In this clip, Iolo Williams and Mandy Mcmath - Senior Marine Ecologist from the CCW visit Bardsey Island to look at the island's grey seal population.
Centuries of hunting and exploitation reduced the UK population of grey seals to a mere 500 individuals by the 1970s.
In 1970, a new ban on culling during the breeding season, and successful anti-sealing campaigns, allowed the species to gradually recover.
Now there are about 125,000 grey seals around the UK, making up nearly 40% of the world's population and around 6,000 of these are found in Welsh waters making it a very important stronghold.
Many people struggle to tell our two native species of seal apart but it's relatively straight forward, providing you can get close enough.
Greys are much bigger seals and have a prominent Roman nose. Their Latin name ''Halichoerus grypus" literally means "hooked-nosed sea pig" which is very appropriate.
Common seals are generally more 'puppy like' in their facial appearance and have joined up nostrils, unlike greys whose nostrils are set parallel to one another.
Large bull (male) seals can grow very large and their curious nature will often bring them into close proximity with surfers in Wales who to a seal, probably resemble, less able seals and pose no threat.
Grey seals tend to prefer rocky outcrops and quiet coves where they rest, mate, give birth and moult. The Irish Sea provides a good variety of fish, shellfish, squid and octopus for them to eat.
Some of the best places in Wales to see grey seals are on on our offshore islands such as Ramsey, Skomer, Skokholm, Grassholm, the Tudwal Islands and Bardsey Island, probably because they're quiet and away from people.
From autumn onwards, you can see new seal pups spending their first 3-5 weeks of life on beaches from September to December. In those few weeks they will double in size and lose their white fur before being left to fend for themselves.
Keep your distance if you stumble across a mother with pup as they can be easily spooked. If you suspect a pup has been abandoned you can call a local wildlife group or RSPCA for advice.
Having weaned the pups, the females are ready to mate almost immediately with the males who invariably stay close by, during the pupping season keeping an eye on the females.
Try one of the walks from Derek's latest walking series on BBC One Wales.
Find out about the wildlife you can find on your doorstep.