Catch Density Research Articles

Assessment of detecting minimum length limit changes for crappie in two Alabama reservoirs

Abstract The objectives of this study were to compare population metrics prior to and after the initiation of a minimum length limit for black crappie Pomoxis nigromaculatus and white crappie Pomoxis annularis in two reservoirs in Alabama, USA. In addition, we estimated recruitment variability and incorporated this stochastic component into a simulation model to assess the effects of three different minimum length limits on population and fishery metrics. Fish were sampled from October 1990–1991 to 2000 with trap nets, aged with otoliths, and population metrics including recruitment (age-0 catch), catch rates of age-2.5 and older fish, and length-based stock density indices were determined. We found no differences in population metrics between pre- and post-length limit time periods. We compared the effects of 203, 229, and 254 mm minimum length limits and predicted the long-term response of abundance of age-3 and older fish, angler catch, and stock density indices. Low, medium, and high levels of exploitation were explored and recruitment was varied at rates similar to observed data. Power analysis was performed using modeling results to estimate the number of years of sampling required to detect differences in population and fishery metrics in relation to changes in minimum length limits. Differences in population parameters resulting from a change in a minimum length limit were not likely to be detected with a reasonable amount of sampling effort in our populations where the recruitment CV was 70% or greater. The ability to statistically detect population and fishery changes in response to minimum length limits was dependent upon recruitment variation, exploitation rate, the magnitude of the change in a minimum length limit, and sampling duration.

Catchability of Walleyes to Fyke Netting and Electrofishing in Northern Wisconsin Lakes

Abstract We quantified relationships between both fyke-net catch rates (catch/net-night) and electrofishing catch rates (catch/mi) and population densities (number/acre) of walleye Sander vitreus (formerly Stizostedion vitreum) for adult population estimates and total population estimates to determine whether catchability was density dependent. Fyke-net catch rates were modeled as a nonlinear function of adult walleye density and of four size-classes of the adult population, and electrofishing catch rates were modeled as a nonlinear function of adult and total walleye density and four size-classes of the adult and total populations. The results showed nonlinear relationships between catch rate and density for the adult and total populations. We accounted for measurement errors in catch rates and densities by estimating bias-corrected slopes by means of Monte Carlo simulations and estimated measurement-error ratios by means of an errors-in-variables model. We found that the bias-corrected slopes were highe...

Estimating limits to the spatial extent and suitability of sole ( Solea solea) nursery grounds in the Dover Strait

There is a growing need for accurate and interpretable maps that describe the spatial extent and suitability of flatfish habitats. A common approach to developing such maps is to construct spatially explicit habitat models from fisheries-independent survey data. As the entire range of factors that define fish habitats can never be fully quantified, habitat models are invariably built from a small subset of factors, which typically consist of physical seabed and water column characteristics. If important physical and biological habitat features have not been measured, conventional modelling techniques may underestimate habitat use and quality. We present a spatial modelling technique capable of estimating the maximum extent and suitability of flatfish habitats, i.e. the potential or upper limits of the habitat, using juvenile sole ( Solea solea L.) in the Dover Strait as an example. To develop the models, juvenile sole catch densities and environmental habitat data were first acquired and assembled within a Geographical Information System (GIS). Regression quantiles were then estimated for models of change in juvenile sole catch density according to changes in a number of habitat variables. Finally, spatial models were constructed within a GIS by combining the quantile regression models with digital maps of the environmental variables. The use of regression quantiles allowed linear model parameters to be estimated near to the upper bounds of the sole-habitat relationships, thereby providing estimates of the limiting effects of the habitat. In turn, the habitat map built from the upper regression quantiles provided robust estimates of the maximum spatial extent and suitability of sole nursery grounds in the Dover Strait region, as confirmed by model tests using independent data. Habitat maps developed using this approach may be desirable from a species conservation perspective, as the likelihood of underestimating the extent and quality of the habitat is reduced.

