Arcachon Basin: on the Banc d'Arguin, space is becoming scarce, infractions are decreasing, and so is attendance

Before the summer season, Sepanso Aquitaine, manager of the Banc d'Arguin National Nature Reserve, published its activity report for 2024. It shows a decrease in site attendance and violations, due to the weather but also the reduction of the bank over the past two years.

Ahead of the 2025 summer season, Sepanso Aquitaine, manager of the Banc d'Arguin National Nature Reserve (RNN), has published its activity report on the site for the year 2024. A document where everything is noted: scientific monitoring of the fauna, birds obviously, flora (we will come back to this), the morphology of the bank, attendance and infractions.

The geomorphological evolution of the Arguin and Toulinguet sandbanks is scrutinized year-round. However, twice a year, in September and March, RNN agents georeference the shoreline of the Arguin sandbank at high tide with a coefficient of 45. These measurements reveal a clear trend in the sandbank's movements over the years. It has been elongating for a long time. During the first lockdown in 2020, the southern tip of Arguin could be seen from the beach at La Salie Nord.

It no longer exists today. The storms of the fall and winter of 2023 swept it away. But "relative stability is noted throughout 2024," the report explains. "However, the thinning of the sandbar is becoming increasingly problematic, generating numerous breaches in the dune ridge during storms and/or high tides."

Even in the northern part of the bank, which was thought to be more solid, breaches are appearing in the dune ridge. "Today, there are about 20 hectares of vegetation, whereas there were 70 or 80 hectares two years ago," Benoît Dumeau, the curator of the RNN, told us this winter. This erosion has consequences for the flora: eelgrass beds have gone from 57,000 m² in 2023 to 12,000 in 2024, and the vegetated dune areas have gone from 39.25 to 12 hectares.

In Arguin, nothing is ever sure or stable, the bank is always in perpetual motion.

The year 2024 was marked by an overall decrease in visitor numbers to the reserve. Why? It's certainly linked, says the RNN, "to a reduction in the surface area of ​​the Banc d'Arguin, the increase in fuel prices, bans on launching motorized watercraft, and the appearance of ephemeral sandbanks within the basin."

You need figures to argue. Here they are: "The peak in nautical attendance was counted on August 11, 2024, with 261 boats in the reserve (compared to a maximum of 636 on July 14, 2023)." The RNN calculates the number of boats every day between 2 and 3 p.m. Over the course of a year, they counted 24,765 vessels in 2018, compared to 23,790 in 2023, and a peak of 57,044 boats in 2020, before a decline, 45,412 boats in 2021, 16,054 in 2022, 7,582 in 2023, and finally 7,305 in 2024. In addition, the RNN has implemented automated monitoring of nautical attendance, which will provide figures for the entire year at any time of day.

Finally, the RNN welcomed 9,314 people during the 198 events organized in 2024.

Violations are also down in 2024, which may explain this, of course. There are simply fewer people on the bench to commit them. 1,679 violations were recorded by agents of Sepanso Aquitaine, manager of the RNN, and/or by environmental inspectors from the Departmental Service of the French Biodiversity Office. This is far fewer than the 9,108 observed in 2018, after the implementation of the regulations resulting from the new decree. The last peak was in the summer of 2020, the Covid summer, a summer when going abroad was complicated and French beaches were very busy. Since then, there has been a decline: 4,868 violations in 2021, 3,444 in 2022, and 2,216 in 2023.

What do we find in the 1,679 offenses in 2024? The RNN notes "a very significant increase in intrusions into the integral protection zone (ZPI)", where no human can go: 232 in 2023, 392 in 2024. Speeding has decreased, while remaining at a high volume (708, compared to 1,076 last year but 240 in 2021). The same goes for playing music at a high volume: 79 in 2024, compared to 150 in 2023. The scourge of connected speakers... There were only two offenses of this type in 2011. These phenomena disturb the peace of the RNN, that of the birds in particular. However, nature must reign supreme in the reserve...

1.3% of these 1,679 offences (which do not include those reported by the nautical gendarmerie, for example ) were the subject of proceedings, i.e. 16 fixed fines and five reports. Repression therefore largely takes second place to prevention.