Fish Assemblage Characteristics Research Articles

Habitat and morphological characteristics affect juvenile mortality in five coral reef damselfishes

The abundance and distribution of demersal fishes rely on larvae successfully settling from the pelagic environment to a benthic habitat and their subsequent survival. With high mortality rates during this life stage, settling to a habitat that maximizes survival is critical. However, relationships between settlement choices and subsequent survival are poorly understood and may vary among species with different habitat preferences. To test this, we focused on five congeneric (Pomacentrus) damselfish species that are known to differ in their habitat choices and explored whether habitat associations at settlement influenced survival. Newly settled individuals were tagged and monitored daily for two weeks to estimate natural mortality rates. Morphological attributes of fish and characteristics of settlement habitats, including depth, rugosity, benthic substrata, and local fish assemblages, were used to predict mortality. We found that some species displayed stronger associations with specific benthic substrata at settlement, but contrary to expectations, these selected habitat characteristics were relatively weak predictors of survivorship. Our survival analysis revealed that the best predictors of survivorship were rugosity (P. adelus and P. amboinensis) and two morphological traits, body depth and ocellus size (P. chrysurus and P. adelus). Interestingly, we found that P. moluccensis that settled in areas of high coverage of mounding coral experienced increased mortality. Of the remaining substrata, analysis showed that instead of associating with habitat characteristics enhancing survivorship, individuals tended not to associate with habitats characteristics that increased mortality (e.g., Turbinaria and sand). This study highlights the species-specific drivers of early post-settlement mortality in coral reef fishes.

Marine protected areas' positive effect on fish biomass persists across the steep climatic gradient of the Mediterranean Sea

Abstract The positive effect of fully protected marine protected areas (MPAs) on marine biodiversity, and specifically on fishes, has been widely documented. In contrast, the potential of MPAs to mitigate the impact of adverse climatic conditions has seldom been investigated. Here, we assessed the effectiveness of MPAs, quantified as increasing fish biomass, across wide geographic and environmental gradients across the Mediterranean Sea. We performed underwater visual surveys within and outside MPAs to characterize fish assemblages in 52 rocky reef sites across an extent of over 3300 km. We used the steep spatial temperature gradient across the Mediterranean as a ‘space‐for‐time’ substitution to infer climate‐driven temporal changes. We found that, as expected, Mediterranean MPAs increased fish biomass. At the same time, higher seawater temperatures are associated with decreased fish biomass, changes in species composition, and shifts towards more thermophilic species. Importantly, we found that the rate of decrease in fish biomass with temperature was similar between protected and fished sites. Taken together, these results suggest that the capacity of MPAs to harbour higher fish biomass, compared to surrounding areas, is maintained across a broad temperature range. At the same time, MPAs will not be able to offset larger‐scale biotic alterations associated with climate change. Policy implications. Our results suggest that sustained warming will likely reduce fish biomass in the Mediterranean Sea and shift community structure, requiring more conservative targets for fishery regulations. At the same time, protection from fishing will remain an important management tool even with future high‐water temperatures, and MPAs are expected to continue to provide local‐scale benefits to conservation and fisheries.

Nearshore marine biodiversity of Osa Peninsula, Costa Rica: Where the ocean meets the rainforest.

Osa Peninsula in remote southwest Costa Rica harbors 2.5% of global terrestrial biodiversity in only 1,200 km2 and has the largest remaining tract of Pacific lowland wet forest in Mesoamerica. However, little is known about the marine ecosystems of this diverse region. Much of the coastline consists of soft sediment exposed to strong wave action. Three major hard bottom habitat types define this region, including: 1) coral reefs around Isla del Caño Biological Reserve, a no-take marine protected area (MPA) of 52 km2, 2) coastal rocky reefs and islets along the peninsula, including Corcovado National Park, and 3) submerged pinnacles just outside the Isla del Caño MPA. Average coral cover at Isla del Caño was 21%, composed primarily of Porites lobata and Pocillopora elegans. In contrast, coastal rocky reefs were dominated by turf algae (39.8%) and macroalgae (20.7%) with low coral cover (1.1%). Submerged pinnacles were dominated by crustose coralline algae (33.3%) and erect coralline algae (25.7%). Fish assemblage characteristics (species richness, abundance, biomass) were significantly higher at the pinnacles compared to the other habitats and was dominated by schooling species such as Haemulon steindachneri, and the herbivores Kyphosus ocyurus, and Acanthurus xanthopterus. Top predators, primarily Triaenodon obesus, Caranx sexfasciatus, and Lutjanus argentimaculatus, were also most abundant at these pinnacles and accounted for the largest differences in fish trophic structure among habitats. Despite Isla del Caño being fully protected from fishing, biomass was similar to fished areas along the coast and lower than the adjacent submerged pinnacles outside the reserve. Similarly, Corcovado National Park includes 20.3 km2 of no-take MPAs; however, there is limited enforcement, and we noted several instances of fishing within the park. The unique configuration of healthy offshore coral reefs and pinnacles connected to coastal habitats provides corridors for many species including large predators such as sharks and other marine megafauna, which warrants additional protection.

