Summary
Understanding of the winter ecology of stream salmonids is biased by research conducted in northern temperate and boreal regions dominated by hard rock geology. Such systems are driven by ...highly dynamic surface‐flow regimes and tend to be physically diverse, nutrient poor and influenced by ice. This study investigated how the behaviour of brown trout, Salmo trutta, inhabiting a stable groundwater‐fed, productive and comparatively warm southern English chalk stream differs from that described for other systems, and how this is translated to performance, measured as growth.
Physical characteristics were mapped, and high‐resolution temperature data collected using a spatial array of data loggers installed throughout the study reach during the winter. A combination of passive integrated transponder and radio telemetry was used to monitor distribution, density, and movement of trout. Micro‐archival data storage tags inserted in some individuals provided information on temperature regimes experienced. Growth performance was calculated for recaptured fish.
Trout density was positively related to depth and there was no evidence that temperature influenced microhabitat selection. Three patterns of movement were observed. Over three‐quarters of tracked fish exhibited high site fidelity and tended to remain in a single focal position throughout the study. Fourteen per cent of trout exploited more than one distinct location, while the remainder were detected at multiple locations and showed no preference for any one.
Trout exhibited regular daily activity patterns and highly periodic local movements at dusk and dawn and tended to experience positive growth performance during periods that included winter.
This study challenges the conventional view of salmonid winter ecology, which is biased towards populations that inhabit hard rock surface‐flow dominated rivers that experience the influence of ice. Despite inhabiting a distinctly different winter habitat template than more commonly studied populations, trout occupying a hydrologically stable and productive chalk stream exhibited behaviours similar to those described for elsewhere, yet performed considerably better.
Background
Biodiversity loss is particularly pronounced in agroecosystems. Agricultural fields cover about one-third of the European Union and are crucial habitats for many species. At the same time, ...agricultural fields receive the highest pesticide input in European landscapes. Non-target species, including plants and arthropods, closely related to targeted pests, are directly affected by pesticides. Direct effects on these lower trophic levels cascade through the food web, resulting in indirect effects via the loss of food and habitat for subsequent trophic levels. The overarching goals of the European pesticide legislation require governments to sufficiently consider direct and indirect effects on plants and arthropods when authorising pesticides. This publication provides an overview of a workshop's findings in 2023 on whether the current pesticide risk assessment adequately addresses these requirements.
Results
Effects due to in-field exposure to pesticides are currently not assessed for plants and inadequately assessed for arthropods, resulting in an impairment of the food web support and biodiversity. Deficiencies lie within the risk assessment, as defined in the terrestrial guidance document from 2002. To overcome this problem, we introduce a two-step assessment method feasible for risk assessors, that is to determine (i) whether a pesticide product might have severe impacts on plants or arthropods and (ii) whether these effects extend to a broad taxonomic spectrum. When each step is fulfilled, it can be concluded that the in-field exposure of the pesticide use under assessment could lead to unacceptable direct effects on non-target species in-field and thus subsequent indirect effects on the food web. While our primary focus is to improve risk assessment methodologies, it is crucial to note that risk mitigation measures, such as conservation headlands, exist in cases where risks from in-field exposure have been identified.
Conclusions
We advocate that direct and indirect effects caused by in-field exposure to pesticides need to be adequately included in the risk assessment and risk management as soon as possible. To achieve this, we provide recommendations for the authorities including an evaluation method. Implementing this method would address a major deficiency in the current in-field pesticide risk assessment and ensure better protection of biodiversity.
