by Dr. Mark Read


Click here to visit Dr Mark Read's site on Satellite Tracking.

The challenge

The cooperative team from the Queensland Parks and Wildlife Service, Australia Zoo and The University of Queensland has expanded on the world-first ‘Crocs in Space’ research program, tracking the movement patterns of large estuarine crocodiles using satellite telemetry, by conducting another experiment to determine the movement patterns of crocodiles resident around urban areas.

This group of crocodiles represents those with the highest probability of interacting negatively with humans and therefore those most likely to require management intervention from the QPWS. Determining the movement patterns of these animals and examining whether they regularly use urban areas and travel around man-made structures is critical for effective management of this potentially dangerous yet vulnerable protected species.



The study site


Weipa, situated on the western side of Cape York Peninsula, is located on Albatross Bay around the mouths of the Pine, Mission, Embley and Hey Rivers. These large rivers and numerous small creeks also exit into Albatross Bay and provide ideal habitat for estuarine crocodiles. Weipa supports a resident population of people who work in the large bauxite mine run by Comalco, or who make their living running support businesses that service the mine or the other functions of the town. Additionally, Weipa also supports a high annual influx of tourists, who are drawn to the township and the Cape for its remoteness, scenic camping and very good fishing.

Vessel-based spotlight surveys conducted by QPWS over the years indicate that the waterways around Weipa support a healthy population of estuarine crocodiles of all sizes, with animals often sighted in close proximity to the township. Over the years QPWS has had to remove a number of ‘problem’ crocodiles from around Weipa – animals that had been displaying some type of aggressive behaviour towards people, thus warranting their removal. Based on these combinations of factors, Weipa represented the ideal experimental model, with crocodiles and people in close proximity and with a demonstrated pattern of intensive use of the waterways for recreational and commercial fishing.

Based on the exciting results following the translocation of ‘Banana-Head’ from the Nesbit River (Banana-Head was translocated 52kms from his capture location, returning home in less than four weeks!) in September 2003, the research team was very keen to translocate additional crocodiles to determine whether they all exhibit the well-developed homing response as displayed by Banana-Head. Therefore it was agreed that at least one of the crocodiles captured around Weipa would be translocated to further test the homing theory.


Working around Weipa


In mid-August 2004 the team assembled in Weipa and mesh bag, gate and aluminium floating traps were set in waterways around Weipa and in the Wenlock River. Male estuarine crocodiles longer than 3.0m were targeted specifically, as these are an ideal size to attach satellite transmitters to. Traps were baited and checked every morning to see what had been captured.

The satellite transmitters were custom-built to fit to large crocodiles (Fig. 2) by Sirtrack in New Zealand and were designed to provide position information on the crocodiles for a minimum period of ten months. To achieve this longevity, the transmitters were programmed to turn on for 24 hours and then turn off for 96 hours, and, when activated, to transmit a signal once every 45 seconds.

The transmitters are attached to the crocodiles using techniques developed by this team during the first phase of this research project. The area around the nuchal shield was anaesthetised using multiple injections of a local anaesthetic, and when the area is numbed small holes were drilled into the bony plates of the nuchal shield using a portable drill. The transmitter package is then wired to the nuchal shield using 250 pound breaking strain plastic-coated stainless steel wire looped through stainless steel attachment loops protruding from the sides of the transmitter. Multiple passes of the wire through the attachment loops and across the satellite transmitter ensure high mechanical strength plus flexibility. Once the wire was passed through the attachment loops and crossed-over, the wire was then anchored using eight crimps. Spraying the area using an aerosol antibacterial completed the process.


The Crocs!


Between August 16 and August 28 nine satellite transmitters were fitted to estuarine crocodiles ranging in size from 3.07m to 4.4m (see Table 1). Five of these crocodiles were captured and released close to Weipa (one from the Embley River; two from the Hey River; one from Wooldrum Creek [=Triluck Creek] and one from Andoom Creek); two were captured and released in the Wenlock River and two were captured from Tentpole Creek on the Wenlock River and then translocated to Temple Bay (east coast) and Jackson River (west coast) respectively.