Habitat and Marine Reserve Status Drive Reef Fish Biomass and Functional Diversity in the Largest South Atlantic Coral Reef System (Abrolhos, Brazil)

The effects of fishing have been documented across coral reefs worldwide. No-take marine reserves do not only act as a conservation tool but also allow an opportunity to study impacts of fishing, by acting as control sites. In addition, well-planned and well-managed no-take marine reserves (NTRs) provide conservation benefits that are essential to marine biodiversity and ecosystem-based management. The Abrolhos Marine National Park, off the tropical Brazilian coast, protects part of the largest coral reef system in the South Atlantic. To investigate the effects of fishing on reef fish richness, abundance, biomass, and functional diversity of the fish assemblage, we compared sites across two protection levels considering the variation in habitats (Fringing Reefs—Protected; Pinnacles Reefs—Protected; and Coastal Reefs—Open Access), using Baited Remote Underwater Stereo-Video systems (stereo-BRUVs). We adjusted generalized additive mixed models of fish assemblage characteristics with protection levels and environmental variables, such as topographic complexity (mean relief and relief variation), visibility, and benthic cover percentage. Inside NTRs, we found higher total biomass and biomass of fishery target species and carnivores, specifically for the Carcharhinidae (sharks) and Epinephelidae (groupers) families, indicating direct fisheries effects on these groups. In contrast, the ecological parameters of non-target fish were positively correlated with habitat characteristics, including mean relief and variance of relief. Moreover, fish functional diversity was higher within NTRs, demonstrating an even distribution of functional entities. The presence of large mobile predators and the overall higher biomass of carnivores inside the NTR indicate the effect of fishing exclusion. Our results point to the value of NTRs to study the effects of fishing and achieve biodiversity conservation and suggest the importance of using remote sampling methods to assess large mobile predators.

The functional ecology of mangrove fishes across the Isthmus of Panama

AbstractAimBiogeographic history and variation in modern environmental conditions can greatly influence local and regional community structure and, more generally, ecosystem functioning. This is clearly exemplified at the Isthmus of Panama where marine communities and environments from the Caribbean Sea and the Tropical Eastern Pacific Ocean differ despite ancient connections during the Miocene and Pleistocene. Here, we compare the functional (implied from traits) and isotopic structure of mangrove fish communities from those two biogeographic regions, which have been separated by the Isthmus of Panama for ~3 my.LocationCaribbean and Pacific coasts of Panama (Eastern Pacific and Caribbean Sea).MethodsWe gathered data on five functional traits (salinity preference, body mass, diet, position in the water column and lifespan) of mangrove fishes from the sampled regions. We also analysed δ13C and δ15C isotopic values and calculated functional isotopic metrics of the most abundant fish species inhabiting mangroves of these two regions.ResultsThe taxonomic composition and functional and trophic diversity differed between the mangrove fish communities of the Caribbean and the Eastern Pacific. Although the species richness of both assemblages was similar, there was very little taxonomic overlap between them: Snooks (Centropomidae) numerically dominated in the Eastern Pacific, whereas grunts (Haemulidae) and snappers (Lutjanidae) dominated in the Caribbean Sea. Functional divergence (FDiv) and isotopic richness (IRic) were higher in the Caribbean than in the Eastern Pacific, indicating differences in the way fishes use mangroves in these areas.Main conclusionsTaxonomic and functional characteristics of mangrove fish assemblages across biogeographic realms can be strongly influenced by local environmental factors (e.g. tidal regimes, the presence of adjacent coastal ecosystems and productivity), and these can override similarities that recent historical connections of faunas might be expected to produce. All such aspects need to be considered when seeking generalizations about ecosystem functioning.

