Ireland David McCormick amp Simon Harrison School of Biological Earth and Environmental Sciences University College Cork Introduction Potential multiple benefits of protected riparian zones ID: 145831
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Slide1
Direct and indirect effects of riparian canopy on juvenile stream-dwelling salmonids in south-west Ireland
David McCormick & Simon HarrisonSchool of Biological, Earth and Environmental Sciences, University College CorkSlide2
IntroductionPotential
multiple benefits of protected riparian zones: -Trap nutrient and sediment runoff - Enhance bank stability
- Prevent excessive sediment input from grazing stock - Increase aquatic and terrestrial biodiversity
Increase
in riparian tree growth
within protected zones is assumed/hoped to be beneficial to stream biotaSlide3
Direct effects:Cover from avian
predatorsDecrease in primary productivity but increase in organic matter input
Effects on water temperatureIndirect
effects:
Impact on
macroinvertebrate communitiesDistribution and abundance of aquatic macrophytes
Effects of riparian
canopy on
salmonid
habitatSlide4
Majority of research conducted in other ecoregions.Considerable variation reported in riparian canopy effects in Ireland.
- Positive, neutral and negative effect on density - Positive effects as cover - Complex effects on diet and behaviour
It may be difficult therefore to predict the local effect
of broad-scale management
.
Best riparian management strategy?Slide5
Role of instream macrophytes
Many Irish streams have abundant submerged or floating-leaved vegetation.Significant contributor to habitat heterogeneity and system productivity.
Influenced by water chemistry, benthic substrate,
flow conditions and
riparian shade
.Slide6
Study design
Paired multi-stream study with open and shaded stretches on each stream.30-50m stretches electro-fished 3 times (May, August and September).Gut contents of captured fish taken for diet analysis.
Macroinvertebrate samples were taken from gravel and macrophytes (where present).Slide7
Results
Significantly greater numbers of 0+ salmon were found in open, unshaded, streams stretches.0+ salmon found in the open stretches were also significantly
longer than those found in the shade.
Mean (±SE) estimated densities of
salmon and trout in open (□) and shaded (■) stretches on the seven study rivers. Streams are arranged in ascending order of
macrophyte
density.Slide8
Macroinvertebrate density was significantly greater in the open stretches.Within the open stretches, macroinvertebrate density was significantly greater in the
macrophyte patches than in the gravel benthos.
(A) C
omparison
between the gravel
surbers in the open (□) and shaded stretch (■) of each pair.
(B) C
omparison
between the gravel surbers (□) and the
macrophyte
surbers
(■) within the open stretches
.
Macroinvertebrate
densitySlide9
Mean abundance of dominant prey
items in the stomachs of 0+ salmon in the open (O) and shaded (S) stretches
Salmonid diet
■
=
Chironomidae
,
▒
=
Simuliidae
,
■
=
Baetidae
,
□
=
Other
.
Trend towards more food in the stomachs of 0+ salmon in the open
stretches
Significant
positive correlation between total gut
contents
of 0+ salmon
and
macrophyte
density in the stream
Composition
of the diet of 0+ salmon showed a greater similarity to the macroinvertebrate community of the macrophytes than of the gravelSlide10
Gut contents were significantly less equitable for salmon in the open, macrophyte-dominated stream sections: a few salmon ate a lot more!
Rank abundance curves for total gut contents of salmonids for all rivers combined
.
Open stretches Shaded stretchesSlide11
Conclusions
Variation in the effect of riparian canopy on juvenile salmon densities and growth may be mediated by macrophytes.Macrophytes are an important source of potential invertebrate prey (Simuliidae,
Chironomidae and Baetidae) for juvenile salmon.
Macrophytes
also provide highly suitable foraging habitat for juvenile salmon.
High macrophyte
densities likely benefits populations of juvenile salmon, providing they are not accompanied by deleterious habitat quality.
Implications for riparian management…