Gonadal analyses of the fishes captured in the reproductive season showed that the overall number of reproductive active fishes (which included fish in maturation, mature and spawned/spent) surpassed those non‐active. Thus, the IFL offers upstream passage for juveniles, some of the so‐called sedentary species, as well as fishes in reproductive migration. Copyright © 2009 John Wiley & Sons, Ltd.     

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

Water 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 & Sons, Ltd.     

Effects of low‐head dams on fish assemblages in subtropical streams: Context dependence on species category and data type

Anthropogenic disturbances may cause cosmopolitan species to replace endemic species, which will alter both the within‐community diversities and between‐community similarities of stream fish assemblages. In this study, we used data collected from headwater streams within the Xin'an basin, China, to evaluate the effects of low‐head dams on the alpha diversity and community similarity of fish assemblages. Our aims were to determine whether the changes in fish diversities and similarities related to dam‐associated disturbance are dependent on the species category (i.e., indigenous vs. native‐invasive species) or data type (i.e., occurrence‐based vs. abundance‐based indices). We found that low‐head dams significantly decreased the alpha diversity of the indigenous species in the impoundments but increased that of the native‐invasive species. However, the magnitude of this change was weakened if the two categories of fishes were not distinguished. Additionally, low‐head dams significantly decreased the occurrence‐based similarities of the indigenous fishes but increased those of the native‐invasive fishes. Despite the positive correlation between the occurrence‐based and abundance‐based indices, the former significantly overestimated the community similarities. Although most pairs of communities showed the same direction of changes for the two indices, some cases presented contrasting outcomes, including “perceived homogenization” (i.e., occurrence‐based differentiation but abundance‐based homogenization) and “perceived differentiation.” Our results suggest the importance of distinguishing indigenous and native‐invasive species and considering both occurrence‐based and abundance‐based indices in future research on how anthropogenic activities affect fish diversities and similarities in streams.     

Hydropower Development,Riverine Connectivity,and Non‐sport Fish Species: criteria for Hydraulic Design of Fishways

Hydropower barriers are among the most conspicuous anthropogenic alterations to natural riverine connectivity, resulting in species‐specific effects linked to dispersal abilities, especially swimming performance. They may present a particular problem for small‐bodied ‘non‐sport fish’, such as those that characterize the freshwater communities of temperate regions in the Southern Hemisphere. Recent studies have suggested that nature‐like fishways could ensure passage of diverse fish assemblages through hydropower barriers. Through experiments performed in a swim tunnel, we present, for the first time, fishway design criteria for two non‐sport species endemic to Chile, a country experiencing rapid hydropower development. In`cremental velocity tests showed that Cheirodon galusdae and juveniles of Basilichthys microlepidotus were capable of very similar standardized critical swimming speeds of 69.7 and 69.6 cm s^?1, respectively. When expressed in units of body lengths, C. galusdae was capable of very high critical speeds of 16.2 bl s^?1, whereas for B. microlepidotus, this was 7.6 bl s^?1. However, fixed velocity tests revealed that the swimming endurance of the latter species was slightly higher. Dimensionless analysis showed a clear relationship between fatigue time and fish Froude number, similar to that already described for subcarangiforms. Based on these results, we present fishway design curves indicating a transition from sustained to prolonged swimming at a fishway length of 15 m. Our results show that the swimming capacity of these species is well‐suited to the mean flow velocity field described for nature‐like fishways. However, more work is required to understand the effects of turbulence on the passage of non‐sport species. Copyright © 2016 John Wiley & Sons, Ltd.     

Environmental factors associated with the occurrence of the Ponto–Caspian gobies in a lowland river belonging to the central European invasion corridor

Ponto–Caspian goby fish belong to the most successful invaders in freshwater ecosystems of Europe and North America. So far, three alien goby species have been present in the Polish section of the Dnieper–Rhine River corridor: the monkey goby Neogobius fluviatilis, the racer goby Babka gymnotrachelus, and the western tubenose goby Proterorhinus semilunaris. Their assemblages in this region are unique because, in contrast to their native region or the Danube–Rhine corridor, they are unaffected by other gobiid species. We conducted electrofishing and habitat quality surveys to gather information on key environmental factors associated with the distribution of these fish in the lower river Vistula, which constitutes a vast middle part of the corridor used by the Ponto–Caspian species to migrate westward in Europe. We showed that the sandy bottom was beneficial for the monkey goby allowing the species to attain the highest abundance among the gobies in the river. Habitat complexity generated by artificial bank structures, as well as dense macrophyte coverage in the main channel, favoured mostly the expansion of the racer goby. Off‐channel areas with vegetation and a muddy bottom (old river beds and pools) were the most suitable habitats for the western tubenose goby. We did not find any negative spatial relationships among gobies of various species and sizes except the avoidance of the monkey goby by small western tubenose goby. Thus, our study demonstrates substantial habitat partitioning, suggesting a low level of interspecific competition among the three species in a lowland river.     