As each crocodile captured during this trip is an individual, descriptions of the capture and subsequent movement patterns of each animal are shown below.

Table 1. Details of all the estuarine crocodiles captured around Weipa and fitted with satellite transmitters.

Date
Name
Length (m)
Sex
Release Location
Release Location

Experimental Model

17/08/2004
Weldon
4.4
M
Tentpole Creek
Temple Bay
Translocation
18/08/2004
Snapper
M
Wenlock River
Wenlock River
Remote
20/08/2004
Scifleet
3.55
M
Hey River
Hey River
Urban
20/08/2004
Fuji
3.07
M
Hey River
Hey River
Urban
20/08/2004
Jed Clampit
3.25
M
Andoom Creek
Andoom Creek
Urban
21/08/2004
Embley
3.91
M
Embley River
Embley River
Urban
24/08/2004
Franklin
3.98
M
Wooldrum Creek
Wooldrum Creek
Urban
25/08/2004
Ronald
3.62
M
Tentpole Creek
Jackson River
Translocation
27/08/2004
Gordon
M
Wenlock River
Wenlock River
Remote


Jed Clampit


This cheeky young male, named because of his ability to ‘clamp’ his jaws onto ropes and lines, was captured on the 20th August in a floating trap set just upstream from the bridge over the Andoom Creek just north of Weipa. Andoom Creek is a very popular waterway for local and visiting fishers, with people fishing there day and night. This combination of people and crocodiles makes studying this animal important for understanding the movement patterns of urban crocs.

Jed Clampit had his satellite transmitters attached during an educational visit to the Weipa School, with hundreds of interested kids as onlookers. Immediately following the attachment of the transmitter Jed was transported and released back at this capture location in Andoom Creek.

Since his release Jed Clampit has been moving within the Andoom Creek system, travelling down to the mouth of the creek and upstream to the headwaters of the creek. Figure HH shows the position locations of Jed from his released to the most recent download on the 15th September. The distance from the position locations in the headwaters of the creek down to the positions near the mouth is >12kms. Many of the position locations indicate that Jed is spending time within 2km of his original capture location.

Figure HH. Map showing the movements patterns of ‘Jed Clampit’ since his capture and release in Andoom Creek on 20th August. The red star denotes his capture and release location.


Franklin


This large crocodile, named after one of the research team Associate Professor Craig Franklin, was targeted for capture because of his size and proximity to Weipa. A large crocodile of a similar size to Franklin was sighted in November 2003 immediately upstream from where this animal was trapped on 24th August, and its likely this animal has been resident in this area for quite some time. Wooldrum Creek is a very popular fishing place for locals and visitors alike. This combination of people and crocodiles makes studying this animal important for understanding the movement patterns of urban crocs.

Franklin was a large and robust crocodile that was extracted and restrained in a very tricky location on the bank of Wooldrum Creek, which gave the research team a limited working space. Thankfully the skills and strength of the team enabled the team to attach the transmitter quickly and safely and the animal was released back into the water safely.

Since his release Franklin has moved upstream into the headwaters of the creek and downstream to the mouth of the creek. Figure GG shows the position locations of Franklin from the time of his release to the most recent position download on the 14th September. The distance from the upper position locations down to the mouth of the creek is >12kms. Based on the position locations it also appears that Franklin has made some movements across the sand dune into the ocean.

Figure GG. Map showing the movement patterns of ‘Franklin’ since his capture and release in Wooldrum Creek on the 24th August. The red star denotes his capture and release location.


Embley


This large crocodile, named after the lovely river he was captured in, was targeted for capture because of his size and proximity to Weipa. The Embley River is a very popular fishing place for locals and visitors alike. This combination of people and crocodiles makes studying this animal important for understanding the movement patterns of urban crocs.

Embley was another large and robust crocodile that was extracted from a floating aluminium trap on the 21st August on a shell-grit bar in the middle of the Embley River. Since his release Embley has been moving around a large area within several kilometres of his capture location. Figure TT shows the position locations of Embley from the time of his release to the most recent position download on the 15th September. Even in these early stages it appears that Embley’s movement patterns are different from those crocodiles captured within creeks (like Franklin and Jed Clampit), and his movements are far more spread out and include several other waterways.


