It seems to be fairly easy to determine within a range of time just when the colonization and settlement of the nation of Zarahemla reached extensively beyond the Sidon Valley as the scripture below will indicate. The Sidon or Magdalena Valley is a wide, large, and long valley. It has room for many cities and many people. But surely there must have been some colonization and use of the land outside of the Sidon Valley. Yet, it would seem that the primary discernable colonization outside of this main and central valley occurred after the coming of the Nephites. Whether the Mulekites had settled in large communities beyond the Sidon Valley seems unlikely and is highly questionable as this Book of Mormon scriptual reference seems to imply. It is not known what settlements flowed into the western valley, eastern plains, or southern highlands before the time when the first Mosiah brought the Nephites into the land. Even then, is seems that any real sizable sustained efforts to build up the land outside of the central valley appears to have happened in conjunction with the return of the Land of Lehi-Nephi peoples of Alma and Limhi. By the time of Alma the younger and the sons of Mosiah II persecutions of the church (about 100-92 BC) major settlements had been established beyond the main valley.
We must leave the question of when Melek and Aaron where establish and just conclude that they where and in order likely before some of the next settlements discussed, but not necessarily so. It just seems to be the logical progression that there was likely some expansion beyond the valley of Zarahemla prior to the time when Alma and Limhi and their people arrived back in the land of Zarahemla since Zeniff's departure. Now as to the northeast, where the river exits into the sea, it is more than likely that the Mulekites used this portion of the land if not for anything more than passage from and to the sea. But whether this was just temporary seasonal usages, similar to the usage of the Jaredites for fishing. or if it were of a permenant nature remains a question. The Book of Mormon never does place any emphasis that the people were prone to fishing and harvesting the ocean. That has to be an assumption. Certainly the fact that the Mulekites arrived by ship would suggest that they would have had, made and kept some type of water craft and had various degrees of access to the river and sea. The Book of Mormon never uses the word 'birds' and only uses the word 'fowls' in Christ's teachings and in the Book of Ether in reference to the Jaredites. The same is true of the word 'fish.' But certainly there where birds and they were used, and certainly there were fish and they were used. The Savior didn't have to explain to the people what he was talking about in reference to fish and fishing. It is just one of those things which was so common place that it did not make it into the history books. And so it was with sea craft. Hagoth was not the first to build a sea craft, he just built one of a very large size to sail the ocean that was significantly different.