Diadromous Fish Species Research Articles

The global geography of fish diadromy modes

AbstractAimGeographical gradients in resource production are likely to translate into macroecological patterns in the biodiversity of migratory organisms, but few studies have addressed this question at a global scale. Here, we tested a hypothesis based on uncoupled latitudinal gradients in marine and freshwater primary productivities aimed at explaining where (e.g., at which latitude) and at which stage of the life cycle (larvae, amphidromy; juvenile, catadromy; or adult, anadromy) migration from ocean to freshwater occurs (diadromy).LocationGlobal.Time periodCurrent.Major taxa studiedFishes.MethodsWe modelled, using multinomial regressions, the proportion of catadromous, anadromous and amphidromous species in 994 river basins as a function of freshwater and marine net primary productivities (NPP; in milligrams of carbon per square metre per day) and additional biotic and abiotic variables. Using data extracted from the Global Biodiversity Information Facility (GBIF) database, we tested whether diadromous, catadromous and amphidromous species differed with respect to the NPP of their marine and freshwater occurrences.ResultsAmong diadromous species, anadromous species are present in higher proportions when conditions for growth are more favourable in the sea (higher productivity, higher temperature and lower number of competitors) than in freshwaters. The model reconstructs the latitudinal pattern observed in the proportion of anadromous species, including an asymmetry between the Northern and Southern Hemispheres. According to GBIF occurrences, the ratio of marine over freshwater productivity is higher for anadromous species compared with catadromous and amphidromous species.Main conclusionsOur results support the hypothesis stating that migration between ocean and freshwater occurs by choosing the biome that optimizes pre‐reproductive growth and is one more example of the importance of primary productivity in shaping large‐scale community patterns. This result suggests that some diadromous fish populations and species may suffer from anticipated climate change if interbiome productivity gradients are affected.

Consideration of habitat quality in a river connectivity index for anadromous fishes

ABSTRACTRiver fragmentation is one of the main threats to diadromous fish species. We aimed to create a new and simple connectivity index to calculate habitat accessibility that considers habitat suitability for fish species, using the Bidasoa River basin in the north of Spain and Atlantic salmon (Salmo salar) as an example. A habitat connectivity index (HCI) was calculated for the river basin using upstream passability and segment length as variables. We then calculated a new habitat quality index for each river segment and multiplied it by river segment length to create the Breeding Habitat Connectivity Index (HCIb). These 2 indices were first calculated using only upstream barrier passability and then by adding downstream passability. In each case, the indices show different outcomes but a similar pattern: in all cases, main-stem obstacles closest to the river mouth most affected the connectivity index, even when habitat quality was considered. Although we cannot compare the indices to the real area used by salmon because spatial tracking was not performed during the study years, we consider that including habitat quality in a river connectivity index adds useful information for scientists and managers.

Otolith microchemistry and diadromy in Patagonian river fishes.

Coastal habitats in Chile are hypothesized to support a number of diadromous fish species. The objective of this study was to document migratory life histories of native galaxiids and introduced salmonids from a wide latitudinal range in Chilean Patagonia (39–48°S). Otolith microchemistry data were analysed using a recursive partitioning approach to test for diadromy. Based on annular analysis of Sr:Ca ratios, a diadromous life history was suggested for populations of native Aplochiton taeniatus, A. marinus, and Galaxias maculatus. Lifetime residency in freshwater was suggested for populations of A. zebra and G. platei. Among introduced salmonids, populations of Oncorhynchus tshawytscha and O. kisutch exhibited patterns consistent with anadromy, whereas the screened population of O. mykiss appeared restricted to freshwater. Salmo trutta exhibited variable patterns suggesting freshwater residency and possibly anadromy in one case. The capacity and geographic scope of hydropower development is increasing and may disrupt migratory routes of diadromous fishes. Identification of diadromous species is a critical first step for preventing their loss due to hydropower development.

