Effective environmental water management for freshwater fish requires a clear understanding of how populations recruit, persist, and respond to flow and habitat conditions. This study draws on 23 years of survey data (2002–2025) and presents a comprehensive analysis of population dynamics for native freshwater fish from 1622 sampling events across 411 monitoring sites in South Australian river systems with a primary focus on the Mount Lofty Ranges.
The Mount Lofty Ranges represent a particularly important system for evaluating these impacts as they support several native fish species of conservation concern. To evaluate existing dynamics, two complementary analytical frameworks were applied. First, a recruitment dynamics analysis examined recruitment–adult abundance relationships, flow dependencies, and habitat associations for seven focal species with length-based age-class data: Mountain and Obscure Galaxias (Galaxias olidus and Galaxias oliros), River Blackfish (Gadopsis marmoratus), Southern Pygmy Perch (Nannoperca australis), Carp Gudgeon (Hypseleotris spp.), Dwarf Flathead Gudgeon (Philypnodon macrostomus), and Murray Hardyhead (Craterocephalus fluviatilis). Second, an occupancy dynamics analysis used a presence-absence dataset to assess site persistence, colonisation, and abundance trends for ten native species.
This work addressed three core management questions: (1) whether local adult populations contribute meaningfully to recruitment and, if so, at what abundance thresholds; (2) how stable local populations are; and, therefore the probability of persistence versus local extinction between years; and (3) what habitat and flow conditions are associated with species occurrence and abundance.
Findings provide preliminary quantitative benchmarks for adult population thresholds supporting recruitment, estimates of site-level persistence and colonisation probabilities, and identification of key flow and habitat drivers of occurrence across species of varying conservation status. These results offer a multi-decadal evidence base to guide environmental water allocation and habitat management aimed at ensuring native freshwater fish populations are at a low level of risk of population decline/loss in South Australia.