Portuguese people love everything that comes from the sea. Not only fresh, but also dried, like bacalhau, or canned, like sardines.

If you ever visited a Portuguese supermarket you probably have seen the large amount of canned fish and seafood.
Once there were hundreds of canning factories in Portugal, where fresh fish was canned. Now there are not many left, but the work often has not changed. There are some factories where everything is still done by hand, they don't use machines. Well, ok, there are 3 large machines: to cook the fish, to put the lids on the cans, and to sterilize the cans. Many generations of mostly women have been doing this work for decades. Some pieces of vegetable in the can? It's done by hand. Cutting off the sardine's tail to fit the can? Done by hand. Fill the cans with oil or sauce? Done by hand. Wrapping the cans in a piece of paper? Done by hand. And they do it very quickly! 

And really, you can taste it. It's a labour of love. And also because the fish is cooked before canning it. The factories that use a fully automated process cook the fish after canning it, which means the liquids and oil stay in the can. And that gives the fish a totally different, a not very nice, taste.
In this video you can see the process at Conservas Pinhais: https://youtu.be/jpTwHAt0Zxw

Not only sardines are canned, but also tuna, bacalhau, squid, clams: you name it and they can it.
Some factories even have their own shops throughout the country, where you can buy all the canned goodness. If you visit Óbidos, you really want to visit the Comur (Conservas de Murtosa) shop. It's beautifully decorated, loaded with beautiful cans. They even sell cans with years printed on them, they make a nice birthday gift for someone (or for yourself).

And don't worry, the cans are not that old, it really is fresh produce.