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Marine and Freshwater Research, 2010, 61, 379–387

Using biological information to support proactive strategies for managing freshwater fish during drought David A. CrookA,C,D , Paul ReichA,B , Nick R. BondB,C , Damien McMasterB , John D. KoehnA and P. Sam LakeB A Arthur

Rylah Institute for Environmental Research, Department of Sustainability and Environment, 123 Brown St., Heidelberg, Vic. 3084, Australia. B School of Biological Sciences, Monash University, Clayton, Vic. 3800, Australia. C eWater CRC, University of Canberra Innovation Centre, Canberra, ACT 2601, Australia. D Corresponding author. Email: [email protected]

Abstract. This paper provides an assessment of the biological attributes of fish species in south-eastern Australia and rates their potential risk from the impacts of drought. We used scientific literature and expert opinion to conduct a semiquantitative assessment of attributes considered to influence species resistance and resilience to drought for 15 freshwater fish species found in south-eastern Australia. We also present a conceptual framework to guide management of fish populations during drought. The framework focuses on (1) quantifying spatial variation in the severity of drought impacts on particular habitats (rivers, wetlands, etc.), (2) assembling information on drought sensitivities of regionally important species, (3) identifying high risk areas (based on species sensitivity and drought severity), (4) determining and implementing appropriate management actions (pre-emptive, responsive), (5) monitoring outcomes and (6) disseminating information on outcomes. In many regions, historic population declines will serve to exacerbate the impacts of drought, and thus are a major threat to successful recovery from drought. Although we discuss both long-term, pre-emptive planning and short-term, responsive management actions, we contend that a long-term view is required to successfully address the threats posed by drought. Furthermore, although droughts clearly represent a severe disturbance to fish populations, ultimately it is anthropogenic factors that exacerbate drought and constrain recovery pathways (at global, regional and local scales), rather than drought per se. These factors must be addressed if we are to ensure the long-term viability of fish populations in inland aquatic ecosystems. Additional keywords: Australia, climate change, refugia, resilience, resistance, tolerances.

Introduction Drought is a natural phenomenon and plays a critical role as a driver of population dynamics and evolutionary processes in lotic ecosystems in many regions of the world (Boulton 2003; Matthews and Marsh-Matthews 2003; Lake et al. 2008). In south-eastern Australia, the impacts of human activities, such as water extraction and catchment degradation associated with urban and agricultural development, have greatly reduced the resilience of aquatic ecosystems and hence exacerbated the impacts of drought (e.g. Bond and Lake 2005; Lintermans and Cottingham 2007; Miller et al. 2007). Severe drought conditions can be reflected in widespread declines in the abundance and distributions of a range of aquatic fauna (e.g. Morrongiello et al. 2006; Rose et al. 2008). When water in rivers, streams and wetlands is reduced, habitats contract, fragment and disappear, threatening the persistence of local populations, communities and aquatic ecosystems. As a result, waterway managers are often forced to prioritise the protection of ecological values and habitats within their catchments. © CSIRO 2010

A consequence of the unexpected length (>10 years) of the ‘millenium’ drought affecting south-eastern Australia (Murphy and Timbal 2007; Timbal and Jones 2008) is that many management responses have necessarily become reactive as streamflows and water-storages have become critically low. In 2007–8, Catchment Management Authorities throughout Victoria, southeastern Australia, prepared short-term Dry Inflow Contingency Plans (DICPs) to identify priority areas and develop action plans to try and protect critical assets from long-term impacts (e.g. McMaster et al. 2008), and similar plans are also being prepared in other Australian states (New South Wales and South Australia). The preparation of these plans has highlighted the need for more readily accessible scientific information on the effects of drought on aquatic ecosystems and their flora and fauna that can be used to help inform such prioritisation processes. The rate of incorporation of science into conservation and ecological planning is generally not high (Pullin et al. 2004) and there is a need to facilitate the use of knowledge in decisionmaking processes (Koehn 2004; Likens et al. 2009), including 10.1071/MF09209

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drought planning and management. The development of drought plans has also highlighted the degraded state of many streams and rivers – a situation that has greatly exacerbated the impacts of the current drought on aquatic ecosystems (Lake and Bond 2007; Lintermans and Cottingham 2007; Bond et al. 2008). Considerable research and management effort has been focussed on fish populations in south-eastern Australia, as their populations have suffered substantial declines and efforts are now being directed towards their rehabilitation (Murray–Darling Basin Commission 2004). Much concern during the current drought has been focussed on fish species with conservation significance and high value to anglers, although a range of management priorities have been recommended for all species (see Lintermans and Cottingham 2007). It has been recognised that diminished fish populations are likely to be less resilient and are also impacted by a range of threats, including introduced species, habitat degradation and flow alteration (Lintermans and Cottingham 2007). The lack of preparedness for the current drought highlights a common problem in water resource planning, which has had a tendency to assume that the future will largely reflect the past, and, in most cases, the recent past (Green et al. 1991). GivenAustralia’s highly variable climate and the predicted future reductions in catchment runoff and streamflows in south-eastern Australia as a result of climate change (Barros and Bowden 2008; Timbal and Jones 2008), more attention should be given to climate uncertainty, and to proactive, long-term planning for droughts, with pre-emptive actions to help mitigate the impacts of future events, the magnitude, timing and duration of which are unknown (e.g. see Palmer et al. 2008). Furthermore, consideration needs to be given to understanding and potentially managing the recovery of aquatic ecosystems following drought. In this paper, we stress the long-term strategic aspects of implementing preparedness for drought management, but still aim to provide information that will be of use to waterway managers in the shorter term.The aims of this paper are to: (1) provide a basic summary of the physicochemical and biological impacts of drought on aquatic ecosystems; (2) summarise the likely sensitivity to drought of south-eastern Australia native fish species; (3) present a simple conceptual framework for incorporating biological information on native fish into prioritisation strategies for mitigating the effects of drought on stream ecosystems; and (4) identify key areas where further knowledge is required to improve our ability to manage fish through drought. Although the paper focuses on fish in south-eastern Australia as a case study, we anticipate our approach has the potential to be applied to other species, other regions and aquatic systems in general. Impacts of drought on aquatic ecosystems Numerous descriptive and quantitative criteria have been applied to define drought in aquatic ecosystems and, whilst there is currently no universally accepted definition of hydrological drought, the broad impacts of drought have been described (Humphries and Baldwin 2003; Lake 2003, 2008; Bond et al. 2008). In terms of physical impacts, the deficit of inflows characteristic of drought periods reduces water levels, causing a decline in the availability of deep water habitats; this loss of habitat is particularly severe for large-bodied species dependent on deep

