Individual feeding specialisation of a naïve vs. veteran predators

Abstract – We explored the incidence of individual feeding specialisation among a naïve predator (non‐native rainbow trout postsmolts) and two native experienced predators (sea‐run Arctic charr and sea‐trout) in a subarctic Norwegian fjord. Interindividual foraging niche stability was obtained by combining information on stomach contents (recent dietary niche) with trophically transmitted parasite infestation (time‐integrated historical dietary niche) of individual predators. Individual fish showed a high degree of resource specialisation as prey items such as gammarids and small fish (both potential intermediate host of parasites) rarely co‐occurred in stomachs. In both naïve and veteran predators, positive associations between the intensity of a specific parasite species and the occurrence of their respective intermediate host (gammarids or fish) in the stomachs of individual predators demonstrated temporally interindividual feeding specialisations. Several behavioural phenotypes clearly co‐existed in both naïve and veteran predator populations, including gammaridivore (benthic feeders), piscivore (pelagic feeders) or insectivore (pleuston feeders) individuals. The likely mechanism of this observed interindividual resource specialisation in the non‐native naïve predators involves a behavioural component of which rapid learning seems to be a key factor.     

Zum Einfluß organischer Bodenbedeckung auf den lateralen Transport von Isoproturon auf der Bodenoberfläche

On the Effect of Organic Surface Cover on Lateral Transport of Isoproturon on Soil Surface The losses of the herbicide isoproturon with the surface runoff and the sediment loss have been measured by means of rainfall simulations on microplots (0.5 × 1 m²) with different mulch materials and increasing soil cover percentages (wheat straw vs. rape leafs). Soil cover by straw showed no significant effect on the runoff discharge, but the total loss of isoproturon increased between 22 and 37%. Soil cover by rape leafs diminished the runoff by between 13 and 61%, the reduction of isoproturon loss was in the same range. It was shown, that the different influences of different mulch materials on runoff and soil loss can lead to different pesticide losses. Therefore, the only giving of “mulch” without specification does not describe such experiments sufficiently.     

Serosurvey for Toxoplasma gondii in arctic foxes and possible sources of infection in the high Arctic of Svalbard

Samples (blood or tissue fluid) from 594 arctic foxes (Alopex lagopus), 390 Svalbard reindeer (Rangifer tarandus platyrhynchus), 361 sibling voles (Microtus rossiaemeridionalis), 17 walruses (Odobenus rosmarus), 149 barnacle geese (Branta leucopsis), 58 kittiwakes (Rissa tridactyla), and 27 glaucous gulls (Larus hyperboreus) from Svalbard and nearby waters were assayed for antibodies against Toxoplasma gondii using a direct agglutination test. The proportion of seropositive animals was 43% in arctic foxes, 7% in barnacle geese, and 6% (1 of 17) in walruses. There were no seropositive Svalbard reindeer, sibling voles, glaucous gulls, or kittiwakes. The prevalence in the arctic fox was relatively high compared to previous reports from canid populations. There are no wild felids in Svalbard and domestic cats are prohibited, and the absence of antibodies against T. gondii among the herbivorous Svalbard reindeer and voles indicates that transmission of the parasite by oocysts is not likely to be an important mechanism in the Svalbard ecosystem. Our results suggest that migratory birds, such as the barnacle goose, may be the most important vectors bringing the parasite to Svalbard. In addition to transmission through infected prey and carrion, the age-seroprevalence profile in the fox population suggests that their infection levels are enhanced by vertical transmission.     

Early marine survival and movements of escaped Atlantic salmon Salmo salar L. juveniles from a land‐based smolt farm during autumn

The aim of this study was to examine early marine survival and movements of simulated escaped Atlantic salmon Salmo salar L. pre‐smolt and smolt from a commercial smolt farm during autumn. One‐third of the pre‐smolt most likely died in the immediate vicinity of the release location, whereas the corresponding mortality for smolts was lower (8.5%) during the 5‐week study period. The surviving pre‐smolt left the farm area after 2–3 days, predominantly along the shore. In contrast, most of the surviving smolts left the farm area during the first day and 54% seemed to move away from the shore and adopt a more pelagic movement pattern than pre‐smolt. The number of surviving fish recorded in the fjord decreased throughout the study period, possibly due to a combination of fish migrating out of the fjord or undetected mortality. Compared with existing knowledge on migration of released farmed smolts during spring, our results indicate less directional and slower movement rates during autumn. Only two of the tagged fish were detected upstream in the rivers following release. A rapid dispersion of escapees indicates that the potential for recapturing escapees is limited unless recapture efforts are initiated immediately after escape. Hence, there is a need for development of technology that detects and prevents escapees to enter the sea.     