Tidal and diurnal periodicity in macrocrustaceans and demersal fish of an exposed sandy beach, with special emphasis on juvenile plaice Pleuronectes platessa

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 225:263-274 (2002) - doi:10.3354/meps225263 Tidal and diurnal periodicity in macrocrustaceans and demersal fish of an exposed sandy beach, with special emphasis on juvenile plaice Pleuronectes platessa Bregje Beyst, Jan Vanaverbeke*, Magda Vincx, Jan Mees** Marine Biology Section, Biology Department, Ghent University, K.L. Ledeganckstraat 35, 9000 Gent, Belgium *Corresponding author. E-mail: jan.vanaverbeke@rug.ac.be **Present address: Flanders Marine Institute, Victorialaan 3, \f\f8400 Oostende, Belgium ABSTRACT: Macrocrustaceans and juvenile demersal fish were sampled in spring of 1997 in the surf zone of an exposed sandy beach on the Belgian coast. Three consecutive 24 h cycles were sampled to investigate tidal, diurnal and semi-lunar distribution patterns within the epibenthic community. Multivariate statistical techniques and 3-way ANOVA were used to evaluate the effects of the environmental variables measured. The most important variable correlated with the variation in epibenthic catch density was the state of the tide (ebb and flood), but light intensity (day and night) was also important. The individual catch density of several species differed significantly over the three 24 h cycles. Despite the strong turbulent conditions of the site studied, clear tidal (e.g. the brown shrimp Crangon crangon, juvenile plaice Pleuronectes platessa) and diurnal (e.g. juvenile sole Solea solea and clupeids, caught mainly during the night/day respectively) periodicities of many macrocrustacean and demersal fish species were observed. Nevertheless, the extremely turbulent conditions of the surf zone possibly affect the behaviour of many species (e.g. juvenile brown shrimp are not able to bury themselves as the water retreats). To investigate whether the high dynamics of the surf zone suppress the ability of juvenile plaice to actively search for food, stomach contents were analysed. Also, the interaction with potential prey was investigated: the hyperbenthic fauna was sampled simultaneously and macrobenthic data were available from the literature. Clearly, the Belgian sandy beaches are used as a feeding ground by I-group plaice. An opportunistic utilisation of available food resources is suggested. I-group plaice migrate high up the beach during the flood tide to profit from the rich macrobenthic intertidal area, while the 0-group feeds mainly on the most abundant hyper- and macrobenthic organisms from somewhat deeper water. The presence of the 0-group in the intertidal area is possibly linked to refuge for predators or influenced by the strong surf zone currents. KEY WORDS: Surf zone · Sandy beach · Pleuronectes platessa · Crangon crangon · Feeding periodicity · Stomach content analyses · Tidal migration Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 225. Online publication date: January 11, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Acoustic observations of jellyfish in the Namibian Benguela

Multi-frequency acoustic data (18, 38 and 120 kHz) were collected in conjunction with pelagic trawl sampling for gelatinous macrozooplankton during a cruise to the Namibian Benguela in September 1999. Sampling focused specifically on the scyphozoan Chrysaora hysoscella and the hydrozoan Aequorea aequorea, both of which occur in large numbers, are probably of major ecolog- ical importance, and physically hamper pelagic fishing and diamond extraction activities. C. hyso- scella was detected predominantly at an inshore station and A. aequorea was found in greatest abun- dance further offshore in deeper water. Echo-sounder observations were linked directly to net catches, and relationships between catch density (number of individuals m -3 ) and nautical area scat- tering coefficients (sA) at each frequency were determined for both species in order to estimate target strength (TS) using the comparison method. TS for C. hysoscella (mean umbrella diameter 26.8 cm) was -51.5 dB at 18 kHz, -46.6 dB at 38 kHz and -50.1 dB at 120 kHz; for A. aequorea (mean central umbrella diameter 7.4 cm) TS was -68.1 dB at 18 kHz, -66.3 dB at 38 kHz and -68.5 dB at 120 kHz. These TS values compared favourably with previously published estimates for related species. Jelly- fish were caught at high numerical densities (maxima 3 C. hysoscella per 100 m 3 , 168 A. aequorea per 100 m 3 ). These high densities, combined with the not unsubstantial TS at frequencies used for fish- eries surveys, imply that jellyfish could potentially bias acoustic estimates of fish abundance. We sug- gest a simple multifrequency approach that could be used to discriminate between echoes from jelly- fish and some commercially important pelagic fish in the northern Benguela ecosystem.

