Drift Nets Research Articles

Quantifying non-target seahorse fisheries and domestic traditional medicine-based trade in Malaysia

Seahorses (Hippocampus spp.) are sold primarily for traditional medicine (TM) uses in Southeast Asia. Although Malaysia is reportedly an important global seahorse exporter, documentation on the current extent of seahorse catch and trade of seahorse-based TM within the country is limited. This study aimed to quantify patterns of seahorse bycatch, gear-specific biological parameters of caught seahorses, and trade characteristics in Malaysia. Questionnaire-based fisher and TM surveys were administered nationwide from March 2021 to March 2023. Seventy-one percent of fisher respondents (612 out of 860) reported catching seahorses, with gill or drift net fishers (73 %) more likely to have caught seahorses than trawlers (12 %). Significant spatial differences in species composition was observed between Peninsular Malaysia and Malaysian Borneo (Sabah state). The total estimated annual seahorse catch within Malaysia was approximately 3376 kg per year, with 77 % of the catch attributed to gill or drift nets and 23 % to trawling operations. Almost half (40 %) of traditional Chinese medicine (TCM) practitioners/ traders (n = 138), 3 % of Malay TM practitioners (n = 3), and 88 % of other TM traders (n = 7) reported selling seahorse species. This study is one of the first to quantify the often overlooked but critical contribution of small-scale fisheries, especially gill and drift nets, towards seahorse bycatch. The current supply volume and selling price of seahorses were observed to be relatively high, while the present-day demand was reportedly low. Almost half of TCM practitioners/ traders interviewed were still actively selling seahorses, indicating that there is still considerable demand. To ensure the sustainability of seahorse populations in Malaysia, efforts in both small-scale and trawl fisheries must be reduced while strictly enforcing seahorse trade regulations.

Experimental Assessment of Egg Mat Gear Retention and Collection Efficacy.

Abstract Assessment of egg deposition is widely used to provide an index of spawning efforts for lithophilic spawning fishes. However, little is known about the collection efficacy and bias of fish egg collection methods. We conducted a two-phased study consisting of a simulated-river flume study (two-part design), and a field study (an egg drift comparison with capture on mats) to assess egg collection methods and evaluate egg retention and capture on egg mats. Lake whitefish Coregonus clupeaformis egg retention on seeded mats decreased with increasing velocity and walleye Sander vitreus egg retention was variable as velocity increased. Fewer lake whitefish eggs were collected on egg mats when limestone reef rock was present in the flume study during the simulated spawned trials, but the inverse was true for walleye. Similarly, during field collections more lake whitefish eggs were collected in benthic D-shaped frame (D-frame) drift nets set near a known spawning reef compared to egg mats set on the reef, indicating lake whitefish eggs were drifting downstream along the river bottom. In contrast, fewer walleye eggs were observed in D-frame drift nets compared to number of eggs captured on the egg mats. Therefore, egg mats are an informative tool for evaluating walleye egg deposition in an immediate area but may underestimate egg deposition of lake whitefish, especially in lotic systems. Compared to other egg collection methods in the current literature, our study indicates that egg mats are useful for assessing egg deposition by lithophilic spawning fishes, but that the collection and retention efficacy and bias of this gear may vary between species and habitat types.

Effectiveness of an ecological flow regime to assure successful recruitment of anadromous Coregoninae populations in the Rupert River (northern Quebec, Canada)

AbstractObjectiveAs part of a large‐scale hydroelectric project, the mean annual flow of the Rupert River (northern Quebec, Canada) was reduced by 52% at its mouth in 2009. To protect fish habitat, an ecological flow regime that was modulated according to the biological seasons was implemented downstream from the diversion point. An 8‐year monitoring program, including 2 years before partial diversion, was carried out to verify the effectiveness of this mitigation measure on the total annual abundance of anadromous Coregoninae (Cisco Coregonus artedi and Lake Whitefish C. clupeaformis) larvae, which was used as biological indicator of recruitment success. The monitoring also aimed to determine the effects of flow modification on the timing of the larval drift and the spatial distribution of larvae in a river cross section.MethodsEach year, sampling consisted of installing drift nets during the entire downstream larval migration in a river cross section of the lower Rupert River. Drift nets were systematically placed to ensure representative sampling of the river section.ResultPrior to flow reduction, the estimated total number of larvae varied between 1.8 and 8.6 million. Over the following 6 years, the estimated larval population has remained steady at 3–4 million. Otherwise, larval drift characteristics have not changed since the flow reduction, as (1) the duration of the larval drift is the same as before, about 1 month in May and early June, with a peak period of about 8 days; (2) rise in water temperature in spring is a determining factor in the timing of larval drift; and (3) the larvae drift mainly near the surface of the water.ConclusionThe monitoring results indicate that the ecological flow regime implemented in the Rupert River was adequate to maintain anadromous coregonine populations.

