Methods to monitor the impact of cage diving on white shark populations in South Australia

Nazimi, L., Robbins, W. D., Schilds, A., & Huveneers, C. (2018). Comparison of industry-based data to monitor white shark cage-dive tourism. Tourism Management, 66, 263-273.

This study compares two methods for collecting shark data during tourist trips to cage dive with white sharks in South Australia.  The methods compared are: self-reported electronic logbooks and photographic identification. The study found there are advantages in each system, but the logbook method is easier and faster.

Wildlife tourism is a big industry that has many benefits including public education, increasing wildlife awareness and conservation, and helps with local economics.  It can, however, have a negative impact on both the animals and their environment, and therefore, needs to be closely monitored and regulated.  White shark cage diving is a popular tourist activity at a number of locations throughout the world.  This paper focuses on cage diving around the Neptune Islands off the coast of South Australia, where white sharks often aggregate.  It is important to collect data, monitor shark populations and interactions with tourist boats to assess the impact of tourism.  Since 1999 this has been achieved through mandatory self-reporting of shark sightings by cage-diving operators; in 2013 this was modernised by the introduction of electronic logbooks.  More recently, there has been interest in an alternative method for recording the sharks. This new method is using photography to identify individual sharks (photo-ID).  This study compares the strengths and weaknesses of the two methods, in an attempt to identify the most suitable tool to monitor the industry.

Overall the electronic logbook method was the easiest and most economic method but the photo-ID method was better for identifying individual sharks and monitoring their movements.

Both methods gave important information on shark populations and both detected a seasonal variation in relative numbers of males and females. There are more females in winter when seal prey numbers peak and more males when larger females were not present.  The electronic logbook method recorded more sharks per day (possibly due to difficulties photographing all sharks seen, but also perhaps due to recording of multiple sightings of one shark as different individuals).  The electronic logbook method was also much easier, faster and less labour intensive. This method also provided data on more days including days when no sharks were sighted but the tourist boats were still there.  This information is not available with the photo-ID method i.e. photograph free days could reflect no sharks or just an absence of photographs on a day when sharks are indeed sighted.  However, the photo-ID method was more reliable for identifying individual sharks, whereas, the electronic logbook method could only really identify easily recognisable sharks.  This can be useful for assessing the movements and length of time these individuals stay in the area, and so, identify them as transient sharks just passing through or as temporary residents which stay for a while.   It also provides a permanent visual record of the individual sharks.  It does, however, underestimate shark numbers, requires more resources, and is more labour intensive.

Overall the electronic logbook method has the advantage of being an inexpensive, efficient easy-to-use tool which provides rapid, up-to-date real time information about the sharks.  It also gives information about movement of easily identifiable sharks.   Additional information such as shark size, time of day and behaviour can also easily be added.  The photo-ID method gives more detailed accurate data about individual sharks and provides more information about shark movement and residency and give estimates about population size.  However, it is labour intensive and relatively expensive. This study concludes that the electronic logbooks should continue to be the main long-term method for the recording of shark information and monitoring of the tourist industry, but the photo-ID method should be employed every 2-3 years to update detailed information.  The combination of the two methods will help to monitor the impact of the tourist industry on the sharks and help to manage cage-diving and maintain long-term sustainability.

World Animal Protection’s view

This study is important as it is vital to use the best methods to monitor the effect of tourism on wildlife and to minimise any negative impacts.