Addressing knowledge gaps and questions from the Fitzroy River (Kimberley region, Western Australia) fishway review.

Transcription

1 2011 Addressing knowledge gaps and questions from the Fitzroy River (Kimberley region, Western Australia) fishway review. Report to the Department of Water, Government of Western Australia P age

2 Addressing knowledge gaps and questions from the Fitzroy River (Kimberley region, Western Australia) fishway review. Prepared for the Department of Water, Government of Western Australia. This project is supported by funding from the Western Australian Government s State NRM Program. Prepared by the Freshwater Fish Group, Murdoch University Contributors: D. Morgan, S. Beatty, M. Allen, A. Gleiss, J. Keleher and J. Whitty December 2011 Disclaimer: The views in the document represent the view of the authors and do not necessarily represent the views of the Department of Water, Government of Western Australia. Much of the data in this report represents the authors background intellectual property and is not be used for any purpose without the authors consent. 2 P age

3 Contents Background... 4 Executive summary.. 5 Introduction 9 Chapter 1 Ecology of Freshwater Sawfish, including migratory periods and habitat utilisation Interannual variation in recruitment and flow Acoustic tracking of Freshwater Sawfish An assessment of Freshwater Sawfish habitat in the Fitzroy River catchment.. 25 Chapter 2 Camballin Barrage: a barrier to Freshwater Sawfish movement in the Fitzroy River? Population abundance estimate below the Camballin Barrage during Results and discussion Impacts of the barrage on Freshwater Sawfish Consideration of Myroodah Crossing as a management priority. 35 Chapter 3 Critical flow levels for Freshwater Sawfish migration in the Fitzroy River.. 36 Chapter 4 Utility of acceleration data-loggers for enhancing fishway design Field deployments Processing of acceleration data Preliminary results Future applications of the technology Informing fishway design Population monitoring: from individual to population health.. 51 General conclusions. 52 References P age

4 Background The Department of Water, Government of Western Australia, has posed a series of questions relating to the ecological benefits of constructing a fishway at the Camballin Barrage on the Fitzroy River in the Kimberley region of Western Australia. This is in particular reference to the Freshwater Sawfish (Pristis microdon). As well as providing background information of the ecology of Freshwater Sawfish in the Fitzroy River, which is based on a long term data set ( ), this report addresses the knowledge gaps posed by DoW with regard to (1) the bathymetry of pools upstream and downstream of the barrage using satellite imagery; (2) duration of flow events and significance to fish migration; (3) factors on the migratory period of key species and depth utilisation for migrating up a fishway; (4) flow requirements for drowning out natural barriers and the barrage and the level of enhancement to migratory periods if a fishway was installed and functional; (5) impact of the barrage on fish populations; (6) whether the other barrier on the river (Myroodah Crossing) is a priority for management response over the barrage; and (7) the degree of Freshwater Sawfish habitat above and below the barrage and the ecological significance of this. Plate 1 Clockwise from top left: the Camballin Barrage 29/6/07, Myroodah Crossing (July 2007), Freshwater Crocodiles below the barrage August 2006 (photographs D. Morgan and S. Visser). 4 P age

5 Executive Summary This report provides an overview and summary of the research that has been conducted to date on Freshwater Sawfish (Pristis microdon) in the Fitzroy River, Western Australia, by the Centre for Fish and Fisheries Research at Murdoch University. The report utilises this research to address knowledge gaps and questions arising from the Fitzroy River fishway review (see Background) and seeks to address the core question underpinning this review: Is a fishway at the Camballin Barrage necessary? The Freshwater Sawfish is listed as critically endangered by the International Union for Conservation of Nature (IUCN) and is the only freshwater fish in the Fitzroy River protected at both State and Federal level under the relevant Acts. The species has declined massively over large parts of its geographical range (East Africa to Australia New Guinea) and is particularly susceptible to commercial net fishing. The highest abundance for this species anywhere in the world has been recorded in the Fitzroy River in the pool located immediately below the Camballin Barrage (Money Pool). Sawfish become congregated below the barrage which is an impassable obstacle to upstream migration for large portions of the year, on average. Sawfish are born (pupped) in coastal waters from January to April (i.e. the wet season), and it is believed that the major pupping ground in W.A. is King Sound in the vicinity of the Fitzroy River mouth. Newborn sawfish have an instinct to migrate into the nursery habitat of the riverine environment where they spend their first 4 or 5 years. Their growth is rapid and they attain a length in excess of two metres during these years before migrating back downstream to coastal waters to mature and reproduce. The species is reliant on seasonal and predictable river flow for both upstream and downstream migration. The number of sawfish recruits (and other important freshwater species such as Barramundi and Cherabin) is closely linked to river flow each year. In years with high freshwater discharge and sustained river flow late into the wet and early dry season catches of 0+ recruits comprise a significantly higher proportion of the total sawfish catch than in years with low discharge. In 2011, the number of 0+ sawfish captured was unprecedented suggesting that conditions were ideal for their recruitment this year with high wet season rainfall and sustained river flow throughout the dry season. Consequently, the negative impact of the barrage on sawfish has been especially pronounced this year as large numbers of recruits have become congregated in the pool immediately downstream. Evidence of attempted predation by sharks and crocodiles in 5 Page

6 the form of bites and wounds were recorded on roughly 45% of individuals captured which reflects a build up in numbers of large predators of sawfish. The carcasses of four 0+ sawfish, including one tagged animal, were also found dragged up on the bank below the barrage where they had been left to die by anglers. Furthermore, many tagged animals that were re captured towards the end of 2011 were found to have reduced body mass and girth and were visibly emaciated, which suggests that food resources below the barrage had become scarce due to competition within and/or between species. This weight of evidence suggests that the potential for an increase in sawfish numbers resulting from the boom recruitment event of 2011 has been counteracted to some extent by the restriction on natural upstream migration imposed by the Barrage and its associated effects. Much information on movement and habitat utilisation of Freshwater Sawfish in the Fitzroy River has been gathered in recent years through the use of acoustic tags on animals in combination with an array of acoustic receivers. Habitat partitioning by depth has been demonstrated between different age classes, with 0+ animals occupying shallow water (<0.6 m) and 1+ and older animals occupying deeper water. Additionally, accelerometer tags are now being used on sawfish and the data gathered from this research (currently being analysed) will be extremely valuable for informing fishway design by ensuring that flow characteristics of any proposed fishway do not exceed the swimming capacity of the 0+ sawfish. No tagged fish have been detected by acoustic receivers moving over the barrage into the pools upstream, however, we know that sawfish are capable of moving past the barrier as they have been captured much further inland. Indeed, there is a total of about 179 km of suitable refuge pool habitat situated in the main channel of the Fitzroy River upstream of the barrage compared to about 84 km below the barrage. If pool habitat in the larger tributaries upstream such as Margaret River are taken into account this disparity is even greater. An analysis of stage heights and stream connectivity both upstream and downstream of the vicinity of the barrage revealed that a fishway structure would lead to at least a threefold increase in the window of opportunity to allow sawfish and other key species to bypass this barrier and migrate well upstream of it, which equates to about 3 4 months extra per year on average. A fishway over the barrage has the potential to be of great benefit to Freshwater Sawfish by: a) allowing extended access to large amounts of upstream refuge habitat, b) alleviating high rates of mortality due to predation and competition for limited food resources while densely congregated in the pool below the barrage. Additionally, other species such as Barramundi and Cherabin, which are 6 Page

