Fish movement strategies in an ephemeral river in the Simpson Desert, Australia

Abstract

Arid zone catchments experience extreme hydrological variability and some rivers are entirely ephemeral, replenished only by intermittent flooding. The ecological roles of ephemeral systems are rarely studied. This paper describes movement patterns of fish in the Mulligan River, an ephemeral system in the Lake Eyre Basin, central Australia. Several sites were sampled along a temporal gradient encompassing floods and dry periods. After a single major flood in 2007 up to seven fish species were found at sites up to 300 km from the closest permanent waterhole. Following a series of floods (when waterholes were replenished and remained wet between 2009 and 2011) a further five species were recorded including the first records for the Lake Eyre hardyhead, Craterocephalus eyresii, from the rivers of far western Queensland.The presence of all species known from the parent catchment (the Georgina, where permanent waterholes occur) in the ephemeral catchment (the Mulligan) suggests that many fish species present in the river systems of central Australia are capable of dispersing long distances following the opening of movement pathways during flooding. However, two distinct groups of species were identified: extreme dispersing species, that move as far as possible into intermittently wetted habitats, and conservative dispersing species, that do not move as far, tending to inhabit deeper waterholes within mid-reaches of the river that are more likely to hold water for longer. Preservation of the natural flow regime of Australia's arid-zone rivers is important for maintaining these fish communities and facilitating study of their adaptations to ephemerality.

Fish Distribution in Far Western Queensland, Australia: The Importance of Habitat, Connectivity and Natural Flows

“…However, overall catchment fish species richness is not increased by flooding except in instances where an ephemeral sub-catchment (such as the Mulligan [31]) is connected to a more diverse source catchment such as the Georgina. In contrast, results from the Diamantina catchment provide evidence that prolonged dry periods are likely to result in a more depauperate fish fauna in Australian dryland systems, as this catchment did not experience major flooding during the study.…”

“…Results demonstrating a preference for ephemeral habitats by certain fish species are also supported by data from this study, however it should be noted that the number of species declined dramatically in the ephemeral Mulligan catchment as it dried throughout 2007, a result not replicated in the Mulligan's parent river, the Georgina. The presence of permanent waterholes in the Georgina, and their absence in the Mulligan, accounts for this difference, and suggests that species and individuals likely to capitalise on the conditions afforded by ephemeral habitats originate from source populations in permanent refuges [31].…”

“…The Mulligan River, in the far west of the study area, has no permanent waterholes and is an entirely ephemeral river, The number of permanent waterholes increases along a west-east transect (i.e., from the Georgina east to the Cooper), however all of the catchments are characterised by intermittent rivers that persist as isolated waterholes for the majority of the time and periodically connect during flow and floods. [31], but these results are not presented and are mentioned only if they are relevant to the main dataset.…”

“…On-going sampling of the Diamantina and Georgina catchments following major floods is required in order to accurately map the distribution of Lake Eyre hardyhead in Queensland, as these are the first records of the species from Queensland rivers. Prior to this work Lake Eyre hardyhead was assumed to be a South Australian species [12,13], and its presence in Queensland suggests that, like many other species, it demonstrates wide-ranging migration behaviour when conditions are favourable [31]. None of the endangered species known from spring complexes in Queensland, such as red-finned blue-eye, Scaturiginichthys vermeilipinnis, Edgbaston goby, Chlamydogobius squamigenus, and Elizabeth Springs goby, Chalmydogobius micropterus, have been recorded in Lake Eyre Basin rivers.…”

“…The main sampling effort (from 2006 to 2008) formed part of his PhD research [29], and since that time Adam has continued to work in the rivers and spring complexes of arid Queensland, as well as advocate for their preservation [18,[30][31][32].…”