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Functional response and size-dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.)
Karlstad University, Faculty of Social and Life Sciences, Department of Biology.
Karlstad University, Faculty of Social and Life Sciences, Department of Biology.ORCID iD: 0000-0003-2220-1615
Karlstad University, Faculty of Social and Life Sciences, Department of Biology.ORCID iD: 0000-0002-3191-7140
2010 (English)In: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633, Vol. 19, no 2, 170-177 p.Article in journal (Refereed) Published
Abstract [en]

Terrestrial invertebrate subsidies are believed to be important energy sources for drift-feeding salmonids. Despite this, size-specific use of and efficiency in procuring this resource have not been studied to any great extent. Therefore, we measured the functional responses of three size classes of wild brown trout Salmo trutta (0+, 1+ and ≥2+) when fed either benthic- (Gammarus sp.) or surface-drifting prey (Musca domestica) in laboratory experiments. To test for size-specific prey preferences, both benthic and surface prey were presented simultaneously by presenting the fish with a constant density of benthic prey and a variable density of surface prey. The results showed that the functional response of 0+ trout differed significantly from the larger size classes, with 0+ fish having the lowest capture rates. Capture rates did not differ significantly between prey types. In experiments when both prey items were presented simultaneously, capture rate differed significantly between size classes, with larger trout having higher capture rates than smaller trout. However, capture rates within each size class did not change with prey density or prey composition. The two-prey experiments also showed that 1+ trout ate significantly more surface-drifting prey than 0+ trout. In contrast, there was no difference between 0+ and ≥2+ trout. Analyses of the vertical position of the fish in the water column corroborated size-specific foraging results: larger trout remained in the upper part of the water column between attacks on surface prey more often than smaller trout, which tended to seek refuge at the bottom between attacks. These size-specific differences in foraging and vertical position suggest that larger trout may be able to use surface-drifting prey to a greater extent than smaller conspecifics.

Place, publisher, year, edition, pages
2010. Vol. 19, no 2, 170-177 p.
National Category
Biological Sciences
Research subject
Biology
Identifiers
URN: urn:nbn:se:kau:diva-6898DOI: 10.1111/j.1600-0633.2009.00401.xISI: 000277787300002OAI: oai:DiVA.org:kau-6898DiVA: diva2:393988
Note

I manuskriptform hade denna artikel titeln "SIZE-DEPENDENT FORAGING ON AQUATIC AND TERRESTRIAL PREY BY BROWN TROUT (SALMO TRUTTA L.)".

Available from: 2011-02-01 Created: 2011-02-01 Last updated: 2016-02-17Bibliographically approved
In thesis
1. Forest – stream linkages: Brown trout (Salmo trutta) responses to woody debris, terrestrial invertebrates and light
Open this publication in new window or tab >>Forest – stream linkages: Brown trout (Salmo trutta) responses to woody debris, terrestrial invertebrates and light
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Forests surrounding streams affect aquatic communities in numerous ways, contributing to energy fluxes between terrestrial and lotic ecosystems. The five papers in this thesis focus on woody debris, terrestrial invertebrates and light, three factors influenced by riparian zone structure, potentially affecting streams and brown trout (Salmo trutta). The individual strength of these stressors and their interactions with each other are not well studied, and their qualitative effects may differ both spatially and temporally as well as with the size-structure of specific fish populations.

Using a combination of laboratory and field experiments, I examined the effects of woody debris, terrestrial invertebrates and light on prey availability and on the growth rates, diets and behavior of different size-classes of trout. My field experiments showed that addition of high densities of large wood affected trout growth in a positive way. This positive effect of large wood on trout growth may be related to prey abundance, as indicated by the high standing crop of aquatic macroinvertebrates on the wood. The positive effects on trout may also be related to decreased energy expenditures in wood habitats, as trout increased the ratio between numbers of prey captured and time spent active and that swimming activity and level of aggression decreased as wood densities were increased in a laboratory experiment. Terrestrial invertebrates are generally assumed to be a high quality prey resource for fish and my field experiments showed that reduction of terrestrial invertebrate inputs had a negative effect on trout growth. The availability of terrestrial prey in the stream was also coupled to trout diet and linked to growth, as fish with high growth rates had high proportions of terrestrial prey in their diets. Light, measured as PAR, did not have an effect on chlorophyll biomass, nor was there an effect on aquatic macroinvertebrates or trout. Hence, even if light levels were sufficient for increased photosynthesis, other factors such as low nutrient content may have limited the effects. Many of my results were dependent on fish-size. I observed, for example, that large trout had higher capture rates on surface-drifting terrestrial prey than small trout when prey densities were intermediate or high, but at low prey densities, the consumption of terrestrial prey by large and small trout were similar. Moreover, although large wood and terrestrial invertebrates affected growth of both small and large trout, the effects were generally more consistent for large trout.