State of the Siberian sturgeon population in the Middle Lena in summer

The purpose: to obtain modern data on the distribution, abundance, size composition and biological state of the sturgeon in the middle reaches of the Lena River.Material: data of scientific accounting survey using bottom drift nets in summer 2022.The results: Siberien sturgeon is dstributed irregularly on a 400‑kilometer stretch of the river from the city of Yakutsk to the Vilyui River, with the highest average density near the Vilyui River mouth 163 ind./km2, while sturgeon densities in the areas of Yakutsk and the Aldan River mouth were 71 and 44 ind./km2 respectively. The highest density of fish with the smallest average size in the area near the Vilyui mouth indirectly indicates the presence of a separate herd in the Vilyui River. The average density of fish over the entire 400‑km area was 93 ind./km2. The sturgeon length to the end of the middle rays (ac) was from 21 to 86 cm; on average 43.4 ± 10.7 cm. The modal size class for the sturgeon in catches in 2022 was 41–50 cm (44% of the total catch). The fish weight ranged from 40 to 3800 g. The average weight of individuals was 0.557. More than 80% of fish from all catches weighed up to 700 g. The weight of fish with a length ac 62–71 cm ranged from 0,400 to 1.415 kg, on average 1.0 kg. There were only 2.5% of commercial individuals in the total harvest. Sexually mature females were noted only near the Aldan mouth, where their share was 11% that may indicate the presence of spawning grounds in its channel. In the sample of fish that underwent a complete biological analysis (one third of the catches), sexually mature males were not observed. Estimated number of sturgeon: in Yakutsk city area — 17000 ind., in the Aldan mouth area — 47000 ind., in the Vilyui mouth area — 55000 ind. The total number of Siberian sturgeon on a 400‑kilometer stretch of the Lena River was at least 120000 ind. The state and structure of sturgeon population corresponds to the average statistical retrospective data.Practical value: the results obtained will improve the efficiency of assessing the distribution and stock of sturgeon in the Lena River.

Comparing passive and active macroinvertebrate sampling gear efficacy during biomonitoring in Southern Appalachian mountain streams

AbstractAquatic invertebrates are important components of any aquatic ecosystem and are frequently monitored to determine the ecological integrity of those systems. Various gear types are used to collect aquatic macroinvertebrates in wadeable streams. We analyzed commonly used active and passive gear types, including kick seines, Hess samplers, drift nets, and Hester–Dendy samplers, across a watershed in the Great Smoky Mountains National Park to determine their efficacy under various habitat conditions in wadeable Southern Appalachian mountain streams. Hester–Dendy samplers were significantly different from other gear types for most univariate and multivariate analyses. Kick and Hess samples were most similar in multivariate comparisons of macroinvertebrate assemblages. Drift samples were similar in most univariate analyses but were distinct from other gear types when analyzed with multivariate techniques. Our results indicate that comprehensive assessments of macroinvertebrate assemblages require multiple gear types, various analytical approaches, and consistent taxonomic resolution. The complexity of the fluvial system in question should be thoroughly assessed prior to formulating a macroinvertebrate biomonitoring protocol to better ensure robust and meaningful results.