7 important species for recreational and Indigenous fisheries, will have improved access to areas upstream of the barrage as well. The likely increase in abundance of these important angling targets will be well received by fishers throughout the upper Fitzroy River catchment. The pool below the causeway at Myroodah Crossing (situated roughly 50 km downstream of the barrage) has had a high CPUE for sawfish throughout the course of the monitoring program indicating that this structure is another barrier to sawfish migration. We argue that it is not a management priority as any measures taken to enhance fish movement beyond the causeway would only allow upstream migrants access to a relatively short section of river before they encountered the impassable obstacle of the barrage, and would only be of benefit in drier than average years with low discharge in the later part of the wet season. Recommendations Continuation of Murdoch University s long term sawfish monitoring program in the Fitzroy River. This will allow the robustness of the Freshwater Sawfish population in the river, including recruitment success, to be gauged into the future (with particular emphasis on determining the potential impacts of climate change). It will also allow for further exploration of the relationship between river flow and sawfish recruitment in the Fitzroy. Deployment of an expanded acoustic array consisting of numerous receivers above and below the barrage. Considering there were ~200 Freshwater Sawfish congregated below the barrage in June 2011, an excellent opportunity to determine the number that move upstream or downstream with the first floods of the 2012 wet season has unfortunately been missed. A more detailed analysis of stream connectivity and stage height for the entire main channel of the Fitzroy River to more accurately quantify the extension of the window of opportunity for upstream migration past the barrage for sawfish and other aquatic species if a fishway were installed. Further experiments to quantify the relationship between swimming speed and acceleration of sawfish to ensure that any proposed fishway design does not exceed their swimming capabilities. 7 P age

8 An experiment comparing sawfish recruits that have been captured below the barrage, tagged with accelerometers and translocated into the pool immediately above the barrage with animals from the same cohort that remain downstream of the barrage. This will provide data to determine if any behavioural differences exist between animals occupying the two different pools which might provide evidence of a competitive advantage for animals that move over a fishway. Design a concept for an experimental fishway project that could be used to assess swimming performance of captive Freshwater Sawfish (housed in public aquaria) in a fishway under different flow regimes. 8 P age

9 Introduction This report synthesises all knowledge of Freshwater Sawfish (Pristis microdon) in the Fitzroy River, Western Australia, gained from a long term monitoring study. It aims to address a number of knowledge gaps on the impact that instream barriers have on the life history and conservation of the species, and the data presented herein provide objective evidence that can be used to inform the planning and management of the proposed construction of a vertical slot fishway over the Camballin Barrage. The Freshwater Sawfish is listed as vulnerable under the Environment Protection and Biodiversity Conservation Act 1999 in Commonwealth waters of Australia, as fully protected under the Fisheries Management Act 1994 in Western Australian waters, and is listed by the IUCN (2006) as critically endangered. This is the only listed fish species under the various Acts that occurs in the fresh waters of the Fitzroy River (Morgan et al. 2004, 2011), although a number of other species are recognised as threatened by the IUCN including the Freshwater Whipray (Himantura dalyensis) and the Bull Shark (Carcharhinus leucas). It is only very recently that any ecological work has been conducted on fishes in the Fitzroy River. The first study on the distribution of fishes was conducted in 2001 and 2002 and the species distributions were mapped across 70 sites in the catchment, which drains ~90,000km 2 (Morgan et al. 2004). In that study, 40 species of fish were recorded, 23 of which are freshwater species, the remainder being diadromous species that spend only part of their life cycle in fresh water. This latter group includes Barramundi (Lates calcarifer) and Freshwater Sawfish, which hatch or are born in the estuary (or King Sound) and then migrate into the freshwater pools of the Fitzroy River, which they utilise as a nursery (Morgan et al. 2004, 2011, Thorburn et al. 2007, Whitty et al. 2009a). The access to these upstream nursery areas is largely dependent on river flow and thus stage height, and although somewhat variable between years, it is believed that the climate of the Kimberley and resultant predictable wet and dry seasons of this river provides these diadromous species with the environmental stability required to maintain large population sizes. It is also a key reason that populations of these, and other, diadromous species are far greater than in rivers to the south (Pilbara), which only flow during epizootic rainfall events and thus provide little suitable habitat due to their unpredictable flow regimes and ephemeral nature. Their ecology is not only reliant on seasonal and predictable flows for the annual upstream migration of the new recruits to the population, but it also allows large juveniles and sub adults to migrate downstream out of the river during the wet season where they mature and breed. 9 P age

10 Figure 1 Map of localities in the Fitzroy River catchment referred to in this report. 10 P age

11 Chapter 1 Ecology of Freshwater Sawfish, including migratory periods and habitat utilisation The Freshwater Sawfish has suffered massive declines throughout its geographical range, largely due to loss of habitat and from being particularly vulnerable to entanglement in fishing nets (Simpfendorfer 2000, Peverell 2005, Morgan et al. 2011). Furthermore, the rostra are also often taken as curios, and this is evident in Western Australia, where Morgan et al. (2011) provide the distribution of W.A. sawfish species based on 376 sawfish captures and 283 occurrences of removed rostra held in various private and public collections. Freshwater Sawfish are found in northern W.A. between the Ord River and Cape Keraudren, but there are scant records of mature individuals in this region (see Figure 2), and the vast majority of juvenile Freshwater Sawfish in this state have been recorded from the Fitzroy River (Thorburn et al. 2007, Whitty et al. 2008, 2009a, b, Morgan et al. 2011, Phillips et al. 2011). The Fitzroy River is indisputably W.A. s most important nursery for Freshwater Sawfish and is arguably the world s most important nursery as well in terms of abundance (Morgan et al. 2011). However, there is genetic subdivision between the west coast populations and those in the Gulf of Carpentaria (Queensland), and females are thought to be philopatric, and thus return to their natal river to pup (Phillips et al. 2009, 2011). Limited information suggests that females have litter sizes of between six and 12 pups (Peverell 2008), and that the major pupping ground in W.A. is in the vicinity of the Fitzroy River mouth, which is based on the presence of many newborn pups in this region with fresh umbilical scars (Whitty et al. 2008, 2009a, b, Morgan et al. 2011). Pups are born at between 72 and 90 cm total length (TL), with the smallest recorded in the Fitzroy River estuary being 76.3 and 78.9 cm TL for males and females, respectively (Whitty et al. 2009, Morgan et al. 2011). Pupping is thought to occur from at least January until April 11 P age