1. Thirgood '' Redpath (2008) propose ways in which red grouse : hen harrier conflicts could be resolved. It has also been suggested that grouse management could accept lower bag sizes (number of ...birds shot) thus reducing the need for intensive management of predators and habitats. This would allow hen harriers to co-exist more easily on grouse moors. 2. We compare the bags, costs and incomes from these less intensive forms of grouse shooting with the more intensive driven shooting. 3. Allowing high density grouse moors to decline to low density ones will result in greater loss of income than the corresponding saving of costs. This can result in moor owners abandoning grouse management and thus gamekeepers losing their employment. 4. Losing gamekeepers from the uplands would jeopardize the protection of heather moorland and Special Protection Areas for birds, large areas of which are keepered and which currently support high numbers of breeding waders. 5. Synthesis and applications. We agree with the study by Thirgood '' Redpath that consideration of social and economic factors will be needed to resolve conflict but a reduction in management effort from driven to walked-up shooting is not the answer. A more satisfactory approach to the harrier : grouse conflict could be to try to reduce harrier predation by means of diversionary feeding and to address the problem of the rapid build-up in harrier numbers by exploring the use of a ceiling on harrier densities.
The response of a brown trout habitat modification Needham, Robert J; Gaywood, Martin; Tree, Angus ...
Canadian journal of fisheries and aquatic sciences,
11/2021, Letnik:
78, Številka:
11
Journal Article
Recenzirano
Globally, freshwaters are the most degraded and threatened of all ecosystems. In northern temperate regions, beaver (Castor spp.) reintroductions are increasingly used as a low-cost and ...self-sustaining means to restore river corridors. River modifications by beavers can increase availability of suitable habitat for fish, including salmonids. This study investigated the response of a population of brown trout (Salmo trutta) to reintroduced Eurasian beaver (Castor fiber) habitat modifications in northern Scotland. The field site comprised two streams entering a common loch; one modified by beavers, the other unaltered. Electrofishing and PIT telemetry surveys indicated abundance of post-young-of-the-year (post-YOY) trout was higher in the modified stream. Considering juvenile year groups (YOY and post-YOY) combined, abundance and density varied with year and season. In the modified stream, fork length and mass were greater, there was a greater variety of age classes, and mean growth was positive during all seasons. Beavers had profound effects on the local brown trout population that promoted higher abundances of larger size classes. This study provides important insight into the possible future effect of beavers on freshwater ecosystems.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
1. A study of skylark Alauda arvensis L. breeding ecology in relation to crop type was carried out from April to August 1992 on arable land in southern England. Set-aside land was included in this ...comparative study. 2. Territory density averaged 0.15 ha-1. It was 2-3 times higher in fields of set-aside and grass, especially permanent pasture, than in winter and spring-sown cereals. 3. Territory size was nearly twice as large in fields of winter cereals (4.5 ha) than in other crop types (2.5 ha). Where set-aside was present on one farm, territory size in set-aside (1.7 ha) was a third lower than in cereals and grass. 4. Nesting began in set-aside and permanent pasture in April and peaked in late May. Nesting was not detected in spring barley until late May and in silage grass until early June. The density of successful nests in set-aside fields was more than double that in any of the arable crop types. 5. Average clutch size at hatching was 3.91 eggs in fields of set-aside, over 15% higher than in silage grass (3.40) and in spring barley (3.27). 6. Fledging success did not differ according to crop type, but productivity, expressed as the number of fledglings produced per hectare, was 0.50 in set-aside, 0.13 in silage grass, and 0.21 in spring barley. Nests with chicks were not found in fields of winter cereals. The causes of chick death were thought to be predation in set-aside fields, farming practices in silage grass fields, and suspected starvation in spring cereals. 7. The potentially high nesting success of skylarks in set-aside implies that sympathetic set-aside management could play an important part in reversing its decline across the European Union.
