Bull sharks in the harbour

The following is a research paper published on 10/2023

Capture Response and Long-Term Fate of White Sharks (Carcharodon carcharias) after Release from SMART Drumlines

Summary
During the first three days after release, the sharks moved away from the shore and stayed mostly offshore. Although sharks gradually moved closer to the shore 10 days after release, 77% of the sharks remained more than 1.9 km away from the coast and an average of 5 km away from where they were tagged. These findings demonstrate the effectiveness of SMART drumlines as a non-lethal method to mitigate bites by White Sharks. 

The following is a research paper published on 31/8/2023

"Bull Shark (Carcharhinus leucas) Occurrence along Beaches of South-Eastern Australia: Understanding Where, When and Why"

By Amy F. Smoothey,Yuri Niella,Craig Brand,Victor M. Peddemors and Paul A. Butcher

Summary
In Australia, bull sharks are one of the species implicated most regularly in shark–human interactions. The factors affecting bull shark presence in nearshore waters of New South Wales (NSW), Australia were examined to determine periods of increased overlap with beach-users and thereby potentially increased risk of shark–human interactions. We investigated the spatial ecology of 233 juvenile and large (including sub-adult and adult, >175 cm total length) bull sharks acoustically tagged and monitored over a 5.5-year period (2017–2023) along 21 coastal beaches of NSW. Our study highlights that large bull sharks were present more in waters north of 32° S with a southward distribution during summer and autumn. The occurrence of large bull sharks in nearshore waters was greatest from midday to 04:00, when water temperatures were higher than 20 °C, after >45 mm of rain and when swell heights were between 1.8 and 2.8 m. We show that current shark bite mitigation educational messaging, incorporating proximity to rivers, turbidity (rainfall) and time of day, reflect heightened periods of the occurrence of large bull sharks. We concur with the current shark smart advice that nocturnal swimming and surfing, especially in warm waters and when water visibility is poor, should be avoided for many reasons, not the least of which being the potential presence of bull sharks. However, we suggest that time of day messaging for large bull shark presence should be modified from “dawn and dusk” to instead refer to afternoon and low-light periods 

The following is an article written in July 2021 by Marco Bordieri and reviewed by Dr Amy Smoothey

Since the question of the Bull sharks presence in the harbour seems to be a topic of interest, I have collected the available resources for being informed to what the science says about that. Thanks to Dr. Amy Smoothey (a known presence in most of the videos below) for the support in putting this content together.

So, is it true that there are many Bull Sharks living in the harbour? 

There is a consistent number of large (2-3.2m length) Bull sharks swimming throughout our harbour waterways, from the entrance to the river reaches and back , but their presence is largely seasonal as the studies have revealed.

Two incidents in the harbour over the recent years: the Navy diver Paul De Gelder at Woolloomooloo Bay in February 2009 and the actress Marcia Hathaway at Middle Harbour in January 1963. But they are not the only ones, over the years 52 fatal attacks have taken place in Sydney, most of the times in the Harbour.  Warning - gore images: here an article from the Daily Telegraph.

Personally, between November and June, I would not swim in the harbour unless I am in the most popular beaches and dive sites: Manly harbourside, Balmoral, Clifton Gardens, Camp Cove, etc.. In these sites there are dozens of divers and swimmers every day and the lack of interactions with sharks gives some statistical confidence. In the same period I would also stay clear of Middle Harbour and the area around the Spit Bridge (check out the first video below), as well as the harbour West of Clifton Gardens.

Findings by DPI:

By tagging and tracking bull sharks in Sydney Harbour we have found that:

• Bull sharks occur in Sydney Harbour during summer and autumn.

• Bull sharks use all areas of Sydney Harbour from Parramatta and Lane Cove Rivers to Middle and North Harbour.

• Bull sharks used slightly deeper water during the day and shallower water at night.

• Water temperature is a key predictor of their presence, 20-26 °C.

• When water temperature drops below 19°C, bull sharks leave Sydney Harbour and travel north to QLD for the winter & spring

• 87 Bull sharks have been tagged in the harbour from 2009 to 2022 

• During the summer period up to 18 Bull sharks have been detected in the harbour on a single day

The International Shark Attack File by the University of Florida, the only comprehensive collection of worldwide attacks

Information around sharks in the Sydney Harbour

A study on the presence of Bull sharks in the harbour from which the following figures have been taken

Information around sharks in NSW