Standardization of sperm motility analysis by using CASA-Mot for Atlantic salmon (Salmo salar), European eel (Anguilla anguilla) and Siberian sturgeon (Acipenser baerii)

It is essential to define an optimized standard method to assess the fish sperm quality to minimize the differences between the results obtained by different laboratories. Only this optimization and standardization can make them useful from academia to industry. This study presents the validation of sperm motility assessment using a CASA-Mot system for three endangered diadromous fish species: European eel (Anguilla anguilla), Atlantic salmon (Salmo salar) and Siberian sturgeon (Acipenser baerii). To attain this goal, different technical and data processing methods were tested: 1) magnification lens (×10 and ×20), 2) Spermtrack® reusable chambers (10 and 20 μm depth) and 3) different frame rates (50 ≥ FR ≤ 250). The results suggested that the sperm motility assessment for eel, salmon and sturgeon should be performed at 200, 250 and 225 frames s−1, respectively. Moreover, to obtain a high number of analysed spermatozoa in less time and a natural movement of the sperm cells, it is recommended to use ×10 objective and 20 μm depth. In conclusion, different technical settings influence sperm kinetic parameters and should be validated for each fish species to allow the comparison of results between laboratories.

Measuring 30 years of improvements to aquatic connectivity in the Greater Toronto Area

Instream barriers (e.g. dams, weirs and road crossings) fragment aquatic habitat and prevent the upstream movement of fish, impairing the ability of fishes to complete critical life stages, access critical habitat and for dispersal among local populations. Mitigation efforts have improved aquatic connectivity to some degree, but it has been challenging to quantify the overall improvement in connectivity without long-term and costly field assessments. The development of spatially explicit habitat connectivity indices make it possible to evaluate current stream connectivity, and quantify the improvement prior mitigation projects have had on connectivity. We combined a list of instream barrier mitigation projects completed in five watersheds in the Toronto (Ontario, Canada) area from 1987–2016 (mitigated barriers) and a previously established inventory of all known instream barriers in 2016 (current barriers). The cumulative improvement to connectivity was measured for potadromous (remain in tributaries) and diadromous (move between tributaries and lake) fish species using the dendritic connectivity index. Aquatic connectivity improved for diadromous species between 0 and 14.5% and for potadromous species between 0.1 and 4.4% in the five studied watersheds. Some variation in improvement among the watersheds can likely be attributed to differences in mitigation strategies among the watersheds and a historical emphasis on mitigating instream barriers to benefit migratory salmonid species.

Quantifying exchanges of Allis shads between river catchments by combining otolith microchemistry and abundance indices in a Bayesian model

Similar to many diadromous fish species, dramatic declines were observed for Allis shad, an anadromous Clupeidae, since the beginning of the 2000s. The knowledge of population and metapopulation dynamics is a key issue for the management of migratory species. Although homing behaviour is dominant in Allis shad, staying causes exchanges between populations of each river catchment. Currently, the management of Allis shad is applied at the population scale, without accounting for a potential metapopulation structure. Herein we propose a method to estimate the exchanges flux between rivers and a method to identify source and sink rivers. We used otolith microchemistry within a Bayesian model of reallocation coupled with abundance estimates of spawners per watershed. Results showed a metapopulation dynamic with several rivers acting as sources and other as sinks. However, the lack of precision and homogeneity in abundance data resulted in large credibility intervals, which calls for a better standardization in the acquisition of abundance data. Nevertheless, this method should provide an overview of the metapopulation dynamics of other anadromous species with management concerns. © International Council for the Exploration of the Sea 2017. All rights reserved.

Elevated carbon dioxide and temperature affects otolith development, but not chemistry, in a diadromous fish

Ocean acidification threatens marine ecosystems by altering ocean chemistry and calcification processes in marine organisms. This study investigated the effects of predicted future CO2 levels, under varying temperature levels, on otolith development (size and shape) and chemistry, with the latter aimed at developing a chemical tracer of environmental pCO2. Juvenile barramundi (Lates calcarifer), a diadromous fish species, were reared in ambient (pCO2: 640μatm; pH: 7.9) and elevated (pCO2: 1490μatm; pH: 7.5) pCO2 treatments representing current and projected coastal systems crossed with three temperature levels (26°C, 30°C and 34°C) for 42days. Otolith shape and size parameters (length, width, perimeter and area) were measured and element concentrations (Na, Mg, Sr, Ba, Li, Mn and B) were quantified using Laser Ablation Inductively Coupled Plasma-Mass Spectrometry (LA ICP-MS). There was an interactive effect of elevated pCO2 and temperature on otolith shape and perimeter, whereas otolith chemistry did not vary among treatments. This study demonstrates that combined elevated pCO2 and temperature can affect the development of important internal structures in diadromous fish, but also suggests that otolith elemental chemistry was not a suitable tracer for pCO2 histories in fish. Future climate change conditions affect an important auditory and balance organ; consequently, rising CO2 levels may interfere with sensory function.