Figure TT. Map showing the movement patterns of ‘Embley’ since his capture and release in the Embley River on the 21st August. The red star denotes his capture location and the blue circle his release location.


Fuji


This medium-sized male crocodile, named in recognition of our generous corporate sponsor David Marshall from Fuji, was targeted for capture because of his proximity to the township of Weipa. The Hey River is a very popular fishing place for locals and visitors alike. This combination of people and crocodiles makes studying this animal important for understanding the movement patterns of urban crocs.

Fuji was extracted from a floating aluminium trap on a beach near Hey Point on the 20th August, and the research team used the services of Cape York Helicopters to fly the trap to this location. He was extracted from the trap and the satellite transmitter was fitted quickly and the animal released. Since his release Fuji has been moving around a large area within several kilometres of his capture location, with several position locations indicating an overlap with the areas used by the crocodile Embley. Figure PP shows the position locations of Fuji from the time of his release to the most recent position download on the 14th September. Even in these early stages it appears that Fuji’s movement patterns are different from those crocodiles captured within creeks like Franklin and Jed Clampit, and his movements are far more spread out and include several other waterways. These movement patterns resemble those exhibited by Embley, who was captured from similar habitat in the Embley River.

Figure PP. Map showing the movement patterns of ‘Fuji’ since his capture and release in Hey River on the 20th August. The red star denotes his capture location and the blue circle his release location.


Scifleet


This medium-sized male crocodile, named in recognition of our generous corporate sponsor Andrew Scifleet, was targeted for capture because of his proximity to the township of Weipa. The Hey River is a very popular fishing place for locals and visitors alike. This combination of people and crocodiles makes studying this animal important for understanding the movement patterns of urban crocs.

While wrapped within his mesh bag gate trap, Scifleet was flown from his original capture location to the extraction location at Hey Point using Cape York Helicopters on the 20th August. He was extracted from the trap and the satellite transmitter was fitted quickly and the animal released. Since his release Scifleet has been moving around a large area within several kilometres of his capture location, with several position locations indicating an overlap with the areas used by the crocodiles Fuji and Embley. Figure II shows the position locations of Scifleet from the time of his release to the most recent position download on the 10th September. The movement patterns of the crocodile Scifleet are very similar to those exhibited by Embley and Fuji, with the movement patterns of these crocodiles more spread out and include several other waterways.

Figure II. Map showing the movement patterns of ‘Scifleet’ since his capture and release in the Hey River on 20th August. The red star denotes his capture location and the blue circle his release location.


Snapper


This large crocodile, named after his enthusiastic attempts to launch himself at Steve whenever possible, was captured in a mesh bag trap on the 17th August downstream from the Batavia Landing in the Wenlock River. The trap was located in thick, sticky black mud, making extracting the crocodile in this location very dangerous, so the team used the helicopter provided by corporate sponsor Kevin Weldon to move Snapper and his trap from the muddy creek to a grassy plain where he could be handled easily. This section of the Wenlock River is not exposed to the same intensity of use as the waterways around Weipa, so this crocodile represents one of the animals in our ‘remote’ category.

Snapper was extracted from the mesh bag trap the following day and the satellite transmitter was attached while he was restrained in the middle of the grassy plain. He was then transported to the release site on a trailer towed behind one of the vehicles. Surprisingly, Snapper travelled well and did not thrash around when bumped and jostled on the trailer. Once at the release location the animal was released back into the water safely, some 6.5kms upstream from his original capture location.

Since his release Snapper has been moving around a large area of the Wenlock River within several kilometres of his original capture location. The position locations indicate that Snapper travels up several smaller creeks on a regular basis. Figure YY shows the position locations of Snapper from the time of his release to the most recent position download on the 12th September. Interestingly, Snapper was recaptured in another mesh bag trap set in the next creek upstream from his original capture location on the 23rd August, only 5 days after his release. The satellite transmitter appeared snug and secure on his back, and he exhibited very dominant behaviour after the second release, raising his body high in the water and not submerging until he was out of sight of the research team (some 80m away).

