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The effective electrical conductivity (Cf ) of Murray cod Maccullochella peelii peelii was evaluated as part of an investigation into effective electric fishing settings for this important species. We describe an evaluation of minimum thresholds of power applied to an electrical field required to elicit four responses (escape, forced swimming, immobilization, and narcosis) from Murray cod. Estimates of Cf varied from 46 to 80 μS/cm depending on the response threshold of interest; these results support hypotheses that a global standard for Cf could be applied to power transfer calculations. Results indicate that at 60 Hz, pulse widths (PWs) of 6.7-10 ms are most efficient; however, the electrical dose required for all responses is minimized using higher frequencies resulting in PWs of less than 2 ms. Our observations support other work suggesting that the complexity and range of responses are determined jointly by the nature of the stimulus and the orientation to the field. We suggest that a measu...

The effects of cold water releases, as a by-product of storing irrigation water in large dams, has been a source of great concern for its impact on native freshwater fish for some time. The Mitta Mitta River, northeast Victoria, is impacted by altered thermal regimes downstream of the fourth largest dam in Australia, Dartmouth dam, with some daily temperatures 10–12°C below normal. Murray cod (Maccullochella peelii peelii) were endemic to the Mitta Mitta River; however, resident Murray cod have not been found in this river since 1992. The response of eggs and hatched larvae from Murray cod to different temperature gradients of water were measured and the post-spawning survival recorded. As a case study, post-spawning survival was then inferred from flow data for each year of operation of Dartmouth Dam, recorded since first operation in 1978, and included in a stochastic population model to explore the impact of the altered (historical) thermal regime on population viability. Experimental results revealed no egg and larval survival below 13°C and predicted historical temperature regimes point to more than 15 years of low temperatures in the Mitta Mitta River. Population modelling indicates that the impact of cold water releases on post-spawning survival is a significant threatening process to the viability of a Murray cod population. Additionally, we consider changes to the thermal regime to explore how the thermal impact of large dams may be minimized on downstream fish populations through incrementally increasing the temperature of the releases. The modelled Murray cod population responds to minor increases in the thermal regime; however, threats are not completely removed until an increase of at least 5–6°C. Copyright © 2005 John Wiley & Sons, Ltd.

Summary Adaptive management (AM) remains a commonly cited, yet frequently misunderstood, management approach. The aim of AM is to improve environmental management through ‘learning by doing’ and understand the impact of incomplete knowledge, but AM more commonly consists of ad hoc changes in managing environmental resources in the absence of adequate planning and monitoring. Here, we trace and review the development of AM, the central roles of consultation, collaboration and of monitoring, and of quantitative models and simulations. We identify a series of formalized, structured steps included in one AM cycle and review how current AM programs build upon such cycles. We conclude that the best AM outcomes require rigorous and formalized approaches to planning, collaboration, modelling and evaluation. Finally, simulating potential outcomes of an AM cycle in the presence of existing uncertainty can help to identify management strategies that are most likely to succeed in relation to clearly articulated goals.

As part of an ongoing program of management for a critically endangered fish, we explored adaptive management as a method to overcome pervasive uncertainty regarding the reintroduction of trout cod (Maccullochella macquariensis Cuvier). We simulated the entire adaptive management cycle to explore the suitability of the approach for guiding threatened species management and to identify problems and barriers to "learning by doing". During the planning phase, a number of compromises were identified between specification of goals and objectives, the available management options, and current monitoring capacity. Undertaking a simulation of the implementation of alternate adaptive approaches to this reintroduction provided a number of insights into adaptive management in general. First, identifying the weak link in the process of inference emphasized the need to consider whether goals and objectives are achievable and meaningful and whether they complement monitoring and (or) any other limitations of the system. Second, in natural resource management, it is crucial to negotiate objectives in the light of what one can measure. Third, although there are lessons to be learned from each stage of the adaptive management cycle, there is value in simulating the entire adaptive management cycle, including management actions, monitoring, and the states of the system that lead to management intervention.

In 1998 the protected population of Perameles gunnii (eastern barred bandicoot) at Woodlands Historic Park, Victoria, Australia became functionally extinct following removals of individuals for translocation between 1994 and 1996. Population viability analysis and data collected whilst the population was in decline are used to explore the impact that these removals had on the decline of the P. gunnii population at Woodlands. Due to some ambiguities in the life history of P. gunnii at Woodlands, two structurally different population models were used. Explicitly including the removal of animals in the analysis indicates that there may be at least a three-fold increase in the risk of quasiextinction due to removals. In some scenarios, over 17% of the trajectories decrease to a level less than or equal to 10 females within the observed time period of the collapse of the population, that is by April 1998. The modelling approach identified a number of critical factors in the decline of the population, such as variation in survival rates. By representing the life history strategy using two alternate models, quantitative statements about the impact that removals had on the population decline at Woodlands are made. While removals probably contributed to the collapse of the population, removals were not the sole cause of population decline. The real reasons for decline remain unknown; however, it is likely to be closely linked to habitat decline, difficult environmental conditions and predation. If P. gunnii are reintroduced to Woodlands again, then the models presented here may help to develop management strategies to establish a self sustaining population, as well as exploring translocations options.

Recently, there have been attempts to identify a set of key environmental indicators for Victoria’s marine and coastal environments. The recommendation that seagrass density and abundance be used as indicators requires that the effects on seagrass resulting from changes in the physical environment be predictable. This paper presents a stochastic population model for Zostera muelleri in Port Phillip Bay, Victoria. Building the model identified a number of issues that relate to constructing models for modular organisms. Of particular importance are the assumptions made when devising demographic structure and modelling complex population ecology in data poor environments. The project has provided a preliminary framework for the evaluation of potential environmental indicators and the monitoring programs developed for them. Using the probability of falling below a range of population densities, we were able to specify a background risk against which impacts may be measured. In this case, there was a 50% chance that the population density would fall below 230 individuals per m 2 at least once in the next 20 years. Simulations representing the impacts of turbidity plumes are presented.