Nondestructive Monitoring of Soft Bottom Fish and Habitats Using a Standardized, Remote and Unbaited 360° Video Sampling Method

Lagoon soft-bottoms are key habitats within coral reef seascapes. Coral reef fish use these habitats as nurseries, feeding grounds and transit areas. At present, most soft-bottom sampling methods are destructive (trawling, longlining, hook and line). We developed a remote, unbaited 360° video sampling method (RUV360) to monitor fish species assemblages in soft bottoms. A low-cost, high-definition camera enclosed in a waterproof housing and fixed on a tripod was set on the sea floor in New Caledonia from a boat. Then, 534 videos were recorded to assess the efficiency of the RUV360. The technique was successful in sampling bare soft-bottoms, seagrass beds, macroalgae meadows and mixed soft-bottoms. It is easy to use and particularly efficient, i.e., 88% of the stations were sampled successfully. We observed 10,007 fish belonging to 172 species, including 45 species targeted by fishermen in New Caledonia, as well as many key species. The results are consistent with the known characteristics of the lagoon soft bottom fish assemblages of New Caledonia. We provide future users with general recommendations and reference plots to estimate the proportion of the theoretical total species richness sampled, according to the number of stations or the duration of the footage.

Spatial and seasonal variation in littoral fish assemblages of four estuarine lagoons on the Mexican Pacific coast

The shallowest zones of coastal lagoons are particularly appropriate nursery habitat for many fish species by providing refuge from predators and abundant food, among other benefits. However, little is known about the characteristics of fish assemblages and their relationship with environmental factors in these areas. The main objective of this study was to investigate the abundance and composition of the fish assemblages in the shallow zones (≤1 m) of four coastal lagoons in the Central Mexican Pacific and determine the correlation of their spatial and seasonal variations with selected abiotic variables. Fish samples were taken with a beach seine in the months of May and December during two consecutive years. Simultaneously, the physical and chemical variables of the water were measured, and the particle size of the sediment and content of organic matter were determined. A total of 26016 fish belonging to 60 species were collected, but only eight species (Poeciliopsis turrubarensis, Lile stolifera, Poecilia butleri, Eucinostomus currani, Anchoa sp, Gerres simillimus, Atherinella guatemalensis and Mugil setosus) accounted for more than 80% of the specimens. Significant differences in the composition of the fish assemblages between lagoons were found. The changes were principally related to the type of communication with the ocean, second to physical and chemical variables, primarily salinity, followed by size of the sediment particles (% of mud or sand). Observed seasonal changes could have been related to environmental and biological factors (e.g. recruitment) acting synergistically. No evidence was found that the state of eutrophication of the lagoons is severe and could be affecting the composition of the fish assemblages.

Factors associated with distributions of six fishes of greatest conservation need in streams in midwestern USA

Abstract Many fish species of greatest conservation need (SGCN) in Iowa and Minnesota, USA, have been in decline for decades. A key reason for the decline is the alteration and degradation of naturally flowing streams owing to land use changes resulting from agricultural practices. Populations of several fishes have been adversely affected by widespread stream channelization that has resulted in more homogeneous stream habitats throughout Iowa and Minnesota. The goal of this study was to determine the abiotic and fish assemblage characteristics associated with the presence of these rare fishes. Electrofishing and seining were used to sample fish assemblages and 43 abiotic characteristics were measured at 111 sites in the North Raccoon and Boone River basins in central Iowa and the Rock River and Beaver Creek basins in north‐west Iowa and south‐west Minnesota during 2016 and 2017. Six SGCN, including the federally endangered Topeka shiner (Notropis topeka), were included in statistical modelling to determine habitat and fish assemblage characteristics associated with their presence. Species‐specific nonmetric multidimensional scaling ordinations indicated that abiotic characteristics and fish assemblages often differed between sites where SGCN were present and absent. Random forest and logistic regression models suggested that the presence of four of six SGCN were positively associated with species richness, whereas all other 10 important abiotic and fish assemblage variables were unique to only one or two of the six SGCN. Topeka shiners were present at 36% of sites and were positively associated with orangespotted sunfish (Lepomis humilis) catch per unit effort while being negatively associated with canopy cover and fantail darter (Etheostoma flabellare) catch per unit effort.