D. A. Crook et al.

pool habitats (e.g. Magoulick and Kobza 2003). Similarly, shallow habitats such as floodplain wetlands and macrophyte beds around the margins of lakes are often the preferred habitat of small fish species, and these might be drastically reduced as water levels recede (Closs et al. 2006; Hardie et al. 2007). The decrease in depth also reduces the potential for longitudinal connectivity of fish populations within rivers and streams, with riffle zones either becoming too shallow for fish to cross or drying out completely (Schaefer 2001). Lateral connectivity between the river channel and floodplain wetlands can also be severed for extended periods during times of drought (e.g. Merron et al. 1993). In the case of drift-feeding fish, reductions or loss of flow can also result in loss of access to prey (Closs 1994). As disconnected pools and wetlands dry out and decrease in volume, the densities of fish might increase, resulting in an increased potential for competitive interactions, predation and disease transmission (Magoulick and Kobza 2003; Matthews and Marsh-Matthews 2003; Lake et al. 2008). Complete drying of habitats will, for most species, cause mortality, potentially resulting in regional population losses and reductions in genetic diversity within species (Vrijenhoek 1996). Reduced flows associated with drought also have strong impacts on water chemistry, with potentially critical consequences for biota. Lack of flow can result in reduced dissolved oxygen (e.g. Chessman and Robinson 1987; Elliott 2000), increased temperatures (e.g. Mundahl 1990; Magoulick and Kobza 2003) and increased electrical conductivity and ammonium concentrations (e.g. Muchmore and Dziegielewski 1983; Chessman and Robinson 1987). In extreme cases, these factors can reach lethal levels for fish, thus causing mass mortalities (Tramer 1977; Koehn 2005). In addition to the direct effects on fish, declines in water quality associated with drought can affect the availability of food resources, such as riffle-dwelling macroinvertebrates (Chessman and Robinson 1987; Boulton 2003; Rose et al. 2008), with subsequent impacts on the survival and productivity of fish populations. Impacts can occur at a range of levels, and understanding the biology of the species concerned and the effects on populations will allow for more clearly defined management approaches (e.g. provision of supplementary flows) and complementary actions (e.g. fishery closures in refuge pools to protect brood stock). The impact of these various factors on individual species is ultimately governed by their demographic range, physiological tolerances and behavioural attributes, which collectively determine the ability of populations to persist through and/or recover from drought; concepts respectively referred to by ecologists as resistance and resilience (Lake 2000, 2003; Fritz and Dodds 2004). Together, resistance and resilience summarise both the likely short- and longer-term impacts of drought on species and/or populations (Lake 2003), with resistant species likely to show only minor, or delayed responses, and resilient species likely to recover well after a drought, even if they may be severely affected at the time. For example, species able to tolerate high temperatures and poor water quality show high resistance, while those capable of rapid population growth owing to high reproductive output may be seen as resilient. Resistance and resilience are not mutually exclusive, with some species exhibiting both high resistance and high resilience. Summarising information on the attributes that collectively contribute to the resistance and

Biological information for managing fish during drought

resilience of different species provides an indication of their relative sensitivity to drought. Such information can then be used by managers to develop and prioritise drought response strategies. Australian inland fish species rely on numerous adaptations to cope with one of the most hydrologically variable environments on Earth, and arguably are well-adapted to cope with drought (Unmack 2001; McNeil and Closs 2007). However, the ability of species to withstand conditions during drought and, most importantly, recover following drought, has been greatly compromised since European settlement. Widespread land and waterway degradation, introduction of exotic species, construction of instream barriers and human demands on water resources have all altered the way in which the impacts of drought are manifested across the landscape. It is critical that this aspect of the consideration of additional ‘man-made’ impacts is not lost amid expectations of species’ natural tolerances to drought and their ability to recovery following drought. As drought can be described as a ramp disturbance, with its severity increasing over time (Lake 2000; Humphries and Baldwin 2003), at any given location the most resistant species will likely be the last to reach their tolerance thresholds as the impacts of drought intensify (Matthews 1998). Conversely, the most resilient species would be the first to recover. In terms of prioritising management actions, therefore, we might expect species with low resistance to reach tolerance thresholds earlier in a drought, whereas more resistant species may only be at risk from longer-term droughts. Hence, highly resistant species might be a lower priority for responsive management at the onset of drought. However, overlaid onto this premise must be the consideration of how other factors might modify these basic expectations. For example, the impacts of a drought of a given duration or severity on a particular species will differ from place to place depending on a range of natural features (e.g. geology, catchment architecture, geomorphology) and anthropogenic impacts (e.g. land use, water quality, artificial barriers). For instance, in highly modified rivers and streams, even naturally resilient species may require ongoing management (both before and during drought) to ensure that natural pathways to recovery are intact. Understanding the links between species attributes and those factors (especially human) that exacerbate drought impacts is a vital component to effective drought management. Both resilient and resistant species types might require pre-emptive management actions to minimise the impacts of other degrading influences that increase susceptibility to drought. Although actions may be taken to alleviate individual threats, the cumulative impacts of concurrent threats to the ecosystem already under stress also need to be considered. Evaluating the resistance and resilience of fish to drought To demonstrate the way in which information on the biological attributes of fish might be used to guide management strategies, we used the scientific literature and expert opinion to identify 14 attributes thought to influence a fish species’ resistance (10 attributes) and resilience (4 attributes) to drought (Table 1). We compiled information on each of these attributes to develop a semiquantitative assessment of the relative resistance and resilience of 12 species of freshwater fish native to south-eastern


