As inhabitants of the oceans for over 400 million years, sharks stand as formidable guardians here, orchestrating a delicate balance that sustains life beneath the waves. High-level predators, they orchestrate the intricate dance of marine ecosystems, regulating the abundance and behavior of myriad mesopredators and prey species. Their role in maintaining ecosystem health is pivotal, a fact underscored by mounting evidence linking healthy shark populations to the preservation of marine biodiversity and the achievement of UN Sustainable Development Goals. However, recent decades have witnessed a harrowing decline in shark populations. Human activity, particularly overfishing. This relentless exploitation, coupled with the encroaching impacts of non-extractive activities like noise pollution, has pushed many shark species to the brink of extinction. The scale of the threat is staggering, with over one-third of shark and ray species facing extinction due to overfishing alone.
Other anthropogenic activities, such as wildlife tourism, also disrupt their natural behaviors and habitats. The burgeoning global ecotourism market, generating billions annually, boasts over 120 million participants. Yet, this industry, particularly in marine habitats, carries a hidden threat. A comprehensive review reveals that most interactions between humans and wildlife, even in protected areas, yield negative consequences. The pressure on marine habitats intensifies, with sharks becoming unwitting victims of the very tourism designed to protect them.
Enter the COVID-19 pandemic—a global crisis that unwittingly offered a rare glimpse into the intricate dance between sharks and human disturbance. Amidst the chaos and uncertainty, the lockdown measures imposed by nations worldwide inadvertently provided scientists with a unique opportunity to study the effects of reduced human activity on wildlife. For scientists studying sharks, this presented an unprecedented opportunity to observe how these creatures responded to the sudden absence of human presence.
Dr. André S. Afonso of the Centre for Functional Ecology, University of Coimbra, was one who took advantage of this, with his study focused on the Archipelago of Fernando de Noronha. A pristine marine reserve nestled in the western South Atlantic Ocean, Afonso’s team meticulously tracked the movements of tiger sharks (Galeocerdo cuvier) and lemon sharks (Negaprion brevirostris), two apex predators that call these waters home. “Tiger and lemon sharks are two abundant, large-bodied apex predators in coastal waters off Fernando de Noronha (FEN). Yet, they strongly differ in their association with FEN because lemon sharks complete their life cycle (i.e., they reproduce and the offspring grow to maturity) in the area and can be regarded as a resident species, whilst tiger sharks do not reproduce in FEN and, being highly migratory, they arrive to FEN during the juvenile or adult stage after roaming across the ocean,” Afonso explains. “Hence, the exposition of the two species to local anthropogenic stimuli across their ontogeny differs, thus making them two appropriate biological models to examine the impact of non-extractive anthropogenic pressure on sharks.”
While lemon sharks exhibited a notable 43% increase in coastal habitat use during the lockdown, tiger sharks displayed a surprising resilience, maintaining their behaviors despite the absence of human interference. “The seasonality in habitat use exhibited by both species tends to be similar, with higher detection rates in the austral summer and lower rates during the winter. Summertime is also the period of highest tourism influx. The acoustic data revealed that lemon sharks increased their detection rate during the winter (coinciding with the lockdown stage) when they should have decreased it. Hence, the lockdown influenced lemon shark behavior and promoted higher coastal residency,” he says. “As for tiger sharks, since the decrease in detection rates matched the expected seasonal trend, no conclusions about how they could be influenced by humans could be developed, but they seemingly did not increase coastal habitat use while humans were absent. These differences in species behavior might relate to lemon sharks being a more resident species living in an anthropogenic landscape of fear (which was released during the lockdown) and tiger sharks being a migrant less acquainted with human stimuli and less responsive to changes in the anthropogenic landscape.”
The study’s findings underscored the nuanced responses of shark species to fluctuations in human activity, offering valuable insights into the delicate interplay between wildlife and anthropogenic influence. But it also raised critical questions about the future of shark conservation. As human populations burgeon and coastal development accelerates, the need to safeguard our oceans has never been more urgent. From sustainable fishing practices to responsible ecotourism, concerted efforts are needed to ensure that sharks continue to thrive in their natural habitats.
“Even in non-extractive scenarios built mostly for ecotourism, sharks will be subject to an anthropogenic landscape which may inhibit the success rate of some fundamental behaviors such as reproducing and feeding. Under this perspective, ensuring that sharks will be able to make full use of pristine essential areas for carrying out their reproductive and feeding activities might depend on a more conservative ocean spatial management incorporating human accessibility regulations for both extractive and non-extractive socioeconomic development,” concludes Afonso. “Before the global goal of protecting 30% of the ocean by 2030, the need to address marine spatial planning in the most effective, future-oriented way became utterly urgent. […] Evidence-based ecological knowledge will be required to design efficient protected areas to optimize shark rebound potentials, and we have now the opportunity to plan the use of our oceans thoroughly so that future generations will benefit from a flourishing recovery of marine ecosystems.”
The COVID-19 lockdown, an inadvertent ecological experiment, has shown us it is imperative to weigh the unintended consequences of the Anthropocene era on these marine animals. Only then can we hope to preserve our oceans.