The Diversity and Distribution of Fish at the Port and Urbanized Areas of Pulau Pinang Strait, Malaysia

Marine fish in Malaysian waters are impacted by various stressors, including resource exploitation, urbanization and industrialization. Therefore, this study examines the fish diversity and distribution at five sampling stations with different natural processes and anthropogenic activities in the coastal waters of Pulau Pinang, Malaysia. A total of 669 fish specimens belonging to 47 species from 23 families were collected using drift nets in two sampling periods from October to November 2017 and October to November 2019. The fish abundance is determined based on the catch per unit effort, (CPUE; ind/hour). Among the dominant families, Leiognathidae and Ariidae accounted for 21.22 and 14.44 of the total catch, respectively. Three fish species, namely, Eubleekeria splendens, Anodontostoma chacunda, and Pennahia anea, dominated the catches. The CPUE near the ongoing reclamation projects and landfill was lower than that of the port and industrial areas with mangrove estuaries. The dendrogram clearly differentiated the fish species composition between the reclamation sites and natural shorelines. Given no previous research on the fish distribution along the Pulau Pinang strait featuring different habitat types, this study therefore serves as a contemporary fish assemblage for future research and surveys.

Technical Efficiency and Financial Feasibility of Drift Net Fishing Business in Tanjung Pasir Village, Indragiri Hilir, Riau

Efficiency is an important aspect that can be used as a benchmark for making decisions in production with various available production input alternatives. Knowing efficiency both technically and economically will reduce the gap between productivity that should be produced. Efficiency is used as an indicator in seeing the ability of the production unit in the fishing business, to know the potential for production inputs it is necessary to analyze its efficiency both technically and economically as well as its development potential. So this research was conducted to see how the efficiency of the dominant fishing gear used by fishermen in Tanah Merah District is technically by looking at the factors that affect fishing production and its financial feasibility. This study uses a quantitative descriptive analysis with a survey method approach and uses an analysis of technical efficiency and financial feasibility. The results showed that the technical efficiency of the capture fisheries business using drift nets by looking at the Cobb-Douglas production function showed a VRS value of 1.185 > 1, which means that it is in the increasing return to scale category where the percentage increase in production is greater for the addition of production factors so that the use of production factors is technically efficient. . Based on the results of the financial feasibility analysis it was concluded that the fishing business using drift nets is feasible to be cultivated in terms of financial parameters in the form of R/C ratio, PPC and ROI.

Characterization of Fisheries Violations From the Türkiye's Mediterranean Coasts Within the Scope of Fisheries Law No. 1380

In this study, fisheries violations within the scope of the Turkish Fisheries Law No. 1380 were characterized for the Mediterranean Coasts of Türkiye. For this purpose, by taking into account the frequency and amount of the fines, the patterns of violations in terms of fishing gear, region, season, region-season and fishing gear-season by regions interactions were determined. Data were derived from the Turkish Coast Guard Command’ fisheries surveillance activities during 2014 for areas between coordinates of (36°00’00” N-29°00’00” E) and (36°00’00” N-35°45’00” E). A total of 491 violations against the Fisheries Law No. 1380 were considered. It was determined that the most violations were made by angling (23.22%) and the least by drift nets (0.4%). According to penalties amounts for the 2014, a total of $298,817 administrative fines were imposed. Trawl violations accounted for the highest total administrative fines (48.38%), while the lowest total administrative fines (0.17%) were for violations with drift nets. While the most violations were detected in Antalya region, the highest administrative fine was applied in Adana-Mersin region. According to seasons, there was a decrease in fisheries violations due to closed season measurement for fishing during summer. In terms of administrative fines, the season-region interaction was experienced the most in Adana-Mersin region during winter, and the least in Hatay-Adana region during summer. In season-region interaction, the most violations were observed in Antalya region in spring, while the least in summer in Hatay-Adana region. In interaction related to fishing gear-season by regions, it was determined that the highest number of violations and administrative fines occurred in winter during angling in Adana-Mersin region and in autumn during purse seine fishing in Hatay-Adana region. As a result, in short term, these findings could assist decision-making mechanisms for the effectiveness and efficiency of MCS (Monitoring, Control and Surveillance) system, which is an important part of fisheries management regime. In long term, these findings could also be used in a regional Decision Support System for fishery management with integrating with other elements of fisheries management regime.

