Smarter Than Your Average Drumline
Let's be honest... when a lot of people hear the word 'shark', they think of shark attacks, bites and a certain two-toned soundtrack from a rather famous movie. Many people remain very frightened of sharks, and therefore, shark control programs are popular in several places around the world. But beach nets and drumlines are actually fatal to sharks and are contributing to their global population declines! So is there some way that we can protect ocean users from unpleasant interactions with sharks without causing them harm? Modern day technological advances might offer a light at the end of the tunnel...
Traditional Shark Control Programs
It is incredibly rare for a shark to mount an attack on a human being. Yet, as these incidents can inflict such serious injuries and cause such enormous emotional trauma to the communities where they occur, several governments have implemented shark control programs. Originally this involved installing large-scale nets that extend along long stretches of coastline. The idea is to stop large, potentially dangerous sharks from coming into contact with ocean users at popular bather beaches (Guyomard et al, 2019, Madliger, 2019, Cliff & Dudley, 2011).
However, these nets are not merely a barrier, they are designed to entangle sharks. As a result these methods have been incredibly destructive. Sharks are killed in very high numbers in these nets every year, including many endangered species. As they do not discriminate, the nets are also very dangerous to other marine creatures, like dolphins, seals and turtles, that wander into them (Cliff & Dudley, 2011, Guyomard et al, 2019, Roff et al, 2018, Madliger, 2019).
In some places there have been efforts to reduce the mortality of shark control programmes, by replacing nets with drumlines. This involves installing unmanned baited hooks, which float near to the surface thanks to buoyant drums. The idea is to lure in and hook sharks, so they do not approach too closely to a beach. Drumlines are an effective way to protect ocean users from coming into close proximity with potentially dangerous sharks, but they are still a lethal control method for sharks (Cliff & Dudley, 2011, Guyomard et al, 2019, Madliger, 2019).
Introducing a Smarter Method
In response to rising concern about the ecological impacts of shark control programs, engineers have been seeking to develop protective methods which are less destructive to marine life, whilst still offering security to ocean users.
One such technology that has been developed is the "Shark-Management-Alert-in-Real- Time" (SMART) drumline" (aka the “Catch-A-Live”® system). This methodology is based on a traditional drumline set-up, but includes an advanced solar powered buoy (MLi-S buoy from Marine Instruments) with GPS capabilities. Thanks to its innovative triggering system, whenever the SMART drumline successfully hooks a shark, a signal is sent out to fishers and scientific researchers via satellite. This allows the shark to be removed from the fishing gear and moved to another location, away from popular beaches (Guyomard et al, 2019, Madliger, 2019, Tate et al, 2021).
SMART Drumlines are a More Sustainable Way to Protect Ocean Users
Over a two year trial period in Australia, SMART drumlines have successfully hooked potentially threatening tiger sharks (Galeocerdo cuvier) and great whites (Carcharodon carcharias). The method is thought to be very successful for preventing shark-human interactions (Government of Australia, 2021).
Whilst SMART drumlines have been very effective in trapping large, potentially dangerous sharks, they have significantly less "bycatch" than other shark control methods. Because the gear is selective, catches of non-target animals like dolphins and turtles are very low and catches of endangered species of sharks like smooth hammerheads (Sphyrna zygaena) and sandtiger sharks (Carcharias taurus) are also greatly reduced (Tate et al, 2021).
" SMART drumlines have relatively low bycatch and mortality rates"
- Guyomard et al, 2019
Survival rates of all animals caught on SMART drumlines are also significantly higher compared to other shark control programs. Over a two year testing period in Australia, scientists responded to catches of snapper, small sharks and stingrays so successfully than less than 1% of non-target animals were killed by the SMART drumline (Guyomard et al, 2019, Government of Australia, 2021).
SMART Drumlines Are Not Fatal to Sharks
The vital difference between the SMART drumline and more primitive drumline systems is the prioritisation of the hooked shark's wellbeing. Because the kit automatically generates a signal when a shark is caught, research scientists can immediately swoop in to ensure that the shark is removed from the hook as soon as possible. During trials, the average response time to a SMART drumline alert was just a little over 11 minutes (Guyomard et al, 2019, Madliger, 2019, Tate et al, 2019, Tate et al, 2021).
This is critical because research has shown that when sharks remain struggling on a hook for an extended period of time, they are much more likely to suffer "post release mortality" - dying days after their ordeal as a result of the stress (Guyomard et al, 2019, Tate et al, 2019, Tate et al, 2021). To learn more you can check out If You love Me, Let Me Go.
During testing scientists found that 94.8% of hooked great white sharks (Carcharodon carcharias) were retrieved from SMART drumlines alive Madliger, 2019, Tate et al, 2019, Tate et al, 2021).
In order to assess whether the sharks were surviving over a longer time-frame, scientists took blood samples from captured sharks. When sharks experience stress, chemical reactions in their blood produce "metabolites" - the higher the levels of these metabolites the more likely a shark will die from stress. The researchers found that the levels of metabolites in white shark blood were not dangerous if they were released within 30 minutes after their capture on SMART drumlines (Madliger, 2019, Tate et al, 2019, Tate et al, 2021).
SMART Drumlines Could Replace Destructive Beach Nets
Many species of sharks are seriously threatened with extinction, yet recreational ocean use is rising every year. We must come up with less destructive ways to simultaneously protect people in the ocean, whilst also ensuring we do not contribute to the precipitous decline of sharks. In the future, if SMART drumlines or other less destructive devices could replace destructive beach nets, many, many sharks could be saved every single year! Scientists are still testing SMART drumlines, but there is great hope that this technology could be a much more sustainable way to protect ocean users from potentially dangerous sharks in the future (Guyomard et al, 2019, Madliger, 2019, Tate et al, 2019, Tate et al, 2021).
Cliff G & Dudley SFJ (2011). Reducing the environmental impact of shark-control programs: a case study from KwaZulu-Natal, South Africa. Marine and Freshwater Research, 62, 700–709. Access online.
Government of Australia (2021). SharkSmart SMART Drumline Report. Access online.
Guyomard D, Perry C, Tournoux PU, Cliff G, Peddemors V & Jaquemet S (2019). An innovative fishing gear to enhance the release of non-target species in coastal shark-control programs: The SMART (shark management alert in real-time) drumline. Fisheries Research, 216, 6-17.
Madliger CL (2019). ‘SMART’ shark capture technology may keep beachgoers and sharks safe. Conservation Physiology 7, 1. Access online.
Roff G, Brown CJ, Priest MA & Mumby PJ (2018). Decline of coastal apex shark populations over the past half century. Communications Biology, 1:223. Access online.
Tate RD, Cullis BR, Smith SDA, Kelaher BP, Brand CP, Gallen CR, Mandelman JW, Butcher PA (2019) The acute physiological status of white sharks (Carcharodon carcharias) exhibits minimal variation after capture on SMART drumlines. Conservation Physiology, 7:1. Access online.
Tate RD, Kelaher BP, Brand CP, Gallen CR, Smith SDA, Butcher PA (2021). Shark behaviour and marine faunal assemblage beneath SMART drumlines. Fisheries Research, 243:206102. Access online.
By Sophie Adele Maycock for SharkSpeak.