Acoustic tracking of Glyphis sp. A in the Adelaide River, Northern Territory, Australia

R. D. Pillans1, J. D. Stevens2, P.M. Kyne3 and J. Salini1

August 2005

1CSIRO Marine Research, PO Box 120, Cleveland, Queensland 4163, Australia

2CSIRO Marine Research, PO Box 1538, Hobart, Tasmania 7001, Australia

3University of Queensland, School of Biomedical Sciences, Brisbane, Queensland, Australia

Correspondence

Richard Pillans

CSIRO Marine Research

233 Middle Street

Cleveland

Queensland, Australia

ISBN: 064255336

The views and opinions expressed in this publication are those of the authors and do not necessarily reflect those of the Australian Government or the Minister for the Environment and Heritage. Abstract

In December 2004, 28 Glyphis sp. A were captured in the lower reaches of the Adelaide River, salinity 3.2 – 15 parts per thousand (ppt). The majority of individuals were new recruits of 55-60 cm TL. Three Glyphis sp. A (a 66.5 cm TL male, 165 cm TL female and a 158 cm TL female) were tagged with acoustic tags and tracked for 28.5, 27.0 and 50.2 h, respectively. All sharks showed initial, rapid downstream movements of 4 - 6 h, probably a stress reaction to capture, before settling into a behavioural pattern of cycling up and down-stream with the tidal cycles. Average rate of movement (ROM) for all three sharks varied from 0.45 – 0.52 m.s-1. In the smallest shark ROM did not change between ebb and flood times. However, in the two larger sharks ROM during the ebb tide was significantly faster. There was no difference in ROM and swimming depth between day and night. The movement patterns of these sharks are discussed in relation to the conservation of this species.

Introduction The genus Glyphis comprises a group of poorly understood Carcharhinids with a patchy Indo-West Pacific distribution in tropical riverine and coastal habitats (Compagno1984; Last and Stevens 1994). Of the two species found in Australia, Glyphis sp. A is listed as Critically Endangered by both the IUCN (Cavanagh et al., 2003) and 1999 Commonwealth Environmental Protection and Biodiversity Conservation (EPBC) Act while Glyphis sp. C is listed as Critically Endangered by the IUCN and Endangered by the 1999 EPBC Act.

Glyphis sp. A and Glyphis sp. C are medium-sized whaler sharks, greyish on the dorsal surface and white below, without a distinctive colour pattern and no interdorsal ridge. The second dorsal fin is between half to three fifths the height of the first dorsal fin and its origin is slightly anterior to the anal fin origin. They have short and broadly rounded snouts, and erect, broadly triangular, serrated upper teeth, the lower teeth are long and slender (Last & Stevens, 1994).

The systematics of Glyphis (Family Carcharhinidae) species is still not completely resolved with four to six species in the Indo-West Pacific. Glyphis gangeticus is known from three specimens in the Ganges-Hooghly river systems in India (Compagno, 1997). The spear tooth shark, Glyphis glyphis was described from one specimen, but without locality (Compagno and Niem, 1998). Glyphis sp. A is known from Queensland and the Northern Territory in northern Australia (Last and Stevens 1994), but together with specimens from New Guinea, may be synonymous with G. glyphis (LJVC Compagno, Shark Research Center, Box 61, Cape Town 8000, personal communication). Glyphis sp. B is recorded from the Kinabatangan River in Sabah, Malaysian Borneo (Compagno, 1984; Manjaji, 2002). Glyphis sp. C appears to be endemic to northern Australia where it is found in tidal rivers in the Northern Territory and Western Australia (Last, 2002; Thorburn and Morgan 2004).

