The French island called “La Reunion” has always been characterized by its natural hazards. But since 2011, the presence of Sardinian and tiger sharks has become a serious threat.
Over the past decade, it has become the place in the world with the highest mortality from shark attacks. The scientific community, which has mobilized to develop protection measures, is still looking for an explanation for these encounters.
On average, more than a hundred attacks occur in the world each year, but neither Australia, nor South Africa, nor the east coast of the US concentrate as many deadly shark attacks as this small French island with great volcanic activity does.
Of the 27 attacks that have occurred since 2011, eleven have been fatal, breaking a sad world record. In 2011 alone, seven attacks were recorded, of which two were fatal.
The “shark crisis”, as the situation was baptized, was triggered by two deaths to the west of the island of La Reunion in an area called Boucan Canot; one of them was that of a former French bodyboard champion on September 19, 2011, Mathieu Schiller, whose body was never found, and the other, that of a 13-year-old teenager, future promise of French surfing.
In August 2013 the authorities decided to ban swimming and water sports outside the designated areas. "It's a bit like lockdown now with COVID-19 with which we have no answers. But in this shark crisis we don't have masks or protective gels or tests. We can only stay home”, Comments François Taglioni, researcher at the University of La Reunion.
To address this public safety problem, exceptional measures have also been enabled: the capture, monitoring and tracking of specimens, the installation of state-of-the-art networks, underwater observation and surveillance from beaches and by drones to allow activities and watersports.
Surfing, a sport that has been practiced on the French island for 50 years and which was in full swing at that time with more than 30,000 practitioners a year, has been the activity most exposed to attacks. "The risk of sharks has multiplied by 23 in seven years (from 2011 to 2018) while the number of practitioners has been divided by 10”Says David Guyomard, researcher at the Shark Security Center.
According to research published inScientific Reports, there is a shark attack for every 24,000 hours of surfing practiced, an annual rate that is among the highest in the world. In fact, since 1988, 86% of shark bites have involved surfers on the leeward shores, where 96% of surfing activities take place.
Despite bathroom restrictions, which remain in force today, many surfers have ignored the recommendations even during lockdown and attacks have continued. But the scientific community is more active than ever to understand the origin of these unfortunate encounters.
A questioned marine reserve
The marine nature reserve of the island of La Reunion, classified in 2007 and occupying an area of about 3,500 hectares on the west coast of the island, was soon designated by various sectors as the main cause of the increase in attacks by Sardinian or bull shark (Carcharias leucas) - often confused withCarcharias taurus-, which can measure about 3.4 meters on average and the main species involved in the attacks, together with, to a lesser extent, the tiger shark (Galeocerdo cuvier).
Since its creation, the marine protection area has become a sanctuary where fishing is prohibited. "Many thought that the reserve would become a dining room for sharks, that they would proliferate, and this is actually not true”, Says the French researcher. However, the inventory of biomass before and after the creation of the reserve shows that it has not increased. "To say that it is a dining room -because there are more fish- is totally false”, Says the scientist.
“The suspicions are really due to the fact that the reserve's space overlaps exactly with the areas where there have been the most attacks since 2011, because it is where the most people surf. It is concomitant, but there is no relationship between both elements”Says Taglioni.
In a recently published study, a team of French and American scientists analyzed, thanks to passive acoustic telemetry, the spatial distribution of 36 specimens of Sardinian sharks inside and outside the protected area to show that humans and sharks could coincide in some areas.
After 17 months of study, the results revealed that the sharks spent more time outside the reserve than inside. "This reveals that the spatial distribution of sharks is not primarily centered in the marine protected area along the west coast of Reunion Island.”, Say the authors in their work.
However, the scientists identified certain specific locations in the reserve that could overlap with human presence at certain times of the year. "There have actually been more attacks in this area because that is where the surf spots are. There are more surfers and bathers”, Asserts Taglioni.
Discarding the hypothesis of the marine area, why then are there more shark attacks on this island than anywhere else in the world? "We don't have the answer. It's very complicated. We believe that there are a multitude of factors that come into play"Warns the scientist.
Why does the shark attack?
As a result of the recrudescence of the attacks, in 2012 the CHARC scientific program was launched to understand the behavior of Sardinian and tiger sharks, species implicated in attacks on surfers and bathers, and whose ecology had not been much studied.
Within the framework of this project, an investigation published in the journalOcean & Costal Management, collected some data on the spatial-temporal distribution of sharks and people between 2011 and 2013, during which there were eight fatal attacks.
Among the conclusions, it stands out that the distribution of users and sharks overlap and that the areas of medium to high risk of interaction often correspond to those historically implicated in these attacks. But nevertheless, "shark attack locations are not consistently associated with a high presence of sharks”, Indicate the authors led by Anne Lemahieu of the Research Institute for Development (IRD, for its acronym in French), who call for greater measures in priority areas.
For François Taglioni, one of the reasons for the increase in the number of attacks is the greater number of people in the water in a given place: “The risk increases. If you don't get in the water, there would be no attacks”.
In a study published last year inMarine Policy, the French scientist and his team analyzed the factors that could explain the 57 shark attacks that have occurred from 1980 to 2017 on the island. Among the variables studied are rainfall, temperature, time of year, time of day, and water turbidity, among others.
“In reality, the shark attacks at any time of the day as long as there is a human in the water”, Says the expert. The month of the year also affects the results. "During the winter in the southern hemisphere (July and August) there are more attacks. There are several explanations for this: it is the breeding season and the males could be more aggressive, and it is also the time when there are more waves and when water sports practitioners are in the water.”, Indicates the scientist.
Another aspect that researchers have been able to confirm is that the Sardinian or bull shark, capable of climbing estuaries or inhabiting freshwater lakes and rivers thanks to a gland in its kidney that allows it to filter the water, likes cloudy water. "It will attack, especially, when there are waves and, therefore, more surfers”Says Taglioni.
Measures to reduce attacks
- large networks
- shark watchers
- drones, individual or collective protection equipment, electromagnetic barriers
- surveillance on jet skis
- prevention fishing
“Each of these measures contributes to reducing risk. They cannot be deployed alone, but must be complementary. Overlapping them will reduce the risk to an acceptable level for a safe practice of activities in the mar ”, Guyomard explains.
See complete Shark Risk Reduction Strategy Meetings