Fitzroy Fishway Report FINAL - Murdoch University · 2017-03-14 · pools upstream, however, we...
Transcript of Fitzroy Fishway Report FINAL - Murdoch University · 2017-03-14 · pools upstream, however, we...
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2011
Report to the Department of Water,
Government of Western Australia
2011
AddressingknowledgegapsandquestionsfromtheFitzroyRiver(Kimberleyregion,Western
Australia)fishwayreview.
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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
www.freshwaterfishgroup.com
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.
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Contents
Background…………………………………………………………………….………………….. 4
Executive summary………………………………………………………….….………………… 5
Introduction………………………………………………………………………………………… 9
Chapter 1
Ecology of Freshwater Sawfish, including migratory periods and habitat utilisation….. 11
1.1 Interannual variation in recruitment and flow…………………………….…………………. 14
1.2 Acoustic tracking of Freshwater Sawfish……………………………..……………………... 19
1.3 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?..... 30
2.1 Population abundance estimate below the Camballin Barrage during 2011…………….. 30
2.1.1 Results and discussion………..……………………………………………………… 31
2.2 Impacts of the barrage on Freshwater Sawfish………………….…………………………. 32
2.3 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………….…..………… 45
4.1 Field deployments……………………………………………………………..……………….. 45
4.2 Processing of acceleration data………………………………………………………….....… 46
4.3 Preliminary results……..……………………………………………………………………….. 47
4.4 Future applications of the technology………………………………………………….……... 50
4.4.1 Informing fishway design………………………………………………………………. 50
4.4.2 Population monitoring: from individual to population health……………………….. 51
General conclusions………………………………………………………………………….……… 52
References……………………………………………………………………………………..……… 53
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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 (2002‐2011), 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).
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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
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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
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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.
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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.
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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
~90,000km2 (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.
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Figure 1 Map of localities in the Fitzroy River catchment referred to in this report.
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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
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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 2002. 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.
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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 2009.
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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 2009.
1.1 Interannual variation in recruitment and flow
Although there is virtually no information on the adult phase of Freshwater Sawfish life‐
cycle 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
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new recruits surpassed all years combined between 2002 and 2010. 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 ~200 0+ 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).
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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).
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Site
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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).
(a)
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y = 272.8 - (2637.4/x)r2 = 0.46 p = 0.03
Mean April Stage Height (m)
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Figure 6 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 2007‐9, 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 2002‐2005
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2010
2011
19 | P a g e
(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.
20 | P a g e
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.
21 | P a g e
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.
22 | P a g e
Depth of individual sawfish (V13 - Acoustic tags)
Depth (m)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4.0
Per
cen
tag
e (%
)
0
20
40
60
80
100
120
140
160
180
1042224104222610422271042229
Mean depth of sawfish tagged with V13s
Depth (m)
0-0.
49
0.5-
0.99
1-1.
49
1.5-
1.99
2-2.
49>2
.5
Pe
rcen
tag
e (%
)
0
20
40
60
80
100
V13
Figure 8 Depth utilisation of 0+ (new recruits) of Freshwater Sawfish (Pristis microdon) in the Fitzroy River (from Whitty et al. 2008, 2009a).
23 | P a g e
Depth of individual sawfish (V16 - Acoustic tags)
Depth (m)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4.0
Per
cen
tag
e (%
)
0
10
20
30
40
50
1038503 1038505 1038506
Mean depth of sawfish tagged with V16s
Depth (m)
0-0.
49
0.5-
0.99
1-1.
49
1.5-
1.99
2-2.
49>2
.5
Pe
rcen
tag
e (%
)
0
10
20
30
40
50
60
V16
Figure 9 Depth utilisation of 1+ (one year old) Freshwater Sawfish (Pristis microdon) in the Fitzroy River (from Whitty et al. 2008, 2009a).
24 | P a g e
Depth v Time of day
Time of day (hours)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Dep
th (
m)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
V13V16
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).
25 | P a g e
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 (www.landgate.wa.gov.au) was assessed to quantify the total amount
of deep‐water pool habitat situated between Langi Crossing and Dimond Gorge (see
26 | P a g e
Figure 11 for localities). The imagery assessed was captured during the months of August
and November 2007. 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 434.2 km in length
using the distance measurement tool in Google Maps. Camballin Barrage lies at a point
148.8 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).
27 | P a g e
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).
28 | P a g e
Table 1 Summary of deep-water pool characteristics in the Fitroy River catchment located between Langi Crossing and Dimond Gorge.
.
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.
