Fish Relative Abundance Research Articles

Fish and Prey Resources in Reservoir Coves with and without Offshore Artificial Habitat Structures

Artificial habitat structures are used to mitigate habitat loss within aquatic ecosystems and to increase angler catch rates; however, the potential trophic outcomes of concentrating fish at structure additions are rarely evaluated. We compared fish and fish prey assemblages between reservoir coves with and without newly added offshore habitat structures (PVC cubes enclosing 2.25 m3). Further, we tested whether offshore habitat additions changed fish assemblage and abundance in littoral habitats of treated coves. Coves with offshore structures had higher concentrations of fish and an assemblage structure dominated by Pomoxis and Lepomis species at offshore sites compared to coves without offshore structures. There was no evidence for an effect of offshore structures on fish relative abundance and assemblage structure in nearby littoral habitats. Zooplankton and benthic macroinvertebrate abundances did not change because of the addition of habitat structures. Lack of a response of lower trophic organisms may be due to low predation mortality or else losses to predation are replaced by increased prey production or immigration at the offshore structures. Our results indicated that artificial structures effectively concentrated fish, but increases in fish density may be partitioned among newly available structure in offshore habitats and existing structure within littoral habitats. Future studies are needed to test for a relationship between foraging space and food resources provided by artificial habitats, which may be useful for optimizing the number, size, and material composition of structures used in habitat enhancement programs.

The abundance of alien fish species flowerhorn (Cichlasoma trimaculatum (GÜNTHER, 1867) in its fishing ground area at Lake Mahalona, South Sulawesi

Lake Mahalona is located in Towuti District, South Sulawesi Province. There are 29 species of fish found in Lake Mahalona and most of them are endemic fish. The presence of alien species deliberately or unexpected is one of threats causing the declining of the number of biodiversity in fresh waters. This study aims to determine the relative abundance of alien fish species Flowerhorn in its fishing ground area at Lake Mahalona. The research was conducted from January to June 2021 at six stations. Fish samples were obtained by using gill nets. The total Flowerhorn caught during the study were 15,677, the most caught in January was 3,346 and the least in June was 1,451. The Flowerhorn in January were the most number of fish at Kusapa (735), February and March at Muara (566 and 618), April at Tandumata (593), May and June at Badilla (434 and 375). The highest number and relative abundance of Flowerhorn fish were found at Kusapa in January (735 and 33.23%), while the lowest number and relative abundance of Flowerhorn fish were found at Lengkomali in June (129 and 4.62%). Flowerhorn as a alien fish species is distributed throughout the Lake Mahalona station. Flowerhorn fish occupy a lot of habitats with lots of aquatic plants, sandy and rocky substrates.

Volatility in coral cover erodes niche structure, but not diversity, in reef fish assemblages.

The world’s coral reefs are experiencing increasing volatility in coral cover, largely because of anthropogenic environmental change, highlighting the need to understand how such volatility will influence the structure and dynamics of reef assemblages. These changes may influence not only richness or evenness but also the temporal stability of species’ relative abundances (temporal beta-diversity). Here, we analyzed reef fish assemblage time series from the Great Barrier Reef to show that, overall, 75% of the variance in abundance among species was attributable to persistent differences in species’ long-term mean abundances. However, the relative importance of stochastic fluctuations in abundance was higher on reefs that experienced greater volatility in coral cover, whereas it did not vary with drivers of alpha-diversity. These findings imply that increased coral cover volatility decreases temporal stability in relative abundances of fishes, a transformation that is not detectable from static measures of biodiversity.

Fish stock mass reduction is indicated in standard abundance and biomass estimates from gillnets and hydroacoustics

