Streamlined bodies, webbed feet, underwater agility and sharp instincts ensure Eurasian otters are apex predators in riverine, wetland and coastal habitats – but this role does not come naturally. Otter cubs, which average two or three to a litter, rely on their mother for their first nine to 15 months. Dog otters, meanwhile, lead a more solitary life, not involving childcare at all. Born blind, the cubs open their eyes at four weeks, and remain protected in the natal holt until about eight weeks. By 12 weeks they are weaned and ready for their first swimming lesson when, despite squeaks of protest, they are carried from the holt and fully immersed. They find floating easy, thanks to a double-layered covering of soft, fluffy fur that traps air. Swimming takes practise,…