Glyphis sp. A was originally reported from Australia in 1982 when two small (70-75 cm) specimens were taken 17 km upstream in the Bizant River, Queensland. Despite several research surveys and commercial fishing occurring in the Bizant River, Glyphis sp. A have not been recorded there since this discovery. Between 1983 and 2002, only 21 specimens of Glyphis were recorded from Australia with all records coming from the Northern Territory. These included the first records of Glyphis sp. C in 1989 and 1996 from the Adelaide River and South Alligator River, Northern Territory (Tanuichi et al., 1991b and John D. Stevens, CSIRO Marine Research, pers. comm.), respectively). Since 2002, a further 104 specimens of Glyphis have been recorded from Northern Australia. This included the first record of Glyphis sp. C in Western Australia as well as records of Glyphis sp. A in the eastern Gulf of Carpentaria. Of these, 80 were Glyphis sp. A, 21 Glyphis sp. C and 3 were identified only to genus. Despite intensive surveys in riverine and coastal habitats in northern Australia, the majority of the Glyphis sp. A (n = 75) have been recorded from the Adelaide River suggesting that this species have a narrow habitat preference but are abundant within this river system.

There is almost no data on the biology, distribution, habitat requirements and movement patterns of members of the genus Glyphis. The largest recorded specimen was a 175.0 cm TL female of unknown maturity. The largest recorded male was a 157 cm TL animal with uncalcified claspers of 5% TL (R. D. Pillans, unpublished data) and the maximum size is estimated at 200 – 300 cm TL (Last and Stevens, 1994). Most records of Glyphis species have come from turbid, tidal tropical rivers and the genus is thought to include both euryhaline and obligate freshwater species (Compagno, 2002). Glyphis sp. A and C were classified as obligate freshwater species by Last (2002), however Glyphis sp. C has been recorded in salinities between 2 and 26 ppt in the Northern Territory (Larson, 2000) and between 32 and 36.6 ppt in Western Australia (Thorburn and Morgan, 2004) and can therefore be classified as euryhaline. Glyphis sp. A has only been recorded from a few rivers and estuaries despite intensive sampling of suitable estuarine and coastal habitat and it is uncertain whether it is limited to low salinity environments. . Given the conservation status of Glyphis sp. A, the complete lack of data on habitat preferences and movement patterns, and the apparent abundance of this species in the Adelaide River, acoustic tags were used to determine its rates of movement, movement patterns and habitat utilisation in the lower reaches of the Adelaide River.

Methods

Study site The Adelaide River is a highly flushed, turbid and tidal river located east of Darwin, Northern Territory (mouth = 12º13’ 18.0” S, 131º 13’ 6.6’’ E). Salinity and flow in the river varies seasonally with more than 95% of the flow occurring in the wet season (December to April). Dry season currents are driven by large tides which ranged from 3.5 – 7.5 m during this study. Due to the large tidal range the period of slack tide was less than 10 minutes. The banks were dominated by mangroves and bottom substrate throughout was fine mud. Turbidity was extremely high (sechi disk reading of approximately 3 cm (Tim Berra, Ohio State University, personal communication). Sharks were tracked from within Marrakai creek, a tributary of the Adelaide River approximately 96 km from the mouth to within 55 km of the mouth of the Adelaide River (Fig. 1). Salinity throughout this area ranged from 3.7 ppt in Marrakai creek to 18.2 ppt at the furthest downstream position. Temperature within the river showed a diurnal pattern and ranged from 31.9 – 33.4 ºC.

Capture and tagging

The majority of specimens were captured using either a 60 m monofilament gillnet with a 4 m drop and a stretched mesh of 15.2 cm, or a 30 m net with a 2 m drop and a stretched mesh of 10.2 cm. The net was set during the day and checked about every 10 minutes, or when fish were seen to hit the net. Gillnets were mostly set across the creek except when the tidal flow was too great; at these times the net was occasionally set parallel to the banks or fishing was carried out with rod and line. Captured Glyphis were identified to species, measured (TL), sexed, sampled for genetics (fin clip) and released if they were not tracked. Tags were attached by suturing them with dissolving sutures, one end through the leading edge of the first dorsal fin and the other end through the dorsal musculature.

