RESPONSES OF BROWN TROUT AND BENTHIC INVERTEBRATES TO CATCHMENT-SCALE DISTURBANCE AND IN-STREAM RESTORATION MEASURES IN BOREAL RIVER SYSTEMS, ACTA UNIVERSITATIS OULUENSIS A Scientiae Rerum Naturalium 565
|Kustantaja:||Oulun yliopisto|| |
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|Tekijät:||LOUHI PAULIINA|| |
Maintaining connectivity in boreal streams by rehabilitation procedures is a challenging task thatrequires ecological understanding based on empirical research. In this thesis, I examined theeffects of stream rehabilitation on densities and growth of brown trout (Salmo trutta L.), as wellas on benthic biodiversity. As streams are known to be closely connected to their watersheds, Ialso examined the effects of watershed drainage activities on stream organisms.
The results of this thesis have implications for enhancing salmonid populations, as well formaintaining stream biodiversity. First, regional climatic variability was shown to override localimpacts of watershed management on stream biota. This highlights the importance of placingresults from local studies in a regional context. Second, increased sedimentation that typicallyfollows anthropogenic actions in the watershed did not only cause direct mortality on the early lifestages of brown trout, but also forced them to emerge earlier from gravel and constrained theirdevelopment. Thus, sedimentation may have far-reaching fitness consequences on juvenilesalmonids.
Third, while instream rehabilitation did enhance habitat diversity for salmonid fish, there wereonly marginal effects on juvenile fish and benthic biodiversity. Therefore, the factors limitingstream biota, and obscuring positive effects of rehabilitation, are to be found elsewhere. For thispurpose, my thesis offers at least three potential, not mutually exclusive explanations: (i)land usechanges have altered watersheds and this can be seen as decreased stream biodiversity that cannotbe corrected through local-scale restoration efforts; (ii)a habitat-forming organism group, streambryophytes, is dispersal limited, slowing down any positive responses to restoration by fish orinvertebrates that depend strongly on bryophytes; and (iii)changes to stream habitat heterogeneitycaused by channelization for timber floating were rather modest to start with, and therefore anyeffects of stream habitat rehabilitation on stream biota are likely to be subtle.
Based on these findings, I suggest that future restoration efforts should be prioritized accordingto a comprehensive watershed assessment. Also, monitoring of projects should be more rigorousand preferably multidisciplinary, documenting the ecological as well as hydrological andsocioeconomic outcomes of rehabilitation projects.