Comparison of Day and Night Fyke Netting, Electrofishing and Snorkelling for Monitoring a Population of the Threatened Golden Galaxias (Galaxias auratus)

The littoral zone of small off-stream water storage containing a translocated population of Galaxias auratus was sampled fortnightly at day and night with fyke nets, electrofishing and snorkelling over 3 months. Variation in population data provided by each method, including relative abundance indices, size structure, and habitat preferences, were examined. Aspects of behaviour and activity patterns were also investigated. Night sampling using all methods consistently yielded larger catches than day sampling. The size structure of catches varied, with electrofishing at night and fyke netting during the day having higher proportions of juveniles, whilst snorkelling at night and electrofishing during the day had higher proportions of adults. Fyke netting at night yielded by far the largest catches (~3-fold more than other methods) and also captured balanced proportions of juveniles and adults. Galaxias auratus had a strong diel activity pattern and were most active at night. The majority of the population migrated into the littoral zone during the night and back into deeper water during the day. A small number of juveniles remained in the littoral zone and some adults sheltered in the dense cover of species-rich littoral vegetation during the day. Shores with shallow depth profiles appeared to be preferred due to higher catches in these areas using all methods. Based on the results of this study, fyke netting at night in littoral habitats is recommended for monitoring populations of G. auratus. Fyke netting is likely to be an effective method for monitoring other lacustrine galaxiid species; however, further work is required to investigate the effects of habitat variables and fish community structure on activity patterns of galaxiids, and hence their catchability with various methods, in more extensive lentic environments.     

Using new electrofishing technology to amp‐up fish sampling in estuarine habitats

A prototype, boat‐mounted electrofisher capable of operation in estuarine waters (where electrical conductivities often exceed 20 000 µS cm^?1) was assessed. Electrofishing was compared to fyke and mesh netting in four riverine estuaries and to seining in a lagoonal estuary (consisting of a series of brackish coastal lakes separated from the sea by a barrier system of sand dunes). Fish assemblage composition, length distributions and the probability of detecting ecological fish guilds (relating to estuary use, position in the water column and body size) were compared among gears. The assemblage composition of electrofishing samples differed from those of fyke nets in all riverine estuaries and from mesh netting in two. The assemblage composition of electrofishing samples differed from those of seining in structured seagrass habitats of the lagoonal estuary. When all species were pooled, the electrofisher sampled a broader range of lengths than either fyke or mesh netting in riverine estuaries or seining in lagoonal estuaries. The bias of electrofishing and netting towards particular species and size classes affected the probability of detecting some ecological guilds, highlighting the potential implications of gear choice on understanding estuarine ecological function. The detection of guilds varied with gear type and environmental conditions, including stratification, water depth and surface electrical conductivity. Assessments with the aim to characterize the structure of fish assemblages will benefit from the use of multiple gears. Electrofishing shows immense promise for discretely sampling highly structured habitats to test hypotheses about their use.     

Length‐weight relationships of three freshwater fish species from the Nandu River and Changhua River in Hainan Island,China

Length‐weight relationships (LRWs) were determined for three fish species from the Hainan Island, China. Fish specimens were sampled across the Nandu River and Changhua River from May 2017 to June 2018 with benthic fyke‐nets (stretched mesh size: 0.4 cm), multi‐mesh gillnets (stretched mesh size ranging from 1.0 to 12.5 cm) and electrofishing. Relationships between length and weight were fitted very well for all species (all R²>0.95). The b values of the LRW equations ranging from 2.938 for Liniparhomaloptera qiongzhongensis to 3.259 for Toxabramis houdemeri.     

Length–weight relationships of three fish species from Piediluco Lake,Italy

Length–weight relationships for Leucos aula, Scardinius hesperidicus, and Squalius squalus from the Piediluco Lake were provided. Data were collected by means of electrofishing, gill‐nets (mesh sizes varying from 5 to 55 mm) and fyke‐nets (mesh size 16 mm, total length 8 m, mouth width 1.5 m). The monitoring campaigns were carried out seasonally in the years 2004 and 2011, and in autumn 2012. A total of 5,198 specimens were analyzed. For all the species the value of b ranged between 3.163 for Leucos aula and 3.297 for S. hesperidicus. For L. aula a new maximum total length was also reported.     

