Lumbering around during the final weeks before delivery is tough for any pregnant mum. Most females adjust their movements to compensate for the extreme physical changes that accompany the later stages of pregnancy. However, no one had been able to find a distinct gait change such as a change in stride length or frequency associated with the latter stages of pregnancy. Intrigued by the ways that newborn dolphins learn to swim after birth, Shawn Noren from the Institute of Marine Science, University of California Santa Cruz, realised that she had the perfect opportunity to find out how pregnancy affects female dolphins. Joining a pod of dolphins at Dolphin Quest, Hawaii, just before two of the females gave birth, Noren analysed the impact of pregnancy on the animals' streamlined shape and mobility. She publishes her discovery that pregnant dolphins are significantly disadvantaged by their burden and adopt a new swimming style (gait) in The Journal of Experimental Biology at http://jeb.biologists.org.
'The pregnant females had huge protrusions where the fetus was sitting towards the back end of the body', says Noren, who donned SCUBA gear and spent a large portion of the final fortnight of the dolphins' pregnancies filming under water as they swam parallel to her camera between their trainers. Noren also filmed the dolphin mothers immediately after their calves were born and at regular intervals until the calves were 2 years old. Comparing the footage before and after delivery, Noren realised that pregnant females were slower. Their top speed was restricted to 3.54 m s, whereas they were able to swim at much higher speeds after giving birth. 'Two to three metres per second is a comfortable speed for most bottlenose dolphins,' says Noren, 'but these pregnant animals did not feel comfortable going beyond that.'
She also measured the animals' girth and calculated their frontal surface area, a
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The Company of Biologists