Rhithrops capensis gen. et sp. nov., a new aquatic dryopid beetle from the Western Cape of South Africa (Coleoptera: Dryopoidea: Dryopidae)

Rhithrops capensis gen. et sp. nov. is described from the Matjies River, in the Cedeberg range of the Western Cape Province, South Africa. The new genus is apparently related to the South African endemic genera Rapnus Grouvelle, 1899 and Strina Redtenbacher, 1867, but exhibits a number of distinct character states, including gibbosities outside the sublateral pronotal furrows and a transversely upturned labral apex, unique within the family. Rhithrops gen. nov. was collected from around the roots of aquatic plants in fast flowing deep water runs, as well as being sampled in nocturnal drift nets. The new species has relatively long legs and well-developed tarsal claws, and appears to be adapted to an entirely aquatic, benthic existence. A revised key is provided to the dryopid genera of South Africa.

Which metrics drive macroinvertebrate drift in neotropical sky island streams?

Despite long-standing interest, the mechanisms driving aquatic macroinvertebrate drift in tropical streams remain poorly understood. Therefore, the objective of this study was to evaluate which environmental metrics drive macroinvertebrate drift in neotropical sky island streams. We evaluated whether altitude, the abundance of food resources, and variations in water quality influenced macroinvertebrate drift density, diversity, richness, and functional feeding groups. An hypothesis was developed to test whether increased altitude, lower food availability (particulate organic matter), and discharge would increase the density, taxonomic richness, and diversity of drifting invertebrates. Nine headwater stream sites were sampled in the rainy and dry seasons in the Espinhaço Meridional Mountain Range (EMMR) of southeast Brazil. Samples were collected using drift nets deployed from 5:00 p.m. to 8:00 p.m. The abundance of food resources was assessed through estimates of coarse (CPOM) and fine (FPOM) particulate organic matter, and primary producers. CPOM availability was an important explanatory variable for Gathering-Collectors and Scrapers, Altitude was important for Shredders and Predators, and Filtering-Collectors were linked to water discharge, suggesting that functional group drift masses were linked to different ecosystem components. Water temperature, conductivity, dissolved oxygen, current velocity, FPOM biomass and microbasin elevation range exerted little influence on macroinvertebrate drift. Regarding taxa composition, this study also found that Baetidae and Leptohyphidae (Ephemeroptera) and Chironomidae and Simuliidae (Diptera) were the most abundant groups drifting.

Efecto de la deforestación ribereña sobre la materia orgánica particulada gruesa en quebradas con influencia ganadera de la región Andina de Colombia

Introduction: Coarse particulate organic matter originated in riparian vegetation is the main source of energy in many headwater streams. However, the transfer of such material is altered by the destruction of forests. Objective: To assess flow differences of this organic matter in streams with forests and grasslands. Methods: We compared input, storage and export of this organic matter in the riparian belts of streams with forests, and streams with grasslands, in the central Andean region of Colombia. For each stream, we measured vertical and lateral litter with baskets; stream bed litter with a quadrant, and matter export with drift nets, in a 100 m reach. Results: The streams with riparian forest received an average of 915 g m-2 of coarse particulate organic matter annually, exported a total of 334 g m-3 and stored 732 g m-2, values that were significantly higher than in grassland streams, where the corresponding values were: 125.4 g m-2; 128 g m-3 and 205.5 g m-2. Conclusions: The removal of tree cover from the riparian zone reduced the organic matter in these headwater streams of Colombia.

Juvenile drift of an invasive crayfishFaxonius virilis(Hagen, 1870) (Decapoda: Astacidea: Cambaridae) in the middle Pecos River, New Mexico, USA

AbstractEcologists have long recognized that dispersal capabilities influence range expansion by nonnative species. Some of the most disruptive crayfish invaders are highly mobile as adults within and across watershed networks. In this study, we contribute a new facet to our understanding of crayfish early life history and invasions by documenting strong evidence of synchronized, behavioral downstream drift by early juveniles. During 2019, we observed a relatively dense springtime pulse of juvenile crayfish in drift nets set at two sites in the middle Pecos River near Fort Sumner, New Mexico. To determine whether this was an anomalous episode or an annual event, we sampled in 2020 and 2021 to: 1) determine the timing and extent of drifting behavior relative to environmental variation, and 2) identify the drifters to species level using DNA barcoding. Across three years, we collected juvenile crayfish (2.4–13.1 mm carapace length) after sunset during April through June in relatively clear water conditions (5–64 NTU) that coincided with minimum flows (41–152 cfs) and seasonally typical temperatures for this region (15–26 °C). To identify specimens to species level, we sequenced the barcoding region of the cytochrome c oxidase I (COI) DNA barcode for 35 juveniles and 6 adult male vouchers that represented all years. Based on morphological identifications of adult males and COI sequence comparisons to published reference specimens, nearly all drifting juveniles were identified as Virile Crayfish Faxonius virilis (Hagen, 1870). Drifters matched the sizes of second-molt juveniles newly released in the laboratory from two brooding females that we captured in the field. Faxonius virilis has been collected throughout the Rio Grande watershed, but not yet been reported in the Pecos River. As drifting early life stages are common across crustaceans, we suspect juvenile crayfish drift is probably not unique to F. virilis nor to our study system. We encourage others to perform targeted surveys of juvenile drift across a broad range of study systems, and to identify causal factors and ecological consequences of juvenile drift using controlled experiments.

