Part 2 in a data series by columnist Duncan Leadbitter
This is the second in a series of four articles where I analyse the data coming from the shark-listening station located offshore from Stanwell Park.
The data sent by text include the species, time and date of the detection, the time, date and location of the last detection and the date and location the shark was first tagged. Sometimes some of the data are not available and the system may collect more than is made publicly available.
In this article I look at what species turn up in each month and the time of day. Three species are tagged – whites, bulls and tigers – but I have dropped the tigers from the analysis as the number of detections is very low (5). I have also dropped detections where the time between the most recent and the previous one was short as its likely the shark just swam in and out of the detection zone whilst visiting the beach.
Figure 1 shows the number of detections of whites and bulls each month. The total number of tagged individuals for each species isn’t known (or available via the Shark Smart website) so it’s not feasible to compare relative numbers across the two species. However, there is a clear pattern where the whites are more common during the cooler part of the year and the bulls when the water is warmer.
Both species are fish feeders so may be chasing mullet during their spawning migration in late April onwards, or Australian salmon which migrate in the summer. Larger whites (3m+) are mammal feeders and so may be chasing whales during their migration (northwards in May/June and southwards in September to November).
Figure 2 shows detections by time of day and there is little variation (numbers too small at this stage). Departmental advice regarding not swimming/surfing at dawn or dusk is based on the times that most attacks have occurred. The detections show that sharks can be around at any time of the day and most surfers here don’t seem to worry anyway.
This is only one year of data and the numbers are small so I wouldn’t get too focused on trying to explain the results at this stage.
