Where: Seal Rocks NSW
When: 6-10-2019
Shark: Great White, Sub-Adult (approx. 3.5mtrs)
Water Temp: 17.5 degrees
Chl.a: 0.5mg/m (large area of chlorophyll from 2 large upwellings)
Injuries: Uninjured, large bite taken out of surfboard
There are several oceanographic features present in the surrounding area of coastline to Seal Rocks leading up to and at the time of the shark-human interaction, relevant to create a high-risk warning for the Seal Rocks area. Let’s look below at those features.
Upwellings
There were two large upwellings off the coast of Seal Rocks at the time of the incident, one to the north and another slightly to the south. Both upwellings were large, strong and in close proximity, creating a large volume of nutrients in the water and contributing to suitable White Shark water temperatures in the region (17.5 degrees).
Image via IMOS https://oceancurrent.aodn.org.au/
The light blue arrow signifies the location of the incident while the light blue circles highlight the two large upwellings present in the area.
These two large upwellings are contributing to the large mass of chlorophyll and nutrients present in the water. Highlighted in terms of density by the green/yellow/red colourations.
Image via IMOS https://oceancurrent.aodn.org.au/
The above image highlights the incident location and the water temperature between 17 and 18 degrees. Not only does this provide an ideal temperature for the presence of Great White Sharks, the upwellings have created temperature breaks throughout the surrounding area to further enhance the likelihood of increased marine life activity.
Seasonality
The whale migration up and down the NSW coastline is often accompanied by white sharks. October sees the start of the southern migration with headlands near to Seal Rocks considered some of the best for viewing the whales as they are so close to shore here at this time of year and in good numbers.
Shark catch data put out by the NSW DPI recorded, during the month of October between 1st of July 2022 and 30th of June 2023, the Forster SMART Drumlines caught 6 white sharks. Over the twelve-month duration a total of 55 white sharks were caught, second only to Port Macquarie with 79.
Since the year 2000, in the month of October there have been 7 white shark attacks on the NSW coastline.
Conclusion
The oceanographic factors mentioned above were water temperatures of 17-18 degrees and high levels of nutrients and chlorophyl over a large area, created by two large upwellings off the coast of Seal Rocks and surrounding areas. These factors combined with known increased whale activity in this area during October would warrant a high risk warning of shark-human interaction with white sharks in Seal Rocks and surrounding areas of coastline.