Environmentally friendly microbeads to model the dispersal of particulates in aquatic systems

The transport of particulate matter including the gametes, larvae and propagules of reproducing organisms and other organic matter involved in nutrient/contaminant transport are important processes, yet there are few environmentally friendly methods available to examine dispersal empirically. Herein we report on the development and application of a biodegradable and non-toxic physical model, based on alginate microbeads with modifiable size, density (ρ), and colour for use in dispersal studies. Specifically, the microbeads were designed to model the size and ρ of parasitic juvenile freshwater mussels (Unionidae; ρ = 1200 kg m−3), which undergo dispersal upon excystment from fish hosts. We released the juvenile-mussel and neutrally buoyant microbeads (ρ = 1000 kg m−3) in a local river and captured them in drift nets downstream. The concentration of microbeads declined with downstream distance, but neutrally buoyant microbeads were transported farther. Analysis of microbead capture rates could be described using the patterns of several mathematical models (negative exponential, power, and turbulent transport), which were consistent with the reported dispersal of mussel larvae and other benthic macroinvertebrates. These results support the use of alginate microbeads in dispersal studies, because their environmentally friendly and customizable properties offer improvements over non-biodegradable alternatives.

Effect of Environmental Parameters on the Reproduction of the White Mullet (Mugil curema, Valenciennes, 1836) in the Saloum Delta (Senegal)

Mugil curema, known as white mullet, was one of the fish species encountered in the fisheries landings of the Saloum Delta. In this study, the morphometric parameters and the reproductive biology of this species were studied as well as the influence of environmental parameters on its reproduction. Experimental fisheries were carried out monthly in the Saloum Delta. The fish were caught using surface drift nets. The captured individuals were measured and weighed. The gonads were collected to determine the sex and the stages of sexual maturity. Out of a total of 406 individuals sampled in the Saloum Delta, 306 females and 100 males were identified, no individuals of undetermined sex were obtained. The sex ratio was globally in favor of females. Individuals in this study ranged in size from 102 to 385 mm and weight from 34.9 to 395 g. The allometric coefficient b was equal to 2.40 and indicated a negative allometry. The exploitation of the monthly IGS results indicated that reproduction was in April, May and June. The size at first sexual maturity indicated that the males matured at a size of 220 mm, lower than that of the females 226 mm.

Efektivitas Alat Tangkap Jaring Insang Hanyut pada Ikan Tongkol (Euthynnus sp.) diPerairan Seraya Timur, Bali

Tongkol fish (Euthynnus sp.) common types of fish resources found in the waters of Bali, especially Karangasem. Fishermen in Seraya Timur Village, Karangasem Regency, use drift gill nets to catch Tuna Fish. The use of drift gill nets is still very simple with the size of the mesh used that is also still diverse, but most use a mesh size of 2 and 2.5 inches. The use of drift gills by fishermen in the village of East Seraya is still very simple and the mesh nets used are also still diverse, but generally use mesh sizes of 2 and 2.5 inches. Therefore, it is necessary to know the level of effectiveness of each of the mesh sizes. The purpose of this study was to determine the amount of tuna fish catch using drift gill nets and the effectiveness of the two mesh sizes in the Seraya Timur waters. This study uses gill drift nets with 2 and 2.5 inch mesh sizes. The number of settings (decrease in net) and haulling (removal of the net) was carried out 22 times in March 2019. The results showed that the total number of catches with a 2 inch mesh size was relatively twice as high as the 2.5 inch mesh. It can be concluded that the net size of 2 inches has a smaller effectiveness compared to 2.5 inch mesh size.

