We are plodding on at a speed of 1 knot towards the northwest. At this speed we will be at Lampedusa in ten hours time if we don't miss our aim (due to a sleep attack?) otherwise we'll find ourselves in Hammamet.

A shark, even a turtle, goes much faster than we do. Many species such as the mako have a "turbo" and are capable of jumping out of the water and seem able to move faster than 35 knots: in effect animal torpedoes with a hair trigger, invaluable for catching and gulping down fast prey such as tuna.
The blue sharks in fact are slower than others and rarely achieve more than 5 knots. They tend to prey on animals such as squid, as well as sardines or mackerel when they can.