Nearshore Fish Assemblages Research Articles

Disentangling determinants of nearshore fish and crayfish assemblages in a canyon-shaped Mediterranean reservoir

The distinct origin and hydrological characteristics of reservoirs, shaped by fluctuating water levels and seasonal variations, play a crucial role in determining aquatic species assemblages across diverse limnological zones. This study aimed to analyze fish and crayfish assemblages in the nearshore area of a canyon-shaped Mediterranean reservoir, seeking to identify seasonal and spatial convergent patterns and infer the factors influencing them. Samplings were conducted at five stations along the longitudinal profile of the reservoir at depths around 7 m using gillnets and hoops nets. A seasonal pattern emerged regarding species abundance and biomass, with higher values recorded during the warmer period. Additionally, a spatial trend was observed, indicating higher species abundance in the middle part of the reservoir and lower abundance near the dam, particularly during the colder period. Water transparency, temperature, and the distance from the dam were identified as the most significant factors affecting species assemblages in terms of abundance and biomass. This research provides valuable insights into the intricate interplay between environmental factors, seasonal changes, and the assemblages of aquatic species in a Mediterranean reservoir, contributing to our understanding of its ecological dynamics.

Spatial patterns and environmental drivers of demersal fish assemblages in the Swartkops and Sundays estuarine to marine seascapes, South Africa

Estuaries are often observed as the boundary between the ocean and the river, separating coastal environments, rather than being seen as a continuum. Owing to insufficient research on demersal fish communities across nearshore marine to estuarine habitats, particularly in South Africa, this study employed a spatial seascape approach, with seasonal sampling of soft-bottom benthic habitats in two permanently open estuaries and the adjacent marine nearshore environment of Algoa Bay on the south coast of South Africa. A total of 790 fish representing 29 species were collected in the marine nearshore, and 6 414 fish (28 species) were caught in the estuarine zone. Two discrete demersal fish assemblages were identified as representing the marine nearshore and estuarine environments. The marine nearshore fish assemblages were dominated by marine species (e.g. Argyrosomus inodorus and Cynoglossus zanzibarensis) that were not recorded in the estuarine environment, whereas marine estuarine-opportunist species (e.g. Pomadasys olivaceus and Galeichthys feliceps) were more abundant in the marine nearshore than in the estuarine environment. The estuaries were dominated by benthic marine estuarine-dependent and marine and estuarine species (e.g. Rhabdosargus holubi, Solea turbynei, Heteromycteris capensis, Psammogobius knysnaensis and Glossogobius callidus). Differences observed in abundance and species richness along the estuarine to marine continuum were primarily related to the salinity gradient. These findings are significant as altered freshwater flows and consequent changes in salinity and productivity can have an impact on the nursery use of both estuaries and the marine nearshore by fish species.

Characterizing Nearshore Fish Assemblages From Intact and Altered Mangrove Shorelines in Biscayne Bay, Florida, United States

Biscayne Bay is an urban bay in Southeast Florida, but the southern region of the Bay is dominated by mangroves. Mangrove wetlands provide important habitat for fish, but some regions are altered by drainage canals in southern Biscayne Bay. This study utilized a large public dataset to determine if fish formed distinct species assemblages throughout Biscayne Bay by examining fish surveyed at 12 different sites over 5 years. Six sites were in front of intact mangrove shorelines, while the other six sites were adjacent to mangrove sites altered by drainage canals or residential marinas. Cluster analyses revealed that fish did form distinct species assemblage clusters which were correlated with salinity and depth. Mangrove shoreline type (intact vs. canal-altered) and geographic location did not appear to affect species composition or diversity in fish assemblages across Southern Biscayne Bay.

