Vertical Gill Nets Research Articles

Seasonal habitat use of yellow perch Perca flavescens in a north‐temperate lake

AbstractKnowledge of species‐specific fish biology, ecology, and habitat use is critical for informing science‐based management. Yellow perch Perca flavescens are an ecologically and recreationally important fish species. Yet, for many north‐temperate systems (e.g. inland lakes of Wisconsin), little is known about yellow perch seasonal habitat use and ecology. We characterised yellow perch seasonal spatial distribution, size–structure, and condition between littoral and pelagic habitats in Crystal Lake (Vilas Co., WI) during the open water period of 2021. Seasonal spatial distribution and population size–structure were characterised by contemporaneous sampling in littoral and pelagic habitats using mini‐fyke nets and vertical gill nets, respectively. Relative abundance estimates for yellow perch in the littoral zone were greatest during early spring and declined throughout the open water season. Yellow perch pelagic relative abundance estimates were lowest in spring, peaked at the onset of stratification, and then declined and remained relatively consistent throughout the open water season. In general, yellow perch population size–structure and condition were greatest in the pelagic zone. Our findings suggest that after spring spawning, larger yellow perch prefer/select pelagic habitats, while sub‐adults and juveniles prefer/select littoral habitats, potentially resulting from increased predator refugia and(or) resource availability. Our results emphasise the importance of evaluating gear and fishery assessment bias, particularly when the target species may use a range of habitat types within a system.

Status and Distribution of Cisco (Coregonus artedi) and Lake Whitefish (Coregonus clupeaformis) in Inland Lakes of Wisconsin

Coregonus artedi (Cisco) and Coregonus clupeaformis (Lake Whitefish) are coldwater fishes native to some inland lakes in Wisconsin. We conducted a statewide assessment of Cisco and Lake Whitefish status using experimental-mesh vertical gillnets during the summers of 2011–2014. Cisco and Lake Whitefish relative abundances varied from 0 to 137 and 0 to 3 fish/net night, respectively. About 29% of the Cisco and 33% of the Lake Whitefish populations were potentially extirpated from inland lakes in Wisconsin; most potential extirpations were from southern Wisconsin, but extirpations occurred statewide. Invasive species, climate change, land-use change, and excess nutrient loading may have contributed to causing extirpations of Cisco and Lake Whitefish. Conservation of remaining populations of Cisco and Lake Whitefish will require efforts to minimize these perturbations.

Morphological Variation of Cisco across Gradients of Lake Productivity

AbstractThe effects of lake productivity and late‐summer hypolimnetic oxygen on the size and shape of Cisco Coregonus artedi were examined in 27 Minnesota lakes. Geometric morphometry analyses of specimens captured in vertical gill nets indicated that Cisco in more productive lakes with hypoxic hypolimnia were larger, with deeper bodies, shorter snouts and caudal peduncles, and longer fins. Cisco in unproductive lakes with oxygenated hypolimnia were smaller, with slender bodies, longer snouts and caudal peduncles, and shorter fins. The effect of hypolimnetic oxygen on depths utilized by Cisco and the resulting vulnerability to predation was an important driver of shape and fin length. Deeper body depths and longer fin lengths were possibly a response to greater vulnerability to predation when hypoxic hypolimnia limit coldwater refugia for Cisco, which are forced to inhabit shallower depths near warmwater predators such as Walleye Sander vitreus and Northern Pike Esox lucius. Differences in size and shape relationships of Cisco in lakes on and off the Canadian Shield were also detected. The availability of late‐summer habitat, depth‐mediated predation risk, and growth potential appear to be important ecological drivers of morphological variation in Cisco.

Size‐Dependent Retention of Pelagic‐Oriented Kokanee in Multimesh Gill Nets

AbstractRecent studies evaluating the size selectivity of standard, horizontal, benthic gill nets for some common sport fish have demonstrated congruence across regions and gear configurations. Studies evaluating retention in gill nets designed to sample pelagic‐oriented fish (e.g., vertical and curtain nets) are rare, which has limited corresponding assessments of generality. This study estimated the retention of kokanee Oncorhynchus nerka (lacustrine Sockeye Salmon) in multimesh vertical gill nets using catch data compiled over three decades from a large montane reservoir in Colorado. The corresponding best‐fit retention model was compared with that developed for kokanee in Idaho using multimesh curtain nets. There was strong congruence (Pearson's r = 0.98) between the total retention values (integrated over all mesh sizes) estimated by the two models for kokanee 50–430 mm total length, and the values followed a 1:1 relationship. This result indicated that the retention of fish in pelagic gill nets may also be largely conserved across regions and gear configurations. Thus, the retention models for kokanee compared in this study should be flexible and broadly applicable. These properties enable practitioners to easily adjust length‐frequency distributions for bias arising from size‐dependent retention when minimally biased estimates of size structure are needed for addressing management or research questions.

