Does the consumption of divergent resources influence risk taking behaviour in juvenile perch (Perca fluviatilis L.)?

Heynen M, Heermann L, Borcherding J. Does the consumption of divergent resources influence risk taking behaviour in juvenile perch (Perca fluviatilis L.)?
Ecology of Freshwater Fish 2011: 20: 1–4. © 2010 John Wiley & Sons A/S     

Explaining recreational angling catch rates of Eurasian perch,Perca fluviatilis: the role of natural and fishing‐related environmental factors

Angling catch records are frequently used to reveal fish population developments. It is therefore important to understand the determinants of angling catches. This study focused on angler‐related, biotic and abiotic factors influencing catchability of Eurasian perch, Perca fluviatilis L. A multi‐lake (21 lakes) study based on angling diaries collected in Mecklenburg‐Vorpommern, Germany (2006/2007), found that angler‐related factors such as fishing experience, species preference and bait/lure type had a large impact on perch catch rates. Additionally, environmental conditions (nutritional status and water transparency) affected either the size or the number of perch caught by anglers. Catch rates varied seasonally, which was confirmed by an experimental fishery on a gravel pit (2008). This portion of the study showed that altered food availabilities in the course of the year caused food limitation in perch, which in turn facilitated high catch rates and female‐biased exploitation in autumn. It is concluded that both angler‐related and abiotic factors interact affecting perch catch rates and size of perch captured in recreational angling.     

Irrigation scheduling and water availability at watercourse command

A model that simulated the irrigation schedules of a farm at watercourse command was developed to predict net farm return, benefit-cost ratio, water use, percent water utilized, deep percolation, rainfall contribution and net return per unit of water applied including rainfall. Schedules for three selected farms on a watercourse command of Tw #62394L from MONA, Sargodha, Pakistan were simulated with 3 fixed-rotation and 2 demand strategies to evaluate the allowable soil water depletion criteria. Evaluation of the simulations (1973–82) showed that the water availability reduced the net farm return of 15 and 31% at the middle and tail farms, respectively, from that of the head farm. Therefore, the existing water allocation procedure (WARABANDI) should include watercourse conveyance losses to provide equitable water distribution on a watercourse command. Demand water availability can increase the net farm return of 25 and 26% in strategies 4 and 5, respectively, by changing the fixed-rotation system to a demand system. Changing the fixed-rotation system to a demand system requires either the use of existing private tubewells or the installation of new private tubewells.     

Interdisciplinary Irrigated Precision Farming Research

The USDA-Agricultural Research Service and Colorado State University are conducting an interdisciplinary study that focuses on developing a clearer scientific understanding of the causes of yield variability. Two years of data have been collected from two commercial center pivot irrigated fields (72 and 52 ha). Cooperating farmers manage all farming operations for crop production and provide yield maps of the maize grown on the fields. The farmers apply sufficient inputs to minimize risk of yield loss. The important variables for crop production have been sampled at a grid spacing of 76 m for two seasons. A spatial auto-regressive model was fitted to the data to determine the critical factors affecting yield variability. Thirty one layers of data were included in the analysis, and a total of over 140,000 models were examined. Up to five predictors were used in each model. Variability in water application, nitrate nitrogen, organic matter, phosphorus, topology, percent silt and soil electrical conductivity were significant in explaining the yield variability for Field 1. Variability in water application, ammonium, nematodes, percent clay, insects, potassium, soil electrical conductivity, and topology were significant in explaining the yield variability for Field 2. The tentative conclusion is that the potential economic benefit of site specific management is small where the farmer's management tolerance for risk is low. The potential of site specific management is in reducing the cost of inputs and environmental impact, but could increase risk.     

