The Shards are said to have once been another small continent, or a land bridge between the eastern and western main continents. At some point, a massive disaster crumbled this continent into large islands, thus creating the shards. Some say Chaac shattered the continent in his rampage many centuries ago, while others say a massive earthquake caused the destruction.
Weather in the Shards can be intense, with high winds, strong currents, and large sea predators awaiting any clumsy sailors who may fall into the churning waters. Sailing through the Shards takes a high amount of skill and patience and most ships just do not make it through.
For shipping routes, they tend to follow paths just north of the Shards, and then follow the coast lines of the main continents when required.