Overview of What caused the surge in shark attacks?
This ABC News Daily episode (host Sam Hawley) interviews shark-bite policy expert Chris Pepper-Neff (Assoc. Prof., University of Sydney) to explain a recent cluster of shark incidents in New South Wales, why they happened, and what practical and policy steps could reduce risk. The key conclusion: extreme environmental conditions—heavy rainfall, sewage runoff, murky/foamy water and warmer nearshore temperatures—drew bull sharks into inshore areas and made bites more likely. Simple public-health and infrastructure responses (warnings, avoiding water after storms, fixing sewage outflows) could reduce immediate risk.
What happened — the incidents covered
- Multiple attacks occurred across a short period in NSW, including:
- Vaucluse (Sydney Harbour): 12-year-old boy seriously injured after jumping off rocks.
- Dee Why (northern beaches): surfer’s board bitten; no injury.
- Manly (northern beaches): young man suffered serious leg injuries; beach had earlier shark sighting closures and pollution warnings.
- Mid-north coast: surfer bitten but no major injuries.
- Authorities described the cluster as “unprecedented” in the region.
Expert diagnosis — why attacks surged
- Heavy rainfall (example: ~125 mm in a short period) flushed raw sewage and organic waste into harbors and nearshore waters.
- If rainfall > ~20 mm, bacterial/organic loads spike in harbors, attracting baitfish.
- Bull sharks (the likely species involved):
- Enter estuaries/nearshore areas to feed on baitfish.
- Are more active in murky, foamy, turbid water and often use silhouette to identify prey.
- Tend to “bite” multiple times; smaller bull sharks are more likely to take repeated bites.
- Murky/foamy water reduces visibility—sharks may bump into and bite humans or boards.
- Water temperature and broader environmental shifts also influence shark distribution; clusters often reflect an environmental trigger.
Limitations of current mitigation tools
- Shark alarms and drone/tower sighting systems:
- Depend on visual detection and are ineffective in turbid/murky water.
- Provide limited early warning during and immediately after storms.
- Tagging and tracking:
- Useful for population- and trend-level monitoring (e.g., showing when sharks shift distribution).
- Not a reliable early warning for every individual shark (can't tag all animals).
- Shark nets:
- Two types: enclosed net cages (harbor pools) vs. open “shark nets.”
- Open shark nets are porous (open top/bottom/side), do not stop bites, can create a false sense of security, catch bycatch (turtles, other sharks), and may attract predators by trapped animals.
- There is no clear scientific evidence over a century that such nets reduce risk to swimmers.
- Political decisions (e.g., to retain nets) are often driven by perceived public safety and electoral concerns.
Policy and behavioral recommendations (what Pepper-Neff recommends)
- Immediate, low-cost public health measures:
- Avoid swimming in harbors/estuaries for 72 hours after heavy rain.
- Avoid ocean beaches for 24–48 hours after big storms (depending on conditions).
- Improve signage and public communication to keep people informed during storm windows.
- Infrastructure fixes:
- Repair and upgrade pipes/sewage outflows that flush raw waste into harbors—reducing the baitfish/food attractant.
- Monitoring improvements:
- Use tagging/tracking to understand population-level trends and environmental drivers (not as a sole early-warning tool).
- Monitor water temperature and other environmental indicators to predict risk windows.
- Public education:
- Reframe the beach as a dynamic ecosystem (like the bush): accept non-zero risk and adapt behavior accordingly.
- Culling/commercial shark fisheries:
- Not recommended as a sensible solution—culling has ecological consequences and bycatch problems and does not address the environmental drivers of shark presence.
Notable quotes
- “The ocean is a dynamic ecosystem… it’s not a zero-risk environment.”
- “We could clean the pipes that are flushing the sewage…and tell the public not to swim for three days after a big storm.”
Bottom line / Action items for beachgoers and policymakers
- For beachgoers:
- Stay out of estuaries/harbors for ~72 hours after heavy rain; avoid ocean beaches for 24–48 hours if conditions are murky/foamy.
- Heed closures, advisories, and shark alarms—don’t assume nets make beaches safe.
- For policymakers:
- Boost storm-related warning systems and public messaging.
- Prioritize fixing sewage runoff and monitoring environmental indicators.
- Re-evaluate reliance on shark nets and invest in evidence-based prevention and education.
Credits: Interview with Chris Pepper-Neff (Assoc. Prof., University of Sydney). Hosted by Sam Hawley. Produced by Sydney Pead; audio production Sam Dunn.