12 and coincides with the high flow period of the river. From the estuary, new recruits then undertake an upstream migration where they colonise the majority of the main channel of the Fitzroy River as far upstream as Dimond Gorge and Margaret Gorge (i.e. over 400 km from the coast, Figure 2) (Morgan et al. 2004, 2011, Thorburn et al. 2007). They utilise the river s food resources and growth is remarkable, with males remaining in the river to a maximum length of 235 cm TL and females to 277 cm TL (Morgan et al. 2011). These lengths are attained by about four or five years of age (Thorburn et al. 2007). Rapid growth in the early life stage helps to reduce predation levels as once a large body size (i.e. total length > 2 m) is attained there are very few animals, with the exception of humans, that are capable of preying upon them. Natural mortality is believed to be high for the new recruits, with only one in five thought to reach maturity (Simpfendorfer unpublished data). Stable isotope analyses below the Barrage have suggested that the primary food source of Bull Sharks (Carcharhinus leucas) that is assimilated into their tissue is sourced from Freshwater Sawfish (Thorburn 2006), and newly recruited Freshwater Sawfish have been found in the stomachs of Bull Sharks below the Barrage (Morgan et al. 2005, Thorburn 2006). The other main predators include Estuarine Crocodiles (Crocodylus porosus), and humans, although many juvenile Freshwater Sawfish have been captured that have obvious bites from Freshwater Crocodiles (Crocodylus johnstoni). Within this report, we document attacks on multiple Freshwater Sawfish from predators below the Barrage for the first time, and report on recent human related impacts. This was due to a boom in recruits from the 2011 year class that is unprecedented since monitoring of Freshwater Sawfish began in The increase in attacks is likely a result of the large congregation of migratory species below natural or artificial barriers, which is often followed by an increase in predators, and increased angler interaction. Mortality is likely to be increased when Freshwater Sawfish become congregated below artificial barriers, such as at the Camballin Barrage. The annual recruitment of Freshwater Sawfish in the Fitzroy River has been monitored since 2002 (see Thorburn et al. 2003, 2004, 2007, Whitty et al. 2008, 2009a, Morgan et al. 2011). This is the only long term monitoring of the species in Australian waters, and has provided information on recruitment and flow regimes that would not have been possible in short term monitoring programs. For example, poor recruitment of the species occurred in each year between 2002 and 2005, and was also marginal in 2010 (Figure 4). In contrast, recruitment was high in 2007 and 2009 and in 2011 was unprecedented. It is plausible that these high recruitment years are crucial to the maintenance of the W.A. population of Freshwater Sawfish. 12 P age

13 Figure 2 Map of Freshwater Sawfish (Pristis microdon) records in the Kimberley and Pilbara regions of Western Australia, from Morgan et al. (2011). Plate 2 A juvenile (0+) Freshwater Sawfish (Pristis microdon) trapped below the barrage in May P age

14 Figure 3 The distribution of Barramundi (Lates calcarifer) in the Fitzroy River (from Morgan et al. 2004). Plate 3 A juvenile (0+) Barramundi (Lates calcarifer) trapped below the barrage in May Interannual variation in recruitment and flow Although there is virtually no information on the adult phase of Freshwater Sawfish lifecycle our long term monitoring of the juvenile population in the Fitzroy River has allowed us to explore the relationship between river flow and recruitment. Between 2002 and 2009 there was a general decline in catch per unit effort (CPUE) in the Fitzroy River (Figure 5a). The CPUE data is presented separately for 2011 (Figure 5b) where catches of 14 Page

15 new recruits surpassed all years combined between 2002 and Note that sampling generally occurred in each year in the early dry (June) and during the late dry (October). A decline in the CPUE also occurred between the early dry and late dry in most years and probably reflects the mortality of new recruits between these periods (Figure 5). This mortality is likely to have increased as fish become congregated below the barriers on the river at Myroodah Crossing and at the Barrage, which are two of our main sampling sites. In most years our only other consistently sampled location is in the tidal pools downstream of Langi Crossing, where, interestingly, we had zero captures in 2011, compared to a population estimate of ~ Freshwater Sawfish trapped below the Barrage (see section 2.1). We had previously hypothesised that that the Barrage would have had a higher impact on recruits during drier years (see Morgan et al. 2005, Thorburn et al. 2007), as the upstream migratory path is obstructed for a longer period, however, the boom in new recruits (0+) during 2011 has led us to revisit this hypothesis. In years of sustained flow, such as in 2011, new recruits, which have an instinct to migrate upstream, have a longer upstream migratory period and thus rather than being spread throughout the lower section of the river as it contracts and pools up during the dry season, they have unimpeded access as far upstream as the Barrage throughout the dry season where they congregate in large numbers. The relationship between the proportion of new recruits of Freshwater Sawfish in our catches in each year between 2002 and 2011 and the river stage height in the late wet season, i.e. April, is presented in Figure 6. A number of different data models were tested (in the statistical program SPSS) in order to determine the model with the highest coefficient of determination that was significant (p<0.05), which was then fitted to the scatterplot (produced in SIGMAPLOT). The relationship between the percentage of the population that consisted of new recruits in the Fitzroy River and mean stage height in April of each year was significant (p=0.03). This suggests that the length of the wet season flows has a significant influence on relative recruitment of pups to the population each year. As mentioned previously, this is based on the assumption that the same number of pups enter the year each river (as we consider that the number of mature (philopatric) females remains unchanged). 15 P age

16 Number Females Males Total length (mm) Number Females Males Total length (mm) Number Females Males Total length (mm) Number Females Males Total length (mm) Number Females Males 2006 Number Total length (mm) Females Males Total length (mm) Number Females Males Total length (mm) Number Females Males Total length (mm) Number Females Males Total length (mm) Number Females Males Number Total length (mm) Total length (mm) Figure 4 Length-frequency histograms of Freshwater Sawfish (Pristis microdon) captured throughout the Fitzroy River between 2002 and 2011 by Murdoch University s Freshwater Fish Group (from unpublished data and Thorburn et al. 2007, Whitty et al. 2008, 2009a). 16 P age

17 (a) (b) CPUE Telegraph Pool Myroodah Pool Barrage Geikie Gorge Site Figure 5 Catch-per-unit-effort (CPUE) of Freshwater Sawfish (Pristis microdon) in the Fitzroy River for (a) all sites combined between 2002 and 2009; and (b) at the four main sampling sites during June 2011 (from unpublished data and Thorburn et al. 2007, Whitty et al. 2008, 2009a). 17 P age

18 Percentage of new recruits (%) y = (2637.4/x) r 2 = 0.46 p = Figure 6 Mean April Stage Height (m) Proportion of new recruits in our catches of Freshwater Sawfish (Pristis microdon) between 2002 and 2011 and the relationship to mean daily April stage height of the Fitzroy River at Noonkanbah (from unpublished data and Thorburn et al. 2007, Whitty et al. 2008, 2009a). Higher water levels are thought to provide juvenile Freshwater Sawfish, and indeed other species that spend part of their life cycle in both marine and freshwater environments (e.g. Barramundi), with more habitat that leads to a reduction in predator interactions. The CPUE data between 2002 and 2009, for Freshwater Sawfish in the Fitzroy River, suggests that there has been an overall decline in the juvenile population during this period. This is despite the capture, during , of a comparatively large number of new recruits (i.e. 0+ fish), unlike between 2002 and 2005 (see Figure 4 and Whitty et al. 2008, 2009a). This may be a continuous overall decline from years past, but a more parsimonious explanation could be that it is a decline from an unusually large and temporary recruitment boom in the year 2000 which was an exceptionally wet year (similar to 2011). Whatever the cause, the observed trend of declining CPUE reflects a drop in captures of larger Freshwater Sawfish (i.e. presumably 2 4 year old animals) post 2006 (see Figure 4) which most likely migrated out of the river into coastal waters to breed. Often, an observed decrease (relative to years prior) in the numbers of an age class can be traced back to a weak year class/recruitment, like those observed in P age

