Author(s): KE Smokorowski, KJ Withers, JRM Kelso
Since the implementation of the “no net loss” policy for the management of fish habitat (DFO 1986), focus on fish habitat rehabilitation has sharpened. However, aquatic resource managers have implemented fish habitat rehabilitation, enhancement and creation efforts as a tool for ecological restoration for decades. Available published information from these past efforts to rehabilitate or create new freshwater habitat in a range of systems was reviewed in terms of cost, durability, aesthetics, side effects, method of assessment, and measurable benefits to aquatic ecosystems. Documentation of the 78 habitat rehabilitation projects was often poor with only 68% assessing costs, 4% considering aesthetics, and 24% considering side effects. Of the 30 projects (38%) that examined durability, 23 reported some type of structure deterioration. Only one example of a failed project was found in the published literature. Because 15% of the projects reviewed were incomplete (12 of 78), the success of those projects could not be assessed. Therefore the 65 completed projects, which reported to have achieved at least a portion of their habitat target (and were considered successful), implies a 98% habitat rehabilitation “success” rate (65 out of 66 completed projects). However in this sense, success was often measured in terms of achieving the habitat change without assessment of the biological benefit. An increase in fish production was detected for only four (5%) of the projects. A greater proportion of studies reported an increase in the biomass and/or abundance of target fish species (27%). However, generally, the source of the increase was not assessed – i.e. whether the increased biomass was produced by an increase in successfully growing and reproducing fish, or was it a redistribution/concentration of fish in the rehabilitated habitat. Evidence of redistribution/concentration was found in 17% of the projects. Improvements in assessment, monitoring, documentation and communication of results of rehabilitation projects are needed.