Gillnetting is a technique commonly used in relative abundance and biomass estimates of fish. However, due to its passive nature, the direct recalculation of the catch to reservoir volume or area is not trivial. This issue is often solved by using hydroacoustics, which provides information about fish density, though without the ability to distinguish species. However, the precision of such density estimates are also questionable. In this study, we estimated the abundance and biomass of dominant fish species before and after a biomanipulation program (fish removal) in 2020 using gillnetting and hydroacoustic surveys in a temperate reservoir. Between the two sampling periods, nearly 27,000 individuals (9000 kg) older than 0 + of bleak (Alburnus alburnus) and bream (Abramis brama) were removed during the biomanipulation program. Decreases in abundance and biomass estimates were expected for both techniques and both species. The gillnet decrease was 68% in CPUE (catch per unit of effort) and 48% in BPUE (biomass per unit of effort) for both species and all gillnets grouped together. Hydroacoustic observations showed a decrease of approximately 79% in abundance and 74% in biomass after fish reduction. Considering the numbers and biomass of fish removed, the absolute hydroacoustic estimates were underestimated for fish abundance but credibly estimated for biomass. The average weight of the fish taken was between the values of the fish caught with gillnets and the weights determined by hydroacoustics. In terms of results, both methods appear to be a suitable tool for estimating fish abundance and biomass in large inland waters, although the spatial and temporal distribution of fish of different sizes should be considered when using different sampling methods for fish monitoring.

Biodiversity in the Cipeles River, Sumedang Regency, West Java Province, Indonesia


 This study aims to determine the diversity of fish species and to analyze the condition of water quality in the Cipeles River, Summedang Regency, West Java Province, Indonesia. The research was conducted for one month. The research method used was census with purposive sampling technique. The sampling period is four times a week. Analysis of the data used in this study is the composition of fish species, relative abundance, diversity, and water quality with quantitative descriptive data analysis. The results showed that the fish caught were baung (Mystus cavasius), singaringan (Mystus singaringan), tilapia (Oreochromis niloticus), hampala (Hampala macrolepidota), paray (Rasbora aprotaenia), genggehek (Mystacoleucus marginatus), lalawak (Barbonymus balleroides), and and julung-julung (Dermogenys pusilla). The fish diversity index value 0,85 – 0,89 was categorized as low with the highest relative abundance of genggehek fish (Mystacoleucus marginatus) at stations I and III, and lalawak fish (Barbonymus balleroides) at station II. The native fish of the Cipeles River that was able to adapt from 2001 until now is M. marginatus.

Using eDNA to assess the fish diversity and spatial characteristics in the Changjiang River-Shijiu Lake connected system

With the decrease in biodiversity in freshwater ecosystems, the monitoring of fish has become a current research hotspot. The eDNA-based method has been applied to a variety of single-type water systems (i.e., rivers, lakes, or oceans), but it has not been applied to river–lake-connected systems. We collected eDNA from water samples from the Changjiang River–Shijiu Lake connected system (including the lake area, river channel, and river section) and discussed the fish diversity characteristics of the connected system. A total of 180 samples were collected, and the fish community was analyzed using eDNA metabarcoding of the mitochondrial 12 s region. We finally identified 66 taxa of fish, including one at the order level, two at the family level, 9 at the subfamily level, 20 at the genus level, and 34 annotated to the species level. The number of fish species in the river–lake connected system was greater than that in a single-type water system. The lake area, river channel, and river section had a high degree of overlap in fish composition, and the maximum number of fish was in the river section. There was no significant difference in α diversity index among the three types of waters, but there were significant differences in fish relative abundance, which was dominated by different species. The distribution of three migratory fish (Elopichthys bambusa, Ctenopharyngodon idella, and Hypophthalmichthyinae sp.) accorded with the unique life history migration strategy in the middle and lower reaches of the Changjiang River. Our results provide detailed data on fish diversity and have important implications for the long-term management and conservation of river–lake connected systems in the lower reaches of the Changjiang River. Our research further proves that eDNA can be used to monitor the biodiversity of river–lake connected systems and reflect their spatial characteristics. As a continuously explored method, eDNA shows great potential in the study of fish diversity in river–lake systems.

Increased juvenile native fish abundance following a major flood in an Arizona river

