The reports blamed a weakening US economy.
The tracker report includes throughput at the key ports of Los Angeles/Long Beach, Houston, Savannah, Charleston, Oakland, Tacoma, Seattle, New York/New Jersey and Hampton Roads.
These ports in total handled 1.46 million twenty-foot equivalent units (TEUs) in October which was a 1.3% drop from the previous month's levels and a 3.5% dip from the 1.51 million TEUs handled in October last year.
November levels also saw a 3.5% dip year-on-year as the falling traffic worsens from the 1.4% dip year-on-year in August and a subsequent 1.9% dip year-on-year in September.
Analysts say retailers are apparently bracing themselves for a 'slower' Christmas.
Inventories and supply stockpiles have thus been downsized or 'managed carefully' to avoid overstocking and possible unplanned discounts, said reports.