Globally, freshwaters are the most degraded and threatened of all ecosystems. In northern temperate regions, beaver (Castor spp.) reintroductions are increasingly used as a low-cost and ...self-sustaining means to restore river corridors. River modifications by beavers can increase availability of suitable habitat for fish, including salmonids. This study investigated the response of a population of brown trout (Salmo trutta) to reintroduced Eurasian beaver (Castor fiber) habitat modifications in northern Scotland. The field site comprised two streams entering a common loch; one modified by beavers, the other unaltered. Electrofishing and PIT telemetry surveys indicated abundance of post-young-of-the-year (post-YOY) trout was higher in the modified stream. Considering juvenile year groups (YOY and post-YOY) combined, abundance and density varied with year and season. In the modified stream, fork length and mass were greater, there was a greater variety of age classes, and mean growth was positive during all seasons. Beavers had profound effects on the local brown trout population that promoted higher abundances of larger size classes. This study provides important insight into the possible future effect of beavers on freshwater ecosystems.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
1. Wildlife reintroductions can help to restore populations and save species from extinction. However, success rates of reintroductions are low due to inherent problems, such as behavioural ...deficiencies resulting in high post‐release predation rates among captive‐bred animals. In particular, the released animals may use habitats maladaptively, leading to an ecological trap, i.e. preference for low‐quality habitats leading to reduced survival and/or breeding success. Ecological traps in reintroductions can be identified only through intensive studies of habitat preferences and survival of known individuals, but such studies are lacking. 2. We investigated habitat preferences and their relationship with survival by radio‐tracking reintroduced, captive‐bred grey partridges Perdix perdix, a widely reintroduced commercial game species and native farmland bird of conservation concern in the UK. The low success rate of grey partridge releases could be due to maladaptive habitat use and a possible ecological trap. 3. Grey partridges released as pairs in spring showed preferences for crop and field margin habitat. The use of crops had a positive, and use of field margins a negative, association with survival, suggesting field margins could serve as ecological traps for released grey partridges. Predation rates were high, and field margins probably hosted concentrated predator activity. 4. Grey partridges released as family groups (coveys) in autumn exhibited a preference for game covers, i.e. areas of tall vegetation specifically planted to provide cover for game birds, and mortality rates were lower than in spring. Habitat use did not affect survival in autumn. 5. Synthesis and applications. We have shown that newly released grey partridge pairs behave maladaptively by preferring a habitat which has a negative association with survival. In grey partridge reintroductions, we recommend releasing grey partridge family groups in autumn rather than releasing pairs of birds in spring, and providing game covers that could induce the groups to settle onto the release areas. In reintroductions in general, the habitat preferences of the released animals should be documented together with their fates, to enable detection of possible ecological traps that could threaten the success of these conservation efforts.
Anti-predator behaviour has direct fitness consequences for prey species and thereby affects their reintroduction success, which has generally been poor. Development of anti-predator behaviour may be ...impaired in captive conditions which favour low emotional reactivity, resulting in poor perception of danger. Therefore, the newly reintroduced, naive animals may not behave adaptively in terms of anti-predator vigilance, resulting in increased vulnerability to predators. Such behavioural deficiencies may have contributed to the low success rates of reintroductions, but few studies have measured post-release vigilance in captive-bred animals, and none has been published on reintroduced grey partridges. Therefore, in this study we investigated post-release vigilance behaviour and time budgets in coveys of captive-bred grey partridges (
Perdix perdix;
N
=
26) released in autumn over two years. We observed the captive-bred grey partridge coveys in the field, and recorded their group vigilance rates as well as time budgets of individual behaviour, including vigilance and feeding. Released grey partridges had low group vigilance rates and showed poor individual vigilance (4–5% of time spent vigilant) compared to their wild counterparts (43% of time spent vigilant;
Watson et al., 2007). Moreover, released individuals spent 30–48% of their time feeding, and fed at this rate throughout the day, instead of concentrating their feeding around dawn and dusk like wild grey partridges do. The revealed vigilance and feeding behaviour in released grey partridges are likely to increase vulnerability to predators, and therefore offer plausible explanations for the high predation rates of released grey partridges observed with these and previous releases. Rearing methods should be developed to encourage wariness in the captive animals. In addition, the adaptive bimodal feeding routine of wild grey partridges should be encouraged in the captive-bred birds, for example by feeding them only at dawn and dusk.
PDF
