Fish and invertebrate responses to dry season and antecedent flow in south-west Western Australian streams (Low Flows report series)

The south - west of Western Australia (SWWA) is one of the world’s 34 biodiversity hotspots . The aquatic ecology has a high degree of endemism, unique species assemblages and low species richness . Recent changes in climate and land use have altered the low - flow characteristics of many SWWA streams and in response, the ecological characteristics have , and are continuing , to change. The project aimed to identify ecological indicators of low - flow stress to guide the management of systems in an increasing drying climate and under growing pressure for water resources. Low - flow classifications (Mackay et al. 201 2 ) developed as part of this project have been applied to the rivers of the SWWA and have been used in interpreting the linkages between low - flow conditions and the ecology of these rivers. The hydrological characteristics of each site were calculated over a perio d of 15 years. Low - flow variables included the number and variation of zero - flow days in the preceding years, monthly low - flow percentiles, annual minima of 30 day means and the variation in the annual minima of 30 day means. The relationship between the fish abundance, fish diversity measures and macroinvertebrate low - flow traits in response to low - flow variables was examined separately by non - parametric multivariate analyses performed using the PRIMER v6 (Plymouth Routines in Multivariate Ecological Research) package (Clarke & Warwick, 2001). Although there was tight clustering of sites based on their low - flow characteristics , this contrast ed with large variation in the corresponding biotic assemblages . The sites classified as ephemeral or moderately ephemeral ( low - flow classes 3 and 4) supported animals with traits suited to conditions of low flow, tolerance of higher levels of salinity, short reproduction times, air breathing and dispersal by flight. In addition to the hydrological characteristics, the biotic assemblages (particularly fish abundance) were also influenced by water quality , geography and land use changes. Context is important in the interpretation of results. Recent changes in land use, climate and water use was helpful in explaining many of the patterns in biotic assemblages . The presence of pools was another factor that aided the interpretation of results which was not characterised in the low - flow variables A large and geographically diverse spatial network of 97 river health monitoring sites from two river health programs were included in this study . Associated f ield work was conducted during the spring and summer of 2008 – 09 and the spring of 2009 with one sampling event per site. Thi s resulted in a biological database consisting of fish and macroinvertebrate populations, and environmental variables including water quality, macroinvertebrate habitat and climate. The drying or connecting of pools within SWWA needs further investigation as this may be more important for interpreting the ecology than the duration or magnitude of the low - flow conditions. Moreover, an index representing the presence or absence of pools is required in any future work of this scale