Telemetry Sharks were tracked using acoustic telemetry equipment comprising a Vemco VR-60 receiver, a V-10 hydrophone and either a Vemco 60 KHz V22TP-01, 51 – 81 KHzV16P- 5HR transmitters with a depth sensor, or a 71 KHz Sonotronics CHP-87S transmitter with no depth sensor. Tracking was carried out from a 4 m aluminium boat. The hydrophone was mounted on a pole and rotated manually to maximise signal strength. The tags had a range of about 1.0 km and a battery life of approximately 14 days. Depth from the tag together with position from a Garmin GPS 12 was assumed to be the position of the shark and was recorded every 15 - 30 minutes. Tracking was continuous apart from periods when it was necessary to change personnel due to fatigue, and to occasional thunderstorm activity. After these periods the shark was re-located by systematically searching the area of last contact. When these periods exceeded 30 min, these data were not used to calculate swimming speed. Bottom depth was recorded using a lead line (marked off in 1 m intervals) and surface temperature and salinity using a WTW LF340 salinity/conductivity meter throughout the track at the position of the shark.

Data analysis Recorded positions were plotted using Geographical Information System (ArcView GIS). Distance between successive positions was calculated following the contours of the river, either manually or using the Animal Movement Analyst Extension (AMAE) (Hooge and Eichenlaub, 1997) for ArcView GIS. Rate of movement (ROM) was calculated by dividing the distance between points by the sampling interval. Data from the first ebb tide (4.1-6.8 h) was not used in calculations of ROM due to increased ROM during this period. The increased ROM was presumably due to handling stress. Point to point estimates of ROM have been shown to underestimate swimming speed (Gruber et al., 1988). However, due to the highly directional (either upstream of downstream) movement of sharks in this study, we assumed that point to point measures accurately estimated ROM. Day and night ROMs were based on local times of sunrise and sunset. To determine the influence of time of day and tide on movement, pooled ROMs were compared using a Mann-Whitney U-test .. A Mann-Whitney U-test was also used to test for differences in ROM between successive tidal cycles.

Depth profiles were only obtained from one shark due to malfunction of some depth tags. Depth of the shark and water depth were recorded at the same time as position. A Mann- Whitney U-test was used to test for differences in swimming depth in relation to bottom depth between time of day and tide.

Results A total of 28 Glyphis sp. A were captured between 9-20 December 2004. Length range and sex of the specimens and range of water temperature and salinity from site of capture are shown in Table 1. Sex ratio of the Glyphis sp. A was 1:0.75 (F:M). The majority of the Glyphis sp. A (78%) were new recruits of 50-65 cm TL that had umbilical scars. A further 11% were between 66-90 cm and 11% were greater than 100 cm TL. Of the larger sharks, a 151cm TL male was still immature with uncalcified claspers of 7.5 cm (5% of TL). Teleost bycatch taken in the gillnet were dominated by Lates calcifer and Kurtis gulliveri; one Eleutheronema tetradactylum and one Valamugil buchanani were also caught.

Three Glyphis sp. A were tracked for periods between 28-50 h and displayed very similar ROMs moving a total distance of 53.1 to 84.1 km (Table 2). An acoustic tag was also attached to a fourth shark; however the tag detached from the animal within five minutes when the animal had only moved 50 m from its release position. The reason for the premature detachment is unknown. All three sharks were tagged shortly after the tide began to ebb and moved downstream after tagging. Movement of all sharks was strongly correlated to tide, with sharks generally moving downstream and upstream with ebb and flood tides, respectively. There was a net downstream movement with sharks being between 28.9 and 34.8 km downstream of the tagging position when tracking was terminated. This downstream movement resulted in animals encountering a significant increase in environmental salinity over a 24 h period. After 24 h, sharks 1, 2 and 3 had encountered an increase of salinity of 8, 11.3 and 11.9 ppt, respectively. There was no difference in temperature throughout the tracks.

Although the movement of all sharks was strongly influenced by the tidal cycles, there was some individual variation between animals. Complete tracks of shark 1, 2 and 3 are shown in Figs. 1, 2 and 3, respectively. Shark 1 was tagged with a Vemco V16P-5HR transmitter, however the depth component malfunctioned and depth was therefore not collected. It was tracked continuously for 10.6 h when tagging was stopped due to dangerous weather conditions. The shark was relocated 9 km downstream after 11.8 h and tracked continuously for 13.9 h. The following day the shark was tracked for a further 3.3 h before tracking was stopped. Shark 1 showed the least variation in ROM over successive ebb and flood tides, and the ROM during ebb and flood tides were not significantly different. During the 1st flood tide ROM was however significantly lower (p<0.01) than all other tides (Figs. 1 and 4). There was no difference in ROM between day (0.55 ± 0.44 m.s-1) and night (0.35 ± 0.23 m.s-1), p >0.1.

