What are the welfare issues with shark incident mitigation strategies?

As human populations continue to grow and coastal areas become more heavily used for recreational activities, the likelihood of encounters between humans and sharks is increasing. To help prevent shark incidents, various methods have been implemented to deter sharks from popular beaches to enhance public safety. However, while these methods aim to mitigate potential dangers, they also pose significant welfare risks to sharks and other marine species. Understanding these welfare risks is crucial for evaluating the effectiveness and ethical implications of shark incident mitigation strategies.

NOTE: A ‘shark incident’ is a human-shark interaction that results in injury or death of a human.

Sharks are shown to be intelligent, with this capability being considered similar to most other vertebrates, including mammals and birds [1]. Furthermore, sharks react to painful or threatening stimuli as demonstrated by escape attempts when hooked [2]. Studies on catch-and-release of sharks also highlight multiple stressors which may impair heart function [3] and increase body temperature which could have immediate and long-term health effects [4].

Traditional drumlines, SMART drumlines and shark nets are used across Australia in attempts to help reduce shark incidents. These methods pose significant welfare risks to target and non-target species including:

• pain, stress and suffering associated with baited hooks or entanglement,
• fear, pain and stress associated with capture and transport offshore for release, and/or
• prolonged death or inhumane killing methods.

Drumlines

A drumline consists of a floating drum (a rubber buoy) with one line attached to an anchor on the sea floor, while a second line features a large, baited hook to lure and catch sharks. These devices have been used in several countries for shark control, and usually result in the killing of target shark species when caught.

However, the use of traditional drumlines for shark control raises significant welfare concerns for both target and non-target species. In fact, the baited hooks that are intended to attract sharks often result in the entanglement of non-target species, such as dolphins, turtles, rays, and other smaller sharks. Entanglements can lead to significant harm to marine wildlife with non-target species suffering injuries, stress and even death. Once caught on the drumlines, animals often remain trapped for prolonged periods of time before being detected by authorities. Species such as turtles or marine mammals often drown as they are unable to reach the surface to breathe, further exacerbating their suffering. Badly injured animals found hooked on drumlines will need to be euthanased rather than released. Drumline operators must therefore have sufficient knowledge to assess injuries and determine the survival prospect of caught non-target animals.

Furthermore, the killing of sharks caught on drumlines raises ethical concerns regarding the humaneness of the practice. The shark brain is a relatively small target. Thus, to kill them with a firearm, the shooter must know the position of the brain in the head. In addition, the most suitable firearm and ammunition must be used in combination with the correct point of aim to achieve a quick and painless death. Shooting sharks using a firearm commonly known as a ‘shark stick’ requires precise targeting to ensure a quick and painless death [5]. However, achieving this can be challenging, and there is a risk of causing unnecessary suffering if the shooting is not conducted effectively. Oher methods including pithing (where the brain is physically scrambled by using a sharp pointed tool) are considered to cause unnecessary suffering.

Drumlines are no longer used in WA and NSW, but they are still being employed in Queensland.

SMART drumlines

In 2017, a federal Senate inquiry recommended that traditional drumlines be replaced with SMART (Shark Management Alert in Real Time) drumlines, and that shark netting programs be phased out [6].

A SMART drumline is designed as a non-lethal capture method which sends an alert via a satellite link when the baited hook has been ‘taken’. The aim is that the shark or other species that has taken the baited hook will be retrieved by authorities within a short period of time to enable live release. Species of interest are generally tagged and released at least one kilometre from the SMART drumline. Though considered overall as a better method than traditional drumlines and shark nets, SMART drumlines still result in the suffering and death (by drowning or being euthanased) of both target species and non-target species and should not be considered as a non-lethal method. Moreover, despite action being initiated as soon as the alarm sets off to retrieve and release these animals, there are still welfare implications of high stress, injuries and potential drowning before authorities attend the SMART drumline.

Shark nets

A shark net is a submerged net placed around swimming beaches to reduce shark attacks by causing entanglement. The nets are placed parallel to the beach and in NSW are 150m long, with the barrier only covering the bottom half of the water column, whilst in Queensland the nets are 183m long, covering the top half of the water column. In Queensland and New South Wales, where shark nets have been used for many years, the evidence shows that they result in indiscriminate trapping, suffering and death of mainly non-target species, including dolphins, rays, turtles, seals, endangered hammerhead sharks and other threatened or protected species [7]. Target species (White, Bull and Tiger sharks) accounted for only 6% of interactions with shark nets in NSW in the latest reporting period [8]. Shark nets are removed during winter months to reduce the risk of entanglement by migrating humpback whales in NSW but not Queensland.

Non-lethal methods

Drones

Aerial surveillance with drones has recently been introduced as a cheaper and non-invasive alternative to manned surveillance. Community surveys indicate strong support for using drones not only for shark mitigation but also for overall beach and ocean safety [9]. However, it is also important to note that drones have the potential to induce stress in certain species, especially birds, leading to adverse effects ranging from collision-related mortality to reduced health and vigour due to stress. The impact on animals can vary depending on multiple factors such as the approach method, flight pattern, noise level, altitude, and season. These are therefore key points to be taken into consideration to regulate drone shark surveillance [10].

Tagged shark listening stations

Real-time detection of tagged sharks provides valuable information to the public and beach authorities to improve safety measures. While considered a welfare-friendly approach, it necessitates capture for tagging which can cause fear, pain and stress in the sharks, as well as being labour intensive.

Climate change

It is also important to consider the potential impacts of climate change on the welfare and survival of sharks as well as other marine species. An Australian study using modelling to predict future impacts of climate change on marine habitats highlights the importance of ongoing monitoring of oceanic temperatures and other changes which may affect survivability of some shark populations [11]. It is well recognised that apex predators play a vital role in maintaining a balanced ecosystem and so any measures which lead to sharks being killed need to be reconsidered carefully on this basis.