Why did the men set sail for Blue Crab Run?

The men set sail for Blue Crab Run to collect salt.

"The place is near the headwaters of the Timucuan, some twenty-two nautical miles, I should judge, up that tributary. It is called by an Indian word meaning Blue Crab Pool. The pool itself is crystal clear, like the Silver Springs. I thought it surrounded by a white beach, but then discovered that what I thought sand was pure salt. It was quite unbelievable. In this pool there were blue crabs, such as are found only in the ocean, yet the pool is many miles inland, and two hundred miles from the mouth of the St. John, or May."