Evaluating the effects of controlled flows on historical spawning site access, reproduction and recruitment of lake sturgeon Acipenser fulvescens

Lake sturgeon Acipenser fulvescens spawn at the base of Kakabeka Falls, a 39 m waterfall on the Kaministiquia River, a tributary to Lake Superior. Access to this historical spawning site can be restricted or delayed due to hydroelectric flow fluctuations that coincide with the A. fulvescens spawning season. The objectives of this study were to determine (a) the necessary flow conditions that facilitate spawning site access; (b) quantity and duration of flow required for successful spawning and dispersal of larvae; and (c) evaluate recruitment of juvenile A. fulvescens in relation to flow. A. fulvescens spawning migrations were tracked using a stationary telemetry receiver that logged the movements of 166 A. fulvescens fitted with radio-transmitters. Unrestricted access to the spawning site was facilitated when spawning flow was controlled at 23 m3 s-1 in 2004 and 17 m3 s-1 in 2006. Fluctuating (0.5-8.5 m3 s-1 ) and delayed spawning flows resulted in restricted and delayed access to the spawning site. Flow duration for successful egg incubation, hatch and larval dispersal was determined by sampling larvae using drift nets and quantified using cumulative temperature units (CTU). Over 10 years, 10,083 larvae were captured between 31 May and 20 July with 97% of the drift occurring prior to 30 June. From the date of first spawning to the end of larval dispersal took an average of 38.6 days, and the mean CTU value was 398.6. In general, a minimum flow of approximately 14.5 m3 s-1 from the date of initial spawning to the accumulation of c. 400 CTU ensured successful hatch and larval dispersal. During the timeframe of this study, recruitment was variable. This study described the complex and variable reproductive life history of A. fulvescens and defined spawning flow requirements ecologically, which can be used to develop operational provisions at hydropower facilities to ensure successful reproduction.

Wasted effort or promising approach – Does it make sense to build an engineered spawning ground for rheophilic fish in reservoir cascades?

Anthropogenic alterations such as the construction of dams and reservoirs led to a loss of quantity, quality and connectivity of habitats for riverine fish species. The resulting decline of freshwater fishes has prompted many restoration efforts addressing bottlenecks in their life cycles such as improving spawning habitat quality. Whilst there is a wealth of studies addressing the benefits and challenges of spawning ground restoration for rheophilic fishes in lotic ecosystems, there is a paucity of information on the usefulness of such measures in almost lentic systems. In this study, an engineered spawning ground with areas of different grain sizes, built as a mitigation measure for a hydropower plant construction in a near-stagnant reservoir cascade, was assessed including physical and chemical characterisation, spawning habitat use and recruitment of target species for conservation. During the six-week investigation period, about 4000 larvae and 18,000 eggs of mainly ubiquitous species such as roach (Rutilus rutilus, L.) and European perch (Perca fluviatilis, L.) were detected by drift netting and sampling of the gravel bed. The engineered spawning ground was successfully used for recruitment by the rheophilic gravel spawning cyprinids asp (Leuciscus aspius, L.) and ide (Leuciscus idus, L.). For all species, the highest density of eggs and larvae was found in the area with the highest current velocity directly at the turbine outlet. The findings of this study illustrate the potential of engineered spawning grounds for fish conservation even in heavily modified water bodies such as reservoir cascades. However, evidence of successful reproduction of rheophilic species on the spawning ground alone does not allow any predictions on further population development, since crucial prerequisites in the further ontogeny may pose additional bottlenecks.

