The Customs House v Northern & Shell Building

On top of the dragon encrusted pediment of the Customs House 1844 sits a philosophical Britannia, Queen of the seas. The Background is a simplified hint of the 1977 glass office block behind. Blink and you'll miss it on Lower Thames Street. What is the swirling figure at the bottom right hand corner? The classical interpretation of a dolphin, I'm not sure if they saw many of them...