Nearshore fish assemblage dynamics in southern Lake Michigan: 1984–2016

Many coastal ecosystems, including those of the Laurentian Great Lakes, suffer from various natural and anthropogenic stressors. Given that multiple stressors often concomitantly impact ecosystems, it may be difficult to disentangle which stressors are most influential. Upper trophic level communities, such as fish assemblages, can provide insights to the influence of diverse stressors as they may integrate cumulative effects over the long-term and also reflect responses of lower trophic levels. We used multivariate analyses and assemblage indices to investigate long-term (1984–2016) patterns in a nearshore fish assemblage indexed via annual trawling in the Indiana waters of southern Lake Michigan. Based on observations from other regions of the Great Lakes, we expected that oligotrophication, due to reduced nutrient loading and filtering by invasive mussels, would have a strong influence on the fish assemblage. However, we were unsure if the very nearshore fish assemblage would track observed decreased production patterns in offshore Lake Michigan or if observed increased primary production in the very nearshore would affect the fish assemblage. Consistent with the former expectation, overall abundance and richness of the assemblage declined over time. However, contrary to observations in other regions there was no overall evidence of species tolerant to more eutrophic conditions being replaced by more sensitive species. Moreover, there was limited evidence of the fish assemblage shifting towards species more tolerant of warm water, as might be expected with climate change. While increased numbers of invasive species added species to the system, overall species richness and native species richness declined.

Multivariate analysis of the spatial species diversity of demersal fish assemblages in relation to habitat characteristics in a subtropical national park, Taiwan

To understand the spatial species diversity of demersal fish assemblages in Taijiang National Park (TJNP) of Taiwan, fishes from 44 demersal trawl hauls and environmental data were collected in the nearshore and offshore areas of TJNP from April 2016 to May 2019. In total, fishes of 47 families, 84 genera, and 113 species were recorded. The nearshore and offshore demersal fish assemblages in TJNP exhibited significant variability in species composition assessed via beta diversity. Using distance-based redundancy analysis, we demonstrated that bottom depth and substrate type were significant explanatory variables of spatial species diversity and identified three habitat types (I: shallow soft bottom; II: deeper soft bottom; III: deeper bottom with mixed sand and gravel substrates). The nearshore assemblage was characterized by type I, where Tarphops oligolepis (flounder), Trachinocephalus myops (snakefish), and Liachirus melanospilos (carpet sole) dominated in terms of abundance. The offshore assemblage was characterized by either type II or type III because differences in substrate types among sampling sites were noticeable. At the offshore sites characterized by a deeper soft bottom (type II), Johnius distinctus (croaker), Cynoglossus kopsii (shortheaded tonguesole), and Coelorinchus formosanus (Formosa grenadier) predominated. In contrast, the westernmost sampling site, characterized by type III habitat, exhibited relatively high Shannon indices, and Scorpaena miostoma (scorpionfish), Urolophus aurantiacus (sepia stingray), and Parabothus taiwanensis (lefteye flounder) predominated. Our results provide the first baseline information on the environmental characteristics and spatial species diversity of demersal fish assemblages in TJNP and have implications for biodiversity conservation in existing spatial management areas.

Revealing the drivers of taxonomic and functional diversity of nearshore fish assemblages: Implications for conservation priorities

AbstractAimUnderstanding patterns and drivers of biodiversity are essential towards developing effective conservation strategies for shallow marine habitats broadly. However, little is known about the natural and anthropogenic factors that structure fish biodiversity of sandy beaches, one of the largest and most socio‐economically valuable nearshore habitats due to their endemic fauna, economic importance and cultural relevance. Here, we investigated how environmental variables and urbanization affect taxonomic and functional diversity of nearshore fish assemblages to provide general biodiversity patterns that can serve as baseline information for management plans when considering conservation prioritization.LocationSoutheast Brazil.MethodsWe surveyed fish communities at 77 sites along 150 km of coastline with different natural features and degrees of human influence using a combination of seine nets and surf‐BRUVS. We used generalized additive models (GAMs) to investigate the influence of environmental variables and urbanization on taxonomic and functional diversity of resident fish assemblages.Main resultsWe found that significant breaker wave height was the most important environmental variable in explaining the taxonomic and functional diversity of fish assemblages. The effects of increasing wave height were mostly negative, except for piscivorous fishes, which were most abundant at high energy sites, and for benthic and zoobenthivorous species, which were most abundant at sites with intermediate wave exposure. The latter species were also associated with higher chlorophyll‐a contributing to increased taxonomic richness and abundance. Further, anthropogenic impacts generally reduced diversity, with highest diversity only observed at the most pristine sites.Main conclusionsOur results demonstrate that both natural environmental variation and human activities structure the fish assemblages of sandy beach surf zones, affecting species that possess specific functional traits differently. These drivers should therefore be considered simultaneously in appointing protected areas in order to preserve a diversity of organisms and functional traits integral to productive beach ecosystems.

