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Fine stream wood: effects on drift and brown trout (Salmo trutta) growth and behaviour
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences. (Naturresurs Rinnande Vatten)ORCID iD: 0000-0001-7160-1290
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Stream ecosystems and their riparian zones have previously been regarded as two different ecosystems, linked through numerous reciprocal subsidies. Today, ecologists agree that the stream and the riparian zone should be regarded as one system, the stream-riparian ecosystem, which is characterised largely by the subsidies between land and water. The terrestrial subsidies to the stream affect stream-living biota in several ways, some of which are well-known while others less so. The input of wood to the stream from the riparian zone is believed to play an important role in the population dynamics of stream-living fish. In this doctoral thesis, I explore effects of fine stream wood (FW, <10 cm diameter) on wild stream-living young-of-the-year brown trout (Salmo trutta) by reporting and discussing results from laboratory, semi-natural and field experiments. My results show that the local density of drifting prey is higher in the presence of FW than in its absence, and also that young-of-the-year brown trout decrease their diurnal foraging time and prey capture success when FW is added to their habitat. I show that trout decrease their swimming activity in the presence of FW, aggregate in FW bundles, and have lower growth rates than trout without FW access. Also, the degree of sheltering in FW bundles was higher during day than at night in a study performed at low water temperatures; moreover, the presence of an ectothermic nocturnal predator (burbot, Lota lota) did not affect the degree of sheltering in FW bundles by trout. Taken together, my results indicate that young-of-the-year brown trout with access to FW bundles spend considerable amounts of time sheltering in the FW, and by doing so they miss the opportunity for higher growth and foraging rates outside of the shelter. The most probable explanation for this behaviour is that growth is traded off against survival, i.e., the predation risk is higher outside of the shelter.

Abstract [en]

Stream ecosystems and their riparian zones have previously been regarded as two different ecosystems, linked through numerous reciprocal subsidies. Today, ecologists agree that the stream and the riparian zone should be regarded as one system, the stream-riparian ecosystem, which is characterised largely by the subsidies between land and water. In this doctoral thesis, I explore one such subsidy – the input of fine stream wood (FW) to streams. Wild stream-living young-of-the-year brown trout (Salmo trutta) was chosen as study species. My results show that the local density of drifting prey is higher in the presence of FW than in its absence, and that young-of-the-year brown trout decrease their diurnal foraging time and prey capture success when FW is added to their habitat. I show that trout decrease their activity in the presence of FW, aggregate in FW bundles, and have lower growth rates than trout without FW access. Taken together, my results indicate that young-of-the-year brown trout spend considerable amounts of time in FW bundles, and by doing so they miss the opportunity for higher growth and foraging rates outside of the shelter. The most probable explanation for this behaviour is that growth is traded off against survival.

Place, publisher, year, edition, pages
Karlstad University Press, 2016. , 43 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 34
Keyword [en]
stream fish, wood, salmonid, trout, aquatic invertebrates, behaviour, sheltering
National Category
Biological Sciences
Research subject
Biology
Identifiers
URN: urn:nbn:se:kau:diva-44537ISBN: 978-91-7063-715-5OAI: oai:DiVA.org:kau-44537DiVA: diva2:950545
Public defence
2016-09-23, 9C 203, Universitetsgatan 2, Karlstad, 10:15 (English)
Opponent
Supervisors
Available from: 2016-09-02 Created: 2016-08-01 Last updated: 2016-09-02Bibliographically approved
List of papers
1. Effects of fine wood on macroinvertebrate drift in four boreal forest streams
Open this publication in new window or tab >>Effects of fine wood on macroinvertebrate drift in four boreal forest streams
2016 (English)In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 765, no 1, 317-327 p.Article in journal (Refereed) Published
Abstract [en]

Most studies of stream wood have focused on pieces a parts per thousand yen0.1 m diameter. However, this approach may overlook an important feature of small streams, where wood < 0.1 m can constitute the majority of wood pieces. We examined the effect of fine wood (FW) on local drift of stream macroinvertebrates. The study was carried out at seven sites in four boreal forest streams, from early June to mid-August 2011. This was done by anchoring bundles of FW at each site and measuring drift upstream and downstream of each bundle. We hypothesized that FW would increase drift density, biomass and diversity of aquatic invertebrates. Ten weeks after FW addition, aquatic drift density was higher downstream than upstream of FW bundles, while drift biomass and drift diversity did not differ significantly downstream and upstream of FW.

Keyword
Invertebrates, Colonization, FWD, In-stream wood, Small woody debris
National Category
Biological Sciences
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-40971 (URN)10.1007/s10750-015-2423-x (DOI)000366641200022 ()
Available from: 2016-03-03 Created: 2016-03-03 Last updated: 2016-09-02Bibliographically approved
2. Effect of fine wood on juvenile brown trout behaviour in experimental stream channels
Open this publication in new window or tab >>Effect of fine wood on juvenile brown trout behaviour in experimental stream channels
2015 (English)In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, 1-10 p.Article in journal (Refereed) Published
Abstract [en]

In-stream wood can increase shelter availability and prey abundance for stream-living fish such as brown trout, Salmo trutta, but the input of wood to streams has decreased in recent years due to harvesting of riparian vegetation. During the last decades, fine wood (FW) has been increasingly used for biofuel, and the input of FW to streams may therefore decrease. Although effects of in-stream FW have not been studied as extensively as those of large wood (LW), it is probably important as shelter for small-sized trout. In a laboratory stream experiment, we tested the behavioural response of young-of-the-year wild brown trout to three densities of FW, with trout tested alone and in groups of four. Video recordings were used to measure the proportion of time allocated to sheltering, cruising and foraging, as well as the number of aggressive interactions and prey attacks. Cruising activity increased with decreasing FW density and was higher in the four-fish groups than when fish were alone. Foraging decreased and time spent sheltering in FW increased with increasing FW density. Our study shows that juvenile trout activity is higher in higher fish densities and that trout response to FW is related to FW density and differs from the response to LW as reported by others. © 2015 John Wiley & Sons A/S.

Place, publisher, year, edition, pages
John Wiley & Sons, 2015
Keyword
salmonid; YOY; streams; wood; small woody debris
National Category
Ecology Biological Sciences
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-42488 (URN)10.1111/eff.12244 (DOI)2-s2.0-84938718603 (ScopusID)
Available from: 2016-05-27 Created: 2016-05-23 Last updated: 2016-09-02Bibliographically approved
3. Winter sheltering by juvenile brown trout (Salmo trutta): Effects of stream wood and an instream ecothermic predator
Open this publication in new window or tab >>Winter sheltering by juvenile brown trout (Salmo trutta): Effects of stream wood and an instream ecothermic predator
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-45641 (URN)
External cooperation:
Available from: 2016-09-02 Created: 2016-09-02 Last updated: 2016-09-02Bibliographically approved
4. Fine stream wood decreases growth of juvenile brown trout (Salmo trutta)
Open this publication in new window or tab >>Fine stream wood decreases growth of juvenile brown trout (Salmo trutta)
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-45653 (URN)
External cooperation:
Available from: 2016-09-02 Created: 2016-09-02 Last updated: 2016-09-02Bibliographically approved

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