ABOVE
BARRAGE
BELOW
BARRAGE
TOTAL
Total number of pools 104 67
171
Total pool length (km) 178.9 83.7 262.6
River channel length
(km)
285.4 148.8 434.2
% pool habitat 62.70% 56.24% 60.48%
Mean pool length (km) 1.72 1.25 1.54
Median pool length
(km)
1.02 0.94 0.96
Maximum pool length
(km)
14.10 7.18 14.10
Minimum pool length
(km)
0.15 0.10 0.10
29 | P a g e
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.
30 | P a g e
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).
31 | P a g e
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).
2.1.1 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 super‐
population 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
195.5 (±38.7 S.E.) individuals between June 9‐21, 2011. 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.
32 | P a g e
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.
33 | P a g e
Plate 5 Scars from attempted predation, fishing and overcrowding on juvenile sawfishes caught below the Camballin Barrage in June 2011. 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.
B
D
F
C
A
E
HG
34 | P a g e
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.
35 | P a g e
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.
36 | P a g e
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 2009. Based on the
principals of the interactions between surface water and near infra‐red radiation (NIR),
analysis was undertaken using the NIR‐band (0.75 ‐ 0.90μm). 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 16‐32 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 13.69 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 10.99 m. An analysis of data between the years 1998‐2010 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 10.37 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
37 | P a g e
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
10.37 m.
At a stage height of 10.35 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.
38 | P a g e
31 May 2009
2 July 2009
Camballin
Barrage
39 | P a g e
Figure 13 Near infra-red band (0.75-0.9 µm) satellite imagery of the Fitzroy River channel in the vicinity of Camballin Barrage captured during late May to late September 2009. 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.
03 August 2009
20 September 2009
40 | P a g e
Date
1/Ja
n
1/Feb
1/M
ar
1/Apr
1/M
ay
1/Ju
n
1/Ju
l
1/Aug
1/Sep
1/Oct
1/Nov
1/Dec
1/Ja
nS
tage
hei
ght (
m)
10.0
10.5
11.0Average stage height 1998-2010
Lower CI
Upper CI
Disconnection below barrage Disconnection above barrage
Figure 14 Average daily stage height at the barrage (including 95% confidence intervals) over the period 1998-2010. The horizontal lines are the stage height at which the Fitzroy River becomes naturally disconnected below (solid line = 10.37 m, barrier located 9.46 km below the barrage) and above (dotted line = 10.35m, barrier located 13.69 km upstream of the barrage). On average, this date was 22nd July below the barrage, and 6th August above the barrage. See text for details.
Barrage able to be negotiated by fish (stage height = 10.99 m)
41 | P a g e
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 1st
disconnection 1st
reconnection 2nd
disconnection 2nd
reconnection 3rd
disconnection 3rd
reconnection 4th
disconnection 4th
reconnection
Days (%)
connected
1998 10‐May 1‐Dec 159 (43.6)
1999 24‐Jun 9‐Nov 20‐Nov 29‐Nov 217 (59.5)
2000 23‐Oct 24‐Oct 14‐Nov 12‐Dec 327 (89.6)
2001 19‐Oct 14‐Nov 340 (93.2)
2002 22‐Aug 4‐Dec 262 (71.8)
2003 13‐Jul 25‐Dec 200 (54.8)
2004 4‐Aug 215 (58.9)
2005 7‐Jan 24‐Apr 27‐Jun 1‐Jul 19‐Dec 125 (34.2)
2006 7‐Aug 14‐Nov 9‐Nov 28‐Nov 3‐Dec 28‐Dec 231 (63.3)
2007 12‐Aug 18‐Nov 28‐Nov 20‐Dec 246 (67.4)
2008 21‐Jul 30‐Nov 3‐Dec 9‐Dec 227 (62.2)
2009 3‐Jul 20‐Dec 196 (53.7)
2010 9‐Jan 15‐Jan 3‐May 27‐May 4‐Jun 16‐Oct 29‐Oct 12‐Dec 161 (44.1)
Total 223.5 (61.2)
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Table 3 Dates (based on available satellite passes) when the natural barrier 13.69 km above the Camballin Barrage disconnects the Fitzroy River. N.B. the river often disconnects and reconnects more than once within each year.