Spring floods trigger spawning in many native fishes of the desert Southwest (USA), but less is known about fish community response when native fishes are rare. Here, we document change to native and nonnative fish captures and instream habitat features following a decade-high flooding event (2019) in the Verde River (AZ) where native fish captures were rare in the years pre-flood. Using prepositioned areal electrofishing devices (PAEDs), we sampled the fish community at 90 sampling units pre-flood (2017) and resampled those same units post-flood (2019) to compare and identify changes to catch and habitat features. Relative abundance of native fishes increased from 0.6% pre-flood (0.01 fish/PAED) to 53.0% post-flood (1.66 fish/PAED) and was largely attributable to the presence of juvenile Roundtail Chub Gila robusta (≤ 70 mm total length (TL)) and juvenile Sonora Sucker Catostomus insignis (≤ 100 mm TL). Juvenile Desert Sucker Catostomus clarkii experienced a lesser increase. One adult native fish was captured in 2017 and adult native fishes were absent from 2019 sampling. The catch of adult/subadult Common Carp Cyprinus carpio (> 100 mm TL) declined; however, this could be related to reservoir management and not the flood. The abundance of all size-classes of Black Bass Micropterus spp., Red Shiner Cyprinella lutrensis and other nonnative fishes did not change. The majority (97%) of juvenile native fishes were captured at the uppermost sampling reach. A 54% reduction to canopy cover across all sampling reaches and an increase of fine sediments at the most downstream reach demonstrates how floods can restructure the river environment. This case-study adds evidence that protection of spring floods is vital to the persistence and recolonization of fishes native to the desert Southwest, especially where they are rare. The continued presence of nonnative species may preclude juvenile native fishes from recruiting to adults.

Large mesopelagic fish biomass in the Southern Ocean resolved by acoustic properties.

The oceanic mesopelagic zone, 200–1000 m below sea level, holds abundant small fishes that play central roles in ecosystem function. Global mesopelagic fish biomass estimates are increasingly derived using active acoustics, where echosounder-generated signals are emitted, reflected by pelagic organisms and detected by transducers on vessels. Previous studies have interpreted a ubiquitous decline in acoustic reflectance towards the Antarctic continent as a reduction in mesopelagic fish biomass. Here, we use empirical data to estimate species-specific acoustic target strength for the dominant mesopelagic fish of the Scotia Sea in the Southern Ocean. We use these data, alongside estimates of fish relative abundance from net surveys, to interpret signals received in acoustic surveys and calculate mesopelagic biomass of the broader Southern Ocean. We estimate the Southern Ocean mesopelagic fish biomass to be approximately 274 million tonnes if Antarctic krill contribute to the acoustic signal, or 570 million tonnes if mesopelagic fish alone are responsible. These quantities are approximately 1.8 and 3.8 times greater than previous net-based biomass estimates. We also show a peak in fish biomass towards the seasonal ice-edge, corresponding to the preferred feeding grounds of penguins and seals, which may be at risk under future climate change scenarios. Our study provides new insights into the abundance and distributions of ecologically significant mesopelagic fish stocks across the Southern Ocean ecosystem.

The Effect of Largemouth Bass Virus on Bass Populations in Kansas Impoundments.

Largemouth Bass virus (LMBV) first became a concern in Kansas when it was identified as a potential cause of decreased catch rates at Crawford State Fishing Lake in 2007. The discovery of LMBV in eight additional impoundments from 2008 to 2017 increased concern about the prevalence and effects of LMBV in Kansas. In response, the Kansas Department of Wildlife, Parks, and Tourism tested 25 Largemouth Bass Micropterus salmoides impoundments for the presence of LMBV. The objectives of this study were to quantify the incidence of LMBV and examine differences in population metrics (i.e., body condition, relative abundance, and growth). A total of 1,260 Largemouth Bass were collected by using standard spring electrofishing surveys, and sagittal otoliths were collected from all of the sampled fish to estimate growth rates. Of the 25 study impoundments, 14 tested positive for LMBV. There was no evidence of LMBV effects on body condition, relative abundance of quality-length fish, or growth rates. The initial dates of LMBV infection of Largemouth Bass in these impoundments are unknown. The LMBV-positive populations in Kansas may have been exposed to the virus many years ago, and the fish may be in the process of rebounding from any potential negative effects.

Characterization and spatial variation of the deep-sea fish assemblages on Pioneer Bank, Northwestern Hawaiian Islands

Knowledge of the spatial variation of deep-sea fish assemblages is a critical gap in understanding seamount ecology. Pioneer Bank in the Papahānaumokuākea Marine National Monument (Hawaii, USA) has a history of hook-and-line fishing but not trawling; thus, it is a good location to further describe deep-sea fish assemblages. From replicated autonomous underwater vehicle transects at 300, 450, and 600 m on 3 sides of Pioneer Bank, we observed 4190 fish representing 81 species. Fish assemblages were dominated by Gadiformes, Perciformes, and Stomiiformes. The relative abundance of fish was significantly different among sides of the seamount and the interaction of side and depth, with the NW side having the highest relative abundance at 450 m. Species richness, rarefaction estimates of expected species richness, Shannon diversity, and Simpson dominance showed significant differences by side, but not by depth. These differences were between the S and NW sides, with the S side having the lowest diversity and high dominance. The structure of the fish assemblage was significantly different among both sides and depths, with depth as the most important factor. Fish assemblage structure was most strongly correlated with salinity, % rugosity, chlorophylla, and mean direction of substrate. These scales of spatial variability both with depth and across short horizontal distances on a single seamount are similar to those found on nearby Necker Island, which reaffirms the spatial heterogeneity in deep-sea fish assemblages on seamounts. This study provides an ecological baseline for the management and conservation of seamounts.