Modeling nearshore fish habitats using Alaska as a regional case study

Nearshore areas represent important habitats for many species, at least for part of their life cycle. Therefore, modeling and mapping nearshore habitats is essential for natural resource management and conservation, such as determining potential impacts to marine populations and their habitats from human activities and identifying conservation measures. Although fish survey and habitat data are uncommon for nearshore areas, two regional databases, the Nearshore Fish Atlas of Alaska (NFA) and ShoreZone, provide a rare opportunity to evaluate nearshore habitats for Alaska’s shallow, nearshore fish assemblages. In the present study, we used the NFA and ShoreZone databases in a practical approach to model and map Alaska nearshore fish habitats. Specifically, we fitted generalized additive models (GAMs) to NFA and ShoreZone data to map the spatial patterns of probability of encounter and density of Pacific cod (Gadus macrocephalus) early juveniles in the northern southeastern Alaska (NSEA) area and walleye pollock (Gadus chalcogrammus) early juveniles in Prince William Sound (PWS). The density of Pacific cod early juveniles was found to be high in all of the western part of the NSEA area, particularly around Port Alexander. The density hotspots of walleye pollock early juveniles were found to be located in the northern and southernmost parts of PWS. Data inventories and modeling and mapping Alaska nearshore fish habitats provide valuable information to manage marine resources and human activities (e.g., to identify the main nursery areas of commercially important species along the Alaska coastline), and allow for other important ecological and ecosystem issues to be addressed (e.g., producing marine protected area planning scenarios to protect forage fishes used by large marine predators). The NFA and ShoreZone are valuable resources, and our efforts to leverage them to model and map nearshore fish habitats establishes a reference for similar efforts throughout Alaska’s regions and beyond.

Pelagic-benthic coupling in kelp forests of central California

Pelagic-benthic coupling in the marine environment influences productivity, trophic interactions, and community structure in nearshore ecosystems. It is also intrinsically variable as oceanographic conditions, species abundances, and the availability of basal resources shift. Kelp forests are home to a nearshore fish assemblage that accesses not only energy derived from kelp but also from pelagic, phytoplankton-based primary production, providing a clear example of pelagic-benthic coupling. Here, I used a combination of stomach content analysis and carbon and nitrogen stable isotope analyses to explore rockfish use of kelp- and phytoplankton-based carbon in kelp forests in central California from 2013-2016. I examined connections between rockfish diet and 2 large-scale events that influence the influx of pelagic-based energy to the kelp forest: seasonal upwelling and the recruitment of juvenile rockfish. I show that phytoplankton-based carbon use was higher in species that forage in the water column (~65%) as opposed to species on or near benthic substrates (~50%), and that both pelagic and benthic foragers consumed a diversity of prey taxa advected to the kelp forest from pelagic environments. Furthermore, multiple lines of evidence indicate the importance of variable juvenile rockfish recruitment in understanding rockfish use of phytoplankton-based energy. This research advances our understanding of how ecosystem connectivity influences species’ diets and the many ways that cross-ecosystem subsidies shape the marine environment. Results suggest that to truly understand how kelp forest communities function, we must give more attention to the dynamics of pelagic energy sources and the conditions that lead to variability in pelagic-benthic coupling.

Multilevel decomposition of spatial and environmental effects on nearshore fish assemblages in tropical semi-enclosed ecosystems

We investigated the effects of local- and landscape-scale environmental variables and spatial structure at three hierarchical levels (i.e. type of system, individual systems, and zones within each system) on the fish species composition and abundance in bays and coastal lagoons in southeastern Brazil. The effects were assessed at the assemblage level, and between and within habitat use groups. Exclusive and shared effects of environmental, hierarchical, and spatial variable sets were quantified by variation partitioning, and individual environmental effects were assessed by partial canonical correspondence analyses. The hierarchical and spatial structures were more relevant for habitat use groups less widespread due to the lower dependence on estuarine areas, and influenced primarily the landscape-scale environmental differences between individual systems. At the assemblage level, the exclusively environmental effects were primarily indicative of the marine (e.g., higher depth, pH, and transparency) versus continental (e.g., greater distance from the ocean and mangrove cover) influence. Estuarine, marine migrant, and marine straggler species were more widespread across these gradients, but the former species were primarily associated with greater mangrove cover and the marine stragglers with a higher marine influence. Semi-diadromous and freshwater species were less associated with greater mangrove cover and primarily restricted to coastal lagoons. The different multi-scale environmental effects within each group reinforced the relevance of intra- and inter-specific differences in environmental tolerances and requirements, and evidenced the relevance of the connectivity between alternative habitats in maintaining the structure of fish assemblages. Disentangling multilevel spatial and environmental effects, this study evidenced the critical roles of the maintenance of the environmental heterogeneity in nearby estuarine habitats for nearshore fish assemblages in different types of tropical semi-enclosed estuarine ecosystems.