Detecting Fish Population Responses to a Minimum Length Limit: Effects of Variable Recruitment and Duration of Evaluation

Abstract We used a simulation model to evaluate how recruitment variability and evaluation duration would affect fisheries managers' ability to detect fish population responses to a minimum length limit. Length limits modeled were 254 mm for white crappie Pomoxis annularis and 305, 356, and 457 mm for largemouth bass Micropterus salmoides. Simulations were conducted at recruitment variation (coefficient of variation, CV = 100 × SD/mean) of 20–100% for age-1 recruits. We evaluated how population density, population biomass, total catch (fish harvested and released), yield, and proportional stock density (PSD) would differ in response to a single 3-year or 5-year length limit evaluation. For white crappies, simulations suggested that a 254-mm length limit would not provide detectable differences (P > 0.10) in any population parameter if recruitment variability exceeded 90% for either evaluation period. Mean CV in recruits to age 0 or age 1 for empirical white crappie populations was 82% (range = 55–124, N =...

First use of pheromones to detect phenology patterns and density relationships of pine sawflies in German forests

Abstract1 Monitoring studies of pine sawflies with pheromone traps were performed for the first time in Germany. Pheromone traps baited with species‐specific pheromone substances were installed in pine forests at different locations in Bavaria, Brandenburg and Lower Saxony during two years.2 It was possible to track the flight phenology of Diprion pini, Gilpinia pallida and Neodiprion sertifer reliably and to get information about the number of generations of these species in 1997 and 1998.3 A clear relationship between trap catch and population density could not be detected, but qualitative changes in trap catch caused by different density levels were observed.4 For D. pini, trap catches were different among endemic populations of different forest types. Furthermore, catches of males reflected the results from the regular cocoon collections by foresters during the previous winter.5 For N. sertifer, trap catches in endemic populations were well separated from trap catches on sites with higher sawfly densities. However, no significant correlation between trap catch and sawfly density or defoliation level could be found. These results suggest that the efficacy of the pheromone traps probably varied with biological features (sex ratio, density level, immigration) of the particular population.

Distribution of Todarodes pacificus (Cephalopoda: Ommastrephidae) paralarvae near the Kuroshio off southern Kyushu, Japan

The distribution and abundance of Japanese common squid [Todarodes pacificus (Steenstrup, 1880)] paralarvae off southern Kyushu Island near the Kuroshio were examined in relation to water types in the region. Surveys were conducted in 1996 and 1997 using paired, 70 cm diameter Bongo nets. Temperature–salinity plots from 0, 50 and 100 m depths were used to assign sampling stations to three water types: inshore, mixing and Kuroshio. In total, 4103 T. pacificus paralarvae were collected at 59 of 72 stations. Catch densities at positive stations ranged between 8 and 4282 ind./50 m2 sea surface area. Catches during both years were highest in mixing waters, followed by inshore and Kuroshio waters. Total catches were highest just north of the oceanographic front at the inshore edge of the Kuroshio and declined with increasing distance away from the front. Catches of paralarvae ≤1.0 mm mantle length also peaked near the front. In both years, ≥85% of all paralarvae and ≥69% of those ≤1.0 mm mantle length occurred less than 25 km from the front. We conclude that most spawning off southwest Kyushu occurs near the frontal zone, where Kuroshio and inshore waters meet.

97/01194 Particulate control device testing at the power systems development facility, Wilsonville, Alabama

The objectives of this study were to compare population metrics prior to and after the initiation of a minimum length limit for black crappie Pomoxis nigromaculatus and white crappie Pomoxis annularis in two reservoirs in Alabama, USA. In addition, we estimated recruitment variability and incorporated this stochastic component into a simulation model to assess the effects of three different minimum length limits on population and fishery metrics. Fish were sampled from October 1990–1991 to 2000 with trap nets, aged with otoliths, and population metrics including recruitment (age-0 catch), catch rates of age-2.5 and older fish, and length-based stock density indices were determined. We found no differences in population metrics between pre- and post-length limit time periods. We compared the effects of 203, 229, and 254 mm minimum length limits and predicted the long-term response of abundance of age-3 and older fish, angler catch, and stock density indices. Low, medium, and high levels of exploitation were explored and recruitment was varied at rates similar to observed data. Power analysis was performed using modeling results to estimate the number of years of sampling required to detect differences in population and fishery metrics in relation to changes in minimum length limits. Differences in population parameters resulting from a change in a minimum length limit were not likely to be detected with a reasonable amount of sampling effort in our populations where the recruitment CV was 70% or greater. The ability to statistically detect population and fishery changes in response to minimum length limits was dependent upon recruitment variation, exploitation rate, the magnitude of the change in a minimum length limit, and sampling duration.