19 (McGlennon et al. 2000). A weak year class/recruitment can be caused by a number of factors including increased predation, reduced health of breeding stocks and reduced river levels, to name a few. River discharge has been shown to be positively correlated with the survivorship of estuarine and freshwater species (Mills & Mann 1985, Drinkwater & Frank 1994), including Freshwater Sawfish in the Fitzroy River between 2002 and 2007 (Whitty et al. 2008). Although no significant relationship was observed between wet season river stage height and CPUE, the significant difference between early and late dry season CPUE, and the correlation between late wet season discharge and proportion of new recruits in our catches does suggest that water level influences survivability of Freshwater Sawfish juveniles. It is reasonable to hypothesise that a sustained increase in water levels would increase the survivability of newborn Freshwater Sawfish by increasing productivity and available habitat as well as decreasing predation (Flores Verdugo et al. 1990, Staunton Smith et al. 2004, Whitty et al. 2008). It could also be suggested that the drop in CPUE between early and late dry season is due in part to dispersal of the animals through the river. However, as upstream movement of Freshwater Sawfish has been shown to be extremely restricted by low water levels and made impossible beyond the Camballin Barrage during this time (Morgan et al. 2005, Whitty et al. 2008), dispersal is not as likely to be the cause for this decrease. To better understand the exact influences causing this decrease, continued sampling efforts are needed. As this project is in a unique position having monitored CPUE since 2002, the continuance of sampling would also allow for this project to be able to establish a better understanding of what a current typical CPUE is for this system. 1.2 Acoustic tracking of Freshwater Sawfish Our recent studies (see Whitty et al. 2008, 2009a, b) utilised an acoustic array (Figure 7) for the passive tracking of P. microdon in the Fitzroy River. Tag and receiver details are provided in Whitty et al. (2009a). Although a receiver was placed above and below the barrage, no detections of tagged sawfish were recorded immediately above the barrage. This suggests that no tagged sawfish below the barrage moved over the structure during the wet season, or that due to high flows they were not detected. It is recommended that an acoustic array consisting of numerous receivers above and below the barrage be installed. Considering there was ~200 Freshwater Sawfish congregated below the barrage in June 2011, this would provide an excellent opportunity to determine the number that move upstream or downstream with the first floods. 19 P age

20 Plate 4 Acoustic tag (left) and acoustic receiver placed throughout the Fitzroy River (see Whitty et al. 2009a). Figure 7 Map of the acoustic receiver array deployed throughout the lower Fitzroy River catchment to passively track movements and habitat utilisation of Freshwater Sawfish. 20 P age

21 Whitty et al. (2009a) demonstrated a high degree of habitat partitioning between different age classes, with the new recruits (0+ fish) clearly remaining in the shallows (typically <0.6 m depth, see Figure 8 10) for much of the day compared to the larger 1+ individuals that rarely moved into the extreme shallows. Furthermore, these larger individuals moved to deeper water at dawn (Figure 10), before moving shallower in the afternoon. Thus, the 1+ fish displayed predictable movements, exhibiting diel vertical migration patterns and similar diel movement patterns have been observed in a number of other predatory elasmobranchs (Skomal & Benz 2004). This ontogenetic habitat stratification may be related to foraging activities and/or predator avoidance, noting that these environments are also inhabited by Estuarine Crocodiles (Crocodylus porosus) and Bull Sharks (Carcharhinus leucas). The smaller individuals are potentially more susceptible to predation by these species, and it is particularly relevant that C. leucas has been shown to predate on P. microdon in the Fitzroy River (Thorburn et al. 2004, Thorburn 2006). Simpfendorfer (2006) reported similar behaviour for Pristis pectinata and suggested that along with decreasing predation, the occurrence of the larger individuals in the slightly deeper water allows the animal more space to manoeuvre while also maintaining a close proximity to potential prey. Simpfendorfer (2006) also suggested that the smaller individuals (< 1 m) of P. pectinata may reside in the shallows to take advantage of warmer temperatures to maximise growth rates. 21 P age

22 Depth of individual sawfish (V13 - Acoustic tags) Percentage (%) Depth (m) 100 Mean depth of sawfish tagged with V13s 80 V13 Percentage (%) Depth (m) >2.5 Figure 8 Depth utilisation of 0+ (new recruits) of Freshwater Sawfish (Pristis microdon) in the Fitzroy River (from Whitty et al. 2008, 2009a). 22 P age

23 50 40 Depth of individual sawfish (V16 - Acoustic tags) Percentage (%) Depth (m) 60 Mean depth of sawfish tagged with V16s 50 V16 Percentage (%) Depth (m) >2.5 Figure 9 Depth utilisation of 1+ (one year old) Freshwater Sawfish (Pristis microdon) in the Fitzroy River (from Whitty et al. 2008, 2009a). 23 P age

24 Depth (m) V13 V16 Depth v Time of day Time of day (hours) Figure 10 Depth utilisation of 0+ (new recruits) (blue circles) and 1+ (white circles) Freshwater Sawfish (Pristis microdon) in the Fitzroy River during the different times of the day (from Whitty et al. 2008, 2009a). Importantly, the acoustic study demonstrated that the small P. microdon in the estuarine reaches of the river moved between pools at will, even though most pools at low tide are separated by very long stretches of shallow waters. Furthermore, on the incoming tides, ~98% of movements of the 0+ fish between pools was in an upstream direction, i.e. they moved in the same direction as the tide. This contrasts the 1+ fish, which moved to another pool only when tidal waters reached the sites and this movement was in both an upstream (i.e. 50% with the tide) and downstream (i.e. 50% against the tide) direction. The ability to swim between pools and utilise the shallow runs and riffle zones between both tidally influenced and riverine pools is a beneficial adaptation. It allows the 0+ fish to not only avoid deeper bodied predators but to also forage in areas not being exploited by larger fishes, such as older P. microdon, L. calcarifer, C. leucas or crocodiles. Moreover, it allows the new recruits to continue to migrate upstream relatively unimpeded until the late dry; to at least the Barrage (Plate 1), a substantial unnatural barrier on the system (Morgan et al. 2005). 24 P age

