(CNN)A pair of orca sharksGreat white sharksSouth Africa {10 According to a new survey, 2017 On the shore after killing 5 sharks in just a few months.
The Gunsbay coast was once a popular spot for great white shark spotting, but sightings have declined significantly in recent years. In this study, long-term sightings and tagging data were used to show that great white sharks (also known as killer whales) are driving away great white sharks.
Researchers also found that five great white shark carcasses were washed ashore, four had their nutrient-rich liver removed, and one had their heart removed. I analyzed it. According to researchers, they could all have been injured by the same pair of orca and killed more great white sharks.
The study tracked 14 great white sharks for five and a half years and found that they fled the area when orca were present. Researchers believe that shark fear causes rapid, long-term mass migration when sharks are aware of the presence of predators.
"Initially, after the Great White Shark attack on Gunsby, individual Great White Sharks did not appear for weeks or months," said the study's lead author, the Great White Shark of the Dier Island Conservation Trust. Alison Towner, a senior biologist at Great White Shark, said. ,News release.
Towner believes this is a "massive evasion". This is similar to how Serengeti's wild dogs avoid certain areas when there are lions.
"The more orca that live frequently in these areas, the longer the great white shark will stay away," she added.
Changing ecosystems
Sharks weren't in Guns Bay for a week in 2007 and three weeks in 2016 before orca began to attack great white sharks. rice field.
This means that the long absences witnessed by the study are unprecedented, which is changing the ecosystem of the region.
Bronze predator sharks have emerged as new medium predators in the region, Towner said.
"These brown fur seals are also being attacked by oakers who show their level of experience and skill in hunting large sharks," said Cape Fur Seals, which are currently preying on African penguins. Added Towner said. It is on the verge of extinction.
"This is a top-down effect, and there is also" bottom-up "nutrition pressure from the massive removal of abalone grazing the kelp forest where all these species are connected," she said. I added.
"Simply put, this is a hypothesis for now, but the pressure that ecosystems can receive is so great that the effects of shark extermination by orca can be much more widespread. There is sex. ”
“ Rapid decline ”
Townner also believes that sharks are becoming more prevalent off the coast of South Africa. A particular pair is a shark eater.
"This change in behavior of both apex predators may be associated with a decrease in prey populations, including fish and sharks, causing changes in their distribution patterns." She said.
She said the orca is focused on young sharks. This can have a significant impact on the vulnerable great white shark population, as sharks grow slowly and mature in later years.
Researchers acknowledge that sea surface temperature can also affect great white shark sightings, but "witnesses dropped sharply in early 2017, lengthening absenteeism, and so on. I can't explain the increase. "
Other explanations may include direct fishing of great white sharks and a reduction in prey due to fishing, which may contribute to the overall reduction in the number of great white sharks in South Africa. There is a possibility, but it is unlikely. To explain the sudden local decline. ”
According to another 2016 survey, South Africa has an estimated thousands of previous animals. Compared to, there were only a few hundred white sharks left.
In addition, DNA analysis of shark tissue showed that Caucasians in South Africa have very low genetic diversity and are susceptible to external shocks such as illness and environmental changes.