Length–weight relationships for four species in the Dogxung Zangbo River,a main tributary of the Yarlung TsangpoRiver,Tibet, China

Length‐weight relationships (LWRs) for four species are presented, captured in the Dogxung Zangbo River, a main tributary of the Yarlung Tsangpo River, Tibet, China. Fish were captured in summer and autumn between May 2006 and September 2017 with three fyke nets from six sites.The results of LWRs for Schizothorax oconnori Lloyd, 1908, Schizopygopsis stoliczkai Steindachner, 1866, Triplophysa orientalis (Herzenstein, 1888), and Glyptosternon maculatum (Regan, 1905) provide basic data useful in fisheries science. They can assist in converting length data in to weight and biomass in cases where weight can not be taken during field studies. If regularly taken in an annual monitoring programm together with other parameters, using a standardized sampling procedure, they can also helpful in stock assessment of fish species in the Dogxung Zangbo River and the upper reaches of the Yarlung Tsangpo River basin.     

Comparison of nine different methods to assess fish communities in lentic flood‐plain habitats

This study compares the effectiveness and representativeness of electrofishing, snorkelling, seining, baited lift netting, multi‐mesh gillnetting, baited fish traps, fyke netting, angling and longline fishing, considering three typical lentic flood‐plain habitats at different times of day. Electrofishing was by far the most effective method yielding highest species richness, species trait representation and catch per unit of effort (CPUE), followed by seining. For single species like dace Leuciscus leuciscus, European ruffe Gymnocephalus cernua, common bream Abramis brama and silver bream Blicca bjoerkna, seining was more effective than electrofishing. With both methods, some species were more consistently caught during night, dusk or dawn than during daylight. All other methods tested cannot be generally recommended for fish community assessments in shallow backwaters due to their low representativeness of species inventory and generally low CPUE. Based on these results, electrofishing of 30 m transect replicates at different times of day for monitoring the fish community in shallow backwaters, can be recommended, enabling the maximum possible comparability to adjacent river habitats. Seining should be considered as an alternative if accessibility of habitats is restricted or electrofishing is prohibited. The 25 species detected in the backwaters also suggest that these habitats contribute a large proportion of fish diversity and should be included in standard assessments of river ecological status.     

Length‐weight relationships of nine fish species from the upper reach of the Gan River,a tributary of the Yangtze River in China

Length‐weight relationships (LWRs) are reported for nine fish species belonging to four families from the upper reach of the Gan River, one of the main tributaries of the Yangtze River, China. A total of 807 specimens were collected from April 2016 to July 2017. Fishes were both sampled using a backpack electrofishing unit and collected from local fish markets that using various fishing gears such as electrofishing boats, gillnets (mesh sizes: 1–12 cm), hooks, and benthic fyke nets (mesh sizes: 0.5 cm and 0.7 cm). The fish species were Siniperca undulata (Fang & Chong, 1932), Pseudogobio vaillanti (Sauvage, 1878), Sarcocheilichthys parvus (Nichols, 1930), Barbodes semifasciolatus (Günther, 1868), Spinibarbus hollandi (Oshima, 1919), Gobiobotia meridionalis (Chen & Cao, 1977), Pseudobagrus albomarginatus (Rendahl, 1928), Pseudogastromyzon changtingensis (Liang, 1942), and Pseudogastromyzon fangi (Nichols, 1931). The a values for the nine species varied between 0.0056 and 0.0366, the b values ranged from 2.333 to 3.318, and r² values from .952 to .994.     

Length‐weight relationships of three fish species from the Jatinga River (Barak drainage) in Assam,India

The present study reports the Length‐Weight relationships of three freshwater fish species, Amblyceps laticeps (McClelland, 1842), Danio dangila (Hamilton, 1822) and Lepidocephalichthys berdmorei (Blyth, 1860), based on monthly collections between November 2016 and October 2017. Fishes were collected from selected sampling sites along the Jatinga River (a tributary of the Barak River drainage) using cast nets (2.5 m; mesh size: 1.0–1.5 cm) and electrofishing device (Safari Surveyor, 12 V 7 amp). Estimated b values were 2.78 for A. laticeps, 3.19 for D. dangila and 2.92 for L. berdmorei respectively.     

