2009-10 Condition Monitoring at Lindsay-Mulcra-Wallpolla Islands - M/BUS/87-2,3,4 BW283
MDFRC Publication 28/2010
This report details the condition monitoring undertaken at Lindsay, Mulcra and Wallpolla (LMW) Islands as part of the 2009/10 Living Murray Condition Monitoring Program. Icon Site condition monitoring has been developed to: Determine the change in environmental condition of individual assets resulting from water application and the implementation of works programs under The Living Murray (TLM). Assess whether sustainable native fish, bird and vegetation communities are being maintained across the Icon Sites. The Outcomes Evaluation Framework stipulates that measurable targets be created to unambiguously assess whether a pre-determined level of condition has been achieved. At the time of writing, such targets had not been developed for LMW. In the absence of defined targets, this report focuses upon Icon Site specific objectives. Icon Site specific objectives presented in the Outcomes Evaluation Framework have been further refined as part of the Lindsay-Mulcra-Wallpolla Environmental Management Plan. Together these objectives form the basis for condition monitoring at Lindsay-Mulcra-Wallpolla of which there are six vegetation components and one fish component. River Red Gum The ecological objectives for River Red Gum (RRG) at Lindsay, Mulcra and Wallpolla are: Current area maintained. Maintain current condition and extent of River Red Gum communities to sustain species assemblages and processes typical of such woodland. Large scale mapping at regular intervals is required to quantify changes in the distribution and areal extent of River Red Gum at LMW. Currently there is no such mapping program underway, so it is not possible to know if current area of RRG is being maintained. Significant increases in Crown Condition scores between the sampling events of 2008/09 and 2009/10 suggest changes in the conditions favourable for tree growth on the LMW floodplain. This is attributed to environmental watering at Mulcra Horseshoe Lagoon and a break in drought conditions. However, with the notable exception of the relatively small area of extant Red Gum with Flood Tolerant Understorey (RGFTU) at Mulcra Island, the recent improvement observed for RRG trees at LMW represents a change in the previous downward trend in condition rather than a return to acceptable condition. Stand condition modelling conducted by Cunningham et al.(2009) reports that the extent of severely degraded stands was higher in the Mallee (Hattah, Chowilla and LMW) than at other TLM Icon Sites, that the majority of stands were in a stressed condition in 2003 and that this had increased by 4% by 2009. Recruitment must keep pace with mortality for a population to remain sustainable and this must occur within the current spatial context if the present distribution is to be maintained (i.e. ecological objectives are to be met). Size-class frequency distributions for Fringing Red Gum Woodland (FRGW) indicate a relative abundance of trees within the smaller size classes suggesting sustainable recruitment. However, despite indications of recent improvement in the condition of trees on average, population viability assessments suggest there are long-term sustainability concerns for Red Gum Forest (RGF) communities at LMW. Black Box The ecological objectives for Black Box (BB) at LMW are: At least 20% of the original area of Black Box vegetation maintained. Improve condition to sustain species assemblages and processes typical of Black Box woodland. Ecological Vegetataion Class (EVC) mapping conducted in 2005 provides the most accurate and up to date information about the areal extent of Black Box at LMW and is therefore the logical choice for a BB areal standard. However, in the absence of an ongoing program mapping the distribution of Black Box at the Icon Site scale, it is not possible to know what proportion of the original area of Black Box is being maintained. Size-class distributions for Black Box communities do not approximate inverse J-shaped curves indicative of sustainable populations. Further, between 2008/09 and 2009/10 there was a reduction in the relative proportion of Diameter at Breast Hight (DBH) <15 cm individuals indicating a trend away from population maintenance. Robust Reproductive Extent scores indicate a recent lack of recruitment can be attributed to factors other than seed production such as the absence of a suitable water regime for the successful germination, growth and establishment of seedlings. Similar Crown Condition scores for 2008/09 and 2009/10 indicate the condition of BB at LMW has not recovered from an earlier decline. The only exception was for Black Box Swampy Woodland (BBSW) at Lindsay Island where there was evidence of some improvement in tree condition between 2008/09 and 2009/10. The apparent decline in tree condition at most BB communities at LMW between site establishment in March 2007 and the most recent sampling events in January/February 2010 indicates a trend away from achievement of the second ecological objective. Wetlands The site specific ecological objectives for Lindsay, Mulcra and Wallpolla that relate directly to wetland vegetation are: Sustainable communities of wetland and terrestrial plant assemblages. Provide a diversity of structural aquatic habitats and increase diversity and abundance of wetland aquatic vegetation. Maintain and improve the populations of threatened flora that are flow dependent. Restore habitat and community diversity for permanent, semi-permanent and ephemeral wetlands. Re-instate the communities typical of these wetlands. In line with the objectives, pumped environmental water is helping to provide a 'diversity of structural aquatic habitats and increase the diversity and abundance of wetland aquatic vegetation‘, and 're-instate communities typical of ephemeral wetlands.