Guest blog written by our ambassafor Patrik Rollefson
One of my favorite sharks in the ocean is the obvious, the Great White Shark. They are such powerful and ferocious predators, but also graceful and curious individuals. They are at the top of the food chain making sure the ecosystems they live stay balanced and healthy, removing the sick, weak, and dying, and making sure only the strongest survive. White sharks are vital to the areas they live in, and their role cannot be filled by many other organisms in the ocean. Conserving their populations is an important step in ensuring a healthy ocean for the future, but unfortunately in some areas their numbers have declined greatly. One such location is along the coast of South Africa, and more specifically in False Bay near Cape Town. This area was the iconic White Shark hotspot, which used to be a serious hunting ground for Great White sharks, due to the seal colony that lives on island in the middle of the bay. At dawn and dusk, the white sharks would hunt the seals from below, sometimes jumping out of the water entirely as they launched from the depths for an ambush attack. However, in recent years Great Whites no longer hunt, or even show up to this seal colony. A similar event has occurred at the seal colony in Gaansbaai, South Africa where I volunteered for 6 weeks, just down the coast. Here there are two islands very close to each with a channel in between, one island is a seal colony, while the other is a protected area for African Penguins. However, this deep channel used to provide the Great Whites with the perfect situation for hunting the seals as they left the island, so much so that they used to call it Shark Alley. However, in recent years with declining shark populations, and climate change resulting in an overgrowth of kelp in the alley, the sharks no longer visit or hunt at the seal colony, but instead prefer to remain at their inshore feeding grounds. Here they predate on fish and possibly smaller sharks, but do not hunt seals. This marks a drastic change to the ecosystem out near the island, as the seals are no longer hunted, and their population explodes. This has led to a population decline of the penguins next door, as the seals hunt them.
Yet, an interesting change has occurred at the False Bay island, that has not at Gaansbaai, a new seal hunter has risen. Here the seven gill sharks that call the same waters home have taken over as the primary predator of the seals, exhibiting similar behaviors to those of Great Whites when hunting them. Previously, these sharks were thought to be scavengers eating the leftovers and other easy meals, yet with the disappearance of the white shark these animals have moved in to take their place and start actively hunting the seals. This is an interesting difference between False Bay and Gaansbaai, as the seal population in False Bay can still be regulated by the seven gill sharks, but the Gaansbaai population of seals is growing uncontrolled. It’s possible that the difference is the adjacent kelp forests that exist close to the False Bay island that allowed the Seven Gills to change, whereas there are no major kelp forests as close to the Gaansbaai island.
However, the question remains, why are the White Sharks disappearing, and where are they going? This is one of the questions we looked at while I was in South Africa by monitoring and identifying what sharks were coming by the cage diving boats, which is done throughout the year, as well as using baited remote underwater video systems to monitor areas we could not reach, such as the ocean floor, and around the island. Unfortunately, these sharks are facing a whole mess of issues in South Africa, from bycatch by international long liners that do not necessarily report their catch, to overgrowth of kelp forests due to changing climate and currents, as well as poaching of abalone that eat the kelp. Additionally, shark protection measures like beach nets and drum lines on the east coast of South Africa take out numerous white sharks every year. Thus, it is very important to understand the population size, their movements, and how many are being removed each year so that regulations can be made and these beautiful animals can be better protected and preserved in South Africa and their other ranges.