Frequency Analysis of Yield for Delineating Yield Response Zones

The yield in any given field or management zone is a product of interaction between many soil properties and production inputs. Therefore, multi-year yield maps may give better insight into determining potential management zones. This research was conducted to develop a methodology to delineate yield response zones by using two-state frequency analysis conducted on yield maps for 3 years on two commercial corn fields near Wiggins, Colorado. A zone was identified by the number of years that yield was equal and greater than the average yield in a given year. Classes producing statistically similar yield were combined resulting in three potential yield zones. Results indicated that the variability of yield over time and space could successfully be assessed at the same time without the drawbacks of averaging data from different years. Frequency analysis of multi-year yield data could be an effective way to establish yield response zones. Seventeen percent of the field #1 consistently produced lower yield than the mean while 43 of the field produced yield over the mean. Corresponding values for field #2 were 6% and 42%.The remainder of the fields produced fluctuating yields between years. These spatially and temporally sound yield response maps could be used to identify the yield-limiting factors in zones where yield is either low or fluctuating. Yield response maps could also be helpful to delineate potential management zones with the help of resource zones such as electrical conductivity and soil maps, along with the directed soil sampling results.     

Size-dependent energy storage and winter mortality of perch

Abstract –  Size is a crucial factor affecting the survival of fish during winter. Pond and laboratory experiments with three size classes of perch (small: 40–70 mm, medium: 71–100 mm, large: 101–186 mm) revealed that the feeding history of perch prior to winter is reflected in the amount and type of accumulated energy reserves. The minimal amount of reserves was 2% of the perch's biomass for fat and 9% for protein. An increase in glycogen levels either reflected mobilisation of energy in the body when perch were starving or an increase in accumulated energy over winter. In the laboratory, only the smallest perch suffered from high mortality rates, even if all were fed with low amounts of food. However, feeding the fish reduced the mortality rate after a certain time lag. Size-selective mortality rates occurred in the pond experiments as well. Small perch which survived the winter were able to rebuild their energy stores.     

‘User friendly’ software for an integrated water-energy management system for center pivot irrigation

Computers are becoming more commonly used by farmers for improving their management. The big need is ‘user friendly’ software for use by farmers. An integrated water-energy management system was developed. It includes ‘user friendly’ software run on a microcomputer which communicates to center pivot irrigation systems via radio. The program provides monitoring, control, irrigation scheduling and electrical load control. The system has been used and accepted by our cooperator for three irrigation seasons. He has been able to improve his management and reduce the amount of overirrigation and the variation between systems of total water applied.     

Survival and behaviour of Atlantic salmon smolts passing a run‐of‐river hydropower facility with a movable bulb turbine

Downstream migration of radio‐tagged Atlantic salmon smolts, Salmo salar L., was studied in the Kinzig, Germany, to examine effects of passing a run‐of‐river hydropower station with a movable bulb turbine. Immediate mortality for smolts passing the power station was low (3%–6%), probably facilitated by a curved rack in front of the turbine and the possibility to pass over it. Mortality in the impounded stretch above the power station was also low (1.5% extra mortality compared to a control stretch). The combined mortality due to hydropower was 5%–8%, excluding delayed effects. Most smolts followed the main flow passing through the turbine area (94%). Only few used a fishway (4%) or a nearby millstream (2%). Migration speed was slowed down at the power station, but the passage only caused a short delay (average/median 8.6/1.3 hr). However, even low mortality and short delays at several power stations and reservoirs may have considerable cumulative effects.     

Winter short-distance migration of juvenile fish between two floodplain water bodies of the Lower River Rhine

Abstract –  During winter, large numbers of juvenile fishes (mainly roach, Rutilus rutilus L.) were observed to migrate at dawn from a floodplain lake into a connected channel, whereas they migrated in the opposite direction at dusk. The diurnal migration pattern was strongly correlated to light intensity. The total number of migrating fish decreased from autumn to spring. Ice coverage and water temperature were the only abiotic factors that affected the seasonal migration pattern significantly. Moonlight, water level, current velocity, rainfall, insolation and wind velocity did not influence the observed migration of juvenile fish. The results are discussed in relation to food availability, predation risk and energy conservation.