Mortality induced by electrofishing and handling in five young‐of‐the‐year cyprinids: effect of the fish size,species and anode size

Immediate mortality induced by electrofishing and handling of young‐of the‐year (YOY) fish of five cyprinid species (bitterling Rhodeus amarus, chub Leuciscus cephalus, bleak Alburnus alburnus, barbel Barbus barbus, roach Rutilus rutilus) was quantified during routine YOY fish monitoring (point abundance sampling with backpack electrofisher, in situ identification and measurement). Sampled, identified and measured fish were held in screened containers immersed in the river for 5 h after electrofishing. Bleak exhibited significantly higher mortality (17%) than all other species (1–3%). Mortality decreased significantly with fish length; fish <35 mm exhibited the highest mortality. Anode size (10, 20, and 30 cm diameter) had no direct effect on mortality. Point abundance electrofishing with in situ identification and measurement is a safe method for sampling riverine YOY cyprinids.     

Length–weight relationships for 15 fish species from the Three Gorges Reservoir

The length–weight relationships (LWRs) for 15 fish species from the Three Gorges Reservoir (TGR) were described in this paper. Specimens were collected using gill nets (mesh size: 6, 8, 10, 12 cm), cage net (mesh size: 1 cm), benthic fyke net (mesh size: 1 cm), hook longlines (80 m long, 3 barbless hooks per meter line) and electrofishing (power: 1,500 w; distance of electrodes: 1–2 m; water depth: 0.2–1.0 m; water area: 1–2 m²; catch by dip net [mesh size: 0.4 cm]) at four sections of the TGR, monthly in June–August and October–November in 2017 and 2018. The first LWR reference for Zacco acutipinnis (Bleeker, 1871), Discogobio brachyphysallidos Huang, 1989, Squalidus nitens (Günther, 1873), Leptobotia pellegrini Fang, 1936, Sinibotia reevesae (Chang, 1944), Pseudobagrus tenuifurcatus (Nichols, 1931), Pseudobagrus medianalis (Regan, 1904), Liobagrus marginatoides (Wu, 1930), Glyptothorax fokiensis (Rendahl, 1925), and Ctenogobius szechuanensis (Liu, 1940) and new maximum total length for 12 species are provided.     

Length–weight relationships of three montane fish species from upper Chang River,a tributary of the Poyang Lake,China

Length–weight relationships were estimated for three montane fish species Acrossocheilus fasciatus (Steindachner, 1892), Sarcocheilichthys parvus (Nichols, 1930) and Vanmanenia stenosoma (Boulenger, 1901) from upper Chang River, a main tributary of the Poyang Lake, China. Fish specimens were collected using benthic fyke nets (0.4 × 0.4 × 15 m; mouth opening: 10 × 10 cm; mesh size: 0.5 cm) and electrofishing equipment (12 V) from September 2017 to July 2018 seasonally. New maximum total lengths were recorded for S. parvus and V. stenosoma.     

Effects of sampling techniques on population assessment of invasive round goby Neogobius melanostomus

In this study, a comparison of point abundance sampling (PAS) electrofishing, angling with two different hook sizes and trap‐based fishing was performed in a non‐wadeable river to analyse their effects on catch per unit effort (CPUE) and population characteristics of invasive round goby Neogobius melanostomus. PAS electrofishing was identified as the most effective (mean ± s.e . CPUE = 57 ± 4 N. melanostomus min^?1) and least selective method in terms of size, feeding status and species composition. Angling had the second highest CPUE, but was more size selective and resulted in a higher proportion of males compared to electrofishing [overall sex ratio angling (female:male) = 1:0·92, electrofishing 1:0·65]. Owing to low CPUE (0·012 ± 0·004) and low frequency of occurrence, minnow traps were least suitable for N. melanostomus population assessment. The results of this study suggest that a higher degree of standardization and inter‐calibration is useful to achieve better comparability of population data of invasive N. melanostomus and other benthic fish species.     