Water temperature gradient shapes the structure and composition of nearshore marine fish communities in southern Europe

The nearshore ecosystem is an important nursery ground for many fish species. Considering that these areas have a considerable economic value because they support a wide variety of highly valuable species, it is essential to study the structure of their fish communities and the factors that may inlfuence them. The nearshore fish assemblages were studied from March to November of 2015 at 15 sandy beaches, arranged in 6 seaports, along 700 Km in the coast of Portugal. This Atlantic coastline is an important geographical transition area between cold-temperate and warm-temperate regions. Sampling was performed by the beach seine fishery, an artisenal fishery that operates in these areas. The fish assemblage was studied according to its species richness, biogeographical origin, habitat use and resource exploitation, in both biomass and number of individuals. The nearshore fish assemblage was diverse with 70 species belonging to 32 families, though a few species dominated the community: Engraulis encrasicolus, Trachurus trachurus, Sardina pilchardus and Scomber colias. Results indicated that the structure and composition of the fish assemblage from northern and southern seaports are different. Overall, species richness was higher in the southern seaports. Planktivorous species dominated the community in the northernmost seaport, and piscivorous species dominated the community in the remaining seaports. As expected, cold-temperate species presented higher abundance in the northern seaports, and both warm-temperate and sub-tropical species increased in number towards the southern limits. Tropical species were only present in the southernmost area. The main driver for variations in the fish community structure and composition was the water temperature gradient imposed by latitude, highlighting the environmental control in shaping marine biological communities.

Taxonomic and functional β-diversity patterns reveal random assembly rules in nearshore fish assemblages

Taxonomic and functional β-diversity patterns reveal random assembly rules in nearshore fish assemblages

Partitioning multiple diversity dimensions of nearshore fish assemblages within a coastal seascape

The conservation of coastal seascapes requires a better understanding of how different dimensions of biodiversity are represented between juxtaposed habitats. We explored patterns of taxonomic, functional, and phylogenetic diversity of fishes between four habitats (sandy bottoms, rocky reefs of high and low relief, and mixed bottoms) within a semi-lagoon seascape (Las Canteras beach) in Gran Canaria Island. Data on fish presence in each habitat were provided by weekly snorkeling tours, at day and night, from August 2015 to August 2018. Indices that measured ‘how much’ biodiversity, i.e., ‘how many species’ (species richness), ‘how much functional dissimilarity’, and ‘how much evolutionary history’ were larger on rocky bottoms. However, indices that measured phylogenetic differentiation, i.e., ‘how different’, via the taxonomic distinctiveness and the Mean Pairwise Distance index were particularly high on sandy bottoms, because of the presence of elasmobranchs, which were absent from rocky bottoms. The ‘phylogenetic signal’, whether phylogenetically related species are functionally similar, was significant on rocky bottoms, but non-significant on sandy bottoms, reflecting phylogenetic ‘overdispersion’ on sandy bottoms and phylogenetic ‘clustering’ on hard bottoms. From a conservation perspective, sandy bottoms cannot be underrated, particularly in the context of maximizing indices that measure ‘how phylogenetically different’ biodiversity is.

Regional patterns in species richness and taxonomic diversity of the nearshore fish community in the Brazilian coast

