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A recent study featured in the journal Frontiers in Marine Science has revealed significant ecological repercussions following the absence of Great white sharks (Carcharodon carcharias) in False Bay, South Africa. Research conducted by scientists from the University of Miami Rosenstiel School of Marine, Atmospheric and Earth Science over a span of 20 years highlights serious disruptions in marine ecosystems, emphasizing the vital role that apex predators play in sustaining oceanic health.
Highlights of the Study:
Decline of Great white sharks: Once plentiful in False Bay, Great white sharks have seen a startling decrease and eventual disappearance. Factors such as years of unsustainable fishing practices, including their capture in nets designed for protecting swimmers, alongside recent instances of orca predation, are believed to contribute to their decline.
Ecosystem Disruption: The removal of Great white sharks has resulted in a surge in populations of Cape fur seals (Arctocephalus pusillus) and sevengill sharks (Notorynchus cepedianus), while concurrently triggering a decline in the fish species that serve as food for the seals and smaller shark species preyed upon by the sevengills. This situation exemplifies the extensive ripple effects that can result from the loss of a top ocean predator.
Empirical Evidence: The researchers have presented tangible evidence of disrupted food webs stemming from the absence of predation pressure exerted by Great white sharks, reflecting established ecological theories and prior laboratory findings. Utilizing long-term observational data from boat-based shark sightings, citizen science records of Cape fur seals, and Baited Remote Underwater Video Surveys (BRUVS) focusing on fish and smaller sharks, the study articulates the profound changes in the marine food web attributable to the absence of these apex predators.
“The decline of this iconic predator has correlated with noticeable increases in Cape fur seal and sevengill shark sightings, which is subsequently associated with decreasing populations of their prey,” explained Neil Hammerschlag, Ph.D., the lead researcher on the study. Hammerschlag conducted this pivotal research through the Shark Research and Conservation Program at the University of Miami Rosenstiel School. “These findings support well-established ecological theories that suggest the removal of a top predator triggers cascading effects throughout the marine food web.”
“Underwater video surveys executed over a span of ten years allowed us to capture a snapshot of the food web before and after the disappearance of Great white sharks in False Bay,” noted Yakira Herskowitz, a co-author of the study and a former graduate student at the Rosenstiel School who analyzed the underwater footage. “The data recorded concerning species abundance not only highlights numerical changes but can also indicate shifts in behavior, as species facing heightened predation risk often become more elusive and thus less detectable on camera.”
The research concludes that the absence of Great white sharks has profound implications for marine ecosystems. “The vacancy of these apex predators disrupts population regulations, leading to observable changes that may have lasting effects on the health of oceanic environments,” Hammerschlag emphasized.
This study underscores the pressing need for global shark conservation initiatives, as the loss of such keystone species can yield long-term impacts on marine ecosystems. Considering the global dependency on thriving oceans for sustenance, recreation, and vital ecosystem services, the preservation of large shark populations is critical for maintaining biodiversity.
Funding for this research was sourced from the Isermann Family Foundation and the Shark Research Foundation.
Source
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