Unearthing a New Approach to Gravel Extraction: Can It Restore Freshwater Fish Habitat and Improve Their Population Health?

ABSTRACT Despite their dynamic and resilient nature, river systems are degrading worldwide, with gravel extraction a key commercial activity that significantly threatens their integrity and natural functioning. However, extraction methods aiming to combine commercial aggregate harvesting and riverbed ecosystem restoration are being trialled. To evaluate one such approach, we compared the environmental effects of an experimental gravel and overburden skimming technique, designed for restoration, with those of traditional pit mining. Population health indicators—diet, parasite load and growth rate—were assessed in a generalist fish, the upland bully ( Gobiomorphus breviceps ), across three treatments: pit‐mined ponds, gravel and overburden skimming river restoration sites, and unmodified river reaches, all located in a section of the Aparima River, New Zealand. Fish in pit mining ponds had higher parasite loads and faster growth rates than those in the river treatments. These differences are likely due to more suitable conditions for fish growth and parasites in pit‐mined ponds, including elevated nutrient levels, higher temperatures and a lack of flow. Sites harvested via experimental gravel and overburden skimming (restoration) and unmodified river reaches (control) showed minimal differences, leaving the efficacy of the experimental gravel and overburden skimming method as a restoration technique for native fish conservation uncertain, but showing that extraction using this method did not have a negative effect on the fish population health variables assessed. This contrasts with pit mining, which, as indicated by fish population health, was more environmentally disruptive. Further regulation, monitoring, and development of integrative gravel extraction and river restoration methodologies could potentially enhance the ecosystem functioning and native biodiversity of river systems.