And if I can't trap and fish while they cook, not a good spot. There are some of us that klnows the RNG hate us so grinding in specific waters is not worth the time without bait. Cooking traps long enough to improve rare crabs and lobster catches is not smart play for a quester. Pretty sure the vendors that keep stocked of hundereds of crab and lobster aren't long cooking traps in some dark corner of Shame.
No they aren't, that's kind of the point; if you don't care about Rare and Legendary Crustaceans it really, really doesn't matter where you lay the traps. I just put a row of 5x10 down in deep sea Trammel, then move my boat back over the top of the traps so I can pull them all up through the deck. If you're filling quests, you don't have to be in danger at all.
If you're after Dungeon Fish, you can indeed do it in Shame. Leave a row of 2x traps on both sides of the banks and along the bridge. Then fish 5 or more spots along it, by the time you're done at the 5th the 1st has reset and you can keep the permanent fishing going. Just move the odd Mud Elemental away. The collapsed bridge in Underworld just north of the entrance has no spawn at all, and you can teleport onto the broken supports to fish different parts of the river.
However combining the two slows down overall production rate, as you have to break from fishing to lay traps, and break from planting traps to start fishing again. And a trap also works the same spot as the rod, so you "fish out" the spot faster with 2 things drawing on it, thus splitting the total yield. It's more efficient to devote yourself to one or the other, and build your total stocks up that way.
Fish Pies factor. The pies I perfer to keep on hand are the easy areas to catch rares. Cost and easy travel to the NPC vendor make pies not worth the effort. Care less about rare catches most times. S**t happens at times so why not make pies
Fish steaks weigh much, much less than either the pies or the original fish, and will only take one Bag of Sending charge to send the lot to the bank. Fish steaks also are used for City Loyalty, so when I've been out chasing the Legendary I just made steaks of the lot, and pie them later if I want any.
But back to the main question; Ilshenar also doesn't have dungeon fish in it's waters because it's not on the Dungeon server. Open UOAM or UOCartographer or UOMapper and you'll see it's not on the same hardware as even it's Mushroom Cave. It's just how the game is set up behind the scenes. They could change it so the waters spawn Dungeon Fish, but why bother? It wouldn't fit the in game lore, the design of dungeon fish, or the hardware standards...