Tracking the resource pulse: Movement responses of fish to dynamic floodplain habitat in a tropical river

Abstract

Natural river floodplains are among the Earth's most biologically diverse and productive ecosystems but face a range of critical threats due to human disturbance. Understanding the ecological processes that support biodiversity and productivity in floodplain rivers is essential for their future protection and rehabilitation. Fish assemblage structure on tropical river floodplains is widely considered to be driven by dispersal limitation during the wet season and by environmental filtering and interspecific interactions during the dry season. However, the individual‐level movement behaviours (e.g. site attachment, nomadism, homing) that regulate dispersal of fish on floodplains are poorly understood. We combined radiotelemetry and remote sensing to examine the movement behaviour of two large‐bodied fishes (barramundi Lates calcarifer, forktail catfish Neoarius leptaspis) over the flood cycle in a tropical river‐floodplain system in northern Australia to: (a) quantify movement responses in relation to dynamic habitat resources at a landscape scale; and (b) determine the extent of spatial ‘reshuffling’ of individual fish following the wet season. Both species altered their behaviour rapidly in response to changes in the availability and distribution of aquatic habitat, with most individuals undertaking extensive movements (up to ~27 km from the tagging location) on the inundated floodplain during the wet season. Although there was considerable individual variation in movement patterns, overall barramundi distributions closely tracked the extent of floodplain primary productivity, whereas catfish distributions were most closely associated with the extent of flooded area. Most individuals of both species exhibited homing back to previously occupied dry season refugia during the wet‐to‐dry transition, even though other potential refugia were available in closer proximity to wet season activity areas. We postulate that homing behaviour modulates temporal variation in fish assemblage composition and abundance and limits the transfer of aquatic‐derived energy and nutrients into terrestrial food webs by reducing fish mortality on drying floodplains. Our study demonstrates the importance of quantifying individual‐level behaviour across the three stages of dispersal (emigration, inter‐patch movement, immigration) for our understanding of how animal movement influences energetic subsidies and other large‐scale ecosystem processes.

When and where are catfish fat fish? Hydro‐ecological determinants of energy reserves in the fork‐tailed catfish, Neoarius graeffei, in an intermittent tropical river

“…This is particularly the case in tropical or dryland regions where flooding coincides with warm water (Junk et al., 1989; Puckridge et al., 2010), which promotes primary production and the subsequent transfer of energy to higher trophic levels. High flows may also help fish increase their energy reserves by increasing access to energy‐rich habitats (Crook et al., 2019; Jardine, Pusey, et al., 2012; Pusey et al., 2020). Many fish reproduce during seasonal high flows because surplus energy can be diverted to gametogenesis and the food‐rich environment promotes larval survival (Bailly et al., 2008; Balcombe et al., 2012; Welcomme, 1979).…”

New insights into the food web of an Australian tropical river to inform water resource management

“…Elsewhere in northern Australia, N. graeffei and L. calcarifer have been shown to link riverine food webs in time and space 28 . Radiotelemetry research in another northern Australian river revealed that during flooding, L. calcarifer and N. graeffei move, on average, 4 to 6 km, respectively, from their home location along the main-channel network and hundreds of meters onto the floodplain 43 . We recommend that more targeted research using tagging techniques is needed to test whether similar movement occurs in the Fitzroy River.…”

“…For example, we observed many young-of-the-year fish using the floodplain. It is likely these fish retreated to the main-channel of the river as the floodplain contracted during the dry season, as is common in many rivers around the world 43 , 44 taking newly-assimilated carbon with them. Furthermore, Indigenous peoples have observed that L. calcarifer occupy areas where flood-runner creeks join the main-channel and feed on small-bodied fish returning from the floodplain 45 .…”

Tracking Science: An Alternative for Those Excluded by Citizen Science

“…Tracking is also widely used as a metaphor in conservation biology to record biodiversity (Noss 1990;Kremen et al 1994;Lawler et al 2015). Examples include using geolocators to track bird or fish movements (Brlík et al 2019;Crook et al 2019). For almost 30 years, volunteers have been tracking monarch butterflies (Cohn 2008; Ries and Oberhauser 2015).…”