Impact of multiple stressors on the fish community pattern along a highly degraded Central European river – a case study

In this study, we provide a descriptive assessment of how chemical and hydro-morphological stressors have affected the fish community along one of the most impacted rivers in Central Europe. In addition to the toxicity of combined pollutants (expressed in toxic units), a range of hydro-morphological characteristics were measured to assess which stressors have had an impact. No longitudinal spatial trend was observed in fish assemblage characteristics as individual sites were affected by different stressors. Instead, five largely artificial assemblage “zones” were identified corresponding to different combinations of stressors. Water quality (principally dissolved O2) and hydromorphology were the main drivers affecting fish presence and density, with self-purification processes, restocking from tributaries and geomorphology promoting fish survival and/or recovery, despite increasing toxic pressure downstream. Our results suggest that a) toxic units alone are insufficient to establish causative factors in fish community loss as they do not take account of hydro-morphological stressors, many of which interact with and/or mask each other, and b) that a single WFD monitoring site in such heavily impacted rivers is insufficient to assess ecological status; rather, the ecological status of specific “zones” (identified based on fish assemblage structure, habitat and water quality) should be assessed, with the ultimate aim of merging the zones and returning the river to a single functioning longitudinal ecosystem, accepting that this is unlikely to resemble the natural pre-industrial status of the river.

Investigating food limitations in wild fisheries: the attendance and growth responses of fish at an anthropogenic feeding station within a temperate estuary

To investigate whether wild fish populations are food limited, this study explored whether the provision of supplementary food had a positive effect on the abundance, condition and growth characteristics of estuarine fish assemblages in New Zealand. Feed (7690 kg) was delivered from an anthropogenic feeding station over a 60-week period to a naturally occurring assemblage of wild fish. Yellow-eyed mullet (Aldrichetta forsteri) of juvenile, sub-adult and newly matured size classes were the dominant species actively foraging at the feeding station throughout its operation, whereas larger piscivorous species visited and foraged from the feed station over the summer period only. Other species were present in the wider area of Nelson Haven, but not at the feed station. No obvious changes in the condition factor of yellow-eyed mullet were observed across the period of monitoring, and no changes in their catchability were detected - although marked seasonal variation in catch rates was observed. Results from tag-recapture data identify that the length-based growth rates of yellow-eyed mullet recaptured near the feed station were higher than those of tagged individuals recaptured at a nearby comparison site, and were higher than the growth rates observed in natural populations of yellow-eyed mullet in the wider region. Shifts in the median size of fish, as observed by acoustic observations, agreed with the tag-recapture data. Although some of the results identified were not amenable to statistical analyses, the attendance of yellow-eyed mullet at the feeding station, in combination with the improved estimates of growth by most of the techniques employed, indicates that yellow-eyed mullet are food limited in their natural environment and that the growth performance of these fish can be positively affected by the increased availability of food.

Characteristics of effective marine protected areas in Hawaiʻi

Abstract Ancient Hawaiians developed sophisticated natural resource management systems that included various forms of spatial management. The state of Hawaiʻi established its first legislated marine protected area (MPA) in 1953, and today there exists a patchwork of spatial marine management strategies along a range of sizes, with varying levels of governance, enforcement, and effectiveness. Approximately 12% of waters within the 50 m depth contour and 5% of waters within state jurisdiction (≤3 nmi) have some form of marine management. No‐take areas make up <0.5% of nearshore waters, and combined with highly protected areas account for 3.4% of this habitat. Most of the existing MPAs are small, with a median area of 1.2 km2 (confidence interval 0.2–8.1). Twenty‐five datasets, representing 1,031 individual surveys conducted throughout Hawaiʻi since 2000, were used to compare fish assemblage characteristics amongst a subset of MPAs using a regulation‐based protection classification scheme. Fully and highly protected areas had significantly greater resource fish biomass than areas with intermediate or low protection did. High human population density adjacent to MPAs had a negative influence on fish trophic structure within MPAs, whereas remote MPAs harboured higher fish biomass. Complex and heterogeneous habitats were important contributors to MPA effectiveness. Long‐term monitoring of select MPAs showed mixed and complex trajectories. Resource fish biomass increased after the establishment of the Hanauma Bay Marine Life Conservation District in 1967 but plateaued after ~15 years, followed by changes in assemblage structure from fish feeding and invasive species. The Pūpūkea Marine Life Conservation District, established in 1983, was expanded sevenfold in 2003 and showed dramatic increases in resource fish biomass following increased protection. This information is critical to improving effectiveness of existing MPAs, helping inform ongoing efforts to implement a network of MPAs statewide, and aiding in the development of comprehensive statewide marine spatial planning.

