I am genuinely curious about the risk calculus of the remaining 19 percent of firms. Bulk carriers look like the only ones who haven't gone to nearly zero relative to their prior values, indicating that they're a lot less elastic in what they can do, but the fuel costs are, at worst, in the six figures, and the potential losses are well into the eight figure range. 

I would not rate the risk of escalation sufficient to sink an unaffiliated cargo ship below one percent, but more than half of bulk carriers appear to have made that decision, relative to tiny fractions of gas carriers and zero percent of chemical tankers. Nearly 100 percent of ships still passing through are heading eastbound, which probably plays some role here.

This graph is from March 1, so I'm sure things have changed since.