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Australia, as well as three introduced species. These species were chosen to provide a set of fish species to demonstrate our approach and are not intended to represent the full suite of attributes exhibited by fish in south-eastern Australia. Despite several existing compilations of available biological information for many of these species (e.g. Koehn and O’Connor 1990; Pusey et al. 2004), there are still significant gaps in the availability of published information and very little specific information on the resistance and resilience of fish species to drought and other disturbances. We therefore sought expert opinion by surveying 17 fish biologists and aquatic ecologists (including the authors) from research organisations in eastern Australia. Recipients were emailed a brief survey and asked to rate each species as low, medium or high against each of the 14 attributes, as well as rate their confidence in each of their predictions on the same scale. They were specifically asked to leave out those species where they lacked sufficient judgement/expertise to justify a response. The survey responses were then compiled to provide an average ‘score’ for each attribute and confidence rating (1 = low; 2 = medium; 3 = high), and attributes and confidence ratings within each resistance and resilience category were summed to provide an overall species rating. In acknowledging the limitations of our approach, there are two important points: (1) a formal effort to build a quantitative database of life-history information for Australian freshwater fish is much needed, and would provide a useful tool for identifying critical knowledge gaps and cataloguing existing information in one place; (2) we have attempted to address concerns surrounding the use of expert opinion by (a) eliciting measures of confidence in the survey, and (b) restricting our interpretation of the results to draw what we contend are general and robust conclusions. Survey results The results of the survey showed a positive correlation between resistance and resilience, with no species rated as having very high resistance but very low resilience or vice versa (linear regression: r2 = 0.57; P = 0.001) (Tables 1 and 2, Fig. 1). The introduced common carp (Cyprinus carpio) was ranked as the most resistant and resilient species, with golden perch (Macquaria ambigua) and short-finned eel (Anguilla australis) also ranked highly. The threatened native species, barred galaxias (Galaxias fuscus), was ranked least resistant and resilient, with other native species such as the southern pygmy perch (Nannoperca australis) and Macquarie perch (Macquaria australasica) also rating poorly. With the exception of ‘longevity’, the respondents were generally more confident about the attributes relating to species’ resilience compared with resistance. Respondents were least confident in ranking attributes relating to parasites, disease and competitive ability, a result consistent with the limited research in these areas. Using species attributes to prioritise and guide management actions The species attributes we have examined above have the potential to be used as the basis for guiding management actions. For example, barred galaxias, Galaxias fuscus, was listed as the most sensitive species in terms of resistance, ranked as being

Australian grayling Prototroctes maraena Australian smelt Retropinna semoni Barred galaxias Galaxias fuscus Brown trout Salmo trutta* Common carp Cyprinus carpio* Common galaxias Galaxias maculatus Freshwater catfish Tandanus tandanus Golden perch Macquaria ambigua Macquarie perch Macquaria australasica Murray cod Maccullochella peelii peelii Redfin perch Perca fluviatilis* River blackfish Gadopsis marmoratus Short-finned eel Anguilla australis Southern pygmy perch Nannoperca australis Trout cod Maccullochella macquariensis

Species

1.6 2.1 1.0 1.3 2.9 2.1 2.3 2.8 1.9 2.5 2.0 2.2 2.3 2.0 1.9

R

C 1.7 2.4 2.2 2.8 2.8 1.9 2.3 2.5 1.9 2.2 2.4 2.0 2.1 1.8 1.7

Temp.

1.6 1.7 1.1 1.1 2.9 2.3 2.4 2.5 1.8 1.8 2.1 1.8 2.5 2.0 1.5

R

DO

1.8 2.3 2.0 2.8 2.8 1.8 2.3 2.3 1.7 2.2 2.6 2.1 2.4 1.6 1.6

C 2.8 2.6 1.2 2.4 2.9 2.8 2.4 2.7 1.9 2.7 2.3 1.9 3.0 2.0 1.9

R

C 2.6 2.6 2.0 2.5 2.8 2.5 2.3 2.4 1.7 2.4 2.4 2.1 2.7 1.8 1.6

Cond.

