In an article called “Facing up to falling volumes,” Port Strategy published the following excerpt:