Short-Term Response of a Coastal Wetland Fish Assemblage to Tidal Regime Restoration in Oregon

Abstract Bandon Marsh National Wildlife Refuge, Oregon, completed construction of a large-scale tidal marsh restoration project on the Ni-les'tun Unit within the Coquille River estuary in 2011. To understand the initial effects of restoration construction and establish a baseline for long-term monitoring, we documented the assemblage of fish species 3 y before and 2 y after restoration construction. The overall fish assemblage in the Ni-les'tun Unit was substantially different after restoration construction, with an increased abundance, frequency, and richness of estuarine and diadromous fish species. Threespine Stickleback Gasterosteus aculeatus and species of Sculpin (family Cottidae) dominated the Ni-les'tun Unit and control area in both relative abundance and capture frequency throughout this study. Among salmonids, Coastal Cutthroat Trout Oncorhynchus clarkii and Coho Salmon Oncorhynchus kisutch had the highest frequency of occurrence and relative abundance both before and after restoration construction. Fish occupied newly constructed channels within 2 y. Species found in new channels included freshwater species (e.g., juvenile salmonids), introduced species (e.g., Mosquitofish Gambusia affinis), and estuarine species (e.g., Sculpin, Threespine Stickleback, and Shiner Perch Cymatogaster aggregata). Changes were likely due to improved access and changing habitat created by the reintroduced tidal regime. We recommend long-term monitoring to assess the trajectory of the biological response to the restoration over time.

Determining the relative importance of catchment- and site-scale factors in structuring fish assemblages in small coastal streams

Coastal streams provide important habitat for many diadromous fish species, which migrate between freshwater and the sea during their life cycle. However, coastal systems are poorly studied in comparison to large, continental river systems. Furthermore, the relative importance of catchment- and site-scale factors in structuring lotic fish communities is largely unknown. In this study, I addressed these issues by surveying the fish fauna of small coastal streams on Sado Island (northwest Japan) and determining the relative importance of catchment- and site-scale factors to the structure of freshwater fish assemblages. In total, 14 freshwater fish species were collected from the 19 streams. All but one of the fish species collected were diadromous and 9 of the species (64%) were amphidromous, primarily represented by the goby group including the genera Rhinogobius and Gymnogobius . Variance partitioning analyses showed that catchment-scale factors (namely, stream discharge) were better predictors of both fish species richness and composition than site scale and spatial factors. These results indicate that discharge, which is directly linked to habitat stability, can have a major role in structuring coastal fish assemblages, likely because small coastal streams experience extreme discharge fluctuations associated with regional weather conditions.

通し回遊魚に対する震災の影響

通し回遊魚に対する震災の影響

Applying landscape genetics to evaluate threats affecting endangered Atlantic salmon populations

Landscape genetics affords a potential analysis framework to evaluate the effect of contemporary land use on endangered species at a population level. However, historical patterns of population connectivity need to be accounted for prior to testing for the contemporary effect of threats. The goals of this study were to (1) optimally describe historical patterns in population connectivity for a diadromous fish species before (2) evaluating whether residual genetic variation was correlated with ecological changes arising from several types of land use. Using endangered Atlantic salmon populations as a case study, we evaluated whether historical patterns in population connectivity were more likely to result from dispersal limitation (isolation by distance) relative to habitat choice and reproductive success (isolation by environment). Second, we used Reciprocal Causal Modeling to identify the types of land use contributing to three threat indices, and subsequently Multiple Regression on Distance Matrices to evaluate the relative severity of each. These analyses suggest that straying Atlantic salmon avoid watersheds with reduced water quality (resulting from acidification and abandoned mines) and higher road density, yet are not responding to watershed fragmentation (from road-river crossings and dams) at a population level. This study is among the first to explicitly compare alternate behavioural hypotheses leading to dispersal patterns for diadromous fishes and to quantitatively assess freshwater threats for Atlantic salmon at a population level using landscape genetics.

Worldwide patterns of fish biodiversity in estuaries: Effect of global vs. local factors

The main ecological patterns and the functioning of estuarine ecosystems are difficult to evaluate due to natural and human induced complexity and variability. Broad geographical approaches appear particularly useful. This study tested, at a worldwide scale, the influence of global and local variables in fish species richness in estuaries, aiming to determine the latitudinal pattern of species richness, and patterns which could be driven by local features such as estuary area, estuary mouth width, river flow and intertidal area. Seventy one estuarine systems were considered with data obtained from the literature and geographical information system. Correlation tests and generalized linear models (GLM) were used in data analyses. Species richness varied from 23 to 153 fish species. GLM results showed that estuary area was the most important factor explaining species richness, followed by latitude and mouth width. Species richness increased towards the equator, and higher values were found in larger estuaries and with a wide mouth. All these trends showed a high variability. A larger estuary area probably reflects a higher diversity of habitats and/or productivity, which are key features for estuarine ecosystem functioning and biota. The mouth width effect is particularly notorious for marine and diadromous fish species, enhancing connectivity between marine and freshwater realms. The effects of river flow and intertidal area on the fish species richness appear to be less evident. These two factors may have a marked influence in the trophic structure of fish assemblages.

