The first shoe of the season is part of a sole. It is very degraded and I expect it is left over from last year.
I had to flip it over to be sure what it was. You can see little perforations around the edge that indicate that it is part of a shoe.
I’m not really sure if it is from an outer sole or an inner sole.
I also came across this, which does seem recent:
And here’s what the beach looks like right now, in one of the less littered areas. It really was a beautiful day.
Photographed April 2, 2015