UV’s Little Island – by Paul Wildlifewriter

Since late October and November, we’ve seen UV adopt a new location on the Senegal coast where he spends many happy hours indulging in a young adult osprey’s favourite activity… inactivity. This animation sequence covering the last three weeks (only) shows his perching [red] and flying [orange] positions through each day. The scale is 1:12000

play

The “focus” location appears to be a small island on the Langue de Barbarie. Six years ago, this low-lying bubble of sand didn’t exist. Six years before that, it DID exist – but it wasn’t an island.

There’s a reason for all this…

The course of the Senegal River as it approaches the sea has always been variable and its hydrology is unstable. Unlike most major river deltas, the Senegal encounters a strong south-going current where it meets the Atlantic Ocean and this means that a sand spit – the Langue de Barbarie – has formed at this point, forcing the mouth of the river to migrate down the coast. In the geological past, tidal effects and the accumulation of silt meant that the estuary could no longer accommodate the peak river flow during the rainy season. The land behind the river became flooded to a greater extent each year, until a breach in the Langue appeared. There is evidence from drilled core samples that this cycle has happened many times over the last 380,000 years.

In 2003, the city of St Louis/Ndar was threatened with such flooding and the Senegalese authorities decided to give Nature a hand by creating a relieving breach themselves. They dug a channel through the Langue about seven kilometres south of the city centre, allowing the pent-up waters of the river to escape to the sea.

Image credit: Durand, Anselme and Thomas, article in Cybergeo 2010

Image credit: Durand, Anselme and Thomas,
article in Cybergeo 2010

The plan worked and St Louis/Ndar was saved – but the power of the river and the ocean had been underestimated…

The gap in the Langue got wider. The next year, it was wider still. Salt water from the sea contaminated the low-lying fields around Gandiol. People lost their farms and their homes. Some of Senegal’s most popular tourist hotels were inundated and, inland, whole forests died. It was an environmental disaster.

Since then, the coastal erosion of the southern Langue has continued and its pace is accelerating. This sequence of Google Earth images shows that the rate of erosion between 2004 and 2008 was around 300m per year. From 2011 to 2015 it was over 1200m per year and still rising. Some attempts have been made to construct erosion defences at vulnerable spots – but this hydrological genie will not go back in the bottle until his work is complete…

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…because as the Langue de Barbarie is destroyed towards the south, the river and the sea are rebuilding it in the north. It is a process that will take many hundreds or even thousands of years but, in the meantime, some of the local wildlife is already taking advantage. Coastal vegetation is starting to re-establish. Ospreys are adaptable birds and UV has found that the newly-formed little island is an ideal spot for sunning himself, safe from predators and human disturbance. Reports suggest that many other ospreys are still occupying the area: the terrain may have changed but they have worked out how to turn these changes to their own purposes. It may be that the altered river course concentrates fish movements into a smaller area, making hunting easier.

UV at 10.42 on 20 October (c) Rafa Benjumea

UV at 10.42 on 20 October
(c) Rafa Benjumea

As west Africa moves from wet to dry season this winter, we will be watching UV’s activity with keen interest to see what he makes of it.

This entry was posted in Blue UV, Migration, Osprey updates, Osprey video and tagged , . Bookmark the permalink.

3 Responses to UV’s Little Island – by Paul Wildlifewriter

  1. Thank you for this interesting post. Man interferes with nature at his peril….

  2. vivien Finn says:

    Very interesting to read, Paul. Thank you.

  3. thehutts says:

    Thanks Paul for all your hydrological research it make very interesting reading. Sally

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