AN INVADER WITHIN AN ALTERED LANDSCAPE: ONE CATFISH,TWO RIVERS AND AN INTER‐BASIN WATER TRANSFER SCHEME

African sharptooth catfish Clarias gariepinus has become established as a non‐native invasive species in Eastern Cape, South Africa, where it was translocated primarily through an inter‐basin water transfer scheme into the Great Fish and Sundays rivers. This study examined the patterns in catfish distribution and abundance, and compared trophic niches in relation to the ichthyofauna of the two rivers. Correspondence analysis revealed upstream to downstream gradients associated with the spatial distribution in species richness for most species within the mainstream and mainstream to tributary gradients that were associated mostly with the spatial distribution of native minnows in both rivers. Catfish was predicted to occur widely within the mainstream habitats and to decrease progressively from mainstreams to tributaries. Based on classification and regression trees, the physico‐chemical environment was found to be a good proxy for predicting the occurrence and abundance of catfish. Although non‐significant relationships were observed between catfish and other native fish species abundances, the study suggests potential impact due to predation and interference in habitats where the invader co‐occurs with other fishes. Comparisons of trophic niches indicated higher trophic diversity for the mainstream ichthyofauna than the tributary communities in both rivers, suggesting an upstream to downstream continuum in community structure and resource availability. Catfish within the invaded mainstream had comparable trophic niches and similar dispersion patterns among individuals for both rivers, but indicated differences in shapes of scatter. This suggests that the catfish exhibited a differential response, probably in relation to resource availability, that may be indicative of its dietary plasticity. The study suggests the proliferation of catfish and its probable impact within the mainstream flow‐altered habitats where invasion resistance was possibly reduced. Comparisons of trophic niches provided information on its probable impact at different scales and the potential risk of invasion of tributaries inhabited by native minnow species. Copyright © 2012 John Wiley & Sons, Ltd.     

Behaviour of two small pelagic and demersal fish species in diverse hydraulic environments

Increased hydraulic diversity could be a means to promote fish diversity in rivers, but little is known of the behaviour of fish in hydraulic environments. This study concerns the behaviour of two species of small native Australian freshwater fish in variable hydraulic environments and ecological habit, with regard for (a) whether the apparent differences in swimming ability are reflected in the behaviour of the species and (b) the influence of changing hydraulic conditions on their patterns of use. An artificial channel was constructed with three levels of discharge, and fish were allowed to swim freely for 3 h without human interference. Their movements and habitat choices reflected their swimming ability and ecological habit, in that the stronger swimming, pelagic common galaxias (Galaxias maculatus) spent most time cruising in the open channel, preferring the turbulent inflow, and the demersal flat‐headed gudgeon (Philypnodon grandiceps) remained in the shelter of boulders. In effect, the galaxias changed their behaviour with changes in hydraulic conditions, while the gudgeons continued to use their preferred habitat. This study, therefore, provides support for the use of hydraulic diversity as a tool to foster fish diversity. Copyright © 2010 John Wiley & Sons, Ltd.     

Limnetic Larval Fish in the Ohio Portion of the Western Basin of Lake Erie, 1975–1976

A total of 19 taxa of larval fish was collected with metered plankton nets in Ohio and adjacent Ontario waters of the western basin of Lake Erie. Analysis of yellow perch, Perca flavescens, collection data indicates that shallow inshore areas serve as important nursery areas for this species. Collection of larvae provides evidence of relict breeding populations of lake whitefish, Coregonus clupeaformis, and sculpin (Cottus sp.) in the western basin.     

Tracking Change in the Illinois River using Stable Isotopes in Modern and Ancient Fishes

The Illinois River has been heavily modified by human activities. We examined the nitrogen and carbon stable isotope composition of collagen from fish bones in two Native American middens comparing them to modern fishes in the River today. We also compared ancient and modern fishes to three reference samples—(i) Illinois River phytoplankton; (ii) backwater lake sediment; and (iii) tissue from riverside trees. We found a large increase in δ¹⁵N values in modern fish bone collagen relative to ancient collagen. However, there is little change in δ¹³C between ancient and modern samples. Bone collagen from invasive carp species (Hypopthalmichthys and Cyprinus) are similar to modern phytoplankton. All fishes are different from riverside trees and backwater lake sediment. The large shift in δ¹⁵N values between ancient and modern fishes is probably caused by contamination of the river by Chicago treated wastewater and by denitrified fertilizer run‐off. Our results indicate a major change in nitrogen biogeochemistry in the modern river. Comparisons between ancient and modern δ¹³C values suggest little change in feeding behaviour of fishes between ancient and modern times. However, our data for invasive carp suggest strong competition with native planktivores. © 2016 The Authors. River Research and Applications Published by John Wiley & Sons Ltd.     