The nearshore fish assemblage structures and their seasonal changes were compared between two habitats (estuarine and surf zones) in three climatic regions (Tropical, 7°S; Transition, 23°S; and Warm Temperate, 32°S) encompassing ∼3200 km in the Brazilian coast. Regional patterns of species richness and taxonomic distinctiveness of the fish community were also described. We expected the highest richness and lowest seasonal variation in the assemblage's structure in the Tropical region and the opposite pattern in the Warm Temperate region. The assemblage structures differed significantly among regions and habitats. In the estuarine habitats, species richness and taxonomic distinctiveness (AvTD) were highest in the Tropical (84 species, AvTD = 92.3) and lowest in the Temperate (31 species, AvTD = 73.9) region. However, in the surf zone the highest species richness and taxonomic distinctiveness were found in the Transition region (49 species, AvTD = 78.5) and the lowest in the Warm Temperate region (19 species, AvTD = 51.9). The two habitats (estuarine and surf zone) differed consistently in the three regions. No seasonal change was found in the structure for the fish assemblage in the Tropical and Transition regions. However, the assemblage structure differed significantly between the spring and summer and between the spring and autumn in the Warm Temperate region. The most significant predictors of the fish community structure were salinity for the Tropical region, temperature and salinity for the Transition region, and transparency and temperature for the Warm Temperate region. The marine fish communities presented low levels of species redundancy in the Warm Temperate region with few species fulfilling key functional roles. The data provided here are references against which to detect future ecological changes at the regional-scale patterns for the Brazilian nearshore fish community and it is important to better inform fisheries management and coastal conservation planning.

Oceanographic and lunar forcing affects nearshore larval fish assemblages from temperate rocky reefs

ABSTRACTThe influence of oceanographic features and moon phases on ichthyoplankton assemblages in a temperate nearshore rocky reef off El Quisco Bay, central Chile, was assessed during austral spring–summer 2015–2016 using Bongo nets. Wind direction was predominantly south-west, and ocean temperature increased gradually during the study period, fluctuating between 11.6°C and 17.7°C. A relatively cold period (from late September to early December, 12.42 ± 0.64°C) was distinguished from a relatively warmer phase (from mid-December to February, 13.56 ± 1.08°C). Nearshore ichthyoplankton was composed of 13,700 individuals, belonging to 43 taxa. Larval Strangomera bentincki (Clupeidae) were collected in high numbers between late September and late October with peaks during full moon and first quarter (maximum = 734 ind. 100 m−3); larval Engraulis ringens (Engraulidae) was most abundant between late October and late December 2015, with peaks during the third quarter and full moon. Principal Component Analysis of ichthyoplankton data explained more than 44% of total variance and showed the influence of cold/warm periods in the structuring of larval fish assemblages. Water temperature had more influence than lunar phase in the structure and composition of nearshore fish larvae off central Chile. We conclude that larval fish assemblages found in nearshore waters change on a seasonal scale by differences in the reproductive activity among species, and that lunar phase exerts a low, but significant effect on the abundance of fish larvae, but this variability is species-specific.

Marinas as habitats for nearshore fish assemblages: comparative analysis of underwater visual census, baited cameras and fish traps

Understanding the ecological role that artificial structures might play on nearshore fish assemblages requires the collection of accurate and reliable data through efficient sampling techniques. In this work, differences in the composition and structure of fish assemblages between the inner and outer sides of three marinas located in the temperate northern-eastern Atlantic Ocean were tested using three complementary sampling techniques: underwater visual censuses (UVC), baited cameras (BCs) and fish traps (FTs). UVCs and BCs recorded a comparable number and relative abundance of species, which in turn were much greater than those recorded by FTs. This finding supports the use of UVCs and BCs over FTs for broad ecologically studies, especially when dealing with structurally complex habitats such as artificial structures. We found differences in fish assemblage structure between the inner and outer sides of marinas, independently of the sampling method. Four small-sized species (Similiparma lurida, Thalassoma pavo, Sarpa salpa and Symphodus roissali) associated with structurally complex vegetated habitats dominated, in terms of abundance, the outer sides of marinas; Diplodus vulgaris, Diplodus sargus and Gobius niger, species with high ecological plasticity in habitat requirements, dominated the inner sides of marinas. The information provided in this study is of great interest for developing sound monitoring programmes to ascertain the effects of artificial structures on fish communities.