Shark 2 was tagged with a Vemco 50 KHz V22TP-01 transmitter, and data on swimming and water depth were collected. It was tracked continuously for 28.0 h when tagging was stopped due to the tag detaching prematurely. Shark 2 was captured at 1458 h, approximately 1 h after the tide began to ebb and moved steadily downstream for 4.2 h travelling a distance of 17.9 km During the first flood tide shark 2 moved slowly upstream for 1.7 km over 3.2 h before spending the remainder of the flood tide in a small stretch of river around a bend (Fig 5). The shark repeated this pattern moving 15.5 km downstream and only 6.5 km upstream in the next ebb and flood tide, respectively. During the flood tide, the shark spent 2.4 h near a larger eddy in a bend of the river and moved only 0.4 km further upstream during this time.

Shark 3 was tagged with a Sonotronics CHP-87S transmitter and tracked for 50.2 h before tracking was stopped. Shark 3 was captured approximately half an hour after high tide (1515 h) and moved 24.5 km downstream for 6.8 h during the ebb tide. Once the tide began to flood, the shark moved approximately 4.1 km upstream over a 5.7 h period, spending 2.4 h within a 400 m stretch of water close to a large eddy in the river (Fig. 6). Once the tide started to ebb at 0429 h, the shark moved 14.1 km downstream over 5.3 h until 0946 h when the tide turned. The shark moved upstream for 7.6 km over 4 h before moving downstream against the slowing flood tide until high tide (1534 h). On the ebb tide, the shark again moved downstream for 6.8 h covering a distance of 11.2 km until a thunderstorm prevented further tracking for the night. The animal was relocated at 0825 h the next day 2.5 km downstream from its last known position. For the final 2.6 h of ebb tide, the shark moved 5.8 km downstream. During the flood tide, the shark moved 12 km upstream between 1103 h and 1618 h and despite the tide starting to ebb at 1618 h, the shark continued to move upstream for 700 m until the track was ended at 1639 h.

Both shark 2 and shark 3 displayed similar movement patterns with mean ROM during the ebb tide being significantly faster than ROM during the flood tide. This difference was largely due to ROM of both sharks during the first ebb tide being significantly faster than all other tides (Fig. 1). This was further compounded by ROM during the first flood tide in both sharks being slower than all other tidal cycles (Fig. 1). There was no difference in ROM between day (0.46 ± 0.42 m.s-1, 0.57 ± 0.26 m.s-1) and night (0.44 ± 0.47 m.s-1, 0.50 ± 0.32 m.s-1) for both shark 2 and 3, respectively (p>0.1).

Bottom depth and swimming depths of shark 2 in relation to temporal cycles are shown in Fig. 7. There was no detectable pattern in swimming depth and no difference in swimming depth in relation to bottom depth between day and night or tidal cycle (p > 0.1). The only period when swimming depth was relatively constant was the five hour period after tagging. This period coincided with the fastest ROM during the 1st ebb tide (Fig 4) and was attributed to post-capture stress and was omitted from the statistical analysis.

Discussion One juvenile and two sub-adult Glyphis sp. A were tracked in the lower reaches of the Adelaide River, Northern Territory, Australia. Animals were tagged approximately 85 – 90 km from the mouth of the river and 58.3, 27 and 50.2 h after release were 29.7, 34.8 and 28.9 km, respectively, downstream. All three animals showed the same trend in movement, displaying a cyclic downstream and upstream movement pattern that was determined by the ebb and flood tides. There was a net downstream movement which was largely due to all animals being tagged at the beginning of the ebb tide. This downstream movement was further enhanced by faster ROM in sharks 2 and 3 during the first tidal cycle which was attributed to post-capture stress. Post-capture stress has been shown to occur in other elasmobranchs, with animals diving to deeper water (Sciarrota and Nelson, 1977) or a rapid departure from the site (Nelson, 1990; Nelson et al., 1997). All sharks in this study appeared to return to “normal” behaviour following the first tide change, approximately 4-6 h after tagging. We think it is unlikely that the boat used for tracking affected the shark’s behaviour as we were able to track for extended periods with the motor switched off (drifting with the current) or, while the shark remained in one area, moored to the bank. Behaviour during these periods was no different to times when the motor was running. In addition, on one occasion we caught another Glyphis sp. A close to the one we were tracking suggesting it was behaving in a similar way.

