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Wednesday, November 2, 2011
The effects of berleying on the distribution and behaviour of white sharks, Carcharodon carcharias, at the Neptune Islands, South Australia, August 2011
Research SummaryA study by Barry Bruce and Russell Bradford of the CSIRO Wealth from Oceans Flagship for the Department of Environment and Natural Resources South Australia
Cage diving at Neptune IslandsSeas and sealions (pinnipeds) form part of a white shark’s annual diet, and sharks may spend from days to months per year at pinniped colonies. Between these visits they travel to other locations seeking other sources of prey. They can swim thousands of kilometres, from temperate to tropical waters, and across the open ocean during these annual travels.
Pinniped colonies that are regularly visited by white sharks can be ideal for shark-viewing tourism. White shark cage diving activities are established near to such pinniped colonies in South Africa, Mexico, California and Australia.
In Australia, white shark cage diving occurs only at the Neptune Islands Group Marine Park (60–70 km south of Port Lincoln, South Australia) comprising the North and South Neptune Islands.These islands host Australia’s largest pinniped aggregation.
Commercial tour operators involved in white shark cage diving must be licensed under the National Parks and Wildlife Act 1972 and, if berleying to attract sharks, must have an exemption under the Fisheries Act 1982.
Berleying practicesIn South Australia, shark cage diving provides an opportunity to view white sharks in their environment.The sharks are commonly attracted to the viewing vessel through the use of berley (chum), a mix of chopped or minced fish and fish oil. Berleying attracts sharks that are already present in the area to the shark cage-dive vessel and increases the chances of a shark being seen.
Increased frequency of berleyingThe shark cage diving industry has worked under a Code of Practice since 2004 to ensure that its operations minimise negative impacts on sharks. Permit requirements also restrict the type of berley than can be used to fish-based products only and these products must be kept refrigerated prior to use.
Days of berleying activity in the SA shark-cage diving industry had remained reasonably stable at an annual average of 128 days from 2000 to 2007. However, the number of days of berleying activity at the Neptune Islands significantly increased after 2007, reaching 270 days in 2009–2010. Berleying activity increased over this time both within the main bay at North Neptune Island and at a second site outside of the bay.
This increase in berleying activity has caused some concern as wildlife tourism that attracts or rewards the target animals, such as through provisioning (feeding), can cause changes in behaviour.Worldwide experience suggests that such changes in behaviour, if they occur, can often have negative consequences for the target animal.
Increasing interest from potential new operators to enter the SA shark cage dive industry combined with concerns regarding the potential for negative impacts on sharks from berleying operations, prompted the Department of Environment and Natural Resources (DENR) and Primary Industries and Resources South Australia (PIRSA) to set research on the impact of berleying on shark behaviour at the Neptune Islands as a high priority. Such research was also consistent with objectives under the National recovery plan for white sharks as a listed threatened species under Australia’s Environment Protection & Biodiversity Conservation (EPBC) Act.
White shark research at the North Neptune IslandsThe North Neptune Islands is a key site for many white sharks in Australian waters and have been the focus of CSIRO-based research on white shark movement patterns, behaviour and habitat use since 1993.
Sharks tagged with electronic tags (satellite, archival and acoustic) have been tracked from the Neptune Islands to Exmouth in north-western Western Australia and to Rockhampton in central Queensland. Sharks tagged with other (non-electronic) tags at The Neptune Islands have also crossed theTasman Sea to New Zealand.
A 2001–2003 CSIRO study at the North Neptune Islands found that the level of berleying at that time had a localised and short-term effect on the distribution and behaviour of sharks and that the effects were concentrated in the bay of the main island where most berleying and shark cage diving activities occurred. Having the results of this initial study provided an opportunity to examine if white shark behaviour had changed at the North Neptune Islands since the 2007 increase in berleying effort.
Acoustic monitoring study: 2010–2011The purpose of the 2010–2011 study was to see if there had been any changes in the amount of time (residency) white sharks spent at the Neptune Islands since the previous study in 2001–2003 and if there had been any changes in their movement patterns or behaviour.The 2010–2011 study observed the movements of 21 tagged white sharks ranging from 2.8 metres to 4.8 m. The sharks were tagged with acoustic transmitters each of which produces a unique signal that can be identified by moored acoustic receivers.
The presence/absence of individual tagged sharks was monitored by arrays of acoustic receivers at both the North and South the Neptune Islands from December 2009 to April 2011.These receivers were removed at the end of the study so that the data they collected could be examined.These were complemented by monitoring data from a single satellite- linked acoustic receiver maintained inside the main bay at the North Neptune Islands since 2008.The satellite linked receiver automatically sends information on sharks present in the bay each week to researchers at CSIRO in Hobart. Daily logbook records of shark cage dive operator activities from 1999–2011 were also used in the analysis to identify when operators were present and to monitor the number of sharks sighted each day.
Acoustic receivers identical to those used in this study also form a network of stations around the Australian coast as part of the Commonwealth Government funded Integrated Marine Observing System (IMOS).The acoustic receivers form part of the Australian AnimalTracking and Monitoring System (http://imos.org.au/aatams.html) and allow researchers to monitor the long- term movements of tagged sharks after they leave the Neptune Islands.