Although changes in riparian forests typically induce an array of interacting effects that certainly call for further research, the overall conclusion from this thesis is that many of the factors I have studied have profound effects on stream biota and trout. The positive effects from large wood also propose that adding trees to streams may partly compensate for negative effects associated with riparian deforestation.

Place, publisher, year, edition, pages
Karlstad: Karlstad University, 2011. 42 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2011:3
Keyword
Brown trout, growth, foraging, woody debris, terrestrial invertebrates, light, riparian zone, forestry, stream
National Category
Ecology
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-6731 (URN)978-91-7063-335-5 (ISBN)
Public defence
2011-02-25, Andersalen, 11D 121, Karlstads universitet, Karlstad, 13:15 (English)
Opponent
Supervisors
Available from: 2011-02-01 Created: 2011-01-03 Last updated: 2011-10-25Bibliographically approved
2. Forest-stream linkages: Experimental studies of foraging and growth of brown trout (Salmo trutta L).
Open this publication in new window or tab >>Forest-stream linkages: Experimental studies of foraging and growth of brown trout (Salmo trutta L).
2008 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Riparian vegetation along streams and rivers affects the aquatic community in numerous ways and often operates as a link for energy flux between forest and streams. The studies presented in this licentiate thesis focus on light and terrestrial invertebrates, two factors influenced by riparian zone structure, which potentially affect stream ecosystems and thus also brown trout (Salmo trutta). Paper I is a laboratory experiment where I study size dependent foraging behavior on surface-drifting terrestrial invertebrates and benthic invertebrates by brown trout. The results show a size-dependent difference in foraging ability with large trout being better able to use terrestrial surface prey than small trout. I argue that such ontogenetic foraging differences are due to both morphological constraints (eg. gape limitation) and size dependent behavioral differences related to predation risk. Paper II consists of a 5 month-long 2x2 factorial design field experiment where my objective was to examine the effects of terrestrial invertebrate input and solar radiation (PAR) on different trophic levels in a boreal headwater stream. More specifically, I followed the effects of increased light and decreased terrestrial invertebrate subsidies on periphyton, benthic macroinvertebrates and two size classes of the top fish predator, brown trout. The results showed that the reduction of terrestrial invertebrate input had size- and seasonal-dependent effects on trout, where large trout had lower growth rates than small trout, mainly in summer. Diet analyses of trout supported growth differences in that large trout in unmanipulated enclosures consumed relatively more terrestrial prey than large trout living in enclosures with reduced terrestrial inputs. A higher reliance on terrestrial prey subsidies by large trout compared to small may be explained by ontogenetic differences in foraging and habitat choice. Despite a 2.5-fold increase in PAR, light did not have an effect on chlorophyll a biomass, nor was there an effect on the density or composition of benthic macroinvertebrates. The lack of effects on primary production may be explained by very low nutrient levels in the stream.

Place, publisher, year, edition, pages
Fakulteten för samhälls- och livsvetenskaper, 2008. 25 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2008:24
Keyword
Brown trout, diet, growth, riparian zone, forest-stream linkages, terrestrial invertebrates, light, primary production
National Category
Biological Sciences
Research subject
Biology
Identifiers
urn:nbn:se:kau:diva-1649 (URN)978-91-7063-183-2 (ISBN)
Presentation
2008-06-18, 11D121 (Anderssalen), 10:15
Opponent
Supervisors
Available from: 2008-06-18 Created: 2008-06-18 Last updated: 2011-11-24

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