Figure YY. Map showing the movement patterns of ‘Snapper’ since his capture and release in the Wenlock River on 18th August. The red star denotes his capture location and the blue circle his release location.


Gordon


This medium-sized crocodile, named after one of the research team Professor Gordon Grigg, was captured in a mesh bag gate trap on the 27th August upstream from the Batavia Landing in the Wenlock River. The trap was located in thick, sticky black mud, so the team used a helicopter provided by Cape York Helicopters to move Gordon and his trap from the muddy creek to a grassy plain where he could be handled easily. This section of the Wenlock River is not exposed to the same intensity of use as the waterways around Weipa, so this crocodile represents the second animal in our ‘remote’ category.

Gordon was extracted from the mesh bag trap and the satellite transmitter was attached while he was restrained on the edge of the grassy plain. He was then released on site and did a spectacular belly flop to enter the water.

Since his release Gordon has moved upstream in the Wenlock River, and has also made a trip up the Tentpole Creek. The most recent position locations for this animal, downloaded on the 9th September, indicate that this crocodile is some 21.5kms upstream from the original release location. Figure ZZ shows the position locations of Gordon from the time of his release to the most recent position download on the 9th September.

Figure ZZ. Map showing the movement patterns of ‘Gordon’ since his capture and release in the Wenlock River on 27th August. The red star denotes his capture location and the blue circle his release location.


Ronald


This medium-sized crocodile, named in memory of Ronald Read, was captured in a mesh bag trap on the 25th August at the mouth of Tentpole Creek, a major tributary of the Wenlock River. This crocodile was the ideal size to move using the helicopter provided by Cape York Helicopters, so it was decided to fit a satellite transmitter and then move this crocodile to another location to test its ability to home back to its original capture location. Based on local knowledge and a brief reconnaissance trip, it was decided to release Ronald in the Jackson River, which is located 78kms away NNE from the Tentpole Creek. For Ronald to return back to his original capture location would require a minimum swim of 95kms past several major waterways!

Ronald was transported under the helicopter wrapped in a mesh sack and was released in a clear pool upstream in the Jackson River on the same day. Since his release Ronald has spent some days around the release location, but he has also moved downstream within the river and the most recent position location (15th September) has Ronald situated at the mouth of the Jackson River (Fig. FFF). It will be fascinating to watch the movements of this crocodile over time to see whether he’ll head home or take up residence in another location.

Figure FFF. Map showing the movement patterns of ‘Ronald’ since his release 25th August. The red star indicates where the animal was released.


Weldon


This crocodile, the largest we fitted with a satellite transmitter at 4.4m long, was captured in a mesh bag trap on the 15th August at the mouth of Tentpole Creek, a major tributary of the Wenlock River. The research team had been offered the use of a heavy-lift helicopter from one of our generous corporate sponsors, Kevin Weldon, so this crocodile was immediately named ‘Weldon’ in his honour!

In the Northern Territory problem crocodiles had been moved as far as 250kms from the original capture location and recaptured several months later back home, having swum at least 400kms and indicating a well-developed homing ability. Because of this unique combination of a large crocodile and a large helicopter, the research team decided to really test the homing ability of estuarine crocodiles by translocating Weldon across Cape York Peninsula and releasing him at a remote location and see where he would end up. To return to the Tentpole Creek Weldon would face a minimum swim of >450kms!

Weldon was fitted with a satellite transmitter while restrained on the bank of Tentpole Creek and then loaded into a specially made aluminium transport crate. This crate was then airlifted by Kevin’s helicopter and flown across Cape York Peninsula to a remote beach north of Temple Bay. Weldon was released into the ocean and the team departed to let him settle down.

Since his release Weldon has swum south to take up temporary residence in Temple Bay. Weldon has spent the last four weeks in this location, and the most recent position location (15th September) has Weldon situated upstream in Kangaroo Creek (Fig. CCC). It will be fascinating to watch the movements of this crocodile over time to see whether he’ll head home or take up residence in another location.

Figure CCC. Map showing the movement patterns of ‘Weldon’ since his release 17th August. The blue circle indicates where the animal was released.