Best thing you can do for your tree is

Don't Panic.

Seriously. Needles turn brown. They don't live forever. Your description sounds like normal aging process to me. Older needles, on the insides of the branches, will turn brown and fall off when they reach the end of their life span. A 9 yr old tree will be losing older needles.

Excess shading will also cause interior needles to turn brown and fall off. If the tree is dense and bushy, or up against a building, or under other trees, the inside needles won't get any sun, and there's no need for needles that don't get sun.

I'm not aware of any plagues visiting the shore pines this year although of course there are bugs that eat them. It's a native tree after all, which means that the native bugs feed on it. But not to the point of causing problems unless the tree is sick from something else.

If the drainage is poor, then the tree could be suffering from root rot, and we did get way lots of rain this winter and things aren't drying out. But if it's been in for 9 years you probably would have noticed something before, like sitting water in the winter time.

But just because a few branches are dropping needles doesn't mean the tree's dying! You could do more damage by spraying or fertilizing or watering than by just leaving it alone until it's clear that there really is a problem and exactly what it is. Scattershot approaches rarely help.

Posting photos would help with diagnosis if there really is a problem, or take samples to a real nursery for someone knowledgeable to look at. Not a big box store.