Eliminating pond differences with cross-over designs

Large variability between ponds in aquaculture experiments often leads to imprecise estimates of treatment effects. One solution would be to increase the number of experimental ponds but the availability of ponds is usually limited. A cross-over trial makes comparisons directly within the same pond, instead of across ponds, thus taking account of individual pond effects and potentially removing much of the variability. A cross-over trial was initiated to test the feasibility of using such designs in pond aquaculture research. When compared to a completely randomized design, the cross-over trial was more efficient for comparing the fish growth for each of the two treatments, and, on average, a considerable reduction in the standard error of the treatment estimate was achieved. Thus, under certain circumstances, the cross-over design has great potential to improve the precision of pond aquaculture experimentation.     

Statistical aspects of aquaculture research: sample sizes for pond experiments

The present paper illustrates the need for greater pond replication in pond experiments. It demonstrates that increasing the number of fish sampled in each pond will not reduce the number of ponds needed when treatment effects are estimated. Sampling bias, skew distributions and heterogeneous fish populations are discussed in relation to fish sample sizes. When it is impossible to increase the number of replicate ponds, several methods of accounting for the pond variability are suggested.     

Statistical aspects of aquaculture research: pond variability and pseudoreplication

Pond experiments with one treatment per pond are discussed for their sources of variability. Replication of treated ponds, randomization of treatment allocation to ponds and the importance of independence between ponds are emphasized for efficient estimation of both treatment and inherent pond differences. Appropriate models are given for the analysis of data for pond experiments with whole-pond treatments. Corresponding analyses of variance are given to illustrate the estimation of differences between treatments, between ponds and between fish within ponds. Appropriate significance tests for treatment effects are demonstrated to avoid pseudoreplication, the incorrect use of within-pond variation. Using a fertilizer experiment, simple graphical methods are presented for examining between- and within-pond variation to identify ponds with unusual data, and to determine adequacy of design and appropriate analyses.     

Statistical aspects of aquaculture research: one-and two-season cross-over designs

One- and two-season cross-over designs are compared with completely randomized designs for their potential use in pond aquaculture experiments. Cross-over designs allow treatment comparisons to be made within the same pond, removing much of the between-pond variability. Different treatments are applied consecutively to the same pond. The one-season design involves splitting the season into two periods and applying different treatments in each period. The fish growth in each of the periods is compared taking account of both pond and period differences. The two-season design compares the harvest weight or growth over a whole season in consecutive seasons. Each of the designs is explained further. Data from uniformity trials are used to make these comparisons. Trials on the use of buffalo manure supplemented with urea and triple sulphate, which were completed in consecutive seasons, are used to verify the conclusions. The advantages and disadvantages of each design are discussed.     

Seasonal variations in the physical and chemical characteristics of ponds: implications for biodiversity conservation

• 1. The natural evolution of ponds leads to the filling up of these small ecosystems, and human intervention may sometimes be necessary to ensure their continued nature conservation interest.
• 2. In the arid karstic region of the ‘Causses du Quercy’ (France), there are numerous ponds bored into parts of the calcareous rock where water cannot percolate. Without human management they are destined to disappear, although they constitute the only available surface water resource on this limestone plateau.
• 3. Little information is available about the physical and chemical changes occurring as ponds go through different successional stages. A comparative study of three ponds at various stages of succession allowed an analysis to be made of the seasonal changes in a number of abiotic variables.
• 4. There was evidence that the temporal and spatial variability of abiotic factors (such as temperature, water level and dissolved oxygen concentrations) increased as ponds progressed through successional stages.
• 5. This study indicated that ponds varied in terms of plant and animal species richness and rarity, temperature, and oxygen concentration at different successional stages. Each pond supported a distinctive fauna. The results suggest that biotic diversity is, in part, driven by local‐scale physical and chemical heterogeneity. Management plans should be drawn at a scale that maintains the heterogeneity of such pond networks.

Copyright © 2004 John Wiley & Sons, Ltd.     

