Lake Michigan Ferry Traffic

What specific traffic was typical on Lake Michigan ferries between Ann Arbor, Pere Marquette/C&O, and GTW in lower Michigan, and CNW, MILW, and SOO in Wisconsin? I'm sure there weren't many empties, but I'd also imagine there wasn't low-revenue traffic either. I'd imagine state-specific produce like berries, cherries, etc., chemicals from Dow in Midland, or other finished goods from Michigan, but I haven't found much written online about this.

1956 carloadings from a 1957 Moody's Manual.
Agricultural Products 7,548 (8.4%), Animal Products 5,955 (6.7%), Mine Products 17,492 (19.6%)-almost 13,000 CL were bituminous coal, Forest Products 12,115 (13.5%), Manufactured/Miscellaneous Products 46,324 (51.8%). It's probably a good bet that very little coal went onto the Lake ferries. The AA did not originate any of that coal, all came from connections. Most of the big coal shipments to the Upper Midwest went out of lake ports Erie, Conneaut, Fairport, Cleveland, Sandusky, Toledo in Lake freighters. So I'm probably not far off in guessing that most of the bit. coal the AA carried terminated at towns on line. Railroad freight rates were based on the value of the goods shipped, so manufactured goods, being a finished product, were charged higher rates than low value raw materials like coal. I suspect that a lot of those manufactured goods were probably related to the auto industry. The AA originated 11% of its tonnage and received the other 89% from connecting roads, and that would include the connecting roads in the Wisconsin and Upper Michigan ports.