2017
 

A comparison of the survival and migration of wild and F1-hatchery-reared brown trout (Salmo trutta) smolts traversing an artificial lake

År: 2017

Supplementing salmonid populations by stocking is a widely-used method to improve catch or to rehabilitate populations. Though, most studies found that survival and fitness of hatchery-reared salmonids is inferior to wild fish. We compared survival, emigration patterns, migration speed and return rates from the sea of wild and 1-year old F1-hatchery-reared brown trout smolts in a Danish lowland stream that contains an artificial lake using passive integrated transponder telemetry in the years 2011–2013 and 2016. The majority of hatchery-reared smolts descended within 72 h after their release, whereas wild fish migration was mainly triggered by increased water discharge. Increased probability of a successful lake passage was found at higher discharge. Within years, the groups differed in lake passage time, but without a significant overall difference. Overall, there was no difference in lake survival (wild: 30%, hatchery-reared: 32%) between the two groups, but survival differed between years. Only a single fish (0.9%) of the hatchery-reared smolts tagged in 2011–2013 returned from the sea compared to 11 (6.4%) wild smolts tagged in that period, which questions the value of supplementary stocking of smolts for conservation purposes.

Original languageEnglish
JournalFisheries Research
Volume196
Pages (from-to)47-55
ISSN0165-7836
DOIs
StatePublished - 1 Dec 2017

 

Species integrity enhanced by a predation cost to hybrids in the wild

År: 2017

Species integrity enhanced by a predation cost to hybrids in the wild

Nilsson, P. A., Hulthén, K., Chapman, B. B., Hansson, L-A., Brodersen, J., Baktoft, H., Vinterstare, J., Brönmark, C. & Skov, C. 2017 In : Biology Letters. 13, 7, 20170208

Publication: Research - peer-reviewJournal article – Annual report year: 2017

Species integrity can be challenged, and even eroded, if closely related species can hybridize and produce fertile offspring of comparable fitness to that of parental species. The maintenance of newly diverged or closely related species therefore hinges on the establishment and effectiveness of pre- and/or post-zygotic reproductive barriers. Ecological selection, including predation, is often presumed to contribute to reduced hybrid fitness, but field evidence for a predation cost to hybridization remains elusive. Here we provide proof-of-concept for predation on hybrids being a postzygotic barrier to gene flow in the wild. Cyprinid fishes commonly produce fertile, viable hybrid offspring and therefore make excellent study organisms to investigate ecological costs to hybrids. We electronically tagged two freshwater cyprinid fish species (roach Rutilus rutilus and bream Abramis brama) and their hybrids in 2005. Tagged fish were returned to their lake of origin, exposing them to natural predation risk from apex avian predators (great cormorant, Phalacrocorax carbo). Scanning for regurgitated tags under cormorant roosts 3-4 years later identified cormorant-killed individual fish and allowed us to directly test for a predation cost to hybrids in the wild. Hybrid individuals were found significantly more susceptible to cormorant predation than individuals from either parental species. Such ecological selection against hybrids contributes to species integrity, and can enhance species diversification.
Original languageEnglish
Article number20170208
JournalBiology Letters
Volume13
Issue number7
ISSN1744-9561
DOIs
StatePublished - 2017

 

Adaptive management in the context of barriers in European freshwater ecosystems

År: 2017

Adaptive management in the context of barriers in European freshwater ecosystems

Birnie-Gauvin, K., Tummers, J. S., Lucas, M. C. & Aarestrup, K. 2017 In : Journal of Environmental Management. p. 436-441

Publication: Research - peer-reviewJournal article – Annual report year: 2017

Many natural habitats have been modified to accommodate for the presence of humans and their needs. Infrastructures e such as hydroelectric dams, weirs, culverts and bridges e are now a common occurrence in streams and rivers across the world. As a result, freshwater ecosystems have been altered
extensively, affecting both biological and geomorphological components of the habitats. Many fish species rely on these freshwater ecosystems to complete their lifecycles, and the presence of barriers has been shown to reduce their ability to migrate and sustain healthy populations. In the long run, barriers
may have severe repercussions on population densities and dynamics of aquatic animal species. There is currently an urgent need to address these issues with adequate conservation approaches. Adaptive management provides a relevant approach to managing barriers in freshwater ecosystems as it addresses
the uncertainties of dealing with natural systems, and accommodates for future unexpected events, though this approach may not be suitable in all instances. A literature search on this subject yielded virtually no output. Hence, we propose a step-by-step guide for implementing adaptive management, which could be used to manage freshwater barriers
Original languageEnglish
JournalJournal of Environmental Management
Pages (from-to)436-441
ISSN0301-4797
DOIs
StatePublished - 2017

 

30 years of data reveal dramatic increase in abundance of brown trout following the removal of a small hydrodam

År: 2017

Humans and freshwater ecosystems have a long history of cohabitation. Today, nearly all major rivers of the world have an in-stream structure which changes water flow, substrate composition, vegetation, and fish assemblage composition. The realization of these effects and their subsequent impacts on population sustainability and conservation has led to a collective effort aimed to find ways to mitigate these impacts. Barrier removal has recently received greater interest as a potential solution to restore river connectivity,
and reestablish high quality habitats, suitable for feeding, refuge and spawning of fish. In the present study, we present thirty years of data from electrofishing surveys obtained at two sites, both prior to and following the removal of a small-scale hydropower dam in Central Jutland, Denmark. We demonstrate
that the dam removal has led to a dramatic increase in trout density, especially in young of the year. Surprisingly, we found that this increase was not just upstream of the barrier, where the ponded zone previously was, but also downstream of the barrier, despite little changes in habitat in that area. These
findings suggest that barrier removal may be the soundest conservation option to reinstate fish population productivity
Original languageEnglish
JournalJournal of Environmental Management
Volume204
Pages (from-to)467-471
ISSN0301-4797
DOIs
StatePublished - 2017