Energetic aspects of spawning migrations and their implications for the management of southern European diadromous fish populations

Energetic aspects of spawning migrations and their implications for the management of southern European diadro- mous fish populations Migratory species display very important roles in aquatic ecosystem functioning. The journeys between different habitats throughout the lifetime increase survival and reproductive success; however, a large energetic investment is required. Most diadromous fish species cease feeding soon before they start the spawning migration; thus, the energy available for maintenance, gonadal development and migratory journeys is limited. Diadromous species spend up to 90 % of the total energy available, and in some cases, the entire population dies during migration. The energy consumption during this phase is critical and affects the spawning and post-spawning success. Several diadromous species are endangered due to the increase in human activities that have negative effects on aquatic habitats. The southern distribution range of most of the European diadromous species is the Iberian Peninsula. Several threats to diadromous species are present in this region, and extra energy consumption is required during spawning migration which compromises their conservation. Consequently, management measures for such species should consider their energetic limitations. This review presents the energetic implications of diadromous spawning migrations and discusses the anthropogenic factors that negatively affect the spawning journeys of native southern European species. The spawning energetics of the diadromous species should be considered by natural resource managers; however, the integration of this domain still requires additional studies to measure the effects of the anthropogenic activities on these species.

Connectivity between Migrating and Landlocked Populations of a Diadromous Fish Species Investigated Using Otolith Microchemistry

Smelt Osmerus eperlanus has two different life history strategies in the Netherlands. The migrating population inhabits the Wadden Sea and spawns in freshwater areas. After the closure of the Afsluitdijk in 1932, part of the smelt population became landlocked. The fresh water smelt population has been in severe decline since 1990, and has strongly negatively impacted the numbers of piscivorous water birds relying on smelt as their main prey. The lakes that were formed after the dike closure, IJsselmeer and Markermeer have been assigned as Natura 2000 sites, based on their importance for (among others) piscivorous water birds. Because of the declining fresh water smelt population, the question arose whether this population is still supported by the diadromous population. Opportunities for exchange between fresh water and the sea are however limited to discharge sluices. The relationship between the diadromous and landlocked smelt population was analysed by means of otolith microchemistry. Our interpretation of otolith strontium (88Sr) patterns from smelt specimens collected in the fresh water area of Lake IJsselmeer and Markermeer, compared to those collected in the nearby marine environment, is that there is currently no evidence for a substantial contribution from the diadromous population to the spawning stock of the landlocked population.

Optimisation of adjusted barrier management to improve glass eel migration at an estuarine barrier

Estuarine barriers may significantly reduce the upstream migration of diadromous fish species like the European eel (Anguilla anguilla L.). Previous research showed that limited barrier opening during tidal rise was a cost-efficient and effective mitigation option to improve upstream glass eel migration, without significant intrusion of sea water. This paper aims to optimise this adjusted barrier management to improve eel passage at a tidal barrier complex at the mouth of the River Yser, Flanders, Belgium, one of the most important migration routes for glass eel in Flanders. Specifically, three hypotheses were tested. The first hypothesis analysed the impact of the number of barriers opened on the upstream glass eel migration. The second hypothesis evaluated the relation between the size of the barrier opening and glass eel migration. Finally, we tested whether the suggested adjusted barrier management may lead to a significant increase in conductivity in the River Yser. Increased opening of one barrier appeared more efficient than opening several barriers slightly. Conductivity increased during periods of extreme drought and at base flow, but decreased within 24 h after the first peak flow. This indicates that adjusted barrier management does not entail salt intrusion in the Yser basin, as long as this management is not applied in extremely dry periods. Since the adjusted barrier management is easily implemented and could be applied on numerous tidal barriers, the presented results may contribute to restoration of eel populations worldwide and be of interest to a wide range of river managers and stakeholders.