The role of pond management for biodiversity conservation in an agricultural landscape

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Constrained by aliens,shifting landscape,or poor water quality? Factors affecting the persistence of amphibians in an urban pond network

1. Freshwater communities and especially pond‐breeding amphibians are extremely vulnerable to land‐use change, alien species introductions and the use of pesticides or other toxic chemicals, as reflected in their worldwide decline. Effective conservation and management of ponds requires a better understanding of the biotic and abiotic factors that shape diversity patterns and species distribution, especially in cases of habitat loss
2. The present study aimed to reveal and classify which pond and landscape characteristics are the most important determinants for the occurrence patterns of amphibian species as well as for the overall amphibian species richness in an urban pond network. To achieve this aim, 17 biotic and abiotic variables were measured for 61 ponds and the dataset was analysed by means of a machine‐learning approach, suitability indices and co‐occurrence modelling
3. The highest probability of Triturus macedonicus occurrence was found at fishless artificial and semi‐natural ponds. The persistence of Lissotriton graecus in ponds was predicted by high pond connectivity and the absence of fish reflecting the species dispersive potential. Pelophylax kurtmuelleri showed a higher probability of occurrence with increased pond connectivity and macrophyte cover.
4. Amphibian species richness was higher in fishless ponds with well‐oxygenated waters located in sites with a low to intermediate road density network. Ponds categorized as ‘average’ in terms of newt suitability were more frequently inhabited by fish than Triturus macedonicus. Alien fish species showed negative associations with both newt species, while both newt species showed a positive association between them.
5. The results support the view that conserving a greater number of water bodies with increased landscape connectivity and without any fish presence could provide amphibian species with alternative habitat choices, especially in sites with human pressure where pond stability is at stake owing to continuous landscape changes.

     

Chlorination of Channel Catfish Ponds

Abstract— Laboratory studies with pond water samples revealed that 5 mg/L active chlorine was needed to provide enough chlorine residual to reduce biological activity. Treatment of channel catfish ponds with repeated, 0.1-mg/L doses of active chlorine from calcium hypochlorite at 6- to 8-d intervals, as sometimes done by catfish farmers, had little influence on water quality. Dissolved oxygen, total ammonia-nitrogen, and chlorophyll a concentrations and pH were similar between treated and control ponds. Concentrations of chemical oxygen demand and particulate organic matter were seldom different between treated and control ponds. Channel catfish survival and net production were not improved by chlorine treatment. Thus, chlorination of production ponds during the grow-out period is not a useful technique. Treatment of sediment samples from ponds with up to 1,200-mg active chlorinelkg soil did not reduce bacterial abundance, so chlorination of bottoms of empty ponds may not he an effective disinfection procedure. Chlorination of pond waters with 30-mg/L active chlorine caused complete kill of bacteria 24 h after treatment, although heterotrophic bacteria quickly re-populated the water. Thus, chlorination can be an effective way to disinfect ponds before stocking.     

Ecoacoustics as a novel tool for assessing pond restoration success: Results of a pilot study

1. Ecoacoustics is increasingly being used to monitor species populations and to estimate biodiversity in marine ecosystems, but the underwater soundscapes of freshwater environments remain largely unexplored in this respect. Few studies exist concerning the acoustic diversity of ponds, but because aquatic plants and many arthropods such as Coleoptera and Hemiptera are known to produce sound, there is potential to use ecoacoustic techniques to monitor changes in biodiversity and conservation value.
2. This pilot study compares the underwater soundscapes of recently restored open-canopy ponds and unmanaged highly terrestrialized ponds situated in an arable agricultural landscape of North Norfolk, UK, in order to assess the benefits of farmland pond restoration.
3. Daytime sound recordings were made for 10 min in each pond and analysed primarily for arthropod stridulations. In addition, six commonly used acoustic indices were calculated to assess the soundscape biodiversity between the unmanaged and the restored ponds. The stridulations of three diving beetle species (Dytiscidae) were recorded in tank studies to assess the potential for individual species recognition from underwater sound capture.
4. Sound-type richness and abundance, as estimated by visually and aurally identifying arthropod stridulation from spectrograms, were significantly higher in the restored open-canopy ponds compared with the unmanaged terrestrialized ponds. In addition, the acoustic indices ‘acoustic complexity’ and ‘biodiversity index’ were significantly higher in restored open-canopy ponds than in unmanaged terrestrialized ponds.
5. The three dytiscid water beetle species recorded in a tank were found to produce distinctive and recognizable sounds, indicating potential to create an audio reference library that could be used for automatic acoustic monitoring of freshwater arthropods.
6. Pond soundscapes are rich in biological information and this study suggests that, with further development, automated passive ecoacoustic monitoring could be an effective non-invasive technique for assessing pond conservation value and pond restoration and management success.