by South Africa is known for having the world’s largest population of great white sharks.Carcharodon carcharias). Significant declines have been noted, however, in areas where sharks normally congregate off the coast of the Western Cape province. Sharks congregate in these areas to feed, socialize, or rest.
In Cape Town, skilled “shark spotters” reported a peak sighting of more than 300 great white sharks in eight beaches in 2011, but they have not been seen since 2019.
Conserving white sharks is important because they play an important role in marine life. As top predators, they help maintain the health and balance of the marine food web. Their presence affects the behavior of other marine animals, which in turn affects the ecosystem and its sustainability.
Marine biologists like us wanted to know if the decline in shark numbers in the Western Cape reflects a change in the entire population of South Africa or if the sharks have migrated elsewhere.
To investigate this problem, we conducted an extensive study using data collected by scientists, tourists and coastal fishermen. We examined trends over time in the abundance and distribution changes of sharks in the South African range.
Our research has revealed a huge difference in the number of initial meeting points. There was a decline in some areas; others have shown an increase or stability. Overall, there seems to be a steady trend. This shows that the numbers of great white sharks have remained stable since they were given protection in 1991.
When looking at possible changes in the distribution of sharks between certain areas, we found a change in the interaction between people and sharks from the Western Cape to the Eastern Cape. More research is needed to ascertain whether the sharks that have died in the Western Cape are the same sharks recorded in the Eastern Cape.
Bowlby HD, et al., Credited to the author (not to be reused)
The sustainability of white sharks is reassuring, but changing ocean distribution brings its own challenges, such as the dangers posed by fisheries, and the need for ocean management. So there is a need to better monitor the whereabouts of sharks.
Factors influencing shark movements
We have listed the biggest changes between 2015 and 2020. For example, at Seal Island, False Bay (Western Cape), shark sightings have decreased from 2.5 sightings per hour in 2005 to 0.6 in 2017. they only caught six sharks. In 2019, this number increased to 59.
Change at each site is complex, however. Understanding patterns is always a challenge.
These animals can live for more than 70 years. Each stage of life comes with different behaviors: children, especially men, tend to stay close to the coast, while adults and seniors, especially women, move further away from the coast.
Environmental factors such as water temperature, phase of the moon, season and food availability further influence their travel patterns.
Changes in climate and oceans over an extended period of time are also likely.
As predators, they target a wide range of prey and thrive in a wide range of temperatures, preferring 14-24°C. Their migratory nature allows them to seek favorable conditions when faced with adverse conditions.
Harassment of sharks by whalers
The difficulty of the journey deepens with the involvement of expert killer whales with a taste for shark liver. Recently, these common animals have been seen preying on great white, sevengill and bronze whaler sharks.
Cases were first recorded in 2015 off the coast of South Africa, which coincided with changes in the behavior of white sharks in Gansbaai and False Bay.
Although a direct cause-and-effect relationship has not been firmly established, observational and retrieval data support the hypothesis of a differential flight response among great white sharks following confirmed predation events.
Recently, it became clear that in Mossel Bay, when a killer whale killed at least three great white sharks, the remaining sharks were encouraged to leave the area.
Shark survival and conservation
The threat status of great white sharks is complex. A study published in 2022 showed a significant concentration of white sharks by longline and gillnet fisheries, extending to 25% of South Africa’s Exclusive Economic Zone. Sharks spend 15% of their time exposed to this industry.
The largest number of white sharks are caught in KwaZulu-Natal, about 32 per year. This emphasizes the need to combine shark movements with reliable catch records to assess risks to shark populations.
As shark migration patterns move eastward, potential changes in risk must be considered. Increased contact between white sharks, shark nets, drumlines (baited hooks) and gillnets can increase the likelihood of capture.
Maritime security coordination and management
Although shark bites are always low risk, changing shark movements can also have an impact on beach safety. The presence of sharks can have an impact on human activities, especially in popular swimming and water sports areas. Adapting existing shark management practices may be necessary as distributions change.
Increased signage, temporary beach closures, or improved education about shark behavior may be needed.
Leigh de Necker, Credited to the author (not to be reused)
In Cape Town, for example, shark watchers have focused their efforts on certain beaches. Following two fatal shark incidents in 2022, their program has expanded to Plettenberg Bay. Anecdotal evidence shows more areas in the Eastern Cape where mariners and divers are encountering more white sharks than ever before.
Expanded and long-term monitoring systems
Further research is needed to understand the factors that drive shark movements and their impact on distribution in space and time. Our study highlights the importance of coordinating data collection methods to produce reliable quantitative figures across their range. Other countries have the same problem.
In addition, we recommend establishing long-term monitoring programs in the Eastern Cape and continuing work to reduce shark mortality.
Sarah Waries, a masters student and CEO of Shark Spotters in Cape Town, contributed to this article.
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