Assessing key ecosystem functions through soundscapes: A new perspective from coral reefs

Abstract The functioning of tropical coral reefs is imperilled by climate change, overfishing, and decreasing water quality. Maintaining their capacity to provide goods and services will critically depend on our ability to monitor their functioning at appropriate spatial and temporal scales. Given the constraints of traditional methods to respond to those needs, the potential of complementary tools such as Passive Acoustic Monitoring (PAM) is emerging. Coral reef soundscapes (i.e. ambient sound) encompass sounds produced by numerous organisms. Soundscape characteristics quantified by ecoacoustic indices have been found to reflect general ecosystem properties, such as diversity and abundance of fishes, and coral cover. The present study tested, on the virtually pristine coral reefs around Europa Island, South-West Indian Ocean, the capacity of acoustic indices to assess key ecosystem functions. Soundscapes were recorded during 2 h, and ecosystem functions were evaluated using video footage of the fish assemblages and underwater photogrammetry of the benthic landscapes. We found significant and strong correlations between six ecoacoustic indices and six key ecosystem functions, including habitat features and fish assemblage characteristics. The six ecoacoustic indices were representative of several combinations of frequency, amplitude and time analysis domains, highlighting the diversity of the functional information conveyed by soundscapes. Our findings reveal that a 2 h daytime recording on a coral reef could provide sufficient acoustic information to characterise major ecosystem functions of a site. This should facilitate the detection of functional disturbances at temporal and spatial scales adapted to the rapidity of upcoming climate changes. Our results also highlight the potential of ecoacoustics to bring novel and relevant insights in the functioning of ecosystems.

Remote sensing of three‐dimensional coral reef structure enhances predictive modeling of fish assemblages

AbstractLiDAR (light detection and ranging) allows for the quantification of three‐dimensional seascape structure, which is an important driver of coral reef communities. We hypothesized that three‐dimensional LiDAR‐derived covariables support more robust models of coral reef fish assemblages, compared to models using 2D environmental co variables. Predictive models of coral reef fish density, diversity, and biomass were developed using linear mixed effect models. We found that models containing combined 2D and 3D covariables outperformed models with only 3D covariables, followed by models containing only 2D covariables. Areas with greater three‐dimensional structure provide fish more refuge from predation and are crucial to identifying priority management locations that can potentially enhance reef resilience and recovery. Two‐dimensional seascape metrics alone do not adequately capture the elements of the seascape that drive reef fish assemblage characteristics, and the application of LiDAR data in this work serves to advance seascape ecology theory and practice in the third dimension.

Long-term monitoring revealed fish assemblage zonation in the Three Gorges Reservoir

Reservoirs are important artificial ecosystems that modify the hydrological and ecological characteristics of a river. Knowledge of the basic characteristics of fish assemblages in reservoirs is a first step toward the development of effective conservation policies. We used the information collected over a 10-year period (2006-2015) to assess the structure of the fish assemblages in the Three Gorge Reservoir (TGR) in a river-dam gradient. Three fish zones were detected in TGR. Species richness was the highest in the upper zone and lowest in the lower zone. The riverine zones were dominated by rheophilic species Coreius guichenoti and Pelteobagrus vachelli. The transitional zones were dominated by Coreius heterodon and Rhinogobio cylindricus. The lacustrine zones were dominated by eurytopic species Hypophthalmichthys molitrix, Aristichthys nobilis, Hemiculter bleekeri and Cvprinus carpio. For the functional characteristics, fish assemblages in riverine and transitional zones were dominated by insectivorous species, equilibrium strategists and rheophilic species (e.g., Coreius heterodon and Coreius guichenoti). In lacustrine zones, the fish assemblage was dominated by habitat generalists common to lakes and reservoirs (e.g., Hemiculter bleekeri, Hypophthalmichthys molitrix, Aristichthys nobilis). Moreover, 18 exotic species (e.g., Protosalanx hyalocranius, Ictalurus punctatus, Megalobrama amblycephala, Tilapia) were collected in TGR, most of which only existed in the lacustrine zone. The results highlight the importance of freely flowing riverine reaches for conserving native fish in the upper Changjiang River and adaptive management strategies for fisheries in TGR.