25 A number of 0+ P. microdon have been observed over 100 km upstream within a month or two after peak river discharge, which would suggest that there is an instinct within in at least a few individuals to move upstream to the upper pools. As Telegraph Pool and Langi Crossing are the two most upstream pools that P. microdon can access with the aid of tides in the dry season, this requirement to move upstream or a preference to inhabit areas of lower salinity may be a reason for the occurrence of P. microdon in these pools in the late dry season. Further investigation is needed to determine the explanation for the inhabitation of Telegraph Pool. Previous findings (Whitty et al. 2008, 2009a, b) demonstrated flow to be highly influential on P. microdon, dictating interpool movements of 0+ P. microdon and aiding in movement upstream for larger bodied P. microdon in the tidally influenced estuarine pools. Increased river flows have also been shown to be a trigger for the migration of various fish species. During the current study, large (> 2 m) individuals were also documented to leave freshwater pools, where they had previously been confined, and estuarine pools that they could move between with the aid of tides, almost immediately at the onset of a flood event, caused by increased water flows. Three of the four P. microdon tracked during these flood events were > 2 m TL and had all moved downstream, one moving over 100 km to the river mouth (Milli Milli), where it was last recorded. A second of these was last recorded at Milli Milli at the initiation of the first flood event. Disappearance of these large fish from the acoustic array at the mouth of the river is potentially evidence of their migration back to the marine environment and could be the completion of the freshwater phase in their lifecycle. This corresponds with the fact that few P. microdon greater than 2.5 m TL have been recorded in the freshwater pools, and is likely to be approximately the size at which they leave the river. While few P. microdon greater than 2.5 m have been captured, all have been female (Thorburn et al. 2007), which further suggests that females may remain in the river longer than males. For a Freshwater Sawfish to use a fishway, the above data suggest that 0+ fish can swim through very shallow depths (see Figure 8). 1.3 An assessment of Freshwater Sawfish habitat in the Fitzroy River catchment A detailed habitat assessment of the Fitzroy River catchment, both upstream and downstream of the Camballin Barrage, was undertaken in order to determine the extent of suitable sawfish habitat on either side of this structure. Aerial imagery available on the Landgate website ( was assessed to quantify the total amount of deep water pool habitat situated between Langi Crossing and Dimond Gorge (see 25 P age

26 Figure 11 for localities). The imagery assessed was captured during the months of August and November All deep water pools were first identified using Landgate imagery and subsequently located in the web application Google Maps (maps.google.com.au) where the length of each pool was measured using the line tool. The Fitzroy River channel between Langi Crossing and Dimond Gorge was measured at km in length using the distance measurement tool in Google Maps. Camballin Barrage lies at a point km upstream of Langi Crossing (Figure 11). Deep water pool habitat is hereby defined as any continuous stretch of open water in the main river channel of sufficient depth to conceal the underlying river bed as viewed on aerial imagery (see Figure 12). These pools are mostly in excess of 1.5 m depth and capable of housing sawfish. The pools appear on aerial imagery as dark green or blackish in colour, and are separated by shallow sections of river and/or dry sand bars which appear brown to reddish orange in colour (see Figure 12). It should be noted that the analysis of pool habitat covers the dry season of a single year for which imagery was available (i.e. 2007). Some variation occurs in the dimensions of pools from year to year due to variability in freshwater discharge and sediment deposition and this constrains our ability to precisely estimate the amount of deep water pool habitat. Nonetheless, this analysis is useful for making a comparison of the extent of sawfish habitat on either side of the Barrage. Just less than 63% of the total length of the Fitzroy River channel above the barrage comprised deep water pool habitat compared to around 56% of the channel below the barrage (Table 3). Although the proportional difference was not large, this translates to almost 100 km of additional deep water pool habitat lying above the barrage, or nearly double that found below, due to the disparity in total length of river channel analysed on either side of the barrage (Table 3). The mean deep water pool length was greater above the barrage (1.72 km vs 1.25 km). Additionally, there was a greater prevalence of long pools (i.e. > 3 km long) above compared to below the barrage (11 vs 4), with the three longest pools identified in the analysis all being situated above the barrage. The longest pool below the barrage was approximately half the length of the longest pool (i.e. Geikie Gorge 14.1 km) above (Table 3). 26 P age

27 Figure 11 Aerial image of the Fitzroy River catchment showing the extent of the deep-water pool habitat mapping (blue lines indicate pools). Image courtesy of Google Maps (maps.google.com.au). 27 P age

28 Table 1 Summary of deep-water pool characteristics in the Fitroy River catchment located between Langi Crossing and Dimond Gorge. ABOVE BARRAGE BELOW BARRAGE TOTAL. Total number of pools Total pool length (km) River channel length (km) % pool habitat 62.70% 56.24% 60.48% Mean pool length (km) Median pool length (km) Maximum pool length (km) Minimum pool length (km) Whether critical habitat will be lost if fish can not move over the barrier is a moot point as we know that they are capable of bypassing the barrier during periods of inundation. This is evidenced by the fact that juvenile sawfish have been captured upstream of the barrage (Morgan et al. 2004). More important is whether critical habitat will be gained if sawfish can move over the barrier and the answer to this is resoundingly in the affirmative. A substantial amount (i.e. almost 180 km) of suitable deep water pool habitat exists upstream of the Camballin Barrage to Dimond Gorge (Table 3). An assumption of the population model used in this study is that the greater the habitat area (in this case, pool length), the larger the carrying capacity for fish communities, including sawfish. There is a much greater extent of deep water pool habitat above the barrage than below it. Therefore, it stands to reason, that by allowing sawfish (and other fish species) improved access to these pool habitats above the barrage by means of a fishway, it will be of great benefit to the species in this system. 28 P age

29 Figure 12 An example of the method used for measuring the length of deep-water pools. First, Landgate aerial imagery (upper screenshot) is used to identify the extent of each pool in the dry season of 2007, and; second, the line tool in Google Maps (lower screenshot) is used to measure the length of the pool. 29 P age

30 Chapter 2 Camballin Barrage: a barrier to Freshwater Sawfish movement in the Fitzroy River? 2.1 Population abundance estimate below the Camballin Barrage during 2011 An analysis of the raw multiple mark recapture data obtained during sampling that occurred between 9 21 June 2011 below the Camballin Barrage was undertaken in order to determine the abundance of P. microdon in those habitats at that site. This was undertaken in order to: 1) Quantify the degree to which juvenile P. microdon congregate below the Barrage. 2) By estimating the absolute abundance of this species for the first time in the Fitzroy River (or Western Australia), provide a baseline upon which future absolute and relative population estimates of P. microdon may be monitored at that site. By relating the absolute estimate to the CPUE of the species at that site in June 2011, an indication of actual abundance of juvenile sawfish below the barrage during previous sampling occasions could occur to enable an overall assessment of the degree of impediment to the species the barrage represents. A total of seven sampling occasions occurred within the 12 day sampling period using the methods previously described (see Whitty et al. 2009a). On each occasion, newly captured (i.e. un tagged individuals) were tagged (using unique tags as previously described) which allowed subsequent re captures during the period to be individually identified. As the sampling area below the barrage was connected to downstream habitats during sampling in June 2011, the Jolly Seber open population model was employed to provide estimates of population abundance. The POPAN formulation (Schwarz & Arnason, 1996) in the MARK software program was used to parameterise the Jolly Seber model (White & Burnham, 1999). This allows estimates of the trappable population on each of the seven sampling occasions (Nj), the super population size (N) (which is an estimate of the total number of sawfish present throughout the entire sampling period), the apparent survival rate (Φ) between sampling events (combines mortality and emigration), the probability of capture at each sampling event (p), and probability of entry into the sampled population (b). 30 P age

