DARLING RIVERINE PLAINS BIOREGION Background Report

16/08/02 Darling Riverine Plains Bioregion Background Report
provide habitat for benthic plants;
lead to organic enrichment by capturing detritus and contributing to secondary production
by degradation of the debris itself;
provide refuges from predators and interactions between competitors for fish and
invertebrates;
provide velocity refuges that minimise energy costs of swimming;
provide spawning sites essential for successful reproduction;
provide home range markers for territorial and migratory fish species;
provide refuge and spawning habitats in the riparian zone during overbank flooding;
assist in erosion prevention by stabilising sediments of stream banks and riparian zones;
and
assist in the scouring of deep holes adjacent to woody debris which acts as temperature
and drought refuges.
Threatened fish species that occur within the DRP and which are affected by this process
include trout cod (Maccullochella macquariensis) and silver perch (Bidyanus bidyanus) (FSC
2001a).
Degradation of native riparian vegetation along New South Wales water courses
‘Degradation of native riparian vegetation along New South Wales water courses’ has been
listed as a key threatening process under the FMA 1994. The Fisheries Scientific Committee
defines riparian vegetation as “any vegetation on land which adjoins, directly influences, or is
influenced by a body of water” (FSC 2001b). Degradation of native riparian vegetation
includes invasion of riparian vegetation by non-native species. Negative effects of
degradation of native riparian vegetation include increased amounts of sediment and nutrients
via runoff and increased light penetration to the waterbody leading to increased algal growth
and smothering of benthic communities, reduced inputs of organic carbon which are a major
energy source in most stream ecosystems, reduced inputs of large woody debris entering the
system leading to a reduction in spawning and habitat sites of several fish and aquatic
invertebrates, destabilisation of river banks, and reduced overhanging riparian vegetation
leading to decreased shelter and shade for fish. Threatened fish species recorded within the
DRP affected by this process include trout cod (Maccullochella macquariensis), Murray
hardyhead (Craterocephalus fluviatilis), and silver perch (Bidyanus bidyanus) and the
endangered populations of purple-spotted gudgeon (Mogurnda adspersa), and olive perchlet
(Ambassis agassizii) (FSC 2001b).
Introduction of fish to fresh waters within a river catchment outside their natural range
‘Introduction of fish to fresh waters within a river catchment outside their natural range’ is
listed as a key threatening process under the FMA, 1994. Introduced fish recorded in the DRP
(brown trout (Salmo trutta), rainbow trout (Onchorynchus mykiss), European carp (Cyprinus
carpio), goldfish (Carassius auratus), gambusia (Gambusia holbrooki) and redfin perch
(Perca fluviatilis)) all have self-sustaining populations within the waterways of New South
Wales (FSC 2001c). Introduced fish affect populations of native fauna and flora by direct
predation, competition for food, competition for spawning localities, competition for habitat,
habitat degradation through uprooting vegetation and disturbance of sediments and promotion
of the spread of diseases in native species. Threatened fish species recorded within the DRP
affected by this process include Murray hardyhead (Craterocephalus fluviatilis), trout cod
(Maccullochella macquariensis), and silver perch (Bidyanus bidyanus) the endangered
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