Peak in biomass driven by larger-bodied meso-predators in demersal fish communities between shelf and slope habitats at the head of a submarine canyon in the south-eastern Indian Ocean

This study investigated variations in the composition and biomass of demersal fish assemblages over a 570-metre depth gradient on the temperate, lower west coast of Australia (32° S) in the south-eastern Indian Ocean. Fish assemblages were sampled using Baited Remote Underwater Stereo Video systems (stereo-BRUVs, n = 284 deployments) from shallow waters around a mid-shelf island (Rottnest Island) to the continental slope within a submarine canyon (Perth Canyon). A total of 9013 individual fishes (i.e. ΣMaxN) belonging to 179 species and 75 families were identified. Multivariate statistical analyses revealed three distinct fish assemblages associated with the continental shelf (5–199 m), margin (200–300 m) and upper slope (300–570 m). A distance-based linear model revealed that among environmental covariates, benthic biota (sessile invertebrates and macroalgae) accounted for the highest proportion of variation in fish assemblage composition (16.9%) followed by depth (12.5%) and seabed relief (10.5%). Generalised additive models indicated higher biomass of fish associated with habitats characterised by benthic biota. Species richness decreased with increasing depth across the continental shelf but remained constant with increasing depth on the continental slope. Average fish length was not correlated with depth but was greatest at 200–400 m depth. The continental margin and upper slope habitats revealed a distinct change in assemblage composition as well as a peak in biomass of species that was dominated by larger-bodied meso-predators at the continental margin. The trends exhibited in fish assemblage characteristics across this broad depth range can inform ecosystem based management for deepwater fisheries resources.

The Analysis of the Fish Assemblage Characteristics by Wetland Type (River and lake) of National Wetland Classification System of Wetlands in Gyeongsangnam-do.

습지 유형에 따른 어류군집 특성을 파악하고 이를 통해 관리 전략을 마련하기 위해 경상남도에 위치한 29개의 습지 (하천형 20개소, 호수형 9개소)를 대상으로 조사를 실시하였다. 조사결과 하천형 습지에서는 평균( ${\pm}SD$ ) $10.3{\pm}4.8$ 종이, 호수형 습지에서는 평균 $9.1{\pm}4.1$ 종이 출현하였으며, 출현...

A Comparison of Three Paired Modified Fyke Nets for Characterizing Fish Assemblages in the Nearshore Zone of Lake Michigan

AbstractWe performed a gear comparison between three types of paired fyke nets used to monitor fish communities in the nearshore zone of Lake Michigan. Our objective was to identify a single net design that would maximize species diversity and catch. The three types of paired fyke nets included a small frame model with 3‐mm bar mesh (Mini‐fyke), a larger‐framed model with 13‐mm mesh (Fyke), and a large frame model with 13‐mm mesh recommended by the American Fisheries Society (AFS‐fyke). We set all three gear types in triplicate on similar nearshore littoral habitat at 16 sites in Green Bay, an embayment of Lake Michigan. Total catch was dominated by Gizzard Shad Dorosoma cepedianum, Round Goby Neogobius melanostomus, Spottail Shiner Notropis hudsonius, Trout‐perch Percopsis omiscomaycus, and Yellow Perch Perca flavescens, which represented 99.3% of all individuals captured. We found that Mini‐fyke nets selected for smaller individuals, caught relatively few species, and had the highest catch per unit effort; this was largely driven by high catches of Spottail Shiner and Gizzard Shad. Fyke nets captured the largest individuals, had the lowest catch per unit effort, and the greatest diversity of species. Results for AFS‐fyke nets were typically intermediate between Mini‐fyke and Fyke nets for most parameters. Species accumulation curves indicated that Fyke nets acquired more total species at a higher rate than the other two net types. Given the need to balance effort, gear bias, and sampling efficiency, we found that AFS‐fyke nets recommended by the AFS effectively characterized the nearshore fish community of lower Green Bay, especially if used in conjunction with complementary sampling gears.Received November 28, 2016; accepted May 25, 2017Published online August 4, 2017