Vertical distribution of alewife in the Lake Ontario offshore: Implications for resource use

Oligotrophication of Lake Ontario has led to increased water clarity and an increased proportion of zooplankton residing in the metalimnion during the day, which may affect the utilization of different depth regions for planktivorous fish. We investigated day and night distributions of fish using hydroacoustics and suspended vertical gillnets during the summer of 2013 when a deep chlorophyll layer (DCL) was established. We related fish distributions to concurrent measures of temperature and prey (zooplankton) density. Alewife dominated in vertical gill net catches, indicating that most acoustic targets were alewife. Alewife schooled during the day in the bottom of the mixed layer, and at dusk alewife schools broke up and fish moved towards the surface. We hypothesize this movement followed migrating zooplankton to allow feeding at night; alewife sampled from vertical gillnets fed on cyclopoid copepods and cladocerans, prey groups that migrate into the epilimnion at night. Some alewife remained at the bottom of the mixed layer at night and these fish ate deep-water calanoid copepods such as Limnocalanus. Vertical distributions were best predicted by temperature and the interaction between temperature and zooplankton density. We include uplooking acoustics data to complement our downlooking datasets, which provided evidence for potential bias in downlooking acoustic assessments of alewife due to high proportions of alewife found in the surface exclusion zone. Our approach combining several datasets provides a new perspective to understand summer diel distribution of alewife and the factors driving their distribution.

Use of Gill Nets for Target Verification of a Hydroacoustic Fisheries Survey and Comparison with Kokanee Spawner Escapement Estimates from a Tributary Trap

AbstractThe focus of this study was to determine whether gill nets are a valid method for assessing species composition for a hydroacoustic survey and whether the hydroacoustic and gill‐net survey could be used to forecast the spawn escapement of kokanee Oncorhynchus nerka so as to allow fisheries managers to plan ahead for egg takes at Sullivan Lake, Washington. We conducted a mobile hydroacoustic survey of the limnetic zone of Sullivan Lake in September 2003. Species composition was estimated using floating, sinking, and suspended horizontal and vertical gill nets. Spawning escapement was estimated from a weir, trapping, and carcass recovery effort in Harvey Creek, the only spawning tributary of Sullivan Lake. Fish captured in gill nets ranged from 110 to 579 mm total length (TL), but 82% of the fish captured were between 150 and 290 mm TL. Kokanee were the dominant fish species captured in the limnetic gill nets, comprising 77% of the fish captured between 150 and 290 mm TL and 90% of the fish captured between 240 and 290 mm TL. We derived four alternative estimates of age‐3 kokanee abundance to account for the uncertainty in estimating the target strength of individual fish and the percentage of kokanee from the gill‐net catch. The acoustic and gill‐net abundance estimates that did not take into account the uncertainty in estimating kokanee length from target strength were relatively consistent (1–16%) with the Harvey Creek spawning escapement estimate (11,923). When abundance estimates were expanded by the average SE (25 mm) of individually tracked fish targets, the correspondence with the tributary spawn escapement was not as good (110–148%). This study showed that gill nets could be an effective means of verifying the acoustic targets of larger fish (>150 mm) and were adequate for forecasting spawn escapement for management purposes in our situation.

Habitat and food resource use of perch and roach in a deep mesotrophic reservoir: enough space to avoid competition?

Abstract – The aim of this study was to test assumptions about the interaction of perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.) concerning their food and habitat use in a deep and mesotrophic reservoir. From 1998 to 2001 the fish were caught with gillnets to perform diet analyses. Additionally, vertical gillnets were set to study vertical spatial distribution of both species. The results indicate that in a large and deep reservoir perch and roach are able to avoid competition by separating their niches first in the spatial dimension and then in the dimension of food utilisation. These separations result in low inter‐ and intraspecific competition of both species. We conclude that these niche separations can widen the juvenile competitive bottleneck to such an extent that the perch are not forced to compete with their older conspecifics during their first year of life, enabling perch to become large and consequently piscivorous.