Implications of an invasive fish barrier for the long‐term recovery of native fish assemblages in a previously degraded northeastern Illinois River system

Barriers to fish movement have been used to prevent the spread of invasive fishes but may also limit the movements of native fishes. We evaluated the potential consequences of a proposed barrier on the Illinois River Waterway, meant to inhibit the spread of silver and bighead carps, to the continued recovery of native fishes in the Des Plaines River following water quality improvements. We compared changes in upstream cumulative species richness and community structure from 1983 to 2013 in the DuPage River, an adjacent tributary with an impassable dam, to the area upstream of a newly proposed barrier on the Des Plaines River where fish can currently pass through a navigational lock. Fewer species displayed truncated distributions upstream of the passable lock and dam (n = 18) compared with the impassable dam (n = 23). Due to water quality improvements in the Illinois River as a whole, cumulative species richness downstream of both dams steadily increased over time. Richness also increased upstream of the passable dam but plateaued upstream of the impassable dam. Fifteen to 18 species accounted for differences in community structure between areas downstream and upstream of either dam. Most species (78–100%) were found in greater relative abundance downstream of the impassable dam, and only 53% were found in greater relative abundance downstream of the passable dam. The truncation in species richness and abundance at the impassable dam foreshadows the potential consequences of an indiscriminate barrier on native fishes and the continued recovery of native assemblages.     

An Assessment of Fish Assemblage Structure in a Large River

The Penobscot River drains the largest watershed in Maine and once provided spawning and rearing habitats to 11 species of diadromous fishes. The construction of dams blocked migrations of these fishes and likely changed the structure and function of fish assemblages throughout the river. The proposed removal of two main‐stem dams, improved upstream fish passage at a third dam, and construction of a fish bypass on a dam obstructing a major tributary is anticipated to increase passage of and improve habitat connectivity for both diadromous and resident fishes. We captured 61 837 fish of 35 species in the Penobscot River and major tributaries, through 114 km of boat electrofishing. Patterns of fish assemblage structure did not change considerably during our sampling; relatively few species contributed to seasonal and annual variability within the main‐stem river, including smallmouth bass Micropterus dolomieu, white sucker Catostomus commersonii, pumpkinseed Lepomis gibbosus, and golden shiner Notemigonus crysoleucas. However, distinct fish assemblages were present among river sections bounded by dams. Many diadromous species were restricted to tidal waters downriver of the Veazie Dam; Fundulus species were also abundant within the tidal river section. Smallmouth bass and pumpkinseed were most prevalent within the Veazie Dam impoundment and the free‐flowing river section immediately upriver, suggesting the importance of both types of habitat that supports multiple life stages of these species. Further upriver, brown bullhead Ameiurus nebulosus, yellow perch Perca flavescens, chain pickerel Esox niger, and cyprinid species were more prevalent than within any other river section. Our findings describe baseline spatial patterns of fish assemblages in the Penobscot River in relation to dams with which to compare assessments after dam removal occurs. Copyright © 2014 John Wiley & Sons, Ltd.     

Dietary niche and growth rate of the nonnative tubenose goby (Proterorhinus semilunaris) in the Lake Superior basin

The tubenose goby (Proterorhinus semilunaris) entered the Great Lakes in the 1990s via ballast water, but remains poorly studied within North America, making it difficult to predict its effects on native ecosystems. Dietary breadth and somatic growth rate have important ramifications for survival, competitiveness, and dispersal ability of a fish species, and thereby its ecological impact. We studied diet and growth of age-0 tubenose goby within the St. Louis River, a tributary to Lake Superior that contains the largest population within the Lake Superior basin. We sampled tubenose gobies from shallow, vegetated habitats during summer and fall. Stomach contents were identified and weighed to measure fullness and dietary breadth between seasons and several locations. We aged fish based on otolith daily increments to model somatic growth. Diet was dominated by isopods and amphipods, and dietary breadth was low and not significantly different between locations and seasons. Tubenose goby diet strongly overlapped with that of tadpole madtom (Noturus gyrinus), a native, demersal species. We tested several candidate growth models; the Gompertz growth function was the most parsimonious model among those examined. The model demonstrates that tubenose goby obtains a small maximum size and is short-lived. We conclude that tubenose goby presents a unique risk to the Great Lakes and other freshwater bodies because their life history is typical of invasive species, their diet overlaps with native fish, and because they occupy shallow, vegetated habitat which functions as both nursery and foraging habitat for many native fishes.