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Growth, production and bioenergetics of brown trout in upland streams with contrasting riparian vegetation

Authors


Simon S. C. Harrison, Department of Zoology, Ecology and Plant Sciences, University College Cork, The Cooperage, Distillery Fields, North Mall, Cork, Ireland. E-mail: s.harrison@ucc.ie

Summary

1. A series of laboratory-based equations on trout growth and bioenergetics developed by J.M. Elliott were applied to data collected for brown trout (Salmo trutta L.) under field conditions in Co. Mayo, Western Ireland. Fish were collected by electrofishing eight upland streams with contrasting riparian vegetation; grassland, open canopy and closed canopy deciduous.

2. Stream temperatures, one of the main influencing factors on fish growth and energetics, did not differ significantly between riparian types.

3. Observed growth rates were lower than the predicted maximum growth rates and were not influenced by riparian vegetation type. Growth ranged between 0.66% day−1 for 0 + trout to 0.08% day−1 for 2 + trout.

4. Production estimates showed no clear difference between riparian vegetation types over the growing season.

5. Fish densities and biomass tended to be greater in closed canopy streams particularly in summer.

6. Actual ration sizes calculated for trout were similar to the ration required for maintenance metabolism and were only 45–63% of the maximum potential rations. Although there was an ontogenetic increase in ration size with increasing fish age, the proportion of ration available for growth (i.e. the difference between actual and maintenance rations) did not differ between age classes but was greatest in summer. 1+ and 2+ trout show greatest ration available for growth in grassland streams.

7. Trout growth did not differ between riparian vegetation types but did vary seasonally with greatest attainment in summer. Growth was limited in the present study possibly due to combined effects of reduced prey available to fish and low stream temperatures reducing metabolic requirements. In such food limited systems, terrestrial invertebrate energy subsidies could have significant benefits to brown trout growth, production and bioenergetics.

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