Individual movement Individual variation in movement patterns was evident, particularly between the small juvenile shark (shark 1) and the two sub adults (shark 2 and 3). Shark 1 showed less variation in ROM between subsequent ebb and flood tides. The movement of this shark appeared to be more strongly influenced by the tidal currents as it did not spend more than 30 min in a particular stretch of river and appeared to be moving with the tide at all times. The significantly slower ROM during the first flood tide was the exception. The ROM during the first flood tide was slowest in all three sharks (Fig 1) after an initial rapid downstream movement. Sharks 2 and 3 displayed the greatest ROM during the first ebb tide and the slowest ROM during the first flood tide which may suggest a recovery period after an initial rapid downstream movement.

Both shark 2 and 3 had a significantly faster ROM during the ebb tide than the flood tide. The faster ROM during the ebb tide was due to the sharks spending long periods of time in a small area of river during the flood tide. This resulted in underestimation of ROM as sharks were not swimming in a straight line between point to point measurements but rather swimming back and forth within a small stretch of river. These multidirectional movements were evident in the rapid changes in the intensity of the tag signal when the boat was anchored in one position during these periods. This suggests that although ROM was apparently reduced, swimming speed during these periods did not change. That sharks only spent long periods of time in a short stretch of river during the flood tide may be related to feeding behaviour. However, if this were the case, we would expect sharks to feed on both ebb and flood tides. Alternatively, sharks were choosing to stay further downstream and achieving this by limiting their upstream movement during the flood tide. A longer tracking time may have revealed a similar behaviour during the ebb tide. A similar movement pattern has been observed in the bull shark Carcharhinus leucas tracked in the Brisbane River, Queensland (R.D. Pillans, unpublished data). Bull sharks initially displayed a net downstream movement over 48 h, however, after one week, animals were gradually moving back upstream.

Point to point ROM estimates have been shown to underestimate swimming speeds, however given the width (<150 m) and depth (<30 m) of the Adelaide River, sharks are primarily restricted to up or downstream movement. Apart from a few instances when sharks spent a period of time within a small stretch of river, for the majority of time, sharks were moving either up or downstream and point to point measurements of ROM accurately reflect speed over ground between the two points. The ROM of the three Glyphis sp. A were much lower than those recorded for pelagic sharks such as Carcharodon carcharias , Isurus oxyrinchus, Rhincodon typus but faster than other Carcharhinids such as Carcharhinus plumbeus and C. obscurus (see Sundström et al., 2001, Table 1). Given that sharks in this study were moving in the same direction as the tidal current and most probably using tidal current to transport them for most of the track, ROM is surprisingly slow and suggests that Glyphis sp. A are a relatively slow- swimming, sluggish carcharhinid. Observations of net and line caught animals suggest they are less vigorous than the bull shark when captured on identical gear. Also, the high vertebral count (c.a. 198 – 217) indicates that Glyphis sp. A are not capable of swimming as fast at other Carcharhinids with fewer vertebrae (Peter Last, CSIRO Marine Research, personal communication).

There was no evidence of a diurnal change in ROM in Glyphis sp. A. The ROM has been shown to increase after sunset in some species (see Sciarotta and Nelson, 1977; McKibben and Nelson, 1986; Parsons and Carlson, 1998) but remain unchanged in others (see Gruber et al., 1988; Holland et al., 1993). Similarly, shark 2, the only animal that swimming depth was recorded for, did not show any diurnal patterns in swimming depth. Secchi depths in this section of the Adelaide River are approximately 3 cm and as a result the below surface light flux at 1 m would be zero. The average swimming depth of shark 2 was 7.7 m. At this depth, light conditions are more than likely constantly dark which may explain a lack of diurnal changes in ROM and swimming depth. Given the highly turbid conditions, it is likely that Glyphis sp. A relies heavily on an elaborate ampullary electroreceptor system to detect low-frequency bioelectric fields from its prey (see Hueter et al., 2004).

