Strandline - secrets of the seashore
Sussex dolphins and whales
Since 1991, dolphins and whales have been monitored along the Sussex Coastline by the Regional group of the Sea Watch Foundation. The most commonly recorded species is the bottlenose dolphin. Observations of common dolphin, harbour porpoise and pilot whales and recorded most years. There have also been rare sightings of other species including risso's dolphin, minke whale and striped dolphin.
Each year, bottlenose dolphins migrate along the English Channel from west to east. They are mainly recorded between March and September and at Brighton they often come as close as 100 to 200m from the shore.
Harbour porpoise are also seen locally but not commonly, but there has been a small increase in sightings in recent years. They can be distinguished from dolphins because they have a triangular dorsal fin and no beak.
This beautifully marked dolphin reaches 2.6 metres. Common dolphins are usually encountered away from shore also more likely to be seen in deepwater but together with the harbour porpoise they are the most common stranded species off Sussex.
A small migration of pilot whales takes place at the end of the year. These larger toothed whales (average 6m) are deep water species and only rarely seen from the land.
If you see a dolphin or whale, please report it to the Sea Watch Foundation on their hotline number 077 7361 0036
Migration
28 different types of whale and dolphin can be found around the UK. These range from relatively small dolphin species to medium and large whales. Many of the large types of whale migrate pass the western coasts of the following the edge of the continental shelf.
click here for maps of the distribution
Strandings
The earliest record of a stranded whale on a Sussex beach dates back to 1833 when a blue whale stranded near Rottingdean. While stranded sea mammals are always a sad occurrence, they can also provide scientists with valuable information.
In fact until recent years, much of what we knew about whales and dolphins had been discovered from beached animals or on whaling vessels.
Many of the worldwide species of whales and dolphins, 28 of which have been recorded around the UK, are endangered. Nowadays, stranded sea mammals can also provide a valuable insight into the many conservation problems that threaten these magnificent mammals.
Skulls
These skulls are from common dolphin and harbour porpoise. These two species are most commonly found dead on Sussex beaches.
Look at the dolphin sharp pointed teeth. These are used for grasping slippery prey which is swallowed whole.
The harbour porpoise has spade shaped teeth and will occasionally bite fish into pieces before swallowing.
Vertebrae
A whale or dolphin's skeleton is similar to any other mammal. This is a vertebrae from the backbone of a killer whale. The backbone is made up of 50 -52 similar bones. You can see several complete whale and dolphin skeletons in the mammal section of the museum.
Teeth
Most toothed whales, including dolphins, have sharp pointed teeth. These are idea for catching slippery fish and squid which is then swallowed whole. Baleen is used like a sieve to strain plankton and tiny fish from sea water.
Sperm whale tooth
Baleen
Scientists collect teeth and baleen from stranded whales to determine their age,
as they have growth rings just like a tree. By cutting a thin section from the tooth or baleen you can tell how old it is.
Why do whales and dolphins become stranded on beaches?
Scientists now believe there is no single reason for whale and dolphin stranding. Some become stranded because they are sick or injured. Mass strandings are thought to occur when healthy whales follow a sick animal onto the beach.
Some larger whales are through to navigate by detecting the earth's magnetic field. Animals that have strayed off course could follow the earth field where it intersects land causing them to become beached.
Some whales and dolphins are found stranded on beaches showing signs that have been trapped in fishing nets or hit by vessels.
This stranded Fin whale shows how baleen hangs from the jaw.
The baleen is used to filter small animals out of large volumes of water
