Facts about dolphins (page 1)
How do dolphins sleep?
Dolphins have to be conscious to breath. This means that they cannot go into a full deep sleep, because then they would suffocate. Dolphins have “solved” that by letting one half of their brain sleep at a time. This has been determined by doing EEG studies on dolphins. Dolphins sleep about 8 hours day in this fashion.
A dolphin’s behavior when sleeping/resting depends on the circumstances and possibly on individual preferences. They can either:
1. swim slowly and surface every now and then for a breath
2. rest at the surface with their blowhole exposed
3. rest on the bottom (in shallow water) and rise to the surface every now and then to breath. 
How smart are dolphins?
The short answer to this is that we do not know. There is no reliable method to measure intelligence in humans across cultures, so it is not surprising that comparing humans, dolphins, apes, dogs, etc. is impossible. There are some indications of their potential: they are fast learners and can generalize (which is also true of pigs). Also they can learn to understand complicated language-
How much do dolphins eat?
Bottlenose dolphin diet consists of several kinds of fish (including mullet, mackerel, herring, cod) and squid. The compostion of the diet depends very much on what is available in the area they live in and also on the season. The amount of fish they eat depends on the fish species they are feeding on: mackerel and herring have a very high fat content and consequently have a high caloric value, whereas squid has a very low caloric value, so to get the same energy intake (calories) they will need to eat much more if they feed on squid than if they feed on mackerel or herring. On average an adult dolphin will eat 4-
How long do dolphins live?
Dolphin life expectancy is quite long. The maximum age for bottlenose dolphins is between 40 and 50 years. The average age a dolphin can get (the life expectancy) can be calculated from the ASR Annual Survival Rate (the percentage of animals alive at a certain point, that is still alive one year later). For the dolphin population in Sarasota Bay, the ASR has been measured to be about 0.961. This yields a life expectancy of about 25 years. For the population in the Indian/Banana River area, the ASR is between 0.908 and 0.931. This yields a life expectance between 10.3 and 14 years. So the actual life expectancy differs per region. 
Adapted from Dolphin FAQ maintained by Jaap van der Toorn (email@example.com) sources:
 Williams et al, 1990
 S.H Ridgway (1990) The Central Nervous System of the Bottlenose Dolphin, in S. Leatherwood and R.R. Reeves: The Bottlenose Dolphin, pp. 69-
 Th.D. Williams, A.L. Williams and M. Stoskopf (1990) Marine Mammal Anesthesia. In: L.A. Dierauf (ed.): Handbook of Marine Mammal Medicine: Health, Disease and Rehabilitation, pp. 175-
 R.S. Wells and M.D. Scott (1990) Estimating bottlenose dolphin population parameters from individual identification and capture-
 S.L.Hersch, D.K.Odell, E.D.Asper (1990) Bottlenose dolphin mortality patterns in the Indian/Banana River System of Florida, in S. Leatherwood and R.R. Reeves: The Bottlenose Dolphin, pp. 155-