Physicochemical tolerance

2.0 1.8 1.2 2.6 2.5 1.8 1.7 2.8 2.3 2.9 2.5 2.2 2.8 1.6 2.6

R 1.9 1.8 2.4 2.5 2.3 2.1 1.8 2.3 1.6 2.4 2.5 1.8 2.3 1.7 2.2

C

Predation

2.2 1.9 1.9 1.9 2.4 1.8 2.2 2.4 2.2 2.2 2.1 2.4 2.6 2.1 2.1

R 1.4 1.4 1.4 1.8 2.3 1.7 1.9 1.8 1.5 1.5 1.9 1.4 1.8 1.4 1.3

C

Parasites R 1.2 1.3 1.1 1.8 2.2 1.2 1.8 1.6 1.7 1.3 2.0 1.4 1.7 1.7 1.2

C

Disease

1.8 1.8 1.9 1.9 2.6 1.9 2.1 2.4 1.8 2.4 1.7 2.3 2.6 1.6 2.1

Biological tolerance

1.6 2.1 1.4 2.8 2.9 1.8 1.6 2.5 1.6 2.9 2.9 2.0 2.9 1.6 2.4

R

1.4 1.5 1.6 2.4 2.6 1.8 1.5 2.3 1.5 2.2 2.5 1.6 2.2 1.4 1.7

C

Competitive ability

1.3 2.6 1.5 1.8 2.9 2.5 2.2 2.7 2.0 2.4 2.3 2.2 2.5 1.7 1.9

R

1.8 2.5 2.2 2.5 2.8 2.2 2.2 2.6 1.8 2.5 2.5 2.1 2.6 2.4 2.1

C

Occupancy

Hydrological tolerance

1.1 2.7 1.5 1.3 2.4 2.2 2.0 1.7 1.5 2.4 2.0 1.9 2.3 1.5 1.9

R

2.2 2.4 1.4 2.5 2.8 2.0 1.8 2.5 1.7 2.4 2.2 1.6 2.4 1.9 1.7

C

Reprod.

1.9 1.1 1.7 2.7 2.8 1.5 2.4 3.0 2.7 3.0 2.5 2.4 2.9 2.1 2.9

R

2.2 2.6 1.9 2.3 2.6 2.2 2.3 2.8 2.2 2.8 2.3 1.7 2.8 2.5 2.6

C

Longevity

Table 1. Mean rating (R) and confidence (C) for species’ resistance to drought (1 = low, 2 = medium, 3 = high) derived from the questionnaire sent to scientists with fish ecology expertise Species with the highest rating in each category are shaded. Definitions relating to resistance: Physicochemical tolerance – ability to withstand high temperatures (Temp.), low dissolved oxygen (DO), high conductivity (Cond.). Biological tolerance – ability to avoid or survive the effects of predation, parasites or disease (under current conditions – i.e. in the presence of introduced predators, disease, etc.). Competitive ability – ability to out-compete other species for food, habitat and other resources (under current conditions – i.e. in the presence of introduced predators, etc.). Hydrological tolerance – ability to occupy (Occupancy) or spawn and recruit (Reprod.) over a wide range of hydrological regimes. Longevity – typical maximum age (low: 1–2 years, medium: 3–5 years, high: >5 years). *Introduced species

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Table 2. Mean rating (R) and confidence (C) for species’ resilience to drought (1 = low, 2 = medium, 3 = high) derived from the questionnaire sent to scientists with fish ecology expertise Species with the highest rating in each category are shaded. Definitions relating to resilience: Dispersal ability – ability to move large distances to recolonise habitat after drought. Distribution – wide geographic distribution (current not historic). Abundance – high abundance across species’ range (current not historic). Reproductive capacity – capacity to reproduce rapidly based on fecundity and generation time. *Introduced species Species

Dispersal ability

Australian grayling Prototroctes maraena Australian smelt Retropinna semoni Barred galaxias Galaxias fuscus Brown trout Salmo trutta* Common carp Cyprinus carpio* Common galaxias Galaxias maculatus Freshwater catfish Tandanus tandanus Golden perch Macquaria ambigua Macquarie perch Macquaria australasica Murray cod Maccullochella peelii peelii Redfin perch Perca fluviatilis* River blackfish Gadopsis marmoratus Short-finned eel Anguilla australis Southern pygmy perch Nannoperca australis Trout cod Maccullochella macquariensis

Distribution

Abundance

Reproductive capacity

R

C

R

C

R

C

R

C

2.4 2.4 1.1 2.5 3.0 2.5 1.5 3.0 1.6 2.7 2.3 1.5 2.9 1.6 2.1

1.9 2.0 1.8 2.4 2.9 2.4 2.0 2.7 1.7 2.5 1.9 2.0 2.6 1.9 2.1

1.6 2.9 1.0 2.1 3.0 2.6 1.6 2.9 1.5 2.7 2.5 2.3 2.7 1.3 1.1

2.4 2.8 2.3 2.4 2.9 2.4 2.4 2.7 2.2 2.6 2.3 2.4 2.7 2.4 2.5

1.4 2.9 1.2 2.3 2.9 2.2 1.5 2.4 1.1 2.0 2.0 1.9 2.5 1.4 1.4

2.3 2.6 2.2 2.3 2.9 2.4 2.2 2.6 2.1 2.4 2.5 2.3 2.4 2.4 2.3

1.9 2.8 1.8 2.0 2.8 2.6 1.7 2.6 1.5 2.0 2.5 1.6 2.3 1.6 1.7

2.0 2.5 1.4 2.4 2.9 2.2 2.2 2.6 1.9 2.4 2.3 1.9 2.2 2.1 2.3

3.0

Carp Aust. smelt

Golden perch Shortfinned eel

Common galaxias

2.5

Resilience

Murray cod Brown trout

Redfin perch

2.0 Aust. grayling 1.5

River blackfish Catfish Trout cod

Sth pygmy perch

Macquarie perch

1.0 1.0

Barred galaxias 1.5

2.0

2.5

3.0

Resistance Fig. 1. Plot of resistance v. resilience based on mean scores (±s.e.) from survey respondents. Standard errors were calculated using the mean resistance or resilience scores for all survey respondents.

particularly sensitive to poor water quality, predation, and hydrologic stress. It is also considered to have low dispersal ability, high vulnerability to predation and very limited distribution and abundance. These factors imply both low resistance and resilience, and collectively support its high conservation listing and existing management strategies, which include invasive

species management and the maintenance of captive populations to offset localised extinctions caused by physico-chemical or hydrologic stress (e.g. as may be caused by forest fire; e.g. Lyon and O’Connor 2008). However, because most habitats occupied by G. fuscus are relatively intact, in-situ interventions to improve habitat quality may not be as effective. In contrast, Australian