Protection outcomes for fish trophic groups across a range of management regimes

Understanding how Marine Protected Areas (MPAs) improve conservation outcomes across anthropogenic pressures can improve the benefits derived from them. Effects of protection for coral reefs in the western and central Indian Ocean were assessed using size-spectra analysis of fish and the relationships of trophic group biomass with human population density. Length-spectra relationships quantifying the relative abundance of small and large fish (slope) and overall productivity of the system (intercept) showed inconsistent patterns with MPA protection. The results suggest that both the slopes and intercepts were significantly higher in highly and well-protected MPAs. This indicates that effective MPAs are more productive and support higher abundances of smaller fish, relative to moderately protected MPAs. Trophic group biomass spanning piscivores and herbivores, decreased with increasing human density implying restoration of fish functional structure is needed. This would require addressing fisher needs and supporting effective MPA management to secure ecosystem benefits for coastal communities.

Understanding the effects of climate change via disturbance on pristine arctic lakes—multitrophic level response and recovery to a 12‐yr, low‐level fertilization experiment

AbstractEffects of climate change‐driven disturbance on lake ecosystems can be subtle; indirect effects include increased nutrient loading that could impact ecosystem function. We designed a low‐level fertilization experiment to mimic persistent, climate change‐driven disturbances (deeper thaw, greater weathering, or thermokarst failure) delivering nutrients to arctic lakes. We measured responses of pelagic trophic levels over 12 yr in a fertilized deep lake with fish and a shallow fishless lake, compared to paired reference lakes, and monitored recovery for 6 yr. Relative to prefertilization in the deep lake, we observed a maximum pelagic response in chl a (+201%), dissolved oxygen (DO, −43%), and zooplankton biomass (+88%) during the fertilization period (2001–2012). Other responses to fertilization, such as water transparency and fish relative abundance, were delayed, but both ultimately declined. Phyto‐ and zooplankton biomass and community composition shifted with fertilization. The effects of fertilization were less pronounced in the paired shallow lakes, because of a natural thermokarst failure likely impacting the reference lake. In the deep lake there was (a) moderate resistance to change in ecosystem functions at all trophic levels, (b) eventual responses were often nonlinear, and (c) postfertilization recovery (return) times were most rapid at the base of the food web (2–4 yr) while higher trophic levels failed to recover after 6 yr. The timing and magnitude of responses to fertilization in these arctic lakes were similar to responses in other lakes, suggesting indirect effects of climate change that modify nutrient inputs may affect many lakes in the future.

Fish size spectra are affected by nutrient concentration and relative abundance of non-native species across streams of the NE Iberian Peninsula

Aquatic ecosystems are strongly body-size structured with a decline of numerical abundance with increasing body size (hereafter, the size spectrum). Marine and lake fish studies have reported consistent variations of size spectra in relation to environmental conditions and biotic composition, but little is known about stream fishes. Accordingly, in this study we test several hypotheses about the effects of local water conditions, biotic introductions and cumulative pressures (measured as the IMPRESS index) on the fish size-spectrum slope (that is, the linear rate of decline of fish abundance as body size increase in a log-log scale) and the size-spectrum intercept (commonly used as proxy for carrying capacity) among 118 local fish assemblages in streams of the NE Iberian Peninsula. To our knowledge, this is the first time that an extensive river fish dataset is used in a dendritic network to cover systematic changes of size-spectrum parameters. We find that the slope and intercept of the fish size spectrum are negatively correlated with nutrient concentration (mainly total phosphorus), with a greater relative abundance of small fishes but a decline of overall carrying capacity. Moreover, fish assemblages with greater relative abundance of non-native species have flatter size-spectrum slopes. In contrast, the IMPRESS index and climate-related variables are poor predictors of the shape of the fish size spectra. This study contributes to better understanding of the main factors structuring fish assemblages in lotic environments of the Iberian Peninsula. We encourage more research on this line to further explore the use of fish size structure to evaluate the ecological health of riverine ecosystems.