Assessing the performance of a cost-effective video lander for estimating relative abundance and diversity of nearshore fish assemblages

Rocky reefs in the temperate Northeast Pacific constitute a small portion of the nearshore seabed, yet are highly valued as productive habitat for local fisheries. Surveying these structurally complex, untrawlable habitats requires robust gear that can be deployed in rough sea states. Here, a cost-effective, compact video lander was evaluated for its ability to survey the diversity and abundance of nearshore (<40m), rocky-reef-associated fish populations (e.g. Sebastes, Cottidae, Hexagrammidae). To determine the application and limitations of surveying complex rocky reefs with this new tool, this study sought to (1) determine the frequency of observation of known nearshore fish species, (2) evaluate the influence of baiting the lander on the observed fish assemblage, (3) identify the optimal deployment time to maximize observed species richness and abundance, and (4) evaluate species-specific behavioral responses to the lander characterized a priori as attractive, avoidance, or neutral. Seventy percent of lander deployments met established requirements of visibility, view, and habitat. Seventy-seven percent of observed fishes were identifiable to species. The method observed 15 species belonging to 5 families; 5 species were classified as common (observed in >20% of deployments), the remaining rare. Contrary to lander studies in other regions, bait was not found to improve species-specific identification, increase observed species richness or abundance (at the species or feeding guild level), or shorten deployment duration. A deployment time of 8min on the benthos was determined as optimal for observing maximum species richness and abundance in the nearshore, doubling the previously described lander drop durations evaluated in deeper Oregon, U.S.A., waters. Species-specific behavioral responses to this compact lander were evaluated by viewing trends in species abundance (assessed within 30s bins) over the deployment duration; no attractive or avoidance behaviors were observed. Results confirm that this simple, cost-effective video lander configuration is suitable for sampling the suite of fish species found in the nearshore, including rockfish species federally designated as “overfished” (Sebastes pinniger and Sebastes ruberrimus). Furthermore, this study illustrates the importance of evaluating the performance of survey tools in the specific environment in which the tool will be used to determine best-practices from long-term monitoring.

The fish community of Hamilton Harbour, Lake Ontario: Status, stressors, and remediation over 25 years

Hamilton Harbour is a large (21 km2) protected harbour located at the western end of Lake Ontario that was designated as an Area of Concern in 1985 by the International Joint Commission. As part of the designation, the fish community was deemed “impaired.” One of the long-term goals of the Hamilton Harbour Remedial Action Plan is to rehabilitate the fishery to a state, at least in part, to what it was prior to the degrading effects of industrial and municipal pollution, habitat loss, and invasive species. Since the Area of Concern designation, the nearshore fish community has been monitored regularly via a federal boat electrofishing program (1988–2013) and more recently, by a trap net program (2006–2012). During the study period, the harbour underwent significant physical and biological change which was related to both lake-wide (e.g. Dreissenids) and localized harbour events (e.g. habitat restoration). The fish community was assessed temporally using two indices of ecosystem health, the Great Lakes Index of Biotic Integrity and Proportion of Piscivore Biomass, and species-specific catch trends at unaltered sites or sites modified by habitat restoration. Early on, the fish community was dominated by tolerant species characteristic of degraded, eutrophic environments and piscivore abundance was low. The fish community responded positively to ecosystem actions during the first decade that improved water quality, increased physical habitat and reduced invasive species, but further progress was confounded by the interactions with other factors in the last decade that included new invasive species and a decline in water quality. Fish community assessments in the last decade, using both the indices found that the fish community was still impaired and dominated by non-native and pollution tolerant species. The Index of Biotic Integrity was a suitable indicator of ecosystem health strengthened by a consistent assessment with the Proportion of Piscivore Biomass index. A science based refinement of the existing Index in the future would benefit the ability to assess nearshore fish assemblages in the context of conservation goals.

Evidence for Serial Discontinuity in the Fish Community of a Heavily Impounded River

In the Tennessee River, USA, we examined lengthwise patterns in fish community structure and species richness within and among nine reservoirs organized in sequence and connected through navigational locks. Within reservoirs, the riverine, transition and lacustrine zones supported distinct, although overlapping, nearshore fish assemblages; differences were also reflected in measures of species richness. Spatial patterns were most apparent for rheophilic species, which increased in species richness and representation upstream within each reservoir and downstream across the chain of reservoirs. This pattern resembled a sawtooth wave, with the amplitude of the wave peaking in the riverine zone below each dam, and progressively higher wave amplitude developing downstream in the reservoir chain. The observed sawtooth pattern supports the serial discontinuity concept in that the continuity of the riverine fish community is interrupted by the lacustrine conditions created behind each dam. Upstream within each reservoir, and downstream in the chain of reservoirs, habitat characteristics become more riverine. To promote sustainability of rheophilic fishes and maintain biodiversity in impounded rivers, conservation plans could emphasize maintenance and preservation of riverine environments of the reservoir's upper reaches, while remaining cognizant of the broader basin trends that provide opportunities for a lengthwise array of conservation and management policy. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Early summer near-shore fish assemblage and environmental correlates in an Arctic estuary