‘ This conclusion is supported by the increased diversity of plant functional groups detected at the group of sites that has received water (which contained a variety of terrestrial, amphibious and aquatic plant species) compared to the group that did not (dominated by terrestrial species). Submerged and emergent aquatic habitats were present in and around some wetlands this year, which created a wider range of habitats for different plant functional groups to occupy. Some sites displayed a transition from terrestrial damp and dry species to amphibious and submerged species, associated with wetting, while others showed the opposite trend due to drying. These successional changes are typical of ephemeral wetland plant communities that experience natural cycles of wetting and drying in a hydrologically variable river system. Pumped environmental water also appears to be of assistance in ‗maintaining populations of threatened flora that are flow dependent.‘ A total of 143 plant species (125 native) were recorded during the 2010 survey. Twelve of those species are listed as rare or threatened in Victoria by the Department of Sustainability and Environment. The majority of rare species were recorded at wetlands that had received environmental water in 2009. Floodplain Understorey The site specific ecological objectives for Lindsay, Mulcra and Wallpolla that relate directly to floodplain understorey vegetation are: Sustainable communities of wetland and terrestrial plant assemblages. Provide a diversity of structural aquatic habitats and increase diversity and abundance of wetland aquatic vegetation. Maintain and improve the populations of threatened flora that are flow dependent. Restore habitat and community diversity for permanent, semi-permanent and ephemeral wetlands. Re-instate the communities typical of these wetlands. This year, nine threatened flora species were recorded at the floodplain sites sampled. Of the nine species, four were classified as 'terrestrial damp‘ species and require moist conditions maintained either by rainfall or flow. All four terrestrial damp rare species were recorded at the Often or Sometimes flooded levels at sites on Lindsay Island. These sites had either received environmental water, were adjacent to sites that had, or were sites sampled following good rainfall. While these rare species are not all strictly flow-dependent, pumped environmental water does appear to be aiding in meeting the objective of maintaining and improving the populations of threatened flora that are flow (or rainfall) dependent. Pumped environmental water at Site 2 on Lindsay Island is helping to provide a ‗diversity of structural aquatic habitats and increase the diversity and abundance of wetland aquatic vegetation.‘ This is evidenced by the presence of a diverse and abundant aquatic macrophyte community in both 2009 and 2010 at the Very Often inundation level. While pumped environmental water is clearly important for meeting the objectives at this specific site and providing benefit to the neighbouring Often inundation level, this watering is on a very small scale and more relevant to 'wetlands‘. There has been no recent large-scale inundation of floodplain communities at the LMW Icon Site and the overarching objective of sustainable communities of wetland and terrestrial plant assemblages is not being met in relation to floodplain communities. Works currently underway on Mulcra Island should enable inundation of the floodplain adjacent to the Potterwalkagee Creek but will have no influence on the Lindsay and Wallpolla floodplains. Of interest at the species level is the steady increase in abundance of Round-leaf Pigface (Disphyma crassifolium ssp. clavellatum) at Wallpolla Site 2 Rarely. This species is highly salt-tolerant (>16 ds/m, DPI 2008) and an increase in abundance could be indicative of an increase in site salinity. It is recommended that soil salinity testing be undertaken at the LMW Icon Site. Of concern are the appearances and/or increase in abundance of significant weed species. The highly invasive Parrots Feather (*Myriophyllum aquaticum) was recorded for the first time this year from a site at Lindsay Island. This site supports a diverse and abundant aquatic macrophyte community when inundated and the presence of the highly invasive Parrots Feather is of concern. Lippia (*Phyla canescens) was recorded at all three Islands and its abundance increased in 2010 at Lindsay Island Site 1. This species is highly invasive and is believed to be allelopathic, potentially suppressing the germination of River Red Gum trees. Lignum The site specific ecological objective for lignum at Lindsay, Mulcra and Wallpolla is: Improve condition and increase extent to sustain species assemblages and processes typical of lignum communities. Lignum Condition Index scores indicate a general decline in Lignum condition at LMW between 2006/07 and 2009/10. Some fluctuation in condition was observed over the monitoring period and is attributed to rainfall (e.g. spring 2009) and environmental watering (e.g. at Wallpolla Site 1). At present, there is no large-scale environmental watering of water-shed floodplain at Lindsay, Mulcra and Wallpolla Islands and the