Biological attributes of age-0 lake sturgeon in the lower Peshtigo River, Wisconsin

Lake sturgeon Acipenser fulvescens are imperiled throughout the Laurentian Great Lakes basin. Efforts to restore this species to former population levels have been ineffective due in part to limited information regarding its early life history. The objectives of this study were to characterize the larval drift and biological attributes of age‐0 lake sturgeon in the lower Peshtigo River, Wisconsin. Lake sturgeon larvae were captured from May to June 2002 and 2003 using drift nets, while age‐0 juveniles were captured from June through October 2002 and 2003 using wading, snorkeling, backpack electrofishing, and haul‐seine surveys. Larval drift occurred within 14 days of adult spawning and extended from 1 to 3 weeks in duration, with two peaks in the number of fish drifting downstream each year. Larvae had a median total length (TL) of 19 mm (range: 13–23; N = 159) in 2002 and 18 mm (range: 13–24; N = 652) in 2003. Catch‐per‐unit‐effort for larvae was 0.18 fish h^?1 m² and 0.94 fish h^?1 m² in 2002 and 2003, respectively. Age‐0 juvenile lake sturgeon exhibited rapid growth (i.e. 2.57 mm day^?1 in TL and 0.66 g day^?1 in wet weight) throughout summer and fall months; relative condition of fish in both years was approximately 100, indicating good condition. Absolute abundance of age‐0 juveniles in 2003 was estimated at 261 fish using the Schnabel estimator. The results from this study indicate that the lower Peshtigo River contains important nursery habitats suitable for age‐0 lake sturgeon.     

Evidence for selective angling of introduced trout and their hybrids in a stocked brown trout population

Comparisons of the genetic composition of brown trout Salmo trutta captured by anglers and by electrofishing based on three diagnostic microsatellite loci provided strong evidence that angling is selective in a stocked brown trout population. At two sites, anglers caught significantly younger trout and proportionally more introduced hatchery trout and hybrids than were observed in electrofishing surveys. Selective angling, in combination with a small legal catch size, may have considerably eliminated introduced trout and hybrids before spawning at the study sites, and thus may have reduced the introgression of alien genes into the local gene pool. Angling can be an important factor influencing the genetic structure of fish populations and should be taken into account in studies of introgressive hybridization in stocked fish populations and their management. In this study, demographic consequences of stocking were not assessed. Thus, even though the genetic consequences of stocking may be minimal or largely reversible through angling, resource competition between native and introduced trout, until they reach legal catch size, is expected to have a negative effect on the productivity of the indigenous trout population.     

Length–weight relationships of seven fish species from Guijiang River in Guangxi Region,China

Length–weight relationships (LWRs) were estimated for seven fish species from Guijiang River in Guangxi region, China. Fish samples were collected by electrofishing (CWB-2000P, China; 12 V import, 250 V export) and gill nets (length 12 m, height 0.8 m, mesh 10 mm) in January, April, July and October, 2015. The electrofishing was conducted about 2 km long within 2 hr, and ten gill nets were settled over night at each sampling site. All fish were identified and measured in the field immediately. All values for the allometric coefficient (b) of the length–weight equations were within the expected range (2.50–3.50). All values for the coefficient of determination (r²) were above .95 and thus the estimates can be considered reliable.     

Types and extent of fishing gear losses and their causes in the artisanal fisheries of Istanbul,Turkey

Fishing gear losses remain a serious problem for marine life; these losses are also the source of an invisible fishing mortality. This study is an analysis of this problem within the artisanal fisheries of Istanbul. From September 2009 through May 2010, face‐to‐face interviews were conducted in 27 fishing ports for a total of 282 questionnaires. Estimates of lost fishing gear were 229.48 km of set nets, 2700 m of longlines, and 14 fish traps. Turbot nets had the highest loss ratio (54.73%), followed by bonito nets (16%), red mullet nets (7.36%), and encircling trammel nets (4.83%). The four major causes of net loss were: conflicts with other gear types (trawl and purse seine), conflicts with cargo vessels, bottom structure hindrances, and bad weather conditions. Bottom structures were the single factor in net losses for longlines and fish traps. The study observed that large quantities of nets had been lost, and that each net type showed a positive relationship between the number of nets used and the number of nets lost. Separate zones for artisanal and industrial fisheries are recommended as a realistic approach to reduce the losses of fishing gear and the impact of ‘ghost fishing’.     