Abstract Knowledge of reference conditions and species–environment associations is required to ascertain ongoing aquatic biodiversity changes in Arctic regions. The objective of this study was to establish a baseline of fish community structure (species composition, incidence and relative abundance) in relation to salinity, pH and temperature gradients in an Arctic estuary, the Husky Lakes, Canada. Sampling involved an early-summer, standardized, experimental netting survey around the entire perimeter of all estuary basins and peninsulas. Detrended canonical correspondence analysis (DCCA) was used to evaluate species–environment associations. The ecosystem sustains an abundant and diverse fish community, characterized by co-dominance of coregonids and a marine schooling fish, Clupea pallasii , and high abundance of freshwater/freshwater-amphidromous species in the innermost basins. Highest richness and total abundance were related to mixing conditions, warmest temperatures, connectivity to nearby ecosystems, and diversity in species life histories. Salinity determined spatial patterns of fish species abundance and distribution. The incidence of freshwater fish was limited by the availability of low salinity habitat and potential community interactions. These fish, particularly Salvelinus namaycush and Thymallus arcticus , are considered as the most vulnerable to changes in freshwater habitat availability. The fish assemblage reflects environmental information from surrounding fluvial, freshwater, coastal marine and catchment ecosystems, and is thus a prime candidate for monitoring environmental change in the region. The results provide a benchmark against which future studies of fish communities can be compared to evaluate potential effects of climate change and anthropogenic development on fish populations from Husky Lakes and similar Arctic aquatic ecosystems.

Local habitat and regional oceanographic influence on fish distribution patterns in the diminishing kelp forests across the Aleutian Archipelago

Fish distributions can be influenced by changes in their local habitat features and regional oceanographic conditions, both of which can occur at different spatial scales. Currently, the coastal waters throughout the Aleutian Archipelago are dominated by two discrete habitats types, kelp forests and urchins barrens, both of which span known U.S. biogeographic breaks near Buldir and Samalga Passes. These passes roughly divide the western Aleutians from the central Aleutians, and the central Aleutians from the eastern Aleutians, respectively, and have been suggested as important breaks for demersal fishes and deep marine fauna due to corresponding changes in ocean conditions. This study assessed how local habitat features compare to regional oceanographic conditions in how they influence nearshore fish assemblages throughout the Aleutian Archipelago. We hypothesized that these assemblages would differ markedly between the kelp forests and urchin barrens, and that local habitat features such as forest size and the abundance of understory kelps and turf algae are more important to assemblage structure than large-scale oceanographic conditions. To explore these hypotheses, 32 kelp forests and 24 non-forested urchin barren areas occurring on 15 Aleutian islands were surveyed for fish assemblage structure and habitat characters using scuba. Within the kelp forests, both the interiors (middles) and the margins (edges) of the forests were sampled for comparison. In general, fish assemblages did not significantly differ between kelp forests and urchin barrens in the western and central Aleutian Islands. Across all three regions, we found that of 26 habitat characters considered, five (density of the stipitate kelp Agarum, the percent bottom covers of understory foliose algae and encrusting coralline algae, and the availability of gravel and bedrock) together provided the best correlation with the observed variation in the fish assemblages, but this appeared to be due to the greater influence of these in the eastern Aleutians where the abundance of Agarum is greatest. However, the relationship between these habitat characters and fish assemblage structure was weak across the archipelago and not statistically significant in any of the regions. Implications of these analyses suggest that a further reduction in kelp forests may not impact fish assemblages in the western and central Aleutians. However, this is likely an artifact of these forests already being in a diminished state, with most of the kelp forests having been replaced by urchin barrens, and thus the impacts to the fish assemblages have presumably already occurred. However, this may be different in the eastern Aleutians where kelp forests remain more abundant and where the influence of Agarum appears strongest. In addition, while nearshore fish assemblages were not significantly different on the opposing sides of Buldir Pass, they were significantly different on the opposing sides Samalga Pass, suggesting that variation in large-scale oceanographic conditions around this pass were important drivers of differences in fish assemblages. However, if ocean properties, such as temperature and salinity, change around Buldir Pass in the future, then corresponding differences in the fish assemblages may develop.