Plankton composition, abundance and diversity in hilsa (Tenualosa ilisha) migratory rivers of Bangladesh during spawning season

Hilsa (Tenualosa ilisha) is one of the flagship diadromous fish species of Bangladesh that migrate only through the Ganges?Meghna river system route. The biological profile of plankton from the Padma, Meghna and Tetulia reference river sites during 2011 spawning season of hilsa showed that in total of 58 taxa of plankton were present. Of which, 19 taxa (32.76%) were of phytoplankton and 39 taxa (67.24%) of zooplankton. Phytoplankton group belonged to Cyanophyceae (6 taxa), Chlorophyceae (7 taxa) and Bacillariophyceae (6 taxa) while zooplankton including Protozoa (10 taxa), Rotifera (19 taxa), Copepoda (4 taxa), Cladocera (5 taxa) and Ostracoda (1 taxon). The average abundance of plankton was recorded as 194.05 ± 82.58 indiv/l. The highest abundance of total plankton (692 indiv/l) was observed in Godagari, Rajshahi (Station 3) and was lowest (4.00 indiv/l) in Charghat, Rajshahi (Station 2). The highest abundance (49 indiv/l) of total zooplankton was observed in Godagari and lowest (1 indiv/l) in Charghat with mean value of 19.46 ± 4.12 indiv/l. The highest species richness (SR = 45) was observed in Daulotkhan, Vhola (Station 9) and the lowest (SR = 3) in Charghat (Station 2), with mean value of 17.10±4.408. Shannon?Weiner species diversity index (H?) ranged from 3.334 in Daulotkhan (Station 9) to 1.5 in Charghat, (Station 2) with mean value of 2.717 ± 0.147. Based on the plankton profile it may be concluded that the biological quality of hilsa migratory river was not alike throughout the route which may restrict the migration up to up steam and spontaneous spawning of hilsa.DOI: http://dx.doi.org/10.3329/dujbs.v21i2.11516 Dhaka Univ. J. Biol. Sci. 21(2): 177-189, 2012 (July)

Pelagic larval duration of two diadromous species of Kuhliidae (Teleostei: Percoidei) from Indo-Pacific insular systems

Diadromous fish species in the family Kuhliidae are able to colonise freshwater systems in Indo-Pacific islands, but their life cycle and the mechanisms involved in the colonisation of such ecosystems are poorly documented. After validating the daily rate of increment deposition in otoliths of Kuhlia rupestris, we estimated the pelagic larval duration (PLD) of K. rupestris, widely distributed in the Indo-Pacific area, and K. sauvagii, endemic to the Indian Ocean. Median PLD of K. rupestris was significantly longer than that of K. sauvagii (40.6 ± 6.9 and 32.3 ± 3.4 days (± s.d.), respectively), implying that the PLD is probably one factor controlling the extent of distribution range in Kuhlia. Within K. rupestris, individuals from New Caledonia had longer PLDs than those from Réunion Island (44.3 ± 6.7 and 37.3 ± 4.7 days (± s.d.) respectively). Further research on larval migration is needed to determine whether this was due to different environmental conditions or is population-specific. Interestingly, the PLD of these Kuhlia species is shorter than the PLD of other tropical diadromous fishes. These results improve our understanding of the dispersal strategies of freshwater fauna, to colonise and persist in tropical islands.

Quantifying relationships between land‐use gradients and structural and functional indicators of stream ecological integrity

Summary1. Modification of natural landscapes and land‐use intensification are global phenomena that can result in a range of differing pressures on lotic ecosystems. We analysed national‐scale databases to quantify the relationship between three land uses (indigenous vegetation, urbanisation and agriculture) and indicators of stream ecological integrity. Boosted regression tree modelling was used to test the response of 14 indicators belonging to four groups – water quality (at 578 sites), benthic invertebrates (at 2666 sites), fish (at 6858 sites) and ecosystem processes (at 156 sites). Our aims were to characterise the ecological response curves of selected functional and structural metrics in relation to three land uses, examine the environmental moderators of these relationships and quantify the relative utility of metrics as indicators of stream ecological integrity.2. The strongest indicators of land‐use effects were nitrate + nitrite, delta‐15 nitrogen value (δ15N) of primary consumers and the Macroinvertebrate Community Index (a biotic index of organic pollution), while the weakest overall indicators were gross primary productivity, benthic invertebrate richness and fish richness. All indicators declined in response to removal of indigenous vegetation and urbanisation, while variable responses to agricultural intensity were observed for some indicators.3. The response curves for several indicators suggested distinct thresholds in response to urbanisation and agriculture, specifically at 10% impervious cover and at 0.1 g m−3 nitrogen concentration, respectively.4. Water quality and ecosystem process indicators were influenced by a combination of temperature, slope and flow variables, whereas for macroinvertebrate indicators, catchment rainfall, segment slope and temperature were significant environmental predictor variables. Downstream variables (e.g. distance to the coast) were significant in explaining residual variation in fish indicators, not surprisingly given the preponderance of diadromous fish species in New Zealand waterways. The inclusion of continuous environmental variables used to develop a stream typology improved model performance more than the inclusion of stream type alone.5. Our results reaffirm the importance of accounting for underlying spatial variation in the environment when quantifying relationships between land use and the ecological integrity of streams. Of distinctive interest, however, were the contrasting and complementary responses of different indicators of stream integrity to land use, suggesting that multiple indicators are required to identify land‐use impact thresholds, develop environmental standards and assign ecological scores for reporting purposes.