Re‐building brown trout populations in dredged boreal forest streams: in‐stream restoration combined with stocking of young trout

1. Rivers in boreal forested areas were often dredged to facilitate the transport of timber resulting in channels with simplified bed structure and flow fields and reduced habitat suitability for stream organisms, especially lotic fishes. Currently, many streams are being restored to improve their physical habitat, by replacing boulders and gravel and removing constraining embankments. The most compelling justification behind stream restoration of former floatways has been the enhancement of native fish populations, specifically salmonids. 2. We examined the success of a stream management programme aimed at re‐building diminished brown trout (Salmo trutta) populations by monitoring densities of young‐of‐year and older trout in 18 managed and three reference streams during 2000–2005. Rehabilitation included in‐stream restoration combined with a 5‐year post‐restoration period of stocking young brown trout. Our space‐for‐time substitution design comprised four pre‐management, four under‐management, 10 post‐management and three reference streams. 3. Densities of young‐of‐year brown trout, indicating population establishment, were significantly higher in post‐ compared with pre‐management streams. However, density of young‐of‐year brown trout in post‐management streams was significantly lower compared with near‐pristine reference streams. Furthermore, success of managed brown trout population re‐building varied, indicating stream‐specific responses to management measures. Density of burbot (Lota lota), a native generalist predator, was associated with low recruitment of brown trout. 4. Stream‐specific responses imply that rehabilitation of brown trout populations cannot be precisely predicted thereby limiting application. Our findings support the importance of adaptive stream restoration and management, with focus on identifying factor(s) limiting the establishment of target fish populations.     

Length–weight relationships for 35 fish species of the Atlantic Forest,SP/RJ—Brazil

Length–weight relationships (LWRs) for 35 freshwater fish species from the SP/RJ coastal basin in Brazil are presented in this paper. Fishes were captured between 2011 and 2015 on an irregular basis using electrofishing, sieves, trawl nets, cast nets and fish‐traps. In this study new LWRs are reported for 28 species, plus the total weight and length for 34 and nine species, respectively. The study provides new information on less‐studied species and can serve as a basis for management and conservation in this area.     

Induction of gonadal maturation at different temperatures in burbot Lota lota

A rearing experiment was conducted to test whether temperature protocols that differed from a simulation of natural conditions might induce maturation after isothermal grow‐out in burbot Lota lota. Lota lota were acclimated to two different temperature regimes: low temperature (LT), close to natural temperature at 4·0° C and elevated, high temperature (HT) at 8·5° C over 40 and 27 days respectively, with all fish then wintered for 47 days. Every second fish was treated with a gonadotropin‐releasing hormone analogue. Maturational competence of oocytes was assessed with a germinal vesicle breakdown assay using a novel staining strategy. In both treatments, puberty and maturational progress occurred, characterised by an elevated gonado‐somatic index and advanced gonadal stages (histological analysis). Progress of gonadal maturation was reflected by elevated plasma concentrations of testosterone and 11‐ketosterone in males and 17β‐oestradiol in females. Ovulation was not observed. Sperm could be activated equally across treatments. In general, LT was more effective than HT treatment, indicated by advanced gonadal stages, higher numbers of oocytes undergoing germinal vesicle breakdown in vitro and elevated sex steroid levels. Hormone treatment could improve effectiveness at HT. In conclusion, less drastic temperature regimes as previously reported in combination with hormone treatments seem sufficient to induce maturation in L. lota after isothermal grow‐out.     

The sampling efficiency of electrofishing for Neogobius species in a riprap habitat: a field experiment

Even though electrofishing is commonly used to sample Neogobius spp. and other swimbladder‐lacking benthic fishes, its efficiency is considered poor especially in habitats with abundant interstitial spaces. To determine the efficiency of electrofishing Neogobius spp. and quantitatively estimate sampling bias in a riprap (shot rock used to armor shorelines against water erosion) mesohabitat, riprap fragments were set up in a natural riverine environment. The experimental setting enabled us to collect all fish remaining in the riprap fragments after these areas had been electrofished. The sampling efficiency of electrofishing Neogobius spp. (dominated by Neogobius melanostomus) varied between 17.6 and 47.4% (mean 29.7%), while percids (possessing a well‐developed swim bladder) were collected with 74.6% efficiency. Fish size had no effect on the probability of capturing Neogobius spp. by electrofishing. Within Neogobius spp., N. melanostomus was less susceptible to electrofishing than Neogobius gymnotrachelus (23.7% and 50.1%, respectively). Decreased electrofishing efficiency in areas of rocky substrate should be considered in estimates of total abundance of Neogobius spp., especially if they are to be compared with catches of other species possessing swim bladders.