(1) Compile a list of localities in a region where the impacts of drought, based on predicted flow scenarios (e.g. 90th percentile exceedance flow, i.e. flow that is equalled or exceeded in 90% of daily records), are likely to be greatest and associate these with the key exacerbating threats. (2) Compile and assess information on the resistance/resilience attributes for species relevant to the jurisdiction, region or system of interest (here presented in Tables 1 and 2 based on expert survey). Species not present but expected to immigrate into areas during drought should also be considered in this step. (3) Identify priority locations for management actions based on the combination of species resistance and resilience attributes and the localised physical impacts of drought. This step would establish the key threats to be addressed and include specific thresholds and trigger points for intervention. It would also identify locations where drought impacts are not expected to be as severe, thus providing information on potential source populations for post-drought recovery at the regional scale. (4) Consider whether the threats identified at Step 3 can be addressed by short-term management interventions or only by actions that re-establish natural capacity to withstand drought. From this, develop and implement appropriate management actions to mitigate threats during drought or enhance natural capacity to withstand drought. (5) Implement a sound monitoring and evaluation framework to assess the outcomes of specific management actions. This step is critical to refining Steps 1–4, thereby informing future decisions and management plans, and hence the outcomes must be well documented and widely available. (6) The sometimes contentious nature of active interventions during drought (e.g. providing environmental water) requires that key stakeholders and the wider community are properly engaged and informed during the development and implementation of management plans. In many instances, key stakeholders will play a critical role in informing Steps 1–5. Critical to this prioritisation approach is an understanding of the interaction between the relative hydrological and habitat impacts of drought and the resilience and resistance of species

Proactive management investment

smelt were assessed as being highly resilient, but having only moderate resistance to declining water quality, predation and competition. Such attributes would imply a lower priority for management intervention, with a focus on maintaining some core populations to facilitate post-drought recovery. However, their relatively short life-span means that suitable conditions need to be maintained to allow breeding to continue throughout prolonged droughts, with risks to the species increasing as drought length increases. In the following section, we present a simple framework that utilises species’ attribute information to help identify the potential risks or threats posed to different species under various drought impacts. The framework uses a similar approach to that already embodied in several risked-based natural resource management planning documents (e.g. McMaster et al. 2008) and consists of 6 main steps:

D. A. Crook et al.

HIGH


LOW

384

SPECIES

SPECIES

– high resistance/resilience

– low resistance/resilience

LOCALITY – high catchment disturbance – highly susceptible to drought effects – high risk of other threats

LOCALITY – high catchment disturbance – highly susceptible to drought effects – high risk of other threats

SPECIES – high resistance/resilience

SPECIES – low resistance/resilience

LOCALITY – low catchment disturbance – low susceptibility to drought effects – low risk of other threats

LOCALITY – low catchment disturbance – low susceptibility to drought effects – low risk of other threats

LOW

HIGH Responsive management investment

Fig. 2. A framework for considering a mixture of pro-active and responsive measures for managing fish through drought taking into account a species’ capacity to survive during and recover after a drought event as well as the relative impacts of drought conditions on its habitat.

in those regions (Step 3, Fig. 2). For example, an area may have many species with low resistance and/or resilience, but may also be relatively unimpacted in terms of land-use and hydrology. In contrast, some areas may contain mainly droughttolerant species, but be in a degraded state, with greater risk of drying/fragmentation and poor water quality. The worst combination would be species with low resistance and resilience in the most damaged or drought-susceptible areas; a situation that will require the most effort in terms of inter-drought planning and mitigation (Fig. 2). Existing threats may also exacerbate the impacts of drought on such species (Murray–Darling Basin Commission 2004; Lintermans and Cottingham 2007; Drew 2008). For example, the presence of an introduced piscivorous predator (e.g. redfin perch) may greatly exacerbate the risk to native fish in a fragmented pool habitat as it gradually dries during a drought (Matthews 1998; McNeil 2004; Drew 2008). Development of more accurate and sophisticated tools for predicting impending future droughts has the potential to greatly improve assessment of the hydrological impacts of drought under various low-flow scenarios. Barros and Bowden (2008), for example, have developed a model that can accurately predict El Niño droughts in the Murray–Darling Basin 10 months ahead of time. More importantly, however, on-ground management may be increasingly aided in making pre-emptive/pro-active decisions via the incorporation of predictive tools into activityplanning processes. The success of pre-emptive drought management responses, however, will still ultimately rely on a good understanding of low flow hydrology – this is usually lacking at present, particularly in smaller ungauged systems that are at a relatively greater risk from the impacts of drought than larger gauged streams and rivers. Given the potential for increased frequency and duration of low flow periods into the future in south-eastern Australia,