The tagging procedureAcoustic tags were attached to a small stainless steel arrow head by a short tether. Sharks were attracted to the vessel using fish-based berley and tags were attached externally to each shark as they swam past by using a tagging pole.
What did the monitoring reveal?
General shark movementsAs seen in previous research, white sharks tagged during the study were found to be temporary residents of the Neptune Islands. Despite berleying, sharks continue to arrive and leave the Neptune Islands. As in previous years, the number of sharks present at any one time was highly variable.There were some periods when no sharks were present.These patterns are probably driven by differences in the ocean conditions between years and seasons.
Increased berleying has not led to sharks taking up patterns of permanent residency and sharks left the Neptunes Group for other destinations across their Australian range during the study period. For example, three tagged sharks were detected by acoustic receivers moving through south-western Western Australia after leaving the Neptune Islands during the course of the study.
When resident to the Neptune Islands area, some sharks made return transits between the North and South Neptune Islands which are 12 km apart. This occurred regardless of berleying activity and appears to be normal behaviour for sharks in this area.
Changes in shark behaviour
Despite sharks continuing to arrive and depart the Neptune Islands during berleying periods, the 2010-2011 study identified some significant changes in shark behaviour at the North Neptune Islands since berleying effort and regularity increased in 2007.
These changes in behaviour were not observed at the South Neptune Islands where berleying effort has not markedly changed since 2007.
The study found the following changes in the way sharks used the Neptune Islands:
- The average amount of time (residency period) that individual sharks spend at the North Neptune Islands has increased from 11 days in 2001- 2003 to 21 days in 2010-2011.
- The average number of consecutive days (visits) spent at North Neptune Island during residency periods has increased from 2 days in 2001-2003 to 6.5 days in 2010-2011.
- The average number of sharks seen by operators has increased from 2.2 per day prior to 2007 to 3.4 per day after 2007.This does not mean that the abundance of sharks has increased but reflects that they are staying for longer periods and that each individual is seen more often.
- The daily movements of sharks has changed to more closely match the arrival and departure of shark cage dive operators, so that now sharks arrive in the berleying areas at about the time operators arrive and leave the area after the operators leave.This pattern now occurs on days where operators are present and also on days when they are not present.
Why is it important to take notice of these changes?
These observations all suggest that berleying operations have changed the way sharks use the environment at the North Neptune Islands.
Understanding the impacts of such changes is complicated because each shark is only a temporary visitor to the Neptune Islands and thus is only exposed to berleying for the short time they are there. Also, although berleying provides an attraction for sharks, by itself it provides no reward in the form of food. Small ‘teaser’ baits used by operators to lure sharks closer to the vessel offer some form or reward but this is small compared to the source of natural prey in the area.
Research in other areas of the world has identified that a variety of problems can occur where marine wildlife has been attracted for tourism purposes. For white sharks and their environment at the Neptune Islands, this may include increased aggression between sharks if more sharks remain on site, distraction by tourism activities resulting in fewer opportunities to feed on seals and sealions, changes in predation pressure on seals and sealions, sharks provisioning on a food source (teaser baits) that is not as nutritious as their natural prey and increasing the abundance of fish life that can feed on the small particles that make up berley. These problems can lead to unintentional impacts on the overall health of sharks and to changes in the ecology of the area.
White sharks are a listed threatened species and protected in Australian waters. Minimising identified impacts on them and the environment within which they reside is important, particularly when the implications of such impacts are unknown.
In the case of shark cage diving, all parameters measured in this study suggest that berleying operations have changed the way sharks use the area at the North Neptune Islands. Reducing the impacts of these operations on sharks is thus important to ensure that there are no long-term negative effects on sharks visiting this area or the marine ecosystem of the region.
The challenge for government agencies and the SA industry will be to reduce the impact of shark cage diving on sharks and the ecosystem while maintaining a world-class diving experience that contributes significantly to the local economy and provides a platform for education, research and conservation. Achieving this balance has the potential to provide a benchmark for managing cage-diving tourism worldwide.
Reduce berleying/provisioning effortThe current level of berleying should be reduced, or at least capped, to minimise further behavioural changes.‘Teaser’ baits should be of a minimum size required to be effective and all reasonable efforts should be made to minimise the number of baits taken by sharks.
On-going monitoring of shark behaviourShark residency periods, duration of visits and daily patterns of movements should continue to be monitored to evaluate the sharks’ response to any mitigation actions and enable feedback to managing agencies and industry to ensure such actions are effective.
The most cost-effective monitoring approach would be to maintain the satellite-linked receiver at the North Neptune Islands and to continue to tag sharks with acoustic tags. Additional satellite receivers should be installed at the second berleying site at the North Neptune Islands and at South Neptune Island, (the latter to compare shark behaviour).
Education and awareness programThe shark cage dive industry in South Australia should be provided with educational material for clients that explains:
- shark ecology, movements and conservation
- the risks posed to sharks by excessive berleying or provisioning;
- the importance of minimising the impact of shark cage diving on sharks
- the industry and management actions used to achieve this.