Johan Watz

Johan Watz
Karlstads Universitet

PhD

About

32
Publications
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248
Citations

Publications

Publications (32)
Article
Full-text available
Interspecific competition among terrestrial gastropods has previously been considered to have little effect on population dynamics and local distribution. Recent studies, however, demonstrate several cases in which interspecific competition plays a major role in structuring terrestrial gastropod communities. To explore the general importance of int...
Article
Full-text available
The loss of longitudinal connectivity in regulated rivers, both up- and downstream, has been detrimental for biodiversity worldwide. While progress has been made regarding upstream fish passage solutions, many questions remain unanswered regarding downstream passage alternatives. To address these knowledge gaps, we used Atlantic salmon (S. salar) s...
Article
Full-text available
Known as the "king of fishes," the Atlantic salmon (Salmo salar, Salmonidae) is an iconic freshwater species whose contribution to human well-being has long been recognized , as have widespread declines in its abundance, partly due to river regulation. To understand how salmon conservation has been addressed within the ecosystem services (ES) frame...
Article
Full-text available
To predict the effects of habitat alterations on animal populations we need insight into how the habitat configuration influences local scale movements. This relationship may be particularly important for effective management of pest species. We tracked 80 PIT-tagged Spanish slugs (Arion vulgaris) in 16 × 16 m arenas with manipulated habitat fragme...
Article
Full-text available
Reliable methods for assessing the ecological status of degraded rivers are essential for evaluating restoration efforts in lotic habitats. Several methods are based on biological indicators, such as benthic macroinvertebrates. The Hester–Dendy multi-plate sampler is a commonly used tool for sampling macroinvertebrates, but its performance under di...
Article
Full-text available
Arionid slugs can be serious pests on horticultural and agricultural crops. Using slug movement barriers is a potentially effective method to control slug damage. We evaluated the performance of waterglass (sodium silicate) and copper foil as barriers against Arion vulgaris movement both in a controlled experiment and in a semi-field validation und...
Article
Full-text available
Background Temperature affects many aspects of performance in poikilotherms, including how prey respond when encountering predators. Studies of anti-predator responses in fish mainly have focused on behaviour, whereas physiological responses regulated through the hypothalamic-pituitary-interrenal axis have received little attention. We examined pla...
Article
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Cost-effective implementation of fish-friendly hydropower flow operation and habitat restoration measures require an understanding of their effects on fitness-related behaviours of stream fish. Here, we investigated how changes in flow and bottom structure influence the social behaviour of European grayling, using large experimental flumes (700 L s...
Article
The European eel Anguilla anguilla Linnaeus 1758 is critically endangered with recruitment estimated at 5%‑10% of historical levels. Enhancing survival of recruits is pivotal for conservation, and restoration should consider habitat choice of elvers ascending river systems. We experimentally show that newly ascended elvers choose small pebble habit...
Article
Full-text available
To improve the management of the European eel (Anguilla anguilla) in freshwater, it is essential to define important lotic habitats. Electrofishing data from 289 wadeable, hard-bottom sites in 69 Swedish coastal rivers and streams, originally surveyed for salmonid monitoring, were used to evaluate the effects of sampling- and habitat-related factor...
Article
Full-text available
To improve the management of the Euro-pean eel (Anguilla anguilla) in freshwater, it is essential to define important lotic habitats. Electrofish-ing data from 289 wadeable, hard-bottom sites in 69 Swedish coastal rivers and streams, originally surveyed for salmonid monitoring, were used to evaluate the effects of sampling-and habitat-related facto...
Article
Low winter temperatures constrain predator‐detection and escape capabilities, making poikilotherms vulnerable to predation. Investigations of temperature effects on predator–prey interactions can therefore be of special importance in light of ongoing climate change, where winter temperatures are predicted to increase substantially at northern latit...
Article
• Biotic interactions affect species distributions, and environmental factors that influence these interactions can play a key role when range shifts in response to environmental change are modelled. • In a field experiment using enclosures, we studied the effects of the thermal habitat on intra‐ versus inter‐specific competition of juvenile Dolly...
Article
Full-text available
The effects of structural enrichment in the hatchery rearing environment of brown trout Salmo trutta was linked to post‐release performance. Enrichment resulted in reduced swimming activity scored in an open field test and reduced movement in a natural river after release. Also, enrichment increased resting metabolic rates, which correlated positiv...
Article
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• Many diadromous fish populations are declining and at risk of collapse. Lack of river connectivity is a major contributor to these declines, as free migration routes between marine and freshwater habitats are crucial for life‐history completion. For the conservation and ultimately recovery of such species, it is imperative that remedial measures...
Article
Full-text available
Conservation programmes for endangered, long‐lived and migratory species often have to target multiple life stages. The bottlenecks associated with the survival of juvenile anguillid eels migrating into inland waters, the survival and growth of the freshwater life stage, as well as the recruitment and survival of silver eels, migrating back to the...
Article
Full-text available
F or as long as we have been human, people have wondered about our relationship with the rest of the natural world. In particular, freshwater rivers and streams have played a pivotal role in the evolution of human culture. Indeed, our relationships with rivers can be said to be older than humanity itself-ancestral species of the genus Homo certainl...
Article
• Habitat structural complexity affects the behaviour and physiology of individuals, and responses to the environment can be immediate or influence performance later in life through delayed effects. • Here, we investigated how structural enrichment, both pre‐release in the hatchery rearing environment and post‐release in the wild, influenced winter...
Article
To improve the situation for the threatened European eel in regulated rivers, better methods need to be developed that more efficiently collect and transport juvenile eels past dams. In this study, a novel mobile, floating eel trap is described, and the results from an evaluation of the trap in two Swedish regulated rivers are presented. The mobile...
Article
Full-text available
Winter can be a challenging period for fish in northern temperate rivers and streams, particularly in those that are channelized, structurally simple or regulated by, for instance, hydropower. In these systems, dynamic sub-surface ice formation commonly occurs and stable periods with ice cover may be short. Under these adverse conditions, access to...
Chapter
Within the discipline of stream fish ecology, population-, community-, and even ecosystem-level patterns and processes have assumed an increasingly larger role in recent decades. It might be argued, however, that research on the behaviour of individual organisms ought still to play a major role in ecology; it is upon the individual, after all, that...
Article
In boreal streams, juvenile salmonids spend substantial amounts of time sheltering in the streambed and in stream wood, presumably as a means of protection against the physical environment and from terrestrial endothermic predators. Relatively little is known about sheltering by salmonids in response to instream ectothermic predators. We tested the...
Article
Full-text available
Protection provided by shelter is important for survival and affects the time and energy budgets of animals. It has been suggested that in fresh waters at high latitudes and altitudes, surface ice during winter functions as overhead cover for fish, reducing the predation risk from terrestrial piscivores. We simulated ice cover by suspending plastic...
Article
Full-text available
Surface ice in rivers and lakes buffers the thermal environment and provides overhead cover, protecting aquatic animals from terrestrial predators. We tested if surface ice influenced the behavior (swimming activity, aggressive encounters, and number of food items eaten) and stress level (coloration of eyes and body) of stream-living brown trout Sa...
Article
Full-text available
The foraging success of predators depends on how their consumption of prey is affected by prey density under different environmental settings. Here, we measured prey capture rates of drift-feeding juvenile brown trout and European grayling at different prey densities in an artificial stream channel at 5 and 11 °C. Capture rates were lower at 5 than...
Article
Full-text available
Preferring one social partner over another can enhance fitness. This paper reports that juvenile grayling were significantly more likely to enter and forage in new, upstream habitats when paired with familiar versus unfamiliar social partners. Fish paired with unfamiliar partners or when alone were more reluctant to enter the new area. The entry ti...
Article
1. Winter ice conditions in boreal streams are highly variable, and behavioural responses by fish to river ice may affect overwinter survival rates. One type of ice, surface ice, stabilises water temperatures, reduces instream light levels and may provide overhead cover. 2. Because surface ice is believed to afford protection against endothermic pr...
Article
Full-text available
Drift-feeding salmonids in boreal streams face temperatures below physical optima for extensive periods of the year. Because juvenile salmonids react to low water temperatures by becoming nocturnal, knowledge about their foraging ability at low light intensities in cold water is needed to accurately estimate energy intake during non-summer conditio...
Article
Prey capture success and foraging mode were studied in brown trout Salmo trutta at temperatures ranging from 5.7 to 14.0° C. At low temperatures, there was a positive correlation between prey capture success and the proportion of time that the fish spent holding feeding stations. This correlation was not found at temperatures >10° C.
Article
Abstract –  Cold water temperatures are widely supposed to reduce the food intake of stream salmonids. Although cold temperatures have been documented to reduce swimming ability, digestion and gastric evacuation rates, little is known about how temperature influences the ability of fish to capture prey. We examined the effects of water temperature...

