A report written in 1622 stated that the fisheries had been moribund for many years due to the poverty of the Paravars; it is uncertain as to what period this refers or the cause of the poverty. Xavier had recorded that the oyster beds seemed to have an uneven cyclical pattern, with a few good years of production alternating with a rather longer period of poor production. Similarly, around 1490 Ahmad ibn Mājid wrote that the fisheries "flourish in some years, but appear dead in others." One contemporary explanation for these changes was that the beds became covered by the shifting sea sands. A study of the period 1666–1916 showed that while the good harvests did tend to alternate between the Indian and the Sri Lankan sides of the Gulf, the latter side was more than twice as productive.