Proof-of-concept robot platform for exploring automated harvesting of sugar snap peas

Currently, sugar snap peas are harvested manually. In high-cost countries like Norway, such a labour-intensive practise implies particularly large costs for the farmer. Hence, automated alternatives are highly sought after. This project explored a concept for robotic autonomous identification and tracking of sugar snap pea pods. The approach was based on a combination of visible–near infrared reflection measurements and image analysis, along with visual servoing. A proof-of-concept harvesting platform was implemented by mounting a robotic arm with hand-mounted sensors on a mobile unit. The platform was tested under plastic greenhouse conditions on potted plants of the sugar snap pea variety Cascadia using LED-lights and a partial shade. The results showed that it was feasible to differentiate the pods from the surrounding foliage using the light reflection at the spectral range around 970 nm combined with elementary image segmentation and shape modelling methods. The proof-of-concept harvesting platform was tested on 48 representative agricultural environments comprising dense canopy, varying pod sizes, partial occlusions and different working distances. A set of 104 images were analysed during the teleoperation experiment. The true positive detection rate was 93 and 87% for images acquired at long distances and at close distances, respectively. The robot arm achieved a success rate of 54% for autonomous visual servoing to a pre-grasp pose around targeted pods on 22 untouched scenarios. This study shows the potential of developing a prototype robot for semi-automated sugar snap pea harvesting.     

Estimation of economic and environmental potentials of variable rate versus uniform N fertilizer application to spring barley on morainic soils in SE Norway

Spring barley was grown for 4 years (2001–2004) in field trials at two sites on morainic soil in central SE Norway, with five N level treatments: 0, 60, 90, 120 and 150 kg N ha^-1. Regression analyses showed that a selection of soil properties could explain 95–98% of the spatial yield variation and 47–90% of the yield responses (averaged over years). A strategy with uniform fertilizer application of 120 kg N ha⁻¹ (U _N120) was compared with two variable-rate (VR) strategies, with a maximum N rate of either 150 kg N ha⁻¹ (VR_N150) or 180 kg N ha⁻¹ (VR_N180). These strategies were tested using either Norwegian prices (low price ratio of N fertilizer to yield value; P_N/P_Y), or Swedish prices (high P_N/P_Y). The VR_N180 strategy had the highest potential yield and net revenue (yield value minus N cost) at both sites and under both price regimes. Using this strategy with Norwegian prices would increase the profit of barley cropping as long as at least 40 and 31% of the estimated potential increase in net revenue was realized, respectively. Using Swedish prices, uniform application appeared to be as good as or even better economically than the VR methods, when correcting for extra costs of VR application. The environmental effect of VR compared with uniform application, expressed as N not accounted for, showed contrasting effects when using Norwegian prices, but was clearly favourable using Swedish prices, with up to 20% reduction in the amount of N not accounted for.     

Between- and within-site variation of density and bending properties of Picea abies structural timber from Norway

This study provides an analysis on the variability of structural timber of Norway spruce (Picea abies) grown in Norway. Density, modulus of elasticity (MOE) and bending strength were measured on 1188 boards from 205 trees, sampled from 14 sites throughout Southern Norway, Eastern Norway and Trøndelag. The area represents the procurement area for the majority of Norwegian sawmills. The variability of the timber properties was analysed in a linear mixed model where the random variance was divided into variance due to site, variance due to trees and within-tree variance. Models describing variance due to site based on site index, altitude and latitude were developed, and combined with data from the Norwegian National Forest Inventory to estimate mean values and variability of the timber properties. The results showed that major parts of the variance due to site are explained by altitude and site index, and for density also by latitude. Major parts of the variance due to site and the variance due to trees in bending strength and MOE were explained by density.     

Contaminants in Norwegian fjord sediments: industrial history or future source?

Norwegian fjords have been accumulating contaminants since early industrialisation. The key question for sediment management in Norway is whether the sedimentary contaminant record is an archive of industrial history or a future source of contaminants to the fjord environment. Innovative sediment management strategies are being developed in Norway to find solutions which are both cost-effective and sustainable.