Often they do return to the same area. In addition, we have found that released flounder will often stay in the same area for the duration of the summer. That's one reason we release so many, because even when we let a keeper go, we know that often we will be able to recatch him (or one of his big buddies) in the same area later on if we are looking for dinner. Conversely, enough people fishin' one area and keeping everything they catch will clean an area out in short order leaving nothing for later days.
From what I've read and heard from Marine Biologists, when they leave the bay they go to areas of the continental shelf offshore to spawn ...that's an east/west migration from November - January/March.
The commercial dredgers know where they're at out there and how to dig them up and they watch how many they get in January, or they could use up their whole annual allotment getting the big spawners in January.
That being said, nearly anyone you talk to with a history on the bay will tell you about keeper-sized fish coming up in nets and pots in the bay right through the winter. So obviously some of them don't leave, they just aren't caught.
Then the larval fish are moved by wind & tide into the bays and estuaries where they spend the first years of their lives, until about 7" or so, before they join the migratory schools.
The baby flounder are built to tolerate colder water temperatures, but not too extreme.
During the catching season, from April through October, Kimoslobby is absolutely correct, they don't move too much at all.
We've caught fish on a spot in May, then again in July and then again in August. The exact same fish from the same hole on the same bait. They seem to get acclimated to a spot and then sit there and feed. So that's anther reason we never mind throwing a keeper back. We know he'll still stay put.
And finally for 'return to site' migration season-to-season. The smaller ones seem to have more site-affinity year-to-year (ie: a 12" grows to 15" and comes back) than the larger ones. I haven't noticed anything yet on an 18" growing to 21" and coming back.
I think when they get larger they stay deeper and feed on larger prey as well. There was a great web-site I found not too long ago that detailed the variety of prey items that were found in gut-studies of different sized flounder. The diet changes dramatically and decreases in variables when they get to be doormat size.
As when they're smaller 6" to 12", they'll eat anything opportunistically.
Big help, some help, no help. That's all that I know and those facts are what I use to help guide my flounder fishing demeanor.
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