Hey Vic,

What an interesting question. Let's first talk about the marine mammal part of your question. It's important to remember that mammals use a form of sex called "internal fertilization" to get around the problems of sperm viability in the environment. The penis is inserted into the vagina and only has to survive in the environment of the female reproductive system. This internal fertilization also helps terrestrial mammal sperm from drying out. Aquatic mammals, like dolphins and whales, have folds of skin to create a slit to prevent seawater from entering the female reproductive system. Dolphin and whale penises are also exceptionally long so that the sperm is completely protected from salt water. I would also hazard to guess that, like in humans, the components of seminal fluid also help lengthen the vitality of sperm by providing nourishment and modifying their environment. The female and male reproductive systems in mammals have co-evolved to facilitate sperm survival in the female reproductive tract; pH, viscosity and electrolyte balance in the vagina and uterus are specifically designed to aid in fertilization by prolonging sperm viability.

As far as the survival of sperm in water goes, it's not great. In one study, donated sperm that had a baseline viability of approximately 55% dropped to 5% after being exposed to ultra-pure water for ten seconds.

I hope this answers your question!

Billy.

Verheyen G, Joris H, Crits K, Nagy Z, Tournaye H, and Van Steirteghem A. "Comaprison of different hypo-osmotic swelling solutions to select viable immotile spermatozoa for potential use in intracytoplasmic sperm injection." Human Reproduction Update. 3(3). 1997.

Induction Pack. Atlantic Whale Foundation. Accessed: 6 July 2011. http://www.whalenation.org/downloads_new/induction_pack.pdf