delivery of environmental water to wetlands is likely to affect only a very small proportion of the Lignum community. The vast majority of the Lignum on the floodplain has not received flooding from overbank flows or environmental watering events over the last fours years, which accounts for the poor to moderate condition of Lignum in 2009/10. The reduced flood frequencies through river regulation and extraction upstream remain a significant threat in achieving the ecological objectives for Lignum at the Lindsay, Mulcra and Wallpolla Islands. Cumbungi The ecological objective developed for priority sites (Websters Lagoon and Horseshoe Lagoon) at Lindsay, Mulcra and Wallpolla Islands that relates directly to Cumbungi is: Limit Cumbungi growth and promote greater macrophyte diversity. In the past year there has been an increase (at 8 of the 11 reaches surveyed) in the distribution of Cumbungi found in the Murray River channel and anabranches of the Lindsay, Mulcra and Wallpolla Islands. This continues an overall increase in the distribution of Cumbungi over the four years of the study. This trend is away from meeting the objective of ‗limiting Cumbungi growth'. The expanision of Cumbungi is attributed primarily to the altered flow regime caused by the construction and operation of locks and weirs along the Murray River that has provided ideal habitat for the rapid development, growth and expansion of Cumbungi. It could be reasoned that an increase in Cumbungi cover would also be a threat to the maintenance of macrophyte plant diversity. However, the dynamics of a change in Cumbungi upon the macrophyte plant diversity has not been specifically investigated as part of this study. Fish The ecological objectives pertaining to fish at Lindsay, Mulcra and Wallpolla Islands are: Sustainable communities of River Murray channel, non-River Murray channel and generalist fish assemblages. Sustainable populations of Murray cod, Golden perch and catfish and restrict populations of common carp. Increase diversity and extent of distribution of native fish. The decline in abundance of Bony herring during 2008/09 and subsequent recovery in 2009/10 is indicative of a robust population, capable of rapid recovery from natural environmental perturbations. Silver perch were present at low (but stable) numbers between the 2006/07 and 2009/10 surveys. Evidence of recruitment to the young-of-year class was evident within the current monitoring year. This indicates maintenance of sustainable communities of large-bodied River Murray channel, non-River Murray channel and generalist fish assemblages. Large abundances and widespread distribution of Fly-specked hardyhead and Carp gudgeons was evident at all sites surveyed across LMW, exhibiting diverse size-classes indicative of sustainable populations. All other small-bodied fish species recorded, exhibited minor changes in either relative abundance or size-class distribution. Because of the short temporal span of the available data (three years) it is currently unclear if these changes reflect inter-annual variability or are indicative of potential change in community structure. It is therefore unclear if sustainable communities of small-bodied River Murray channel, non-River Murray channel and generalist fish assemblages are being maintained. In 2009/10, a considerable reduction was observed in overall relative abundance of Murray cod compared to previous years. This is a concern that has been raised by several authors that have considered the Mullaroo Creek Murray cod population to be ecologically important to the sustainability of Murray cod at the broader regional level. As such, the objective of maintaining sustainable populations of Murray cod at LMW is not currently being achieved. Murray cod declines have increased concurrently with observed increases in angling effort around Mullaroo Creek. The continuation of recreational angling in Mullaroo Creek warrants consideration as a key threat to the sustainability of the LMW Murray cod population. Length frequency distributions of Golden perch indicate that recruitment to the young-of-year (0+) and juvenile (>1+) age classes has occurred within the region in 2009/10 indicating an improvement in the status of the LMW Golden perch population. This indicates a trend towards achievement of the objective of maintaining sustainable populations Golden perch. Freshwater catfish were not collected during any of the surveys across LMW, suggesting that if this species is present, it occurs in very low numbers. It is not known if sustainable populations of freshwater catfish are being maintained at LMW. Common carp were present and relatively abundant at all reaches surveyed between 2006/07 and 2009/10. The presence of juveniles (<150 mm SL) in all survey years, combined with high relative abundances of individuals greater than the previously recorded size at maturity for males and females, indicate that the population within the Icon Site is robust. This indicates the objective of restricting populations of common carp is not currently being achieved. The influence (both positive and negative) of potential management actions on this population needs to be considered. Of concern is the ongoing presence of a strong population of Eastern gambusia. This introduced species is aggressive, and has been implicated in the decline of a number of native species throughout the Murray-Darling Basin (MDB). Ongoing presence of this species could contribute to substantial change in the structure of the native fish community at the Icon Site.