Seasonal Seas; the effects of the seasons on the world's temperate seas. Grey seals breed and the pups are marooned for weeks until they can swim. Spring heralds the bloom of phytoplankton, providing food for copepods, which, in turn, are prey to vast swarms of jellyfish. Giant kelp grows at a summer rate of a metre a day providing sanctuary for fish and sea otters. Late summer sees Pacific salmon waiting in the open sea, as the water level in their chosen river is too low, and falling prey to a salmon shark. It's early autumn and baby herring create a feeding frenzy for diving auks and rockfish. Pacific white-sided dolphins, when not hunting nocturnally, socialise during the day. As winter arrives herring are hunted by orca, which club the fish by creating waves of pressure with their tails.