Oystercatchers suddenly disappeared

Hi,

We’ve been coming,monthly, for the last few seasons to the same caravan site on the coast of north Antrim, dominated by the beautiful  sound and sight of oystercatchers.Suddenly, since our previous visit a month ago, they have disappeared.All of them. Why? 
Last month, for the first time, we saw men picking some kind of shellfish off the rocks and filling sacks by the dozen. Is this a coincidence?