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Projects

Projects (2)
Project
LIFE CONNECTS is a LIFE+ Nature project with a budget of 10 million euro. The project aims to improve ecosystem functions and ecosystem services in seven southern Swedish rivers and in the long term also the Baltic Sea . This benefits people, biodiversity and sustainable water use. The two threathened mussel species, Thick-shelled river mussel (Unio crassus) and Freshwater pearl mussel (Margaritifera margaritifera), together with the fish species Atlantic salmon (Salmo salar) and European eel (Anguilla anguilla) are target species for this unique project. If we can get these species to thrive again, the project will be a success with cleaner water and greater biodiversity as a result. Not only in the rivers where the project is being implemented but it is reasonable to assume positive effects in the Baltic Sea in the long run. In seven streams, ecosystem features will be enhanced by creating free migration paths, passage opportunities at obstacles, and by adding a more varied bottom structure (sand, gravel, stone, blocks and dead wood), it will improve fish migration opportunities and habitats for fish and mussels for better water quality and more natural rivers. The two mussel species, Thick-shelled river mussel and Freshwater pearl mussel, have a complex lifecycle in which the mussel as a larva lives parasitically on the gills of a host fish. The gills of the fish are both a food resource and a habitat necessary for the mussel to complete its life cycle. At present, we do not know exactly which species of fish are suitable for hosting the mussel in the various rivers, such as Atlantic salmon, Brown trout, European bullhead, and European river lamprey., Thus, within the project we will study this phenomenon by mapping fish species migration, their function as hosts – ie which fish species generate high growth and survival for the mussel larvae as well as the survival and growth of mussels that have been reintroduced into the river. Another focus for the project are information efforts and communication. The project will constitute an engine for further water conservation projects, both nationally and internationally. The project runs during the period of 2019 to 2025. Link to project website: https://lifeconnects.se/?lang=en
Project
To co-produce eco-hydraulic models with hydropower industry partners to assess fish production and ecosystem services in important case studies in regulated rivers.