Food-web manipulation of drinking water reservoirs with salmonids: vertical distribution of prey and predator

In a novel biomanipulation experiment salmonids were used as a tool to improve water quality. The manipulation was initiated in spring 2000 as a response to non-point sources of phosphorus in a drinking water reservoir in Saxony, Germany. Salmonids (brown trout, Salmo trutta forma lacustris) were chosen as predators as the reservoir has a large hypolimnic water body and surface temperatures rarely exceed 20 °C. The vertical distributions of prey fish and brown trout were analysed with a fleet of vertical gill nets set in the pelagic zone of the reservoir. Consumption of brown trout was estimated by means of a bioenergetic model and the diet analyses of the trout. While the dominant planktivore (roach, Rutilus rutilus) was caught almost exclusively in the epilimnion during the stratification period trout were caught mainly below a depth of 10 m. Diet analysis revealed that the trout performed vertical migrations to consume food in the epilimnic layer, as an important food component were adult terrestrial and aquatic insects. The amount of fish in the food increased strongly with the size of the brown trout. The consumption estimate suggested that the trout had consumed 2–3% of the total roach stock during the study period (May–November 2000) of the first year of biomanipulation. We conclude that in general salmonids are suitable for food-web manipulation in deep reservoirs, but the stocked fish should be as large as possible (> 300 mm) and the proportion of large trout (> 500 mm) should be as high as possible.

Impact of hypolimnetic oxygenation on the vertical distribution of cisco (Coregonus artedi) in Amisk Lake, Alberta

Using hydroacoustics and vertical gill nets, we evaluated the efficacy of hypolimnetic oxygenation as a lake management tool by quantifying summer vertical distributions of cisco (Coregonus artedi) in a treated and untreated basin of Amisk Lake, Alberta, during and after oxygenation (1988-1993) and in untreated Baptiste Lake, Alberta. In Baptiste Lake, the hypolimnion remained anoxic and cisco were restricted to epilimnetic waters. Oxygenation increased hypolimnetic dissolved oxygen (DO) concentrations in Amisk Lake, expanding habitat by up to 9 m. During oxygenation, hypolimnetic DO remained above concentrations avoided by cisco (<1.3 mg ·L-1) in the treated basin, but fell below this level by midsummer in the reference basin. Consequently, cisco were distributed up to 8 m deeper in the treated than in the reference basin. In August 1990, a metalimnetic oxygen minimum in the reference basin confined >70% of the cisco to the epilimnion, while >60% of the fish inhabited the metalimnion and hypolimnion in the treated basin. Although DO remained above avoidance concentrations throughout most of the treated basin, the highest densities of cisco occurred in water with mean ( ± SD) DO concentration and temperature of 3.1 ± 1.3 mg ·L-1 and 11.8 ± 2.1oC, respectively. Thus, the extent of habitat expansion for fish during oxygenation programs will also depend on the availability of suitable temperatures.

Evaluation of Gill-Net Sampling for Estimating Abundance and Length Frequency of Reservoir Shad Populations

Horizontal and vertical gill nets were used to intensively sample gizzard shad Dorosoma cepedianam and threadfin shad D. petenense in Lake Texoma, Texas–Oklahoma, in August 1991. We evaluated spatial patterns, sampling precision, mesh-size selectivity, and sample sizes required to detect differences in shad abundance. Abundance patterns differed among species, length-groups, and sampling sites. Age-0 shad occurred mainly near the surface, whereas older fish were more evenly distributed over depth. Spatial variation in abundance was more pronounced among embayments than between nearshore and offshore sites within embayments. Spatial aggregation of shad was similar to that reported for a variety of other aquatic organisms, suggesting that experimental designs for gill-net surveys should incorporate statistical approaches similar to those used in other sampling programs. With horizontal gill nets, investigators can estimate median catch rate (number per net) within 25% of the true median with 95% certainty by using 37 or fewer nets, provided that the variance of the log10-transformed catch data is 0.09 (the median observed variance) or less. At the maximum observed variance (0.55), 4–20 gill nets would be required for a t-test to detect a twofold difference between two independent density estimates at ∝ = 0.05 and power (1 – β) = 0.95. Catch data in vertical gill nets produced less precise abundance estimates, and length frequencies of shad collected in the same mesh sizes differed between horizontal and vertical nets. Estimates of mesh-size retention probabilities, based on relations between shad girth and net mesh perimeter, were used to determine mesh sizes needed for efficient sampling of a wide range of sizes of both shad species. Mesh sizes recommended for sampling shad (55–380 mm) collected at Lake Texoma ranged from 8- to 51-mm-bar measure.