Factors affecting the annual abundance and regional distribution of English inshore demersal fish populations: 1973 to 1995

The 2 m beam trawl and 1.5 m push net were used to sample the small epibenthic fish assemblage during September on the east and south coasts of England. Fishing stations were distributed along the entire coast within four depth bands to 20 m. A total of 104 species were caught between 1973 and 1995, and these included infrequent Lusitanean species such as the big-scale sand-smelt (Atherina boyeri), and the undulate ray (Raja undulata), and infrequent boreal species such as the Norway haddock (Sebastes viviparus). Fifty-four taxa were selected as representative of the small, demersal inshore fish community that would be most vulnerable to capture by the two sampling gears, and were used in subsequent analyses of community structure. The north-east coast assemblage was the least diverse (H*=1.58) and least even (J*=0.47). It also supported the least number of species (55), and the variation in catch of the only dominant genus, Pomatoschistus spp., was partly responsible for large year-to-year variations in diversity and in the total population abundance of selected demersal species. On the east and south-east coasts, both diversity (H*=1.78 and 1.93) and evenness (J*=0.50 and 0.51) were greater than in the north, as a result of larger numbers of species available to the gears, and several species with relatively high catch density, such as Pomatoschistus spp., dab (Limanda limanda), solenette (Buglossidium luteum), and dragonet (Callionymidae). As a result, thefish assemblages of these coasts showed lower inter-annual variation in evenness and diversity. Trends in mean catch density of some species were correlated with the mean surface water temperature and salinity, especially for species which were near the edge of their normal geographic distribution in the southern North Sea. In addition, mean surface water temperatures were positively correlated with the total number of Lusitanean species on the south coast. These data provide evidence that during a period of more than 20 years, hydrographic factors have not only aVected species abundance, but, at low density, also their presence or absence in catches. ? 1996 International Council for the Exploration of the Sea

Mortality and growth of 0-group flatfish in the brackish dollard (Ems Estuary, Wadden Sea)

The population dynamics of three 0-group species, plaice ( Pleuronectes platessa L.), flounder ( Platichthys flesus L.) and sole ( Solea solea L.) in the Dollard (Ems Estuary, Wadden Sea) were investigated in 1992. The instantaneous rate of decrease in catch density of plaice was 0.011·d −1, which corresponded with other calculated mortality rates of plaice in the western Wadden Sea. Catch densities of 0-group flounder decreased at a rate of 0.018·d −1. The rate of decrease in catch density of 0-group sole was estimated at 0.011·d −1, but was less accurate and probably reflected migration. The rate of increase in mean length of 0-group sole was in agreement with experimental growth studies under excess of food. The observed rate of increase in mean length of plaice and flounder appeared to decline from the beginning of June onwards in comparison with simulated growth in length. A number of factors that may be responsible for the observed differences are discussed.