31 A number of assumptions are associated with the open population model (Schwarz & Arnason 2006), these include: 1) No heterogeneity of captures (i.e. all sizes of P. microdon are equally susceptible to capture). 2) Catchability does not differ between marked and non marked P. microdon. 3) Emigration is permanent. 4) No tag loss and tags are read properly (i.e. no mis identification). 5) Each sampling period is short and study area is constant. Although some bias may have occurred with regard to emigration (i.e. sawfish leaving downstream then re entering the sampled area), the sampling regime and tagging methods deployed would have ensured the other assumptions would have been generally adhered to. A number of models were tested in POPAN which allowed the above estimated parameters to either vary between the sampling occasions (t) or to be fixed throughout the sampling period (.) (Schwartz & Arnason 1996). The most appropriate model was then selected using the Akaike Information Criterion (AIC) which weights for quality of fit (deviance) and number of estimated parameters (precision) (White & Burnham, 1999) Results and discussion Based on the most appropriate open population model according to AIC (which was the Φ(t), p(.) b(t) model), the POPAN formulation in MARK revealed that the superpopulation size N below the Camballin Barrage (i.e. the total number of P. microdon within the sampling area throughout the entire 12 day sampling period in June 2011) was (±38.7 S.E.) individuals between June 9 21, Therefore, almost 200 new born pups had become trapped below the barrage, although there is the possibility that they could migrate downstream. However, our long term acoustic data (see Whitty et al. 2008, 2009a, b) suggests that new recruits possess an instinct to migrate in an upstream direction, i.e. into the flow. Based on the limited information available on litter size, this also suggests that these new recruits were from a minimum of 20 mature females, however, in reality the number is likely to be far greater. It also is unprecedented recruitment, and it is of concern that these individuals are exposed to greater levels of competition and predation when trapped below the barrage. 31 Page

32 2.2 Impacts of the barrage on Freshwater Sawfish An unusually large number of Freshwater Sawfish were captured from the pool located approximately two kilometres downstream of the Camballin barrage (Money Pool) in June 2011 (see section 2.1). In total, 47 individuals (all juveniles under 1,600 mm TL) were caught, examined for scarring/evidence of attack and then released. Of these, approximately 45% showed evidence of scarring from prior attacks, presumably by Bull Sharks and/or Freshwater Crocodiles (Plate 5). The fact that so many sawfish were captured from this site is due to them banking up below the barrage, and the high incidence of bite marks and scarring is an indication that their predators (i.e. Bull Sharks and Freshwater Crocodiles) are also building up to unnaturally high densities below this barrier. This is not an isolated phenomenon as high occurrences of Bull Sharks have been previously reported below the barrage (Morgan et al. 2005), and Thorburn (2006) demonstrated that Freshwater Sawfish are the main prey assimilated into the tissues of Bull Sharks below the barrage. There is clearly a competitive advantage to be gained by juvenile sawfish if they were able to bypass the barrage that is currently impeding natural migratory movements and leading to a high incidence of attack by predators. Rainfall was higher than average in the wet season of 2011 which has triggered what appears to be a keystone recruitment event for Freshwater Sawfish (as well as Barramundi and the freshwater prawn known locally as Cherabin). More juvenile Freshwater Sawfish were captured in June 2011 than in the past nine years of sawfish monitoring combined. While it is impossible to know the extent of predation resulting in mortality of Freshwater Sawfish recruits, it is reasonable to assume that it has been significant. It is plausible that the potential for an increase in sawfish numbers resulting from this year s boom recruitment event has been counteracted to some extent by the restriction on natural upstream migration imposed by the Barrage. 32 P age

33 A B C D E F G H Plate 5 Scars from attempted predation, fishing and overcrowding on juvenile sawfishes caught below the Camballin Barrage in June Arc-shaped scars (B, C and F) are bites from Bull Sharks (Carcharhinus leucas); the double row of teeth marks (D) are wounds from another Freshwater Sawfish (Pristis microdon); humans sometimes remove the rostrum of Freshwater Sawfish (G) as a trophy and many are found entangled with fishing line (H); and other wounds (A and E) are from unknown sources. 33 P age

34 The impact of recreational and Indigenous fishing is also likely to be higher during this period. For example, five captures of tagged Freshwater Sawfish have been reported to us by the public at this site since July, while a further four sawfish were found dead on the banks, including a tagged sawfish (see Plate 6). These sawfish had been dragged up the river bank and left to die. A further tagged sawfish was recaptured by a Nyikina Mangala ranger in November 2011 with its rostrum removed. Plate 6 Tagged Freshwater Sawfish (Pristis microdon) (tag #1114) killed by a recreational fisher in the large pool downstream of the barrage (found October 2011). Three other untagged sawfish were also found dead nearby. The construction of a fishway on the barrage also has potential to offer a competitive advantage to sawfish (and other species like Barramundi) via increased access to food resources. Important fodder species such as bony bream (Nematalosa erebi), have been shown to occur in high abundance above the barrage but are rare below (Morgan et al. 2005). Morgan et al. (2005) stated that a high degree of predation below the Barrage accounted for this difference. Construction of a fishway over the Camballin barrage will allow threatened sawfish, as well as recreationally and culturally important species like Barramundi, access to currently underutilised pool habitats upstream where food resources are in much greater abundance. Recaptured juvenile sawfish were found to have sharply declined in weight and body condition (i.e. body girth at the level of the pectoral fins) between the months of June (i.e. early dry season) and October (i.e. late dry season) in 2011, to the point where some individuals appeared emaciated (Gleiss & Morgan unpublished data). This is further evidence of the deleterious effect of the intense level of competition occurring among sawfish congregating below the Barrage. 34 P age

35 2.3 Consideration of Myroodah Crossing as a management priority The initial work on Freshwater Sawfish by Thorburn et al. (2003, 2004) demonstrated that CPUE in the pools located immediately below Myroodah Crossing and the Camballin Barrage were the highest for this species in any river system in northern Australia. Collecting efforts by our research group have concentrated on these areas (more so at Camballin) to best utilise the limited amount of time available to conduct field research into the biology, ecological requirements and habitat utilisation of this species. In light of the fact that CPUE is so high below Myroodah Crossing, this human made structure is unquestionably a barrier to the upstream movement of sawfish. Regardless of this, we argue that it is not a management priority over the proposed fishway at Camballin for several reasons. Myroodah is situated only 50 km downstream of the barrage, so any measures taken to facilitate easier passage over this barrier would only allow migrants access to a relatively short section of river upstream before they encountered the impassable obstacle of the Barrage. Furthermore, any such measures would only be beneficial in drier than average years with low discharge in the later part of the wet season, as in wetter years the vast majority of fish are capable of bypassing Myroodah crossing. Therefore, we recommend that the mitigation of negative impacts upon fish migration of Camballin Barrage be given management priority over Myroodah Crossing. 35 P age