Twenty seven Glyphis sp. A were captured in the Adelaide River approximately 80 – 90 km upstream of the mouth. This suggests that this species is relatively abundant in this stretch of river during December. Although the size of sharks captured in this study are influenced by the selectivity of the fishing gear, the majority were new recruits suggesting that this area of the river may function as a nursery area. Two large sharks were also caught in this section of river, with the 165 cm TL female close to the largest Glyphis sp. A recorded in northern Australia (175 cm TL female). Although no maturity data was obtained from this female, a 151 cm TL male was immature based on uncalcified claspers that were 5 % of TL. This species has not been recorded outside of estuaries and rivers which may indicate a greater reliance on these habitats than other euryhaline elasmobranchs such as the bull shark Carcharhinus leucas. In bull sharks, neonates and juveniles have only been recorded from rivers and estuaries whereas sharks larger than 1.5 m are generally found in marine environments (R.D. Pillans, unpublished data). We caught no Carcharhinus leucas in this stretch of the Adelaide River, and other research sampling in this area has not reported any (T. Berra, Ohio University, personal communication). Carcharhinus leucas is known from the upper reaches of this river system but appears to be spatially separated from Glyphis sp. A. The lower reaches of the Adelaide River where Glyphis sp. A are captured are extremely turbid and may not be favourable habitat for C. leucas.

Although Glyphis sp. A have not been recorded outside of rivers and estuaries, they have been recorded in salinities between 0.8 – 28 ppt (CSIRO Marine Research, unpublished data) and are able to tolerate rapid increases in salinity. All sharks were tagged in 3.7-5.4 ppt and experienced a rapid increase in salinity being in 15.5 – 19.1 ppt 24 h after tagging. Although nothing is known about the osmoregulation in this species, given its ability to live in both freshwater and 80 % seawater as well as move freely between salinity gradients, it presumably has a similar osmoregulatory physiology to Carcharhinus leucas. In freshwater, C. leucas have a plasma osmotic pressure significantly lower (~ 642 mOsm) than animals in seawater(~1067 mOsm) (Pillans and Franklin, 2004). Carcharhinus leucas are able to move freely between freshwater and seawater by regulating the intra and extracellular concentrations of inorganic and organic ions (see Pillans et al., 2005).

Overall movement Home range was not estimated in this study due to the short duration of the tracks. Using ROM, the average distance travelled per tidal cycle was 11.6, 10.0 and 11.4 km per tidal cycle for sharks 1, 2 and 3, respectively (using an average difference between high and low tide from this region over the month of December). Although animals may travel further in a particular direction, these movement patterns result in animals utilising this habitat repeatedly. This tidally assisted upstream and downstream movement enables the sharks to travel up to 25 km in a particular direction over one tidal cycle and therefore utilise a large proportion of available habitat in short periods. Within the Adelaide River, Glyphis sp. A has to date only been recorded from the mouth to approximately 100 km upstream. Thus, animals are capable of covering approximately 25 % of known available habitat in fewer than seven hours. It is well established that elasmobranchs living in rivers and estuaries are bound by physical constraints and are therefore less able to evade pollution, habitat destruction and fisheries (Compagno and Cook, 1995). For Glyphis sp. A the physical constraint of living within a river system (see Compagno and Cook, 1995) are further compounded by a movement patterns which ensure that Glyphis sp. A are more susceptible to capture in commercial and recreational fishing gear than sedentary species or species with more available habitat. Although commercial fishing is not permitted within the Adelaide River, recreational catches of this species do occur. In rivers where commercial gill netting occurs, this practice poses a real threat to the survival of this species. Given the localised movement patterns of the animals in this study, spatial management could prove an effective management tool.