A spatial analysis of the commercial fisheries catches from the Greek Aegean Sea

In the present study, univariate (number of species, species diversity, eveness, richness) and multivariate analysis techniques (cluster analysis and multidimensional scaling) are used, together with dominance curves, to describe the major biogeographical features of the demersal and pelagic fisheries in ten Greek statistical fishing subareas of the Aegean Sea for the years 1982–1987, inclusive. The results from the various statistical techniques applied were in close agreement and all suggested that the ten statistical fishing subareas could be generally grouped into three main areas (northern, central and southern Aegean Sea) for the pelagic fishery and into two main areas (northern and southern Aegean Sea) for the demersal fishery, which differed considerably from each other in terms of species composition, species diversity and catch density (catch weight per unit area). In general, with respect to the pelagic fisheries, the catches from the northern, central and southern Aegean area groupings are dominated, respectively, by anchovy ( Engraulis encrasicolus (L.), 48.2%), horse mackerels ( Trachurus spp., 23.2%) and bogue ( Boops boops (L.), 40.6%). For the demersal fisheries, the catches from the northern and southern Aegean area groupings are dominated by grey mullets (Mugilidae, 10.3%) and pickerel ( Spicara smaris (L.), 28.6%), respectively. The main factors which appear to be contributing to this geographical group differentiation are: (a) the gradient in the relative eutrophy, river runoff, temperature and salinity of the Aegean Sea waters along a NNW to SSE axis; and (b) the differences in extent of the continental shelf within these areas of the Aegean Sea. The managerial implications of the results of these spatial analyses are discussed and emphasis is given to the experimental establishment of marine harvest refugia which provide a refuge for fish populations in space, rather than the ‘refuge in numbers’ which has been the basis of most traditional fisheries management measures so far applied in this area.

Relationship Between Gypsy Moth (Lepidoptera: Lymantriidae) Pheromone Trap Catch and Population Density: Comparison of Traps Baited with 1 and 500 <g (+)-Disparlure Lures

The relationship between the number of male gypsy moths, Lymantria Dispar (L.), captured in pheromone traps and subsequent egg-mass density in the area surrounding each pheromone trap was determined for traps baited with either 1 or 500 mg of (+)-disparlure. Traps were located along transects that extended from within diflubenzuron-treated spray blocks, in which gypsy moth populations were low (252.0 egg masses per ha), to adjoining areas with high populations (3,390.4 egg masses per ha) that had either been treated with Bacillus thuringiensis Berliner or left untreated and that were associated with defoliation of oak, Quercus spp. Traps containing low-dose lures captured means of 5.4 and 32.9 moths in the low and high gypsy moth population density areas, respectively. Traps containing high-dose lures captured means of 431.1 and 874.4 moths in the low and high density areas. Trap captures for both lure doses were significantly correlated with subsequent egg-mass density. Numbers of surviving female pupae under burlap averaged 0.16 and 1.11 per cm in the low- and high-population density areas, respectively. Pupal numbers were also significantly correlated with subsequent egg-mass density. Functional relationships between trap catches and subsequent egg-mass densities for traps containing low- and high-dose lures are given, which explain 60 and 65% of the variation, respectively.

Selection of pheromone trap and attractant dispenser load to monitor black army cutworm,Actebia fennica

Catch rates of black army cutworm moths,Actebia fennica (Lepidoptera: Noctuidae), were determined for different types of traps and different dispenser loads of sex attractant. Of the five traps tested, highest catch (35 males/per night) was obtained with Uni-Traps, whereas Pherocon 1CP, Delta and Hara traps rapidly became saturated at 9, 6, and 11 males/per night, respectively. Multi-Pher traps, like the Uni-Traps, have a covered vertical cone with a large collecting bucket but only catch about 1/3 of the number of moths (9 males/per night) as the Uni-Traps, thus reducing potential saturation. Red rubber septa loaded with 500 μg of attractant blend gave a consistent catch for at least 60 days; 1000 and 2000 μg loadings lasted for a minimum of 90 days. Polyvinylchloride and red rubber septa dispensers containing 100 μg of attractant had similar catch rates, which decreased rapidly with age. Based on these trap and lure-loading experiments, Multi-Pher traps baited with 1000 μg of attractant in a red rubber septum were selected for future calibration studies between catch density and population fluctuations on susceptible sites. Two years of monitoring results also are reported.

FACTORS AFFECTING CATCH IN PHEROMONE TRAPS FOR MONITORING THE WESTERN SPRUCE BUDWORM, CHORISTONEURA OCCIDENTALIS FREEMAN

AbstractThe effects of trap design, lure concentration, lure age, and trap maintenance on the catch of western spruce budworm moths, Choristoneura occidentalis Freeman, in pheromone traps were tested in light to moderate infestations near Ashcroft, B.C. High cumulative moth catches reduced the trapping efficiency of both the sticky traps and the non-sticky Uni-traps relative to traps from which the moths were removed every 2 days. Correlations between the total season’s catch and larval density per plot in the same and following generations were not significant (P>0.05) for any of the eight combinations of trap design, lure concentration, and maintenance regimen tested. However, by dividing the mean moth catch in Uni-traps by either the basal area or foliage biomass per hectare in each plot, correlations with the following year’s larval density were significant (r2 = 0.77–0.98; P<0.05; n=5).

