Dataset for 'Effects of gravel extraction and habitat restoration on fish populations in a braided river'

Despite their dynamic and resilient nature, braided rivers are experiencing global decline due mainly to anthropogenic impacts. Gravel extraction is a key commercial activity that can negatively affect braided rivers. However, innovative methods aiming to combine commercial aggregate harvesting and ecosystem restoration are being trialled. To compare the environmental effects of a novel beach-skimming technique, intended to be restorative, with traditional pit mining methods for gravel extraction, we evaluated aspects of the population health of a generalist fish species as biological indicators. We examined the diet contents, parasite load, and growth rates of the upland bully (<i>Gobiomorphus breviceps</i>) to evaluate ecosystem integrity. These bioindicators were compared amongst three treatments - pit-mined ponds, beach-skimmed river restoration sites, and unmodified river reaches (control) - on a section of the Aparima River, Southland, New Zealand. There were clear differences between the river treatments and the pit mining ponds, with fish sampled in ponds exhibiting greater parasite loads and faster growth. The more suitable conditions for growth and parasites in pit-mined ponds may be attributable to a range of factors including higher temperatures, elevated nutrient levels, and lack of flow. Sites harvested via beach-skimming (restoration) and unmodified river reaches (control) did not show any difference, leaving the efficacy of the beach skimming method uncertain as a restoration technique for native fish conservation, although no adverse impacts of this method were observed. Further development of integrative gravel extraction and river restoration methodology is critical to enhance the ecosystem functioning and native biodiversity of braided rivers.Mean environmental variables among treatments across sampling months - Environmental variables included are depth, nutrients (total phosphorus and total nitrogen), velocity and discharge. All variables were sampled monthly in February, March, and April, apart from POND depth which was sampled in February and April only.The growth of upland bullies in their second year (1+) was estimated to test the effect of treatment on fish growth. The annual growth increments (annuli) of 40 sagittal otoliths from 40 upland bullies (four per site, all captured in March 2023) were independently counted by two observers. An ANOVA was used to test the influence of treatment on growth.Repeated measures ANOVAs were run on parasite load (<i>Apatemon jamiesoni - </i>the most abundant parasite) of upland bully (<i>Gobiomorphus breviceps</i>) among three treatments.Repeated measures ANOVAs were run on diversity (based on shannon diversity index) of upland bully (<i>Gobiomorphus breviceps</i>) diet among three treatments.EPT taxa in upland bully (<i>Gobiomorphus breviceps</i>) diet among three treatments. The percentage abundance by number (%N) of EPT taxa in each treatment was determined by calculating the %N of each EPT taxon for each treatment and month ((number of each EPT taxon per treatment per month / total number of taxa per treatment per month) × 100). These values were averaged across sampling months, followed by summing all taxa per EPT order.The three treatments were: sites where a novel beach skimming gravel extraction method that aims to restore braided river functioning is being trialled (RES), pit mining ponds, which are homogenous in structure and located on the riverbed, but separated from the active channel (POND), and unmodified,<b> </b>degraded river reaches that were used as “controls’’ (UNRES).