Acknowledgements

We are very grateful to the Northern Territory Fisheries for provision of a boat and a vehicle. Daniel Kimberly (Northern Territory Wildlife Park) provided valuable assistance in capturing sharks. We thank Christopher Tarca (NTDBIRD), for assistance with tracking. The Department of the Environment and Heritage funded this work.

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Table 1. Number, length ranges (TL) and sex of Glyphis sp. A captured in Marrakai

Creek and the Adelaide River and the lower Adelaide River, NT. Temperature and

salinity range of the two habitats are also provided.

Location Distance from No. TL (cm ) Sex Temperatute Salinity mouth (km) (ºC) (ppt) Marrakai Creek and 80-90 27 58.0 - 165.0 15F, 12M 31.9 – 33.4 3.7 - 5.5 Adelaide River

Adelaide River (M) 60 1 151.0 1M 32.0 18.2

Table 2. Summary of three Glyphis sp. A tracked in the Adelaide River in December

2004.

Track Size Sex Duration Distance Mean (± SD) Salinity range (h) (km) ROM (m.s-1) (ppt) 1 66.5 F 28.5 53.1 0.52 (0.40) 5.4 - 15.5 2 165.0 F 27.0 53.9 0.45 (0.43) 3.7 - 17.0 3 158.5 F 50.2 84.1 0.51 (0.28) 4.8 - 19.1

131 °20' 131 2°4'

N 17:26 &V#S 17:45 &V #S &V#S16:26

#S 18:08 $ 16:44 #Y 18:59 #S 17:24 #Y $ #S #Y$ #S17:49 #Y$#S #S 19:30 15:11 End track #YS 19:44

#Y 18:51 12 °32' 12 °32' Legend # Day 1 ebb tide $ %U Day 1 flood tide 12:33 $$ $ 12:03$#Y $ Day 2 ebb tide 20:28 Day 2 flood tide #Y$ #Y #Y$ 21:31 11:49 #Y &V Day 3 ebb tide #Y$ 22:38 10:45 $$#Y #S Day 3 flood tide 23:01 $ Point to point direction $ 9:59 $ 9:04 $$ 8:47 #Y

12 °36' 12 °36' Adelaide River

16:03 # 15:21 #%U %U# %U%U 15:03 %U%U 17:20 #%U %U 18:45 %U %U 19:01 %U# 14:50 19:53 # ## # 14:26 # 11:13 # # 13:34 ### # #

10:44 #

10:23# 12 °40' # 12 °40' 10:07## 9:43 # # # Marrakai Creek 9:20 # 2000 0 2000 Metres 9:15# Start track 131 °20' 131 2°4'

Figure 1. Complete track of 66.5 cm female Glyphis sp. A (shark 1) tagged on 9 December 2004.

131 °20' 131 °22' 131 °24' 131 °26'

12 °30' 12 °30' 16:26 #$## # 17:45 18:46

16:03 $ $ ## 8:01 # 15: 36 $$$ 15:06$ 6:58 7:05 # 8:43 14:43$# 12 °32' # 9:05 12 °32'

# 9:25 # # 9:38 4:51 4:33 $$##$##$ 9:49 $ #$ 10:44 12:52 12 °34' 4:16$ 12 °34' $ 3:57 Adelaide River 3:37$ $ $ 3:00 2:38$ 1:54 2:20$ # 20:02 #$ 19:48 12 °36' #$$ 12 °36' # 20:49 1:36 19:15 #$# 19:07 $ ##### 21:51 $ 23:16 $ 18:53 $

18:27 $ $ 18:18 12 °38' $ 12 °38'

$ 16:50$ 17:15 $ $ 12 °40' $ 12 °40' 16:26 $

16:15$ $ 16:01$ $ 15:53 $ Ebb tide $ 12 °42' $ # Flood tide 12 °42' 15:33$ $ $ Direction of movement $$ Marrakai Creek 14:58 2000 0 2000 4000 Metres 131 °20' 131 °22' 131 °24' 131 °26'

Figure 2. Complete track of 165 cm female Glyphis sp. A tagged on 14 December 2004. Times on the western of the river are during ebb tide; times on the eastern side of the river are during flood tide.