MONITORING SPRUCE BUDWORM POPULATION DENSITY WITH SEX PHEROMONE TRAPS

AbstractAnnual catches of male spruce budworm (Choristoneura fumiferana [Clem.]) in sex pheromone traps over a 21-year period in northwestern Ontario were well correlated with larval population densities in each subsequent year (r2 = 81%). On the basis of the criterion of 3 successive years of increasing catches or a threshold of 50 moths per trap, warning of extensive defoliation could have been given 6 years in advance. In 18 plots in northwestern Ontario and 35 plots distributed throughout the province, coefficients of determination (r2) between catch and population density in the same generation ranged from 40 to 74% in 1982 and 1983, but fell below 23% in 1984 when population densities in many plots were high. Coefficients of determination between catch and population densities in the following generation (eggs or larvae) ranged from 41 to 62%. On the basis of several years of cooperative research, sex pheromone traps are now in operational use in eastern North America for monitoring spruce budworm populations.

Estimation of catch efficiency and chum salmon abundance by parallel gillnet experiment.

Parallel gillnet experiments were carried out in order to estimate catch efficiency of gillnet and abundance of chum salmon in the central Bering Sea in July, 1984. In the experiment, two gillnets were simultaneously set in parallel configuration at a distance of about 2km, and the catch in number of salmon by each side of each gillnet was recorded. Release and recovery ex-periments were also conducted to estimate the moving speed of salmon. In order to estimate catch efficiency and density of fish, data were analyzed based on a model that takes into account the moving speed of fish and the catch interaction between two parallel gillnets. A relationship between CPUE (number/tan) and density (number/km2) was constructed, and CPUE at each station was converted into density. The density was weighted by the size of the survey area, and the abundance of chum salmon was calculated.

Relationship between Electrofishing Catch Per Unit Effort and Density of Walleye Yearlings

Relationship between Electrofishing Catch Per Unit Effort and Density of Walleye Yearlings

A METHOD OF ESTIMATING POPULATION SIZE OF THE SHEEP BLOWFLY, LUCILIA CUPRINA, USING MARK‐RECAPTURE DATA CORRECTED FOR VARIATION IN CATCH AND LOSS OF MARKED INDIVIDUALS

AbstractA method of estimating population size, using mark‐recapture data from four classic experiments involving the sheep blowfly, is described which corrects for daily variation in catch and loss of marked flies from the sampling area. The method provides maximum and minimum estimates of population size according to the “survival” characteristics of the marked flies. It suggests a ratio of about 3.3 to 1 between the average daily catch (flies/trap/day) and fly density (flies/ha).

Absolute-Density Estimation from Sweep Sampling, with a Comparison of Absolute-Density Sampling Techniques for Adult Potato Leafhoppper in Alfalfa1

A study of sampling techniques for adults of Empoasca (abae (Harris) in alfalfa was undertaken to derive ahsolute-density estimates from sweep-net sampling. A comparison of three absolute-density techniques showed that either the D-VacR or a modified EchoR suction device, operated with a small drop trap, yielded accurate estimates upon which the relationship of sweep-net catch and absolute density suhsequently was hased. Large drop trap sampling may be highly influenced by the density and uniformity of the alfalfa stand. Sampling several meters in front of the individual to avoid disturhing potato leafhoppers, compared with sampling immediately in front of the individual, gave no measurable advantage. Sweep-net sampling in fields that had been cleanly harvested yielded precise estimates of absolute density, using the equation x = IX.5y, where x = adult potato leafhoppers per m2 and y = catch per sweep. Distribution of five-sweep samples in cleanly harvested fields followed a Poisson series, and optimum sample size curves were determined. Harvesting of a portion of an alfalfa field altered the spatial distribution of potato leafhopper adults.