Precision and Size Structure of Juvenile Percichthyid Samples Collected with Various Gears from Lake Texoma

Abstract We collected juvenile striped bass Morone saxatilis and white bass M. chrysops with various gears to evaluate size selectivity and the precision of mean catch per unit effort (CPUE). We used four types of trawls, horizontal and vertical gill nets, conventional electrofishing and electrofishing with a push net, cove rotenone, and bag seine. Trawling was ineffective for sampling juvenile striped bass (<30 cm total length) and white bass (<15 cm). Striped bass CPUE data were most precise for offshore and nearshore floating gill nets, and least precise for push-net electrofishing. Floating gill nets also provided relatively precise CPUE estimates for white bass. There were substantial differences in the size of fishes collected by the gears, with gill nets collecting the largest juveniles.

Temporal distribution of perch (Perca fluviatilis L.) in a lake-reservoir (Moselle, France): analysis of catches with vertical gill nets

Temporal distribution of perch (Perca fluviatilis L.) in a lake-reservoir (Moselle, France): analysis of catches with vertical gill nets

Gillnet catches as an estimate of fish abundance: a comparison between vertical gillnet catches and hydroacoustic abundances of Baltic Sea herring (Clupea harengus) and sprat (Sptattus sptattus)

We compared the catches in a series of six vertical gill nets (6.25- to 18.75-mm bar mesh) with estimates of fish abundance derived from hydroacoustics. A total of 47 combined acoustic and gillnet surveys were collected between July and November 1987–1992 in archipelago areas of the northern Baltic Sea. Fish abundance determined by hydroacoustics was significantly correlated with gillnet catches but explained only 28% of the variance in catch per unit effort corrected for gillnet selectivity and fish swimming speed. Visibility (measured as Secchi disk depth) significantly decreased the likelihood of fish being caught in gill nets, while the effect of temperature was positive but nonsignificant. These data imply that gillnet catches will be a biased indicator of changes in fish abundance over time or space, if visibility and possibly also temperature change as well.

A Bioenergetics Analysis of Diel Vertical Migration by Kokanee Salmon, Oncorhynchus nerka

Diel vertical migration of fishes is probably a result of the combined effects of several selective forces, including predator avoidance, foraging efficiency, and bioenergetic efficiency. We considered both foraging efficiency and energetic efficiency as a combined effect which we called growth maximization. The importance of growth maximization as a selective force was evaluated with a bioenergetics-based model to estimate growth rates of various migration scenarios of kokanee salmon, Oncorhynchus nerka. Environmental parameters (temperature and zooplankton distributions) in the model were obtained from a North Carolina reservoir with an established population of kokanee. The simulations demonstrated that vertical migrations can be energetically advantageous when kokanee and their prey are thermally segregated and that ontogenetic and seasonal differences in the optimal migration strategy should be expected. The general rule for vertical migration as determined from the simulations is to feed where net energy intake is maximized and then reside when not feeding where energetic costs are minimized and food is digested to the point that consumption during the next feeding period is not limited by the amount of undigested food remaining in the stomach. Data obtained from vertical gill nets and hydroacoustics were compared with model predictions.

Notes: Vertical Distribution of Adult American Shad in the Connecticut River

Abstract Adult American shad Alosa sapidissima were sampled with vertical gill nets during the 1986 and 1987 spawning and postspawning migrations in the Connecticut River. Most (83%) were caught in the lower half of the water column, but not on the river bottom. The vertical distributions of gravid and spent fish were similar for both males and females. American shad showed no diel, seasonal, or yearly changes in depth distributions. Larger gravid fish swam deeper in the water column than did smaller gravid fish.

