Fish larvae and the management of regulated rivers

Abstract

Alterations to the natural hydrologic regime in regulated rivers can disrupt cues that initiate the maturation and spawning of riverine fish, or they can change the conditions which are suitable for the recruitment of larvae into juvenile populations. Observations of fish larvae have the potential to provide insights into the effects of flow regulation, showing whether it has had a greater impact on fish by preventing spawning or by reducing or eliminating recruitment. We investigated historical and current records of native fish in the highly regulated Campaspe River and the moderately regulated Broken River, Murray-Darling Basin, Australia, and compared these with the results from sampling of fish larvae over three consecutive years to assess the likely impact that river regulation has had on fish populations in lowland Australian rivers. Of the 12 native species of fish that have been recorded historically from the Campaspe River, eight still occur, generally in low abundance, but only three of these were recorded as larvae in this experiment. From recent records, ten native fish species are extant in the Broken River from a suite of 15 that have been recorded there; of these, nine were collected as larvae. The presence of Murray cod larvae in this river was a significant finding. Thus, the less regulated Broken River is in a much healthier state than the Campaspe River. The results of sampling in both rivers indicated that most species of fish spawned each year, despite high inter-annual variation in antecedent hydrological conditions. This suggests that for the species present in these two rivers, the hydrology (pattern of daily discharge) during the winter and spring preceding breeding was unlikely to be a cue for final maturation and spawning. These findings are only preliminary, but they may show that river regulation has had more of an impact on post-spawning recruitment than on prevention of spawning. This has important implicatons for the remediation of the effects of river regulation, with targeting of recruitment processes and the factors influencing these, a priority.

Spatial and temporal distribution of ichthyoplankton in the upper Uruguay river, Brazil

“…Although it was the most upstream site of the long free stretch of the Uruguay river -more than 900 km without dams or geographical accidents -this section was located immediately below Itá dam, under the direct influence of water from the turbines and/or discharged by the power plant. There is much evidence that the water from the turbines of reservoirs disrupts the life cycle and causes fragmentation of downstream fish populations (Humphries and Lake, 2000). This control of water produces direct effects on the river flow, altering the volume and period of floods and, indirectly, modifying the quality of the water downstream by, for example, decreasing the water temperature and causing qualitative and quantitative changes in the organic and inorganic matter transported by the river (Humphries and Lake, 2000;Humphries et al, 2002).…”

“…There is much evidence that the water from the turbines of reservoirs disrupts the life cycle and causes fragmentation of downstream fish populations (Humphries and Lake, 2000). This control of water produces direct effects on the river flow, altering the volume and period of floods and, indirectly, modifying the quality of the water downstream by, for example, decreasing the water temperature and causing qualitative and quantitative changes in the organic and inorganic matter transported by the river (Humphries and Lake, 2000;Humphries et al, 2002). Differences were also observed between the abundance of fish eggs and larvae at different times and layers.…”

Missouri River Scaphirhynchus albus (pallid sturgeon) effects analysis—Integrative report 2016

“…Downstream from dams, changes in flow regime, sediment regime, water temperature, water clarity, and nutrient transport provide additional potential to affect pallid sturgeon and their reproductive ecology (Hesse, 1987;Hesse and others, 1988). Particular attention has been given to disruption of hydrologic cues for reproductive synchrony ("spring rises") that have been implicated as necessary factors in reproduction of many fish species (Poff and Allan, 1995;Poff and others, 1997;Humphries and Lake, 2000). Specific application of spring rises to pallid sturgeon reproduction has been under intense investigation, but unambiguous associations between flow pulses and reproductive success have not been established (Doyle and others, 2011;Papoulias and others, 2011;DeLonay, Chojnacki, Jacobson, Albers, and others, 2016).…”

Climate change and its implications for Australia's freshwater fish

“…These fish assemblages are already in a generally degraded state and composed of resistant or resilient species (Humphries and Lake 2000). Further reductions in discharge during spring are likely to result in a loss of flow peaks that act as spawning cues for several lowland river fish species (Humphries et al 1999).…”