Impact of water development on river flows and the catch of a commercial marine fishery

Abstract

The growing demand for freshwater resources has led to dam construction and water diversions in a majority of the world's large rivers. With an increasing demand for freshwater, trade‐offs between water allocations and the preservation of ecological connections between terrestrial and marine ecosystems are inevitable. The ecological links formed by rivers flowing into the ocean benefit many commercially fished species. The degree to which different species and the livelihoods of fishers are negatively impacted by changes in river flows due to water extraction or diversion is important for management across terrestrial and marine boundaries. Our objective was to predict how changes in freshwater flows from three wet–dry tropical rivers in northern Australia, that is, the Mitchell, Gilbert, and Flinders rivers, affect the commercial banana prawn (Penaeus merguiensis) catch. We used a novel spatiotemporal Bayesian approach to model the effects of river flows and key climate drivers on banana prawn catch. We then predicted how the loss of flow due to water extraction or diversion affected prawn catch. Our analyses of three water development scenarios found that catch was most impacted by water extraction during low flows. The impact of water extraction was greatest for a scenario with dams on the Mitchell River, where we predicted catch would decline by 53% during a year with low flow. Overall, our results imply that maintenance of low‐level flows is a crucial requirement for sustained fishery yields. We suggest that water managers must balance agricultural demand for water during drier years against the impact of water extraction on prawn fisheries during low‐flow years. Protecting low‐level flows during drier years is a priority for maintaining terrestrial–marine linkages for adjacent marine fisheries.

River flows affect the growth of a tropical finfish in the wet-dry rivers of northern Australia, with implications for water resource development

“…1). The Mitchell, Gilbert, and Flinders rivers have mean annual end of system discharge of 13,000 GL/year (1 gigalitre = 10 9 L), 5,304 GL/year, and 1,982 GL/year respectively (Broadley et al, 2020). The three regions experience the wet-dry cycle typical of northern Australia (Warfe et al, 2011), with generally summer-associated flow events.…”

“…Multiple hypothetical water development scenarios have been proposed for the Mitchell, Gilbert, and Flinders rivers to inform water resource and agricultural development planning in northern Australia (Hughes et al, 2017;Petheram et al, 2018a, b;Pollino et al, 2018;Broadley et al, 2020;Burford et al, 2020). These represent a range of surface water allocations and utilisation, surface water harvesting via pumping or instream dams, and different thresholds for minimum instream discharge levels prior to beginning harvesting (''pump start threshold'').…”

“…Increased juvenile growth rates may lead to increased catch rates in later years through improved survival of juveniles (Perez & Munch, 2010), which can result in a stronger cohort (Campana, 1996) that is later encountered at higher numbers in the fishery (Ricker, 1979;Maunder et al, 2016). Freshwater flows are similarly important to a number of commercially targeted fishery species in northern Australia (Robins et al, 2005;Halliday et al, 2012), including the high-value banana prawn (Penaeus merguiensis, de Man, 1888) fishery (Duggan et al, 2019;Broadley et al, 2020) and mud crab (Scylla spp.) fishery (Meynecke et al, 2012b).…”

“…However, harvesting and storage of wet season river flows are prerequisites for proposed major developments in northern Australia (Petheram et al, 2008(Petheram et al, , 2018b. There are potential implications of upstream development on downstream ecological processes and fisheries that rely on the same river flows (Gillanders & Kingsford, 2002;Stewart-Koster & Bunn, 2016;Broadley et al, 2020).…”

Ecosystem services in connected catchment to coast ecosystems: monitoring to detect emerging trends

“…Correlations among condition indicators also represent linkages among the different ecological processes across the catchment that are critical for delivery of ecosystem services. Cross-catchment management faces the issue of balancing conflicting objectives, as is exemplified by many coastal fisheries, whose catches are dependent on freshwater flows to support fish life-histories, but those flows may also be reduced by upstream flow regulation for power generation or agricultural purposes (Broadley et al 2020; Robins et al 2005), or by the effects of climate change (Karim et al 2015). Therefore, it is imperative that we quantify the sensitivity of condition indicators to human influences so we know if – and how quickly – such indicators can detect changes in cross-catchment processes.…”