Year 1st disconnection
1st reconnection
2nd disconnection
2nd reconnection
3rd disconnection
3rd reconnection
4th disconnection
4th reconnection
Days (%)
connected
1998 17-May 1-Dec 166 (45.5)
1999 11-Jul 9-Nov 20-Nov 29-Nov 238 (65.2)
2000 27-Nov 9-Dec 353 (96.7)
2001 365 (100)
2002 5-Oct 4-Dec 305 (83.6)
2003 12-Aug 25-Dec 230 (63.0)
2004 1-Sep through 242 (66.3)
2005 through 7-Jan 1-May 27-Jun 3-Jul 19-Dec 134 (36.7)
2006 1-Sep 14-Nov 11-Nov 30-Nov 5-Dec 28-Dec 263 (72.1)
2007 1-Sep 18-Nov 1-Dec 20-Dec 269 (73.7)
2008 15-Aug 29-Nov 5-Dec 8-Dec 258 (70.7)
2009 31-Jul 20-Dec 231 (63.3)
2010 13-Jan 15-Jan 8-May 26-May 8-Jun 16-Oct 1-Nov 12-Dec 181 (49.6)
Total 248 (68.2)
43 | P a g e
Figure 15 Percentage of time that the Fitzroy River is connected and disconnected above and below the Camballin Barrage between 1998-2010. 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 13.69 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. 1.52 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
44 | P a g e
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.
45 | P a g e
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
(2.5‐15 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.
46 | P a g e
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.
47 | P a g e
4.3 Preliminary results
We successfully equipped and retrieved data‐loggers from six individual Freshwater
Sawfish during the early dry season and obtained a total of 840 hours of high‐resolution
time‐series acceleration and depth data. This data‐set represents the largest acceleration
data‐set on any species of elasmobranch obtained to date (Whitney et al. 2010; Gleiss et al.
2011a). Five individuals were 0+ sawfish and a single individual most probably was a one
year old animal.
Table 4 Details of the six individual sawfish that were successfully equipped with acceleration data-loggers in June 2011 at the Lower Barrage Pool, Fitzroy River, Western Australia.
Fish ID Sex Total Length (mm)
Weight (g) Volume of Data (h)
1209 M 1088 4950 144 1210 F 1152 5600 144 1213 F 1064 3400 144 1208 F 1144 4330 144 1214 F 1115 3200 144 1120 F 1580 14200 120
Acceleration data presented quantitative information on both the time‐budgets of sawfish
(time spent swimming and resting), as well as the intensity of swimming events, by
documenting the kinematics of individual tail‐beats (Figures 16, 17) (Gleiss et al. 2009;
Whitney et al. 2010). Sawfish generally swim at a constant and sustained speed and only
undertake very infrequent burst events, which is typical of most elasmobranchs (Gleiss et
al. 2009, Gleiss et al. unpublished data). Burst events were generally short‐lived (Figure
17) (4.2 ± 7.4 s; n=22) but of very high intensity (0.70 ± 0.46 g; n=22, compared to 0.12 ±
0.11g during routine swimming activity), probably representing the relatively poor
capacity of the species to swim at very high intensity for prolonged durations. Time series
depth data confirmed the finding of previous acoustic telemetry studies, namely that
juvenile sawfish spent significant time in very shallow waters of <1.5 m. Moreover, our
time series data also showed that individuals spent a significant amount of time
swimming in shallow waters, confirming their ability to traverse very shallow runs
between pools during the early dry season (Figure 18).
48 | P a g e
Figure 16 a) 12 hours of time-series acceleration and depth data from a single Freshwater Sawfish equipped at Lower Barrage Pool. Note the variations in the amplitude of the acceleration signal which gives an indication of activity. B) 40 second section showing the composition of acceleration signals in relation to swimming activity, note the repetitive signal in the x-axis (lateral acceleration, blue line) representing individual tail-beats. The segment further shows high-activity sustained swimming (1), as shown by high frequency and amplitude in the signal and low activity sustained swimming (2), indicated by lower frequencies and smaller amplitudes.
49 | P a g e
Figure 17 a) Burst events occurred infrequently in Freshwater Sawfish, but were easily identified by increased acceleration amplitudes in the Z-axis acceleration, coding for tail-beating activity. These high acceleration events resulted in clear peaks in the Overall Dynamic Body Acceleration (red arrows). B) Burst events in this case usually consisted of 1-4 rapid tail-beats with high frequency (1) Note the frequency of the z-axis acceleration, resulting in a ~20 fold increase of activity (as ascertained by our activity metric, ODBA).
50 | P a g e
Figure 18 11 hours of time series depth data for a 0+ Freshwater Sawfish (1144 mm TL). Note the projected time the individual is spending in shallow water.
4.4 Future applications of the technology
4.4.1 Informing Fishway design
Some of the main issues surrounding the efficacy of a fishway is ensuring that flow
characteristics are adjusted to the swimming capacity of the species they are designed for.
Whereas for many smaller species, swim‐tunnel respirometry can be utilised to gain
quantitative insight into critical parameters, such as critical swimming speed, such
approaches are logistically challenging for larger species, such as sawfish. Although
construction of a large respirometer for juvenile sawfish is feasible, it comes at very high
cost, in addition to having to house sawfish at a research facility for protracted time
intervals. Accelerometers may provide an alternative to such experimental protocols
through measuring the swimming performance of sawfish in their natural environment.
