Steve, welcome to the posting portion of the forum! We're glad you jumped in.

If you've been lurking for very long, I'd bet you already know the answer to your question and are looking more for confirmation.

First, if there are trespassers, any advice given could be wrong without knowing what damage they may be doing to the pond dynamics.

That said, it sounds from the excellent description you provided you probably are overpopulated with LMB and need to remove any Bass (LMB) that look skinny with big eyes/head compared to their body along with a lot of 10-14 in LMB...I'd say around 150-200 given your pond size.

The turtles can go or stay, your choice. As Mr Lusk like to say, any fish a turtle can catch, deserved to be eaten (or something to that effect).

Other than the LMB appearing to fit the classic overpopulation scenario, it sounds like everything else is in good shape. I'd bet removing the LMB as suggested this spring will get your pond back on track in a few years or less.

As for what to remove in the following years will depend on how well the removal goes and what your creel survey let you get a picture of. Keep records of sizes caught to see if any size class is missing. Regardless, plan on removing around 50 to 100 bass per year every year to help maintain your balance one it's restored.