Large‐bodied fish assemblage characteristics in large rivers across Ontario

AbstractLarge‐bodied fish assemblages were assessed in large rivers across Ontario. The objectives of this study were to (i) determine if there were relationships in large‐bodied fish species within rivers; (ii) determine what factors explain the variability in the abundance of large‐bodied fish within rivers across Ontario; and (iii) assessed variation in large‐bodied fish biodiversity among these river. Standardized index netting was conducted at 22 sites across 12 major rivers and sampled 3889 fish representing 26 species. Species associations were evident based on correspondence analysis. Walleye, Common White Sucker, Northern Pike and Lake Whitefish formed one group; Silver Redhorse, Shorthead Redhorse and Lake Sturgeon (adult and juvenile) formed another; Burbot, Longnose Sucker and Sauger were closely associated; and Cisco, Yellow Perch, Rock Bass, Smallmouth Bass and Brown Bullhead grouped. Canonical correspondence analysis was conducted to link species abundance patterns to environmental conditions. Walleye, Common White Sucker, Lake Whitefish and Smallmouth Bass were ubiquitous. Northern Pike abundance was negatively correlated with river discharge and longitude. Burbot, Sauger and Longnose Sucker abundance were positively correlated with deep rivers and discharge. Whereas Cisco, Yellow Perch and Rock Bass abundance were greater in wider rivers with lower discharge. Lake Sturgeon (adult and juvenile), Silver Redhorse and Shorthead Redhorse abundance were greater in narrow, longer rivers. Juvenile Lake Sturgeon abundance was positively correlated with longitude and river discharge. Mean species diversity and richness of large‐bodied fish among all sites was 1.58 (0.36 SD) and 7.7 (2.6 SD). Species diversity was not significantly related to any of the variables used in the Generalized Linear Model; however, species richness was significantly related to maximum depth. This study demonstrated subtle differences in environmental variables affecting large‐bodied fish at the landscape scale rather than those observed at the river scale.

"How" and "what" matters: Sampling method affects biodiversity estimates of reef fishes.

Understanding changes in biodiversity requires the implementation of monitoring programs encompassing different dimensions of biodiversity through varying sampling techniques. In this work, fish assemblages associated with the “outer” and “inner” sides of four marinas, two at the Canary Islands and two at southern Portugal, were investigated using three complementary sampling techniques: underwater visual censuses (UVCs), baited cameras (BCs), and fish traps (FTs). We firstly investigated the complementarity of these sampling methods to describe species composition. Then, we investigated differences in taxonomic (TD), phylogenetic (PD) and functional diversity (FD) between sides of the marinas according to each sampling method. Finally, we explored the applicability/reproducibility of each sampling technique to characterize fish assemblages according to these metrics of diversity. UVCs and BCs provided complementary information, in terms of the number and abundances of species, while FTs sampled a particular assemblage. Patterns of TD, PD, and FD between sides of the marinas varied depending on the sampling method. UVC was the most cost‐efficient technique, in terms of personnel hours, and it is recommended for local studies. However, for large‐scale studies, BCs are recommended, as it covers greater spatio‐temporal scales by a lower cost. Our study highlights the need to implement complementary sampling techniques to monitor ecological change, at various dimensions of biodiversity. The results presented here will be useful for optimizing future monitoring programs.

Comparing electrofishing and snorkelling for characterizing fish assemblages over time and space

Environmental processes and dispersal movements occurring over long distances (10 to 100 km) continually influence local stream fish assemblages. However, electrofishing protocols are classically implemented in short reaches (∼1 km) and are not suited for frequent characterization of assemblages over long distances. We developed a new sampling protocol (SPA: snorkelling point abundance) for characterizing fish assemblages over long distances, using series of sampling points, as often applied in electrofishing (PASE: point abundance samples by electrofishing). Nine pairs of PASE and SPA surveys, repeated in a narrow and in a wide stream, were compared. Greater species abundance, occurrence, and richness were found on PASE, but relative species abundance were comparable between protocols. Assemblages were highly variable over time (between-surveys) on both protocols. The spatial structure of point assemblages (within-survey) was consistent between protocols and related to species’ habitat use (depth, current velocity). For several species, the longitudinal distribution of abundance along reaches was comparable between protocols when surveys were pooled. Overall, SPA could be an alternative to electrofishing for analysing spatial structure over long distances.