36 Chapter 3 Critical flow levels for Freshwater Sawfish migration in the Fitzroy River Flow requirements that would result in natural instream barriers (i.e. sand bars) being drowned out were determined by an analysis of level 1 processed LandSat5 satellite images (path 109, row 73). Images with a swath width of 128km and a resolution of 30 meter pixels were obtained from the U.S. Geological Survey website. Images were analysed using IDRIS Taiga software, Clark labs Based on the principals of the interactions between surface water and near infra red radiation (NIR), analysis was undertaken using the NIR band ( μm). Reflectance of the NIR band on deep water (> ~ 0.1) is represented as a value below 20 and as the water decreases in depth, in combination of the presence of sandbars, this value increases. Based on this, the first disconnection points were located by screening the high quality satellite images for areas that increased in reflectance within the riverbed (Note: images decreased dramatically in quality when transferred to Microsoft Word, also in IDRISI high quality magnification of areas was possible.). Visual inspections of satellite images were made for each month during the dry season (i.e. May to December) during 2009, in order to determine the approximate date (imagery was available at day intervals) at which the river became disconnected both below and above the Barrage. The first significant natural barriers appeared at points located 9.46 km downstream and km upstream of the Barrage (Figure 13). On average, the river became disconnected at these points on July 22 and August 6 each year for the downstream and upstream barriers respectively (Figure 14, Tables 2, 3). Morgan et al. (2005) determined the stage height at which the barrage became negotiable by fish to be m. An analysis of data between the years inclusive, revealed that the water level at the barrage was above this height for approximately 20% of this time period. The stage height when the nearest natural barrier below the barrage emerged was m. Water levels in excess of this height were recorded approximately 61% of the time during the same period (Table 2, Figures 14, 15). At this stage height there is sufficient stream connectivity to allow sawfish and other migratory species relatively unimpeded access to the foot of the barrage from at least as far away as 10 km. A fishway at the Barrage would therefore allow sawfish and other migratory species an almost threefold increase in the duration of the window of opportunity for bypassing this instream barrier. This figure is, in reality, an underestimate of the true extent of the 36 Page

37 window of opportunity for upstream migration, as Money Pool remains connected to the pool at the foot of the barrage beyond the point in time when the stage height drops to m. At a stage height of m the pool above the barrage becomes disconnected from the river further upstream. This water level was recorded just over 68% of the time between 1998 and 2010 (Figures 14, 15, Table 3), meaning that sawfish and other species would have had the opportunity to migrate beyond the first pool above the barrage for almost two thirds of the time had a vertical slot fishway been in place during this time period. This analysis reveals that a fishway structure at the barrage would lead to a lengthening of the window of opportunity to not only allow sawfish and other key species to bypass this barrier, but to migrate well upstream of it. The important issue to consider here is the timing of migratory movements of these species. As the situation stands, the ability for fish to bypass the barrage during periods of drown out is relatively short lasting owing to the fact that breeding and pupping, which occurs outside the Fitzroy River in King Sound, is triggered by wet season flows. By the time newborn recruits have had the chance to migrate upstream a distance in excess of 150 km to the barrage, water levels may be insufficient to allow them to bypass it, particularly in years when discharge is below average. The key benefit offered by the construction of a fishway is the extended access it would allow fishes to bypass the barrier in the latter part of the wet season and early to middle parts of the dry season, periods when these species are currently becoming congregated below the barrage and suffering high levels of mortality as a result. Freshwater elasmobranchs (i.e. sharks, rays and their relatives including sawfishes) have never been recorded as utilising a fishway structure in Australia (Morgan et al. 2005, AECOM 2009). Therefore it is of paramount importance that any proposed fishway that is designed with the specific objective of facilitating movement of sawfish over the Barrage be built to specifications that will deliver this objective. In light of this, the minimum requirements, in terms of depth and width of water, which juvenile (i.e. < 1,200 mm TL) sawfish required to sustain swimming effort, were ascertained by an analysis of body dimensions and the extent of tail swing during energetic swimming by visual determination in the field. The minimum water depth was determined to be 0.2 m and tail swing was determined to lie within the maximum body width (i.e. distance between both pectoral fin tips) of 0.36 m. 37 P age

38 31 May July 2009 Camballin Barrage 38 P age

39 03 August September 2009 Figure 13 Near infra-red band ( µm) satellite imagery of the Fitzroy River channel in the vicinity of Camballin Barrage captured during late May to late September The formation of the most proximate barriers below (top of images) and above (bottom of images) are circled. Dashed circle is when the barrier begins to form (based on shallowing of water by increased reflectivity of the image). Solid circle indicate the barrier was completely formed. N.B. image quality was substantially reduced during the transfer of these images to Microsoft Word for this report. 39 P age

40 11.0 Average stage height Lower CI Upper CI Disconnection below barrage Disconnection above barrage Barrage able to be negotiated by fish (stage height = m) Stage height (m) /Jan 1/Feb 1/Mar 1/Apr 1/May 1/Jun 1/Jul 1/Aug 1/Sep 1/Oct 1/Nov 1/Dec 1/Jan Date Figure 14 Average daily stage height at the barrage (including 95% confidence intervals) over the period The horizontal lines are the stage height at which the Fitzroy River becomes naturally disconnected below (solid line = m, barrier located 9.46 km below the barrage) and above (dotted line = 10.35m, barrier located km upstream of the barrage). On average, this date was 22 nd July below the barrage, and 6 th August above the barrage. See text for details. 40 P age

41 Table 2 Dates (based on available satellite passes) when the natural barrier 9.46 km below the Camballin Barrage disconnects the Fitzroy River. N.B. the river often disconnects and reconnects more than once within each year. Year 1 st disconnection 1 st reconnection 2 nd disconnection 2 nd reconnection 3 rd disconnection 3 rd reconnection 4 th disconnection 4 th reconnection Days (%) connected May 1 Dec 159 (43.6) Jun 9 Nov 20 Nov 29 Nov 217 (59.5) Oct 24 Oct 14 Nov 12 Dec 327 (89.6) Oct 14 Nov 340 (93.2) Aug 4 Dec 262 (71.8) Jul 25 Dec 200 (54.8) Aug 215 (58.9) Jan 24 Apr 27 Jun 1 Jul 19 Dec 125 (34.2) Aug 14 Nov 9 Nov 28 Nov 3 Dec 28 Dec 231 (63.3) Aug 18 Nov 28 Nov 20 Dec 246 (67.4) Jul 30 Nov 3 Dec 9 Dec 227 (62.2) Jul 20 Dec 196 (53.7) Jan 15 Jan 3 May 27 May 4 Jun 16 Oct 29 Oct 12 Dec 161 (44.1) Total (61.2) 41 P age