131 2°0' 131 °24'

11:58** # N 11:26** # $ # 13:02** # 20:31* $ ## $ $ 09:34** $#$ 13:43** $$$ 19:58* $$$ #$$ # 14:13** 08:25** 19:09* $ 18:34 09:46*$# 11:33* $# 11:04* ## $ $ $# $ # 15:54** 18:10* $# $$## $ #$ 08:32* #$ $$ 12:09* 16:29*$ $ #$ 17:28** End track $$ 15:54* # 13:06* 12 °32' # 12 °32' # Adelaide River

06:40* # # $ $ # 06:15* 13:53* $ 22:45 06:00* $ # # 23:10 $$ 22:05 $ ## 23:40 05:21* $# 21:25 $ $ 03:38* 04:53* $## #### 02:22* $## 20:45 01:45*

20:14 $

19:53 $ 12 °36' 12 °36' 19:32 $

$ 19:18 Legend

$ Ebb tide $ # Flood tide 18:42 $ Direction of movement 12:00 17/12/04 12:00* 18/12/04 $ 12:00** 19/12/04 $ 17:44 $ $ $ 16:43 $ $ $ 12 °40' 12 °40' 16:12 $

15:57$ Marrakai Creek $ $ 15:36 $ $ Start track $ 15:15 $ 2000 0 2000 4000 Metres 131 2°0' 131 °24'

Figure 3. Complete track of a 158.5 cm TL female Glyphis sp. A tagged on 17 December 2004. Time on the western side of the river represent movement during the ebb tide while time on the eastern side of the river represents movements during the flood tide. 1.8 1.6 1.4 1.2 shark 1 1 shark 2 0.8 shark 3

ROM (m/s) ROM 0.6 0.4 0.2 0

b d b o bb e ood t fl e s d ebb th 1 st flo n 3rd ebb 4 1 2 2nd flood 3rd Tide stage

Fig 4. Mean (± SD) rate of movement (ROM) during ebb and flood tides throughout the track of three Glyphis sp. A in the Adelaide River, NT.

131 °23' 3:37 N

$ $ 3:00

2:38 $

$ 12 °35' 2:20 12 °35'

1:54 # 20:02

# $ $ # 19:48 1:36 $

# #

#$ 20:49 # 19:15 # # # ### $ #### # 21:51 19:07 $ 23:16

$ 12 °36' 12 °36' 18:53 $ Legend $ Ebb tide

# Flood tide Point to point direction

200 0 200 400 Metres 131 °23'

Figure 5. Detailed section of track for a 165 cm female Glyphis sp. A to show movements in relation to tidal cycle. Time on the western side of the river represent movement during the ebb tide while time on the eastern side of the river represents movements during the flood tide.

131 °23'

N

22:45 $ # 06:00* 23:10 #

$

05:45 $ 22:05

$ # 23:51 ## 05:21* $ 23:40

12 °34' 12 °34'

21:25$

04:53*$ $

# # # # # 01:45* ## # 02:22*

# # $ 03:38* Legend 20:45 $ Ebb tide # Flood tide Direction of movement 12:00 17/12/04 12 °35' 12:00* 18/12/04 12 °35' 200 0 200 400 Metres 131 °23'

Figure 6. Detailed section of track for 158.5 cm female Glyphis sp. A to show movements in relation to tidal cycle. Time on the western side of the river represent movement during the ebb tide while time on the eastern side of the river represents movements during the flood tide.

Time

5 0:38 1:17 2:20 3:22 4:16 4:51 8:01 8:43 9:25 9:49 0 14:58 15:27 15:45 16:07 16:33 17:24 18:27 18:54 19:15 19:48 20:49 21:32 21:51 23:57 10:44 12:17 12:39 15:06 16:03 17:07 17:58 18:46

-5 sharkdepth bottomdepth -10

Depth (m) -15

-20

-25

Figure 7. Plot of swimming depth and bottom depth throughout track of a 165 cm TL Glyphis sp. A (shark 2) in the Adelaide River. Light and dark shading indicates day and night respectively.