Estimating spatio-temporal distribution of fish and gear selectivity functions from pooled scientific survey and commercial fishing data

Model-based prediction of fish distribution at fine resolutions in space and time has the potential to inform area-based and dynamic forms of management, such as permanent marine protected areas or real-time temporary closures. A major limitation to the spatial and temporal mapping resolution that is achievable is the amount of high quality, standardised data that can be utilized for fitting statistical models. To achieve an adequate spatio-temporal resolution from sparse data, one option is pooling information from several sources, such as scientific surveys and fisheries data. Because surveys and fisheries data usually use different sampling methods, pooling information from different sources requires cross-calibration of catch rates values across multiple gears. However, the individual gear efficiency and selectivity curves (the ratio between catch and availability at a given length) for all fishing gears and species are typically unknown. Using cod (Gadus morhua) in the northern North Sea as a case study, we developed a new formulation of spatio-temporal generalised additive models (GAM) of relative abundance of fish, combining catch data from multiple sources. Differences in gear efficiency and selectivity were internally calibrated within the model by the estimation of the local spatio-temporal variation in abundance. We show that pooling data sources enables the prediction of multi-annual and seasonal spatial variation in cod relative abundance-at-size, at spatio-temporal resolutions that are relevant for informing fishing strategies, e.g., reducing bycatch in real-time, or management objectives, e.g., real-time closed areas. We also show that GAM models fit to catch and effort data can reveal the relative efficiency and selectivity of different survey and commercial gears. The selectivity curve estimates that emerged as a by-product of our analysis are consistent with expert knowledge of the performance of the gears employed for cod. Our analytical approach can therefore serve two useful purposes: to estimate spatio-temporal variation in relative abundance of fish and to estimate relative gear efficiency and selectivity.

Dynamic factor analysis to reconcile conflicting survey indices of abundance

Abstract Stock-wide trends in fish relative abundance are challenging to obtain when a single, comprehensive survey is unavailable, and multiple, spatially, and/or temporally fragmented surveys must be relied upon instead. Indices of abundance from multiple surveys frequently have differing trends, resulting in obscured true abundance patterns of the resource. We use an age-structured simulation model of two coastal shark species in the southeast United States to explore the performance of dynamic factor analysis (DFA) for reconciling multiple indices of abundance that are in conflict. Survey-specific time-variation in catchability was induced to generate conflicting indices of abundance. Key simulation sensitivities included survey variability, abundance pattern in the resource, and missing years of survey data. We caution against using DFA when there is no contrast in the underlying stock abundance or when trends in catchability in all surveys result in no survey that is representative of stock abundance. When multiple representative surveys were available, DFA proved useful across species in estimating stock-wide trends from conflicting survey indices with different selectivities, catchabilities, variances, and, to a lesser extent, with missing data. Our results suggest that resolving contrasting patterns among multiple time-series of relative abundance can improve understanding of the temporal trend in stock abundance.

Comparison of three sampling methods for small-bodied fish in lentic nearshore and open water habitats

We performed a preliminary evaluation of a mobile sampling platform with adjustable push net and live box (Platform) against two common methods for sampling small-bodied fish (i.e., 10–100 mm) in two distinct lentic habitats. Nearshore (NS) littoral habitat was sampled by Platform and beach seine, and open water (OW) pelagic habitat by Platform and Kodiak trawl. Our goal was to evaluate the Platform’s ability to describe fish assemblage structure across habitat types in contrast to common techniques restricted to single habitat types that are less comparable due to gear-specific bias. Platform sample speed had a significant positive effect on recapture efficiency of both nearly neutrally buoyant objects and marked fish. Marked fish recapture efficiencies were similar for Platform in NS and OW, indicating similar efficiency across habitat types. Platform capture efficiency was similar to beach seine and greater than Kodiak trawl. With similar sampling time, the Platform collected more individuals and taxa in NS relative to beach seine and in OW relative to Kodiak trawl. Greater taxa detection by the Platform suggests that it may be effective at detecting species that are numerically rare in specific habitats when compared to these methods. Fish CPUE was significantly greater NS regardless of technique. However, by using the Platform, there is greater confidence that this difference was reliable and not a gear selectivity artifact. Overall, this preliminary study demonstrates the Platform’s potential to collect standardized data across NS and OW habitats, track ontogenetic habitat shifts, and detect differences in small-bodied fish taxa richness, relative abundance, and density between NS and OW habitats. Continued experimentation beyond a single reservoir and fish size range is required before consensus can be established regarding the utility of this new push net design.

