First, on today's article, let me say that I'm completely persuaded by the geological assessment which concludes land silted up below the present[ly-believed-to-be] site of Betsaida, a spot called "et-Tell". This happened elsewhere in antiquity, as with Macedonia's capital Pella, and the harbor of Miletus, near Ephesus. In each case, the town's prominence declined as its shoreline got farther and farther away. So it makes perfect sense, for the two competing candidates in question, that the northernmost site was the eldest, and the southernmost would have replaced it. But how soon replaced it? And how much so? In all ways, immediately? No.
To compare: Alexander's successor Cassander moved the Macedonian fleet to Thessalonica, a city he must've founded partly for that purpose, which tells us that Pella's harbor had probably begun silting up prior to 314 314 BC. However, no Macedonian King is recorded as [possibly?] taking up residence in Thessalonica until Philip V, or his successor Perseus, about a hundred to 140 years later. Point: in a situation like this, the old town doesn't entirely dry up overnight. Pun, I guess, intended.
Obviously the harbor activity moves on about as quickly as harboring becomes crowded, or difficult. However, most of the socio-political, economic and cultural-religious infrastructure (which had grown up slowly around the harbor, over many years) would naturally be far too invested (and very likely too cash-strapped, due to a gradually dwindling population) to simply move right on downstream. Besides, ancient land didn't just go up on the MLS for perusal by realtors. Land was either seized or handed over between business associates, the latter mostly by inheritance. Point: shipbuilders might have moved on sooner than others, but upstream pub [sic] owners and innkeepers had no better option than to ride their diminishing returns all the way into obscurity. Yes, their grandchildren were being doomed to a much smaller inheritance, but they'd keep the roof and the locks for as long as they beat open road. In ancient business, exponentially moreso than today, present needs necessarily trump.
In its turn, the downstream town would have to be settled entirely 'from scratch'. Whatever lord there was of the land would determine a time at which newly silted up territory had become suitable for building. That lord would decide whether and when to run out the squatters, and to whom he might parcel out the (literally) new lands. Again, this shows the inhabitants of the old town were in no hurry to move on. If the King/Tetrarch of their day had some reason to favor them, they could move when he deigned fit and not earlier. But if they had no favor from him, they wouldn't likely risk everything (however dwindling) for the promise of nothing.
Conclusion: In the case of the present controversy, the full replacement of one fishing village by another, more downstream, didn't happen overnight. Therefore, I suggest my TWO questions, as promised above:
(1) When did the harbor activity begin moving south?At the moment, it seems to me that the question of what these towns might have been called at some point or another is of less primary importance. But these are just preliminary thoughts. I've got a lot more reading and thinking to do. Your critical feedback is eagerly hoped for, in the comments below...
(2) When did the old town lose prominence to the new?