What predators and threats do the dolphnis you study face?

In the Bahamas, spotted dolphins have to be on the look out for three species of sharks.  The hammerhead shark, the tiger shark and the bull shark.

Their best defense against these sharks is avoidance.  Contrary to popular belief, dolphins do not seek out shark interactions.  If they should be threatened by sharks, however, they can defend themselves with their strong rostrums and powerful flukes.  Also, sharks in this area tend to travel alone, while dolphins travel in groups-anywhere from 3-30 dolphins.  The more dolphins, the more eyes, ears and echolocation to keep an "eye"

How many calves do they have at a time? In a lifetime?

Although there have been reports of dolphins giving birth to twins, they most often give birth to one calf at a time.  When two dolphins are born together, one usually doesn't survive.  They can stay with mom until she gets pregnant again, between 3-5 years.