The Orca activity in the western end of the Strait at this time of the year is related to the exit of the Red Tuna from the Mediterranean towards the Atlantic. The tuna enter the Mediterranean in April to breed and leave in July and early August. The Strait is very deep, reaching 1000 metres, but in the west a sill rises from the sea bed and the depth is reduced to around 200 metres. Any fish passing this is forced upwards allowing a chance for fishermen (below) and orcas (above) to catch the fast fish.
One interesting aspect is that the highly intelligent orcas have learnt to go for the tuna which have been caught in the fishermen's hooks. It is not unusual for the fishermen to pull up a tuna head, rest of the body missing!
The groups of orcas seem to fuse and split at different times as they hunt for the fish. Here is a pod of females, recognizable by the small, curved, dorsal fins
Male (right) with higher fin than female (left)
Female with young
The Strait is a busy shipping lane so the orcas have to be alert to this danger at all times
Female starting a dive
Male showing the large fin clearly
While watching the orcas we picked up other activity which we illustrate from here down, with images from our own archives, taken in the Strait at other times. Here is a group of Common Dolphins Delphinus delphis
Loggerhead Turtle Caretta caretta
Common Tern Sterna hirundo - steady flow of birds migrating towards the Atlantic
Black Tern Chlidonias niger - The first birds are now moving into the Atlantic
Balearic Shearwaters Puffinus mauretanicus - coming from the western Mediterranean to feed in the rich waters of the Strait
Cory's Shearwaters Calonectris diomedea - also feeding in the upwellings of the Strait