Optimization of eDNA metabarcoding methodology for the biomontoring of the ichthyofauna in the Eastern Mediterranean Sea

Environmental DNA (eDNA) metabarcoding is a relatively new methodology for the detection of organisms in an environmental sample, with emerging applications in the fields of ecology, conservation, invasive biology, biomonitoring and more. Several studies are using eDNA nowadays, yet in the Mediterranean marine ecosystems, its use is limited mostly on plankton studies so far. The icthyofauna of the Eastern Mediterranean is undergoing major changes due to biological invasions, mainly form the Red Sea, in combination with the climate change, and a reliable high-throughput biomonitoring tool is essential to monitor these changes. The main goal of this study was to develop a reliable eDNA metabarcoding protocol to study and monitor fish biodiversity in the oligotrophic ecosystems of the Eastern Mediterranean. The study had two parts: a) standardization of the method by testing two different sets of primers in aquaria with known fish species assemblages, and b) estimation of the heterogeneity of fish eDNA distribution in different habitats within a coastal area, in order to determine the most efficient sampling strategy. In both cases, samples were analysed through Next Generation Sequencing on a Illumina MiSeq platform. To standardize the method, we sampled and filtered water from two tanks of the 'Cretaquarium'. We tested two different sets of primers, one for 16S rRNA and the MiFish primers of Miya et al. (2015) for 12S rRNA, in order to estimate their efficiency in assessing species' composition both qualitatively and semi-quantitatively. Both primer sets performed well and most taxa in both tanks were detected up to species level, with 16S marker exhibiting higher resolution. A rather weak correlation was also detected between actual fish biomass and relative abundance as estimated by eDNA metabarcoding. To estimate the eDNA heterogeneity in natural ecosystems, we sampled water in a coastal ecosystem over three distinct types of habitats: hard substrate, soft substrate, Posidonia meadows, as well as in the mid of the water column. Three samples per habitat were collected, two PCRs per DNA extract were performed and results were obtained only for the 16S marker. A total of 69 taxa were detected, with 55 of them distinguished at the species level, while in each sample the number of taxa detected ranged from 13 to 27. Posidonia meadows and the water column samples showed the greatest heterogeneity, in contrast to the hard and soft substrate samples that showed little differentiation both within and between habitat type. Based on these results, an improved protocol should include more technical PCR replicates per sample (at least 3 PCRs), at least one sample per habitat in each area, and a larger volume of water filtered per sample or alternatively, more samples mixed together in order to achieve better representation of the community. Moreover, it was apparent the need of a more complete and curated reference database for the Mediterranean fishes for the aforementioned markers, in order to be able to reliably identify fishes of the Mediterranean ecosystems at species level. In conclusion, the method seems to work well, and with some small improvements, as well as with the complementation of the respective reference databases, it can be used as a reliable tool for the study of biodiversity and biomonitoring of fish communities of the oligotrophic ecosystems of the Eastern Mediterranean Sea.

Could spatial heterogeneity in flow disturbance drive temporal stability of native–invasive species co‐occurrence in riverscapes?

Abstract Spatial heterogeneity of abiotic influences like disturbance in riverscapes could play an important role in dispersal‐aided community stability. We tested if higher spatial variability in conditions around river confluences caused by different flood disturbance regimes in branches could possibly influence the stability of a fish assemblage dominated by strong negative interactions between non‐native trout and native galaxiid fishes. We used field surveys to evaluate the effects of disturbance‐driven differences between river branches on fish densities and temporal variation in the relative abundance of galaxiids. Three repeated electrofishing surveys were conducted in two reaches of all branches of eight confluences in Canterbury, New Zealand. We found the differences in flood disturbance regimes between the two stream branches joining at a confluence were associated with higher mean fish abundance and more temporal stability in the relative abundance of native fish. Conversely, when flood disturbance conditions in the two streams joining were similar, resulting in a homogeneous confluence, fish abundance was lower and temporal variability was higher. For homogeneous confluences, strong interactions between native galaxiids and invasive trout probably produced lower fish densities where rivers with low flow disturbance met, whereas when two highly flow‐disturbed rivers met, environmental harshness probably lowered fish densities. By comparison, enhanced galaxiid temporal stability at confluences containing both disturbed and stable river branches probably reflected the combined effects of refugia from trout predation in disturbed branches and refugia from flooding in stable branches. Overall, these results are likely to reflect the combined effects of population‐specific responses to physical heterogeneity and spatially variable interspecific interactions. They may mean that river network configuration, and confluences especially, could influence community stability through a habitat portfolio effect. Furthermore, it will be worth investigating further whether preservation or restoration of differences in flow disturbance conditions in riverscapes encourages higher ecosystem resilience in the face of global change.