development of specific and detailed drought management plans should be incorporated into catchment management strategies. In some cases, alterations to existing strategies and programs may be required during periods of drought whereby efforts are directed towards priority sites (i.e. location with threatened species and/or habitats). As is the case in all management strategies, temporal and spatial scale must be given full consideration and the timing and duration of actions need to be specified. For example, the pre-emptive stocking or translocation of a particular native fish species into a region to enhance their natural capacity to withstand drought may be most effective when undertaken during wetter periods. Equally, responsive actions must incorporate specific hydrological or ecological triggers e.g. if water quality drops below a defined threshold, the delivery of an environmental flow may be triggered as an appropriate management action to protect fish species. Management actions must not only identify the immediate threats associated with drought but also recognise the legacies of past disturbances and the impacts of on-going disturbances in order to be targeted at an appropriate scale. For example, habitat restoration through the addition of coarse wood at the local scale may be overridden by on-going disturbances operating at larger (possibly catchment-wide) scales, such as altered flow regimes or the presence of introduced species (Bond and Lake 2003). In the long-term, informing and engaging the community will assist in protecting ecological values – for example, landholders may help to ensure drought refuge pools are maintained by reducing water extraction and restricting stock access. Finally, the outcomes of management actions should be adequately monitored and evaluated in light of their objectives and key learnings disseminated effectively to the community and stakeholders to ensure that future decisions are better informed. A recently established ‘Community of Practice for Environmental Water Managers’ in Australia (http://www.cop4ewm.com.au/ [accessed 17 December 2009]) is one example of how such knowledge and experiences could be shared. Addressing the knowledge gaps The synthesis and management approach outlined above will be most effective if some key knowledge gaps are addressed. Overall, the fish attributes that survey respondents had the least understanding and confidence in ranking were the ability of fish to avoid or survive the effects of parasites and disease, and their ability to out-compete other species for food, habitat and other resources during drought or low flow conditions. While research continues to look at the effects of reductions in water volumes and increased densities on biological and food web interactions (Bunn et al. 2003; Balcombe et al. 2005), further work is still required. Owing to the lack of gauges within smaller headwater catchments, it is difficult to assess hydrological impacts of drought under various low-flow scenarios. There is thus a pressing need for regionalised rainfall/runoff models based on catchment characteristics and climate data to develop historical flow records for ungauged catchments. To respond to drought most appropriately and effectively, there is also a need to understand the timing at which responsive actions should be implemented. Research should be aimed at specifying hydrological and ecological triggers to most effectively mitigate threats


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during drought or to enhance the natural capacity of the ecosystem and its constituent species to withstand drought. Finally, information on the effects of drought – both in terms of its spatial extent and severity, together with the likely impacts on individual species, including tolerance thresholds and other biological attributes (much of which is available in books and reports) – should be made more readily available, preferably online. Conclusions As conditions vary from site to site, potential outcomes of drought-related events are not always clear, hence there are several important considerations regarding the ideas presented in this paper. Management must acknowledge how past and present stresses have affected fish populations. If a population has been reduced by stresses to low numbers before drought, population recovery may no longer be viable, or may only be possible via the active reintroduction of species (Fig. 2). Furthermore, as drought does not affect all environments equally, management needs to devise a ranking of susceptibility, e.g. shallow floodplain wetlands v. deep pools, headwater streams v. large rivers, to guide their management actions. For example, low order streams may dry up completely but this will not happen, even under extreme conditions, in high order rivers. Thus, the risk of catastrophic impacts is higher in some environments than in others. Anthropogenic factors must be fully considered when assessing the need for management interventions, as even species identified as having relatively high resistance and/or resilience may be vulnerable to the effects of drought at a regional level if populations are small, fragmented or under pre-existing threats (e.g. alien species, habitat degradation or over-exploitation). Artificial barriers are a good example of an anthropogenic disturbance that can impede recolonisation and hence the rate and extent of population recovery following drought. The severity and duration of droughts may be exacerbated by human forces, of which some obvious examples are the impacts of water extraction, farm dams and very low flow releases below impoundments. Although we have presented species attributes as being relatively fixed, there may be significant variation in attributes among populations of the same species, particularly those that have widespread distribution. Indeed, such variation is an important factor in species’ abilities to adapt to environmental change, e.g. owing to salinity or climate shifts (Kawecki and Ebert 2004). Similarly, there may be considerable differences in the attributes at different life history stages (Schlosser and Angermeier 1995). Caution should therefore be used in translating very specific information on species attributes, including physiological tolerances between widely distributed populations or ecosystem types. There are considerable gaps in our biological knowledge of the attributes that may be related to withstanding drought for many species and new knowledge would refine this management framework. To ensure optimal outcomes for fish populations, the need for a mix of pre-emptive and responsive strategies to manage aquatic ecosystems during drought must be emphasised. There is also the need to evaluate, and learn from, different scenarios of drought duration and intensity in evaluating the likely outcomes of different management options. Some examples of drought management strategies are discussed in detail elsewhere

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(e.g. Bond et al. 2008; McMaster et al. 2008), but such strategies are best devised by teams comprising ecologists, hydrologists and water and catchment managers (Likens et al. 2009). With predictions for longer and more severe dry spells as a result of human-induced climate change (Commonwealth Science and Industrial Research Organisation and Australian Bureau of Meteorology 2007), increasing aridity and drought impacts are likely to further increase the stress on fish populations in the inland waterways of south-eastern Australia. Ultimately however, the global, regional and local factors that exacerbate the impacts of drought need to be addressed to ensure the long-term viability of aquatic biodiversity in inland river networks. Acknowledgements The authors thank Stephen Balcombe, Lee Baumgartner, Brendan Ebner, John Harris, Alison King, Jarod Lyon, Jed Macdonald, Shaun Meredith, Clayton Sharpe, Jason Thiem, Zeb Tonkin and Brenton Zampatti for their participation in the survey of biological attributes of fish species. Valuable comments on previous drafts of the manuscript were provided by Paulo Lay, Sam Marwood (Victorian Department of Sustainability and Environment), Leon Metzeling (Victorian Environmental Protection Authority), Heleena Bamford and Melissa Morley (Murray–Darling Basin Authority), Gerry Closs (University of Otago) and two anonymous referees. Financial support for this work was provided by the Victorian Department of Sustainability and Environment (Sustainable Water, Environment and Innovation Division), the Murray–Darling Basin Authority (Native Fish Strategy) and the eWater Cooperative Research Centre.

