The effects of berleying on the distribution and behaviour of
white sharks, Carcharodon carcharias, at the Neptune Islands, South
Australia, August 2011
Research Summary
A 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 Islands
Seas 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 practices
In 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 berleying
The 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 Islands
The 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: 2010–2011
The 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 procedure
Acoustic 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 movements
As 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.
At present, there is no evidence to
suggest that these changes have been harmful to the sharks or that
they may lead to changes in their behaviour at any other location.
Many of the sharks also visited South Neptune Island and their
behaviour at that site was not significantly different to the
behaviour of sharks in the 2001–2003 study.
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.
RECOMMENDATIONS
The study makes the following recommendations:
Reduce berleying/provisioning effort
The 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 behaviour
Shark 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 program
The 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.
