The effects of cage-diving activities on the fine-scale swimming behaviour and space use of white sharks

Journal of Marine Biology 06/2013; 160(11). DOI: 10.1007/s00227-013-2277-6


Wildlife tourism has become increasingly popular and is one of the fastest growing sectors of the tourism industry. A radio-acoustic positioning system was deployed to monitor the fine-scale movements of 21 white sharks (Carcharodon carcharias) and investigate the effects of shark cage-diving activities on their swimming behaviour and space use. This study contributes towards improving our understanding of the complex relationship between wildlife tourism and its effects on sharks, and assesses how tourism targeting sharks affects behaviour at a finer spatial scale than previously investigated. Our study demonstrated that shark cage-diving operators (SCDO) influenced the fine-scale three-dimensional spatial distribution and the rate of movement of white sharks at the Neptune Islands. White sharks stayed more than 30 m away from the SCDO on 21 % of the days detected, but spent a significant amount of time in close proximity to the SCDO on the remaining days. Individual variation was detected, with some sharks behaviourally responding to SCDO more than others. The degree of variation between individual sharks and the different levels of interaction (e.g. presence, proximity to SCDO, and consumption of tethered bait) highlights the complexity of the relationships between SCDO and the effects on sharks. To improve our understanding of these relationships, future monitoring of shark cage-diving operations requires proximity to SCDO to be recorded in addition to the presence within the area. Further work is needed to assess whether the observed behavioural changes would affect individual fitness and ultimately population viability, which are critical information to unambiguously assess the potential impacts of wildlife tourism targeting sharks.

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Available from: Charlie Huveneers
    • "Cage-diving operations have been shown to influence local residency times and distribution of C. carcharias at this site (Bruce & Bradford, 2013). In addition, the responsiveness to cage-diving operations is known to vary between individuals and that this influences the ability to visually detect them (Huveneers et al., 2013). Logbook records used in this study, while recording the number of individual C. carcharias and their sex sighted on any one day, did not distinguish between individuals sighted over separate days. "
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A lack of scientifically credible information on population status is one of the key issues limiting the efficacy of conservation efforts for the species in Australian waters because the impacts of current recovery efforts cannot be adequately assessed. In addition, there are regular statements about increasing or decreasing shark numbers that cannot be confirmed or refuted due to a lack of useful data. These statements are popularised by the media, serve to confuse the public and policy makers, and risk actions by Government that may be ill-advised as to the true status of the species. CSIRO has carried out a tagging program on juvenile white sharks in the region each year since 2007. The purpose of the program is to establish the patterns of residency and habitat use by juvenile white sharks when they are present in the region and contribute information on the overall movement and population dynamics of juvenile white sharks along the east coast of Australia. 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Corrected estimates indicate that up to approximately 250 juvenile white sharks may have been present in the nursery area on survey days with peak abundances occurring in October-November as has been previously observed for the region. This study provides further confirmation that the Port Stephens region is a key nursery area for juvenile white sharks in eastern Australia. Continuing an integrated tagging and aerial survey program as well as further refinement of the correction factors applied to aerial survey data is recommended so that juvenile abundance and survival rates can be estimated. These data can then be incorporated into population models to effectively monitor the status of the species.
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