References Balcombe, S. R., Bunn, S. E., McKenzie-Smith, F. J., and Davies, P. M. (2005). Variability of fish diets between dry and flood periods in an arid zone floodplain river. Journal of Fish Biology 67, 1552–1567. doi:10.1111/J.1095-8649.2005.00858.X Barros, A. P., and Bowden, G. J. (2008). Toward long-lead operational forecasts of drought: An experimental study in the MurrayDarling River Basin. Journal of Hydrology (Amsterdam) 357, 349–367. doi:10.1016/J.JHYDROL.2008.05.026 Bond, N. R., and Lake, P. S. (2003). Local habitat restoration in streams: Constraints on the effectiveness of restoration for stream biota. Ecological Management & Restoration 4, 193–198. doi:10.1046/J.14428903.2003.00156.X Bond, N. R., and Lake, P. S. (2005). Ecological restoration and large-scale ecological disturbance: The effects of drought on the response by fish to a habitat restoration experiment. Restoration Ecology 13, 39–48. doi:10.1111/J.1526-100X.2005.00006.X Bond, N. R., Lake, P. S., and Arthington, A. H. (2008). The impacts of drought on freshwater ecosystems: anAustralian perspective. Hydrobiologia 600, 3–16. doi:10.1007/S10750-008-9326-Z Boulton, A. J. (2003). Parallels and contrasts in the effects of drought on stream macroinvertebrate assemblages. Freshwater Biology 48, 1173–1185. doi:10.1046/J.1365-2427.2003.01084.X Bunn, S. E., Davies, P. M., and Winning, M. (2003). Sources of organic carbon supporting the food web of an arid zone floodplain river. Freshwater Biology 48, 619–635. doi:10.1046/J.1365-2427.2003.01031.X Chessman, B. C., and Robinson, D. P. (1987). Some effects of the 1982– 83 drought on water quality and macroinvertebrate fauna in the lower Latrobe River, Victoria. Australian Journal of Marine and Freshwater Research 38, 289–299. doi:10.1071/MF9870289 Closs, G. P. (1994). Feeding of Galaxias olidus (Günther) (Pisces: Galaxiidae) in an intermittent Australian stream. Australian Journal of Marine and Freshwater Research 45, 227–232. doi:10.1071/MF9940227

D. A. Crook et al.

Closs, G. P., Balcombe, S. R., Driver, P., McNeil, D. G., and Shirley, M. J. (2006). The importance of floodplain wetlands to Murray–Darling Fish: What’s there? What do we know? What do we need to know? In ‘Native Fish and Wetlands in the Murray-Darling Basin: Action Plan, Knowledge Gaps and Supporting Papers’. (Ed. B. Phillips.) pp. 14–28. (MurrayDarling Basin Commission: Canberra.) Commonwealth Science and Industrial Research Organisation, Australian Bureau of Meteorology (2007). Climate change in Australia: technical report 2007. CSIRO, Canberra. Drew, M. M. (2008). A guide to the management of native fish: Victorian coastal rivers, estuaries and wetlands. Department of Sustainability and Environment and the Corangamite Catchment Management Authority, Victoria. Elliott, J. M. (2000). Pools as refugia for brown trout during two summer droughts: trout responses to thermal and oxygen stress. Journal of Fish Biology 56, 938–948. doi:10.1111/J.1095-8649.2000.TB00883.X Fritz, K. M., and Dodds, W. K. (2004). Resistance and resilience of macroinvertebrate assemblages to drying and flood in a tallgrass prairie stream system. Hydrobiologia 527, 99–112. doi:10.1023/B:HYDR. 0000043188.53497.9B Green, C. H., Tunstall, S. M., and Fordham, M. H. (1991). The risks from flooding: which risks and whose perception? Disasters 15, 227–236. doi:10.1111/J.1467-7717.1991.TB00456.X Hardie, S. A., White, R. W. G., and Barmuta, L. A. (2007). Reproductive biology of the threatened golden galaxias Galaxias auratus Johnston and the influence of lake hydrology. Journal of Fish Biology 71, 1820–1840. Humphries, P., and Baldwin, D. S. (2003). Drought and aquatic ecosystems: an introduction. Freshwater Biology 48, 1141–1146. doi:10.1046/ J.1365-2427.2003.01092.X Kawecki, T. J., and Ebert, D. (2004). Conceptual issues in local adaptation. Ecology Letters 7, 1225–1241. doi:10.1111/J.1461-0248.2004.00684.X Koehn, J. D. (2004). Rehabilitating fish habitats in Australia: improving integration of science and management by agencies and the community. Ecological Management & Restoration 5, 211–216. doi:10.1111/J.14428903.2004.209-2.X Koehn, J. (2005). The loss of valuable Murray cod in fish kills: a science and management perspective. In ‘Management of Murray Cod in the MurrayDarling Basin: Statement, Recommendations and Supporting Papers Proceedings of a Workshop held in Canberra, ACT, 3–4 June 2004’. (Eds M. Lintermans and B. Phillips.) pp. 73–82. (Murray-Darling Basin Commission and Cooperative Research Centre for Freshwater Ecology: Canberra.) Koehn, J. D., and O’Connor, W. G. (1990). Biological information for management of native freshwater fish in Victoria. Department of Conservation and Environment, Melbourne. Lake, P. S. (2000). Disturbance, patchiness, and diversity in streams. Journal of the North American Benthological Society 19, 573–592. doi:10.2307/ 1468118 Lake, P. S. (2003). Ecological effects of perturbation by drought in flowing waters. Freshwater Biology 48, 1161–1172. doi:10.1046/J.1365-2427. 2003.01086.X Lake, P. S. (2008). ‘Drought, the “Creeping Disaster’’. Effects on Aquatic Ecosystems.’ (Land & Water Australia: Canberra.) Lake, P. S., and Bond, N. R. (2007). Australian futures: Aquatic ecosystems and human water usage. Futures 39, 288–305. doi:10.1016/J.FUTURES. 2006.01.010 Lake, P. S., Bond, N. R., and Reich, P. (2008). An appraisal of studies on the impacts of drought on aquatic ecosystems: knowledge gaps and future directions. Verhandlungen der Internationalen Vereinigung für Theoretische und Angewandte Limnologie 30, 506–508. Likens, G. E., Walker, K. F., Davies, P. E., Brookes, J., Olley, J., et al. (2009). Ecosystem science: towards a new paradigm for managing Australia’s inland aquatic ecosystems. Marine and Freshwater Research 60, 271–279. doi:10.1071/MF08188