Management Brief: A Quickly Deployed Vertical Gill-Net System

Abstract We describe a vertical gill-net system that can be easily and quickly deployed in rough water. Previously described vertical gill nets are retrieved with floating rollers that work poorly when large waves and swells move the net and where surface rollers may interfere with boat traffic. Our system uses a flotation pipe to keep the top of the net at any desired depth while the bottom of the net lies on the substrate. We have consistently retrieved 12 nets and set an additional 12 nets within 45 min on both Lake Erie and an Ohio reservoir. Improved portability allows fish processing to occur on shore.

Resource Partitioning in Summer by Salmonids in South-Central Lake Ontario

Abstract During the summers of 1981 and 1982, we studied resource partitioning by stocked lake trout Salvelinus namaycush, brown trout Salmo trutta, and chinook salmon Oncorhynchus tshawytscha by fishing vertical gill nets at six distances from shore in south-central Lake Ontario. The nets were set at depths of approximately 15–45 m (nearshore stations, <4 km offshore) and more than 55 m (offshore stations, 4–24 km offshore). Salmonids were concentrated near shore, where they partitioned available habitat and, thus, food resources. Horizontal habitat was partitioned with respect to distance from shore; vertical habitat was partitioned in relation to temperature and the thermocline. Salmonids foraged for the most available prey items within their habitat. Overlaps in both food use and horizontal habitat use were inversely related to overlap in use of vertical habitat. There was increased habitat separation between sexes for those species caught farther from shore, At the salmonid stocking and prey density ...

A simple vertical gill net system for variable current conditions

A new technique for suspending vertical gill nets is described. The system is designed to minimize the effects of currents, which otherwise could lift the lead line off the bottom or pull the floating line down. For more than two years, 30 m deep gill nets have been used in a Baltic Sea coastal region and have been found to work well in current, wave and wind conditions characteristic of this area. Setting a net takes about 5 minutes and retrieving it 10 minutes, even under relatively windy conditions (10–15 ms−1). No special equipment is required to set or to haul a net, and we have used a variety of boats, from a small rowing boat to a 16 m long research vessel. The total material cost per net is about US $100.

The influence of submerged pulpwood on feeding and condition of fishes in a reservoir

One hundred and forty years of log driving in the Kennebec River, Maine, left an estimated one to two million cords of submerged pulpwood logs, with major accumulations in reservoirs such as Wyman lake. Commercial salvaging of these logs began in 1978, which prompted a study to assess the importance of these logs to fishes and the potential effects of log salvaging. Vertical gill nets were set in Wyman Lake, in areas with and without logs, to measure fish densities and to obtain specimens for analysis of food habits and body conditions. Yellow perch (Perca flavescens) were more abundant in sites without logs (P < .05), but suckers (Catostomus spp.) were more abundant in sites with logs (P < 0.05). Yellow perch preyed primarily on cladocerans in sites without logs and on larger invertebrates in sites with logs, implying a difference in prey availability between study sites. Although the yellow perch and common shiners captured in non-log areas were longer than those in log areas (P < 0.05), their body conditions were not significantly different. Moderate log salvage operations would probably have little effect on the body conditions and abundances of fishes in Wyman Lake, if precautions were taken to avoid disruption of spawning and nursery areas at critical times of the year; impacts would vary in other lakes with differing topography and species compositions.

Density and Size Estimates of Cisco (Coregonus artedii) Using Analysis of Echo Peak PDF from a Single-Transducer Sonar

We estimated size and density of fish in three Wisconsin lakes from echo peak probability density functions (PDFs) obtained at night with a single-transducer 70-kHz echosounder. At night, cisco (Coregonus artedii) dominated the pelagic zone in all three lakes. The beam pattern effect was removed with a deconvolving filter technique. Fish size was estimated by fitting a combination of Rice PDFs to the deconvolved fish scattering PDF. Vertical density profiles and size estimates obtained acoustically corresponded to distributions and lengths of fish caught in vertical gill nets. The proportion of different size classes caught in gill nets agreed fairly well with the proportions determined acoustically. This analysis can be applied to signals from noncalibrated sonars and can be used to calibrate simultaneously obtained echo squared integration values. With calibrated sonars, target strength can be estimated in situ. For Cisco, TS = 21.9 log10L − 67.2, where TS is target strength in (decibels) and L is fish length (centimetres). The average number of Cisco in the three lakes ranged from 89 to 1551 fish/ha, corresponding to a biomass of 2–223 kg/ha. Maximum densities range from 12 to 49 fish/1000 m3.