One month of dolphins

No guests to see the dolphins but still we record every sighting we can. Since May 24th, common dolphins had been sighted in the Tagus river on a regular basis and very close to the city centre.

On the 3rd week in a row we managed to identify an old acquaintance, the individual DC10 is a very conspicuous common dolphin, due to the missing tip of the dorsal fin (likely cut by fishing lines).
‘He’ (likely a male) was first recorded in 2018 and had been re-sighted every year since then.

We wander why this regularity, environmental factors are unlikely, as water temperature, tides, currents had been shifting all over the entire period. The stronger factors are the ones basic for life, like food. Fishermen gave us a clue, it seems that there is a lot of sardines and mackerel inside the river and these come to be the favourite fish of common dolphins.

Estuaries are among the most productive natural habitats in the world, so it makes sense for large schools of these fish to settle inside or close to the Tagus river, as Tagus has the widest estuary in Europe.

The next questions are to determine if indeed the amount of fish found last month inside the river is significantly higher than past years and if so why. Can the current pandemic played an important rule in the fishing industry? Can these impacts allow the fish stock to grow? It happened before, after BP oil spill in the Gulf of Mexico back in 2010.

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