Lintermans, M., and Cottingham, P. (Eds) (2007). Fish out of water – lessons for managing native fish during drought. Final report of the drought expert panel. Murray–Darling Basin Commission, Canberra. Lyon, J. P., and O’Connor, J. P. (2008). Smoke on the water: can riverine fish populations recover following a catastrophic fire-related sediment slug? Austral Ecology 33, 794–806. doi:10.1111/J.1442-9993.2008.01851.X Magoulick, D. D., and Kobza, R. M. (2003). The role of refugia for fishes during drought: a review and synthesis. Freshwater Biology 48, 1186– 1198. doi:10.1046/J.1365-2427.2003.01089.X Matthews, W. J. (1998). ‘Patterns in Freshwater Fish Ecology.’ (Chapman & Hall: New York.) Matthews, W. J., and Marsh-Matthews, E. (2003). Effects of drought on fish across axes of space, time and ecological complexity. Freshwater Biology 48, 1232–1253. doi:10.1046/J.1365-2427.2003.01087.X McMaster, D., Bond, N., and Reich, P. (2008). Review of the 2007/2008 CMA dry inflow contingency plans. Report to the Department of Sustainability and Environment, Melbourne. McNeil, D. G. (2004). Ecophysiology and behaviour of Ovens River floodplain fish: hypoxia tolerance and the role of the physicochemical environment in structuring Australian billabong fish communities. PhD Thesis, La Trobe University, Bundoora. McNeil, D. G., and Closs, G. P. (2007). Behavioural responses of a south-east Australian floodplain fish community to gradual hypoxia. Freshwater Biology 52, 412–420. doi:10.1111/J.1365-2427.2006.01705.X Merron, G., Bruton, M., and la Hausse de Lalouviere, P. (1993). Changes in fish communities of the Phongolo floodplain, Zululand (South Africa) before, during and after a severe drought. Regulated Rivers: Research and Applications 8, 335–344. doi:10.1002/RRR.3450080404 Miller, S. W., Wooster, D., and Li, J. (2007). Resistance and resilience of macroinvertebrates to irrigation water withdrawals. Freshwater Biology 52, 2494–2510. doi:10.1111/J.1365-2427.2007.01850.X Morrongiello, J., Elith, J., and Crook, D. (2006). Impacts of drought on fish in Victorian rivers and streams. Arthur Rylah Institute for Environmental Research, Heidelberg. Muchmore, C. B., and Dziegielewski, B. (1983). Impact of drought on quality of potential water supply sources in the Sangamon River Basin. Journal of the American Water Resources Association 19, 37–46. doi:10.1111/J.1752-1688.1983.TB04554.X Mundahl, N. D. (1990). Heat death of fish in shrinking stream pools. American Midland Naturalist 123, 40–46. doi:10.2307/2425758 Murphy, B. F., and Timbal, B. (2007). A review of recent climate variability and climate change in southeastern Australia. International Journal of Climatology 28, 859–879. doi:10.1002/JOC.1627


387

Murray–Darling Basin Commission (2004). Native fish strategy for the Murray–Darling Basin 2003–2013. Murray–Darling Basin Commission, Canberra. Palmer, M. A., Reidy, C., Nilsson, C., Florke, M., Alcamo, J., Lake, P. S., and Bond, N. R. (2008). Climate change and the world’s river basins: anticipating response options. Frontiers in Ecology and the Environment 6, 81–89. doi:10.1890/060148 Pullin, A. S., Knight, T. M., Stone, D. A., and Charman, K. (2004). Do conservation managers make use of scientific evidence to support their decision making? Biological Conservation 119, 245–252. doi:10.1016/ J.BIOCON.2003.11.007 Pusey, B., Kennard, M., and Arthington, A. (2004). ‘Freshwater Fishes of North-Eastern Australia.’ (CSIRO Publishing: Collingwood.) Rose, P., Metzeling, L., and Catzikiris, S. (2008). Can macroinvertebrate rapid bioassessment methods be used to assess river health during drought in south-eastern Australian streams? Freshwater Biology 53, 2626–2638. doi:10.1111/J.1365-2427.2008.02074.X Schaefer, J. (2001). Riffles as barriers to interpool movement by three cyprinids (Notropis boops, Campostoma anomalum and Cyprinella venusta). Freshwater Biology 46, 379–388. doi:10.1046/J.1365-2427. 2001.00685.X Schlosser, I. J., and Angermeier, P. L. (1995). Spatial variation in demographic processes of lotic fishes: conceptual models, empirical evidence, and implications for conservation. American Fisheries Society Symposium 17, 392–401. Timbal, B., and Jones, D. A. (2008). Future projections of winter rainfall in southeast Australia using a statistical downscaling technique. Climatic Change 86, 165–187. doi:10.1007/S10584-007-9279-7 Tramer, E. (1977). Catastrophic mortality of stream fishes trapped in shrinking pools. American Midland Naturalist 97, 469–478. doi:10.2307/ 2425110 Unmack, P. J. (2001). Fish persistence and fluvial geomorphology in central Australia. Journal of Arid Environments 49, 653–669. doi:10.1006/ JARE.2001.0813 Vrijenhoek, R. C. (1996). Conservation genetics of North America desert fishes. In ‘Conservation Genetics: Case Histories from Nature’. (Eds J. C. Avise and J. L. Hamrick.) pp. 367–397. (Kluwer: Norwell, MA, USA.)

Manuscript received 20 August 2009, accepted 16 December 2009

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