Diel variation of aquatic insect drift in streams of Southern Brazil

Some organisms, such as aquatic insects, are transported from the upstream to downstream region of streams through a process called drift. This process occurs in passive and active ways and can be variable throughout the day, mainly between the nocturnal and diurnal periods. Here, we evaluate the periodicity of the drift of aquatic insects in two streams of the Middle Iguaçu basin, southern region of Brazil. We predicted that the drift of aquatic insects brings the highest richness, diversity and abundance during the nocturnal period, compared to the diurnal period. In addition, we expected that the composition of species is different between these periods. In each stream, aquatic insect sampling was carried out 10 times, for 24 hours, using drift nets. A total of 2,114 aquatic insect specimens were recorded, distributed in 26 families. Of these families, 20 were recorded during the diurnal period and 24 during the nocturnal period. Our results showed an increase in the diversity and abundance of aquatic insect drift in the nocturnal period. However, only abundance was significantly different between the periods. We attribute the higher abundance in nocturnal drift possibly to biological interactions. Thus, nocturnal drift can be a strategy of some aquatic insects to avoid visual predation by other invertebrates and/or vertebrates, in Neotropical streams. We highlight the importance of our study, because it can be used for comparison in surveys of lotic environments that have been impacted by human activity (e.g. by dam construction), which can alter the water flow, and consequently the pattern of insect drift.

Bigheaded Carp Spatial Reproductive Dynamics in Illinois and Wabash River Tributaries

AbstractFisheries managers are devoting considerable effort, time, and funding toward limiting the spread of invasive Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix (hereafter, “bigheaded carps”). A better understanding of factors that influence spatial patterns of bigheaded carp reproduction can help fisheries managers to prevent their spread. To examine factors that influence spatial patterns of reproduction, we sampled ichthyoplankton by using drift nets and push nets in three tributaries of the Illinois and Wabash rivers during March–September 2016–2018. We compared relative abundances of bigheaded carp eggs and larvae among tributaries by using CPUE. Abiotic data were analyzed from individual study tributaries and were pooled among tributaries with substantial versus minimal evidence of bigheaded carp reproduction. In total, 5,689 larval bigheaded carp were captured during three sampling seasons. Of the six study tributaries, we captured the most bigheaded carp larvae in the Sangamon River, followed by the Little Wabash, Embarras, Spoon, Mackinaw, and Vermilion rivers. Based on previous literature, we investigated differences in watershed area, discharge, water temperature, turbidity, and free‐flowing stretches of river in our study tributaries. In general, tributaries with greater relative abundances of bigheaded carp eggs and larvae had larger watersheds, greater discharge, lower Secchi depths (higher turbidity), and longer free‐flowing stretches than those with minimal evidence of reproduction. This study provides a thorough investigation of bigheaded carp reproduction in six large‐river tributaries and will help fisheries managers to better monitor and mediate the spread of these invaders by facilitating the prioritization of potential monitoring locations.

Comparison of Active and Passive Larval Sampling Gears in Monitoring Reproduction of Invasive Bigheaded Carps in Large‐River Tributaries

AbstractSilver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis, collectively known as bigheaded carps (BHC), are invasive fishes in the Mississippi River and surrounding basins. Increasing evidence suggests harmful impacts of BHC on native fisheries (e.g., competition). Monitoring the abundance of BHC is difficult with traditional fisheries gears, and few studies have evaluated early life stage sampling. Identifying the spawning locations of BHC through early life stage sampling has the ability to enhance management efforts by applying focus to areas that have potential to serve as population sources. We evaluated the performance of three gears in sampling larval BHC and native taxa within large‐river tributaries in terms of abundance, community assemblage, and size structure. We sampled ichthyoplankton in tributaries with active (push net) and passive (drift net, light trap) gears from March through September 2016. Relative abundance of BHC was greatest in push nets followed by drift nets and was lowest in light traps. Native cyprinids and catostomids as well as BHC comprised a large portion of the total catch. Environmental and habitat characteristics (stream velocity, dissolved oxygen, and temperature) related to BHC reproduction influenced each gear’s ability to capture larval BHC, although relationships in final models were not significant. Taxonomic size selectivity existed among gears; in particular, larger BHC were collected in push nets relative to the other gears. Push nets were the most effective in sampling BHC, and remaining gears exhibited unique strengths. Although less effective than active push nets, drift nets proved useful for monitoring BHC in tributaries and may be advantageous in shallow systems with adequate flow. Light traps were ineffective at capturing BHC larvae in tributaries but may offer utility in lentic habitats or for native cyprinids. Our comparison serves as a guide for monitoring larval BHC in their invaded range and for detection in new areas, such as tributaries of the Great Lakes.