42 Table 3 Dates (based on available satellite passes) when the natural barrier km above the Camballin Barrage disconnects the Fitzroy River. N.B. the river often disconnects and reconnects more than once within each year. Year 1 st disconnection 1 st reconnection 2 nd disconnection 2 nd reconnection 3 rd disconnection 3 rd reconnection 4 th disconnection 4 th reconnection Days (%) connected May 1-Dec 166 (45.5) Jul 9-Nov 20-Nov 29-Nov 238 (65.2) Nov 9-Dec 353 (96.7) (100) Oct 4-Dec 305 (83.6) Aug 25-Dec 230 (63.0) Sep through 242 (66.3) 2005 through 7-Jan 1-May 27-Jun 3-Jul 19-Dec 134 (36.7) Sep 14-Nov 11-Nov 30-Nov 5-Dec 28-Dec 263 (72.1) Sep 18-Nov 1-Dec 20-Dec 269 (73.7) Aug 29-Nov 5-Dec 8-Dec 258 (70.7) Jul 20-Dec 231 (63.3) Jan 15-Jan 8-May 26-May 8-Jun 16-Oct 1-Nov 12-Dec 181 (49.6) Total 248 (68.2) 42 P age

43 Figure 15 Percentage of time that the Fitzroy River is connected and disconnected above and below the Camballin Barrage between N.B. green bars is when no natural barriers are present in the River either below or above the Barrage, orange bars are when the barrier is present 9.46 km downstream of the Barrage, red is when a barrier also exists km upstream of the Barrage. Other key species that are predicted to benefit from the installation of a fishway are Barramundi (Lates calcarifer) and Cherabin (Macrobrachium rosenbergii). Both species are culturally important to the Traditional Owners of the Fitzroy River (Morgan et al. 2004, Thorburn et al. 2004) and are highly sought after by recreational fishers. Barramundi recruits (0+) migrate upstream from estuarine waters during the wet season when the river is flowing. This can result in large numbers congregating below the Barrage as was recorded during sampling in May 2009 (see also Morgan et al. 2005). The swimming ability of 0+ barramundi (mean TL 43 mm ± 4) was determined to be 0.66 ms 1 (Mallen Cooper 1992) which is well below the maximum velocity of flow (i.e ms 1 ) through the proposed fishway (AECOM 2009). However, these experiments were performed at lower water temperatures than would be experienced in the Fitzroy River during periods of upstream migration (i.e. May June), and furthermore, our data show that Barramundi typically range in size between 180 and 300 mm TL at this time (Morgan, unpublished data) and therefore are likely to have far greater swimming abilities. As there are genetic differences in Barramundi populations across northern Australia and the population in the Fitzroy River is genetically distinct from those elsewhere (Marshall 2005), swimming abilities can not be inferred with complete confidence based on previous studies from 43 P age

44 other populations. Furthermore, Mallen Cooper s (1992) experiment trialled the swimming ability of hatchery reared fish, which are known to be poorer swimmers than wild caught fish (Taylor & McPhail 1985). Further work is required to establish the size of Barramundi and other migratory species when they migrate upstream and congregate below the barrage. Barramundi recruits, owing to their smaller size, can remain in the small pool that forms at the foot of the barrage structure as the water level drops in the river for longer than sawfish recruits which must retreat to the large pool downstream of the barrage ( Money Pool ) to access adequate refuge habitat. We predict that this will allow Barramundi recruits and other smaller bodied migratory species such as mullet, Oxeye Herring, and Giant Herring, an even longer window of utilisation of the proposed fishway. As discharge in the river reduces with the cessation of wet season flow each year water velocity in the proposed fishway will also reduce which will likely give species with even poorer swimming ability (i.e. those of smaller maximum size such as rainbowfishes and hardyheads) some chance of negotiating the proposed fishway as well. 44 P age

45 Chapter 4 Utility of acceleration data-loggers for enhancing fishway design Studying the ecology and behaviour of large mobile aquatic vertebrates presents a number of logistical challenges, mainly relating to our inability to directly observe such animals. This in turn complicates our ability to effectively assess the impact anthropogenic disturbance has on such animals. Freshwater Sawfish are no exception, despite often only moving over relatively small areas during the dry season, they are almost never directly observed impeding any quantification of their behaviour. Whereas acoustic telemetry can provide some insight regarding the location (both horizontal and vertical) of the tagged animal, it is not able to provide any information regarding the actual behaviour of the animal. Here we performed the first trials to utilise cutting edge acceleration data loggers to document the behaviour of free ranging sawfish with respect to their potential in aiding in pressing management issues, such as fishway construction and population monitoring. 4.1 Field deployments In order to gain insight into the time and energy budgets and swimming performance of Freshwater Sawfish, we equipped five 0+ sawfish and a single 1+ sawfish during the month of June at the Lower Barrage Pool (Plate 7). Sawfish were captured using standard gill net protcols and were subsequently fitted with a data logger (G6a, Cefas Technology Limited, Lowestoft, UK) and a V9 continuous pinger (Vemco, Halifax, Canada). Acceleration was set to be recorded at a frequency of 25 samples per second in all three planes (x,y,z) and depth and temperature was recorded at a frequency of 1 sample per second for a total of 6 days. The data logger was fixed to the first dorsal fin using two strands of monofilament and crimped to plastic sleds (see Plate 7) after piercing two small holes (2mm diameter) into the fin using a dart tag applicator (Hallprint Pty Ltd, Victoria). The entire tag package weighed 22g, representing <1% of the mass of the fish ( kg). Data loggers were recovered by selectively recapturing with either net or line, using the acoustic pingers to locate individuals. After recapturing sawfish, loggers were removed by simply cutting the monofilament and removing all foreign objects. Data were subsequently downloaded to a laptop PC. 45 P age

46 4.2 Processing of acceleration data Acceleration data consist of two components, dynamic and static acceleration (Shepard et al. 2009). Whereas static acceleration gives an indication of posture with regard to the gravitational field, dynamic acceleration represents the body motion of the tagged animal (Shepard et al. 2010; Gleiss et al. 2011b). The two were separated in order to analyse the dynamic acceleration to allude to swimming performance of sawfish. We used a Sovitzky Golay filter to estimate body orientation and isolate dynamic acceleration with a smoothing window of 50 samples (2 seconds) and added the absolute dynamic acceleration from all three axes to yield a single proxy for body motion, Overall Dynamic Body Acceleration (ODBA) (Wilson et al. 2006). ODBA has been shown to tightly correlate with oxygen consumption in a range of species (Halsey et al. 2011), including elasmobranchs (Gleiss et al. 2010) due to the link between body acceleration and energy expenditure (Gleiss et al. 2011b). All Signal Processing was performed in the OriginPro software package. Plate 7 Data-logger employed in the current study attached to a continuous pinger using marine-grade silicone (1). 2-4) series of photos showing the attachment procedure for the tag package. 5-6) showing the attached accelerometer (6) and the sleds (5) to which the monofilament has been crimped. Accelerometers are required to sit tight against the body of fish to avoid any residual movement biasing estimates of body motion. 46 P age