Deep sea shark fishing
Deep-sea shark fishing requires specialized skills and advanced equipment to target sharks in remote oceanic regions far from shore. This activity focuses on various species of sharks, including the great white shark and the tiger shark.
Sharks play a critical role in the marine ecosystem, helping to maintain ecological balance. However, overfishing poses a serious threat to their populations, prompting many international organizations to implement regulations and protections to ensure their conservation.
Deep sea shark fishing
The decline of shark populations
There is clear evidence that shark populations are declining around the world, and humans are largely to blame.
A recent reassessment of the International Union for Conservation of Nature's (IUCN) Red List of Threatened Species found that 37.5% of all shark species are currently threatened with extinction.
Marine biologist and lecturer at the University of Miami, Catherine McDonald, notes that pelagic sharks and rays have declined by 71% since 1970.
Overfishing is the biggest threat, but coastal habitat loss, prey depletion and declining water quality are also contributing factors.
In 2011, Western Australia experienced one of the worst heatwaves on record, with ocean temperatures rising by 5 degrees Celsius for two months. The heatwave was catastrophic for the bay's dominant seagrass species, particularly Amphibolic antarctica, which forms dense, sediment-rich meadows that provide food for fish and marine life. Over 90% of Amphibolic antarctica has been lost, the largest loss recorded in the entire bay.
Conversely, the loss of seagrass benefited the bay's dugongs, which prefer a smaller and harder-to-find type of tropical seagrass that was protected and inaccessible by the dense *Amphibolic antarctica*.
As access to tropical seagrass became easier, dugongs were known to feed destructively on it, uprooting their preferred seagrass and making it difficult to replenish the dense meadows of Amphibolic antarctica.
In Shark Bay, tiger sharks were able to restore some balance by keeping dugong numbers low, and not all of the seagrass in the bay was lost.
This raised the question: What if there were no sharks in the bay? Could the ecosystem dominated by *Amphibolic antarctica* continue to thrive?
To find out, a research team led by Rob Noyce of the University of Florida in Miami spent time in eastern Australia, where shark numbers were lower, and dugongs grazed largely unimpeded.
Divers went down and collected seagrass, simulating dugong grazing in the absence of predators to prevent destructive rooting. They quickly observed a loss of seagrass cover, particularly *Amphibolic antarctica*, and the ecosystem began to shift to a more tropical state dominated by tropical seagrasses.
Noyce says, "We learned that dugong grazing, if unchecked, can rapidly destroy large areas of seagrass as they root around for food".
These changes can be long-term, he notes: "When certain species are absent, the seagrass community looks different, with species that were not present before becoming dominant."
These findings underscore the role of tiger sharks in Shark Bay. Noyce explains, "Without tiger sharks keeping dugong numbers in check, the bay would likely shift to tropical seagrass."
Noyce's team concluded that if shark numbers continue to decline globally at current rates, the resilience of carbon-rich oceanic ecosystems to extreme climate events such as heat waves is likely to be compromised.
However, Becca Selden, assistant professor of biological sciences at Wellesley College, notes that the consequences for Shark Bay may be more severe than for most places because of its unique ecosystem.
Selden explains, "The strong effect may be amplified by the relatively simple food web in the seagrass ecosystem, where predators limit grazing by large herbivores. In other words, other coastal habitats may not fare as badly as Shark Bay under similar pressures.
In addition to keeping dugong numbers low and making seagrass ecosystems more resilient, tiger sharks play another crucial role in maintaining these habitats, as their waste acts as an effective fertilizer, as do their bodies when they die.
Selden says, "Long-lived vertebrates can act as carbon sinks, as carbon consumed at the ocean surface is transported to the depths through feces or dead bodies falling to the seafloor."
This process, known as carbon sequestration, is best known for whales, but research suggests that sharks also play an important role.
A study led by Jessica Williams, a professor at Imperial College London, found that gray reef sharks, commonly found in shallow coral reef ecosystems, contribute to their environment by spreading nutrients such as nitrogen through their feces. The study estimates that the population of over 8,000 gray reef sharks in Palmyra Atoll provides approximately 94.5 kilograms (210 pounds) of nitrogen per day.
Since tiger sharks in Shark Bay spend a lot of time hunting and moving through seagrass beds, they likely provide similar fertilization benefits to these plants.
Selden says, "Large pelagic sharks are likely to be significant contributors to this effect, including blue sharks, mako sharks, and hammerhead sharks."
When it comes to increasing shark numbers, conservationists face a major adversary: the fishing industry. According to Noyce and Selden, there has been a push toward more sustainable fishing practices, but a significant portion of the industry has not adjusted its methods, which is a major reason for the continued decline of many marine predators.
The varying stringency of animal welfare laws in different countries also plays a role.
Noyce explains, "Because many predatory fish live in several places, they can span many countries with different animal welfare laws, meaning that some may not protect them or adopt sustainable fishing practices.
Fighting illegal and unsustainable fishing is an uphill battle, even as consumers become more environmentally conscious and choose sustainable fisheries over unsustainable ones.
"Navigating sustainable, coordinated, and ecosystem-based fisheries management is a key tool for conserving these predators and their ecological roles. Ordinary people can also help by staying informed, reviewing scientific research and advocating for sustainable fishing practices," says Noyce.
Regardless of support for sustainable fishing, Noyce says the only way to effectively protect marine life is to reduce global greenhouse gas emissions. "Ultimately, if we want to preserve our ecosystems for centuries to come, we need to address climate change while preserving species."
Even if shark populations are restored to higher numbers, their contribution to carbon sequestration and mitigation will only be a small part of the broader effort to combat climate change. However, the abundance of sharks has a significant ripple effect on many marine ecosystems that depend on healthy, abundant seagrass in a variety of ways. By maintaining ecological balance, sharks strengthen these ecosystems against the threat of climate change, allowing them to contribute to carbon sequestration for the future.