Last September, ecologist David Johnson and his colleagues were at a Virginia salt marsh at low tide. There, they observed some unexpected behaviour by an aquatic predator.

They witnessed blue crabs waiting in shallow, water-filled pits, stalking and ambushing fiddler crabs above land, at low tide.

After capturing their prey, they would carry it back to the pit to consume it, then discard the large claws of the fiddler crab at the edge of the pit.

The Mexican government has announced the successful conclusion of a project involving the placement of 193 cement blocks on the sea floor in strategic locations in the vaquita’s habitat.

Called the Concrete Block Planting project, the objective was to discourage the setting of gillnets within the Zero Tolerance Area, where the remaining vaquita population is localised. Large steel hooks protrude from the top of the blocks, trapping any gillnets they come into contact with.

In early October, after nearly three months, the 193rd block was finally placed on the sea bed.

Launched in 1629, Applet (Apple) was built by the same shipbuilder as the famed 69-metre Vasa, which was carrying 64 cannons when it went down in a strait off the island of Vaxholm, just outside the capital, Stockholm. Vasa was meant to serve as a symbol of Sweden’s military might at the time but capsized after sailing just over 1,000 metres. It was salvaged in 1961 and is on display at the Vasa Museum in Stockholm, one of Sweden’s most popular tourist spots.