Our success in implementing such field studies will be able to significantly contribute to
successful design by matching flow characteristics within a fishway to the ability of
sawfish to overcome the hydrodynamic regime present. Further experiments are needed
to quantify the relationship between swimming speed and acceleration, which is easily
conceivable with the use of commercially available miniature speed‐sensors, which
would be deployed and recovered in the same fashion as accelerometers in this study.
Furthermore, after the installation of a fishway, such units could be employed to test how
efficiently sawfish ascend the fishway and where potential problems may limit their
passing.
51 | P a g e
4.4.2 Population Monitoring: from Individual to Population Health
The currently employed monitoring of population size is a simple method to detect large
scale changes in demographics as a function of natural and anthropogenic disturbance.
However, such approaches may often fail to capture impact at the individual level, which
is the underlying cause for changes in the population. Our new protocol of weighing
individual sawfish and identifying suitable proxies for body condition are a further step
towards more efficient monitoring, but still only represent a proximate response to
underlying changes in the physiology and ecology of individuals. The behavioural data
collected by accelerometers permit a detailed comparison of time and energy budgets of
individuals exposed to broadly different conditions, by comparing incidence of
ecologically important activities, such as daily number of prey strikes, time spent
swimming or escape responses. Together with conventional monitoring described
elsewhere, such data can provide unparalleled insight into the underlying mechanisms
behind changes in population health and provide an invaluable management tool.
Our preliminary analysis shows that sawfish most likely have the ability to ascend a
vertical‐slot fishway, due to their ability to swim in short bursts, which would allow them
to clear slots between chambers with high water flow. However, the specifics of optimal
design will require further work of this nature, which is on‐going. The implementation of
a large‐scale project using such technology would provide a valuable tool to quantify
population health beyond standard monitoring and allow the efficacy of a constructed
fishway to be tested.
52 | P a g e
General conclusions
Much information is yet to be gathered comparing sawfish recruits upstream and
downstream of the barrage. Plans are in place to conduct an experiment comparing
sawfish recruits that have been captured from below the barrage, tagged with
accelerometers and then translocated into the pool immediately upstream of the barrage
with animals from the same cohort that remain downstream of the barrage. It is
anticipated that this will provide data to ascertain if any behavioural differences exist
between animals below and above the barrage which might provide evidence of a
competitive advantage for animals above. Such data will help to objectively inform the
decision as to whether a vertical‐slot fishway is needed. Further data, using acoustic tags
(see Whitty et al. 2009a) could be generated on the actual stage heights that sawfish move
over the barrage, and this could be achieved by placing a ‘gate’ of acoustic receivers
above and below the barrage.
Negative impacts upon recruitment in species, not only have short term consequences,
but also have an insidious trickle‐down effect throughout successional generations. For a
species like Freshwater Sawfish which appears to experience infrequent successful
recruitment events (for example, as occurred in 2011), perhaps occurring only once or
twice per decade in response to ideal wet season flow conditions, it seems almost certain
that the restriction of access to critical habitat upstream of the barrage has counteracted a
potential boost in sawfish numbers.
We would argue strongly that any effort to alter existing habitat downstream of the
Barrage to offset a loss of species fitness due to restriction of access to upstream habitat
would be ineffective. The main difficulties for sawfish recruits as the situation stands are
at least twofold. Firstly, stress on recruits and mortality due to predation by apex level
predators such as sharks and crocodiles, and illegal poaching by humans is of concern
when large numbers congregate below the Barrage. Secondly, those recruits that avoid
predation are exposed to increased competition amongst themselves for food resources in
the limited amount of deep‐water pool habitat downstream of the Barrage. To mitigate
these pressures, one would have to either reduce the numbers of apex predators by
means of an annual cull, and/or to increase the availability of prey in the downstream
habitats by means of annual stocking. Both of these options are not only ecologically (and
perhaps also ethically) unsound, but would also be much less cost effective in the long
term compared to constructing and maintaining the proposed vertical‐slot fishway.
The data gathered during our long‐term monitoring program thus far points strongly
towards a benefit that will be provided for Freshwater Sawfish and other key fish species
53 | P a g e
in the Fitzroy River by the construction of a vertical‐slot fishway at the Camballin
Barrage. However, a shortfall in our knowledge remains on crucial aspects of the design
and utilisation of the proposed fishway. Highly targeted additional research (mentioned
throughout this report) will be extremely beneficial in order to maximise the effectiveness
of a proposed fishway as part of a strategy to ensure the sustainability of the critically
endangered Freshwater Sawfish in the Fitzroy River.
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