Unfortunately that one eventually became corrupted, perhaps because I was trying to nest a portal within another nested portal in one of my layouts.
That will not and cannot corrupt your file. It's just something that you can't do. When you try, you just end up with one portal placed on top of the other instead of nested inside. Something else damaged your file.
What you are describing should be something that can readily be handled by a series of one to many relattionships as you go from lake to net/trap to the "catches" data.
4 different layouts does not sound like such a bad idea, but tabs are also possible if you set up a "Master detail" pair of portals you could, for example have a portal that lists each net placed in a given lake. When you click a row in this portal, a second portal in the same tab updates to list all the catch records for that net location.
I must warn you, however, that this a more complex design and one that requires scripting to set up. Here's a link on the concept: Need layout solution for nested portals...
And you might also be able to put your data for minnow traps and nets in the same table and use the same Catch table for both traps and nets. Basically, you'd simply treat a minnow trap as a different kind of "net" placed in the lake.