Environmental influences on migration patterns and pathways of a threatened potamodromous fish in a regulated lowland river network

Abstract

In riverine ecosystems, movements of biota among different parts of the river network are fundamental to the functioning and sustainability of populations, especially for fish. Globally, human activities (e.g., dam construction and altered flow regimes) have impaired riverine fish movements through reduced river connectivity, leading to well‐documented population declines. This study examined the timing and extent of movement of a nationally threatened potamodromous fish, silver perch (Bidyanus bidyanus), among different parts of the mid‐Murray River network in south‐eastern Australia using acoustic telemetry to identify the relative importance of different environmental variables (including river discharge) influencing timing and extent of movements. A total of 203 silver perch (fork length range 120–415 mm) was tagged in the Murray River. Silver perch occupied extended reaches of river (hundreds of kilometres) and multiple habitats throughout the river network, ranging from a large mainstem river to inflowing tributaries, anabranches and floodplain habitats. Movements were associated with aspects of the flow regime, such as small to moderate mainstem discharge rises and elevated tributary discharge. These results emphasise the importance of managing silver perch populations within an integrated riverscape context rather than solely focusing on reach/river scales. The inter‐relationship between silver perch movement and river discharge highlights the susceptibility of the species to river regulation, which has previously been implicated in its decline. The information on migratory behaviours in this study provides empirical evidence to support refinement and implementation of targeted restoration strategies, such as environmental flows, to assist the management and conservation of an imperilled species.

Contrasting natal origin and movement history informs recovery pathways for three lowland river species following a mass fish kill

“…Several studies have documented movement of Murray River silver perch into other connected habitats (e.g. Zampatti et al 2018;Koster et al 2021). Further, Zampatti et al (2018) identified that some silver perch captured in the lower Murray River exhibited a Darling River natal origin.…”

“…Reynolds 1983;Llewellyn 2014;Thiem et al 2020). These large movements are often associated with periodic spawning in adult golden perch and silver perch, and the subsequent long-distance dispersal of eggs, larvae and juveniles (Koster et al 2021;Stuart and Sharpe 2020). By contrast, long-distance movements of adult Murray cod appear facultative and are not required for reproduction, with predictable annual spawning occurring under a range of river discharges and the well-developed larvae of this nesting species able to actively settle out in favourable, localised habitats (Reynolds 1983;Kopf et al 2014).…”

Population demographics of golden perch (

“…Worldwide, there is growing recognition of the potential importance of tributaries to the population dynamics of riverine fish in flow-regulated rivers (Rice et al 2008;Pracheil et al 2013;Koster et al 2021). Tributaries that preserve the hydrological and hydraulic conditions that promote spawning and recruitment may subsequently provide a source of recruits to flow-affected main channel habitats (Pollux et al 2006;Webber et al 2013).…”

Does life history mediate discharge as a driver of multi‐decadal changes in populations of freshwater fish?

“…For golden and silver perch, migration of both adults and juveniles is an important life history strategy for reproduction and dispersal (e.g., Koster et al. 2020, Stuart and Sharpe 2020) with recruitment highly variable through space and time (Zampatti and Leigh 2013, Tonkin et al. 2019).…”