The National Geographic Society Deep-Sea Camera System: A Low-Cost Remote Video Survey Instrument to Advance Biodiversity Observation in the Deep Ocean

There is a growing need for marine biodiversity baseline and monitoring data to assess ocean ecosystem health, especially in the deep sea, where data are notoriously sparse. Baited cameras are a biological observing method especially useful in the deep ocean to estimate relative abundances of scavenging fishes and invertebrates. The National Geographic Society Exploration Technology Lab developed an autonomous benthic lander platform with a baited camera system to conduct stationary video surveys of deep-sea megafauna. The first-generation landers were capable of sampling to full ocean depth, however, the form factor, power requirements, and cost of the system limited deployment opportunities. Therefore, a miniaturized version (76 cm × 76 cm × 36 cm, 18 kg in air) was developed to provide a cost-effective method to observe ocean life to 6000 m depth. Here, we detail this next-generation deep-sea camera system, including the structural design, scientific payload, and the procedures for deployment. We provide an overview of NGS deep-sea camera system deployments over the past decade with a focus on the performance improvements of the next-generation system, which began field operations in 2017 and have performed 264 deployments. We present example imagery and discuss the strengths and limitations of the instrument in the context of existing complementary survey methods, and for use in down-stream data products. The key operational advantages of this new instrument are spatial flexibility and cost-efficiency. The instrument can be hand-deployed by a single operator from a small craft concurrent with other shipboard operations. The main limitation of the system is battery power, which allows for 6 h of continuous recording, and takes up to 8 h to recharge between deployments. Like many baited-camera methods, this instrument is specialized to measure the relative abundance of mobile megafauna that are attracted to bait, which results in a stochastic snapshot of the species at the deployment location and time. The small size and ease of deployment of this next-generation camera system allows for increased sample replication on expeditions, and presents a path forward to advance cost-effective biological observing and sustained monitoring in the deep ocean.

FISH HABITAT USE AND FOOD WEB STRUCTURE FOLLOWING POND-AND-PLUG RESTORATION OF A MONTANE MEADOW IN THE SIERRA NEVADA, CALIFORNIA

Montane meadows are areas of high biodiversity and provide many important ecosystem services; however, degradation of 40–60% of these habitats in the Sierra Nevada region of California has left many of these areas impaired. The “pond-and-plug” meadow-restoration technique is 1 type of treatment implemented to restore montane meadows. The objectives of this technique are to re-water the meadow and promote downstream flow by increasing the water-table elevation and providing additional water storage that will promote the growth of mesic and hydric vegetation that maintains and stabilizes stream channels. However, aquatic habitat and the composition and functioning of aquatic communities in these systems post-treatment are poorly documented or understood. We evaluated: (1) fish habitat, community composition, and relative abundance among recently created ponds spanning the range of pond habitats; (2) seasonal movement and survival of fish within and among ponds; and (3) food web structure in ponds. We documented over-summer and winter survival in the fish community and short-distance movement by 1 species occupying the ponds. Mark-recapture data suggest that all fish species present are capable of surviving both summer and winter conditions when pond conditions could be most limiting. Food web structure among intensively sampled ponds was similar, with overlapping isotopic niche width for dominant taxa. However, basal resource diversity (BRD) varied among ponds, with those having higher macrophyte cover also showing greater BRD. Our findings suggest that pond-and-plug techniques can provide habitat for native fishes that are able to tolerate departures from the species thermal and dissolved oxygen optima. Future meadow treatments could benefit from short-term restoration techniques such as pond-and-plug to allow for longer-term processes to influence meadow condition over time.