| Walrus - Two Tonne Tusker: Natural World | 8/10. Sivuqaq is an 18-year-old, larger than life pacific walrus. Reproduction scientist Holley Muraco is taking on the biggest challenge of her life - trying to help him become a dad. [AD,S,SL] | Mon, Nov 27, 2:20 am | BBC FOUR | 60 mins |