Abstract:

This report provides a summary of a two-year study using stereo baited remote underwater video stations (stereo-BRUVs) to assess the viability of using this sampling method to obtain estimates of growth in juvenile white sharks. Surveys were conducted off Bennetts Beach, Hawks Nest, on the New South Wales mid-north coast monthly from January 2017 to December 2018 with six stereo-BRUV units deployed three times each month. A total of 2,160 hours of video footage was collected and analysed for the presence of white sharks.

Over the two year period, a total of 142 white shark sightings were recorded on the stereo-BRUVs. The abundance of white sharks observed on the stereo-BRUVs was highest in November with an average of 4.3 ± 1.1 sightings per day. Overall significantly fewer sharks were sighted during autumn (March to May) than in other seasons, with no significant difference in sightings detected among the other seasons. The average size of white sharks observed on stereo-BRUVs was 191.1 cm ± 2.4 cm, with no significant difference in average size detected between seasons.

A total of seven white sharks tagged with acoustic transmitters were observed on the stereo-BRUVs. Of these, the largest observed growth in a white shark occurred for a shark first tagged in October 2015 at 198 cm (fork length) that was remeasured at 259 cm in November 2017, giving an increase in length of 61 cm over the ~700 day period between tagging and stereo-BRUV measurement. This study demonstrates that stereo-BRUVs are a useful sampling method for recording the presence of white sharks in an area, and that stereo-BRUVs provide a useful non-intrusive method to obtain estimates of shark length and growth.

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