Big Blue Week continues as Hugh Fearnley-Whittingstall takes his daily dip into the UK's extraordinary marine life. Hugh and the team are celebrating the arrival of our sharks. During summer over 30 species are found in the UK - including blue sharks, smoothhounds and basking sharks - so where and how can they be spotted? Lindsey Chapman is on the hunt for mermaids' purses - shark-egg cases that are washed up on our shore. Can she also find live shark embryos in amongst Devon's seaweed? Wildlife photographer Richard Taylor-Jones focuses his camera on surprising shark bait: plankton. These microscopic organisms bring hungry basking sharks to the UK. Using a new lens, Richard brings this extraordinary micro-world into sharp focus, but first he has to board a ferry bound for France - the channel's passenger boats have been collecting plankton samples for scientists at SAHFOS for over 70 years. Richard finds out why. Meanwhile, Hugh is trying to make up for a childhood misdemeanour. As a young boy, he fished for sharks off Cornwall's coast. Now, older and wiser, he hopes to meet the blue shark population under very different circumstances. Will he get chance to make amends?