Hi Yuu,

The two sentences do not have the same meaning, but they are connected. Let me give you another example using a similar form:

I am teaching English on italki, something that other teachers have been doing for a very long time.

 Let's phrase that another way, to keep the same meaning:

Other teachers have been teaching on italki for a very long time and now I am teaching, too. 

So let's phrase the example sentence you provided in a different way:

People have been diving with no breathing apparatus in order to catch fish since the time people started living by the sea, and in 1990, she moved with her family to Mexico and started to do the same.

So, what the sentence doesn't say is that moving to Mexico actually helped her dive, or gave her any special diving skills. It just means that where she moved to, there was a very long history of diving. 

I hope this helps!

Need help with an English sentence...

The part between ‘ ‘ which I can’t understand.

Does it mean that a long time ago, ever since spear fishers lived by the sea. They weren’t using breathing apparatus to swim. So when she started to do freediving in Mexico, she was already used to diving without using an apparatus?

I can understand this sentence but I just can’t understand why the first one and the second one are the same meaning...

Which part of the first sentence says “she was already used to diving without using an apparatus”?

Thank you for taking a look at this.

It simply means that the activity of freediving is not a new activity in human history; people who fish with spears started freediving a long time ago - as soon as they started living by the sea. This does not mean that SHE was already used to it.