THINKING LIKE A FISH: A KEY INGREDIENT FOR DEVELOPMENT OF EFFECTIVE FISH PASSAGE FACILITIES AT RIVER OBSTRUCTIONS

ABSTRACTWorldwide, obstructions on watercourses have interfered with migratory pathways of fish species, reducing life‐cycle success and often eliminating diadromous fish species altogether from river basins. Over the last century, efforts to mitigate these effects were initially directed at developing fishways for upstream, high‐value migrant adult salmon. In more recent years, efforts have turned to developing fishways for other species. Results of past research suggest that the development of effective fishways requires biological knowledge of fish behaviour when encountering variable flows, velocity and turbulence, combined with hydraulic and civil engineering knowledge and expertise to develop facilities that provide appropriate hydraulic conditions that fish will exploit. Further, it often requires substantial financial resources for biological and hydraulic testing as well as engineering design, particularly where prior knowledge of the behaviour of target fish species does not exist. Where biological or engineering knowledge (or both) is absent, development of effective passage facilities must take on a trial and error approach that will almost certainly require years to attain success. Evaluations of existing adult and juvenile fish passage facilities, where they have been carried out, suggest that migrant fish reject areas with hydraulic conditions they determine unsuitable. Even well designed fish ladders or nature‐like bypass channels for upstream migrants, even those with good attraction flows, will fail if incorrectly sited. Although progress has been made, developing successful installations for downstream migrants remains much more difficult, probably because downstream fish move with the flow and have less time to assess cues at entrances to any bypasses that they encounter. Copyright © 2011 John Wiley & Sons, Ltd.

Effects of coupled natural and anthropogenic factors on the community structure of diadromous fish and shrimp species in tropical island streams

Summary 1. Overlapping river and road networks provide a framework for studying the complex interactions between natural and human systems, with river-road intersections as focal areas of study. Roads can alter the morphology of stream channels, pose barriers to freshwater fauna, provide easy access to streams for humans and non-native species and accelerate the expansion of urban development. 2. We determined what variables control the structure of diadromous fish and shrimp communities and assessed whether particular road crossings altered community structure in north-eastern Puerto Rico. We identified 24 sites that represented a range of river and road sizes across two catchments that drain El Yunque National Forest in Puerto Rico. 3. The location of natural barriers and the size of stream pools were the most important variables for predicting six of fifteen fish and shrimp distributions. Predatory fishes were predicted to be limited to areas in the river network below large, steep waterfalls, whereas adult shrimp Atya lanipes (Atyidae) were predicted to be present above these waterfalls. The fish Awaous banana was predicted to be present in pools >11.6 m wide, whereas the shrimp Xiphocaris elongata was predicted to be present in pools <10.4 m wide. The distributions of nine species were predicted poorly, but three of these species were common and three were rare. 4. Although urban and agricultural land covers were among the top three predictors of five species distributions, they were probably good predictors because they were correlated with the natural gradient. Further study is necessary to disentangle natural and anthropogenic gradients. 5. Road crossings, 10 of which were culverts, were not dispersal barriers for fishes or shrimps. On average, species were present both upstream and downstream from road crossings at 68% of sites where they occurred. Absences upstream or downstream from road crossings occurred at 16% of sites each and likely resulted from a failure to detect species. 6. Several existing features of these catchments and taxa may aid in fish and shrimp conservation. The headwaters are protected by management practices of El Yunque National Forest, connectivity within the river network has been maintained, and the diadromous life history of these organisms makes them resilient to pulsed disturbances.