In the previous post we described UV changing behaviour slightly and foraging along the shoreline of the northern part of the Langue de Barbarie. On 3 and 4 November data didn’t show UV foraging activity in any detail. There were very few fixes on 4 November, a day of unseasonal thunderstorms.
UV sat tight inland most of the day although the showers could have missed his spot altogether. The daily recorded rainfall at Saint-Louis airport was 0.51mm. Podor airport (about 180 km upriver in a straight line) recorded 6.10mm.
NASA weather satellite imagery had been showing quite a small area of silt (carried downriver as a result of the earlier seasonal rains) around the Senegal River mouth although it looked dense. Today looks rather different.
The silt is extending about 20 km offshore, well past the 6 km distance UV has been foraging sometimes. The silt plume is heading south. This slideshow of graphics prepared by Paul shows the seasonal currents. Green is cooler water, the arrows show the direction of the currents.
Paul: “The prevailing direction is north-south – “The Canary Current”. This flow starts as an upwelling of cold water from the deep ocean, and gets warmer as it travels south near the surface. The cold source is nutrient-rich, which is why that whole region along the west African continental shelf is such a rich fishing area. (For ospreys and people.)”
Is it possible to discern a change in UV’s behaviour caused by the currents carrying the sediment south and out to sea? On 5 November UV flew further north along the shoreline than previously since his return. The data doesn’t show him heading out to the deeper ocean – blue – at all.
The single offshore fix to the south was at 13.00 UTC when the frequency of fixes was 15-20 minutes apart, so he could have been further afield during that sortie. UV also foraged just off the SW of the spit, a popular place for him.
On 6 November there were many more fixes for much of the day. He had two foraging trips near land to the south of his usual areas. This image shows the longest.
An animation can bring alive so much better than an image how UV foraged. Many thanks to Paul for this one.