The first quarter ended slowly for container-lines operating on U.S.-inbound routes, with a 2% increase in March bringing the quarter to an 8% rise on a year earlier. New duties on steel and aluminum only took effect at month end, while wider tariffs on Chinese goods being considered by the Trump administration could change the picture significantly by June.

The fastest growing shippers in the quarter were Orient Overseas (whose volumes were 27% higher) and COSCO Shipping (up 19%) ahead of their merger. Full regulatory approval by U.S. authorities isn’t guaranteed due to a CFIUS r...