Import cargo volume at the nation's major retail container ports has begun its annual climb toward summer levels but is expected to be largely flat when compared with last year's record high numbers, according to the monthly Global Port Tracker report released today by the National Retail Federation and Hackett Associates.

If Britain votes to leave the European Union, the country's shipping sector faces years of disruption as trade agreements get reworked and currency volatility leads to higher costs at a time when the industry is battling its worst global downturn.

U.S. import volumes, measured in TEUs, have rebounded at West Coast ports so far this year. Imports through the port of Los Angeles increased 36 percent January through February of 2016 and 30 percent through the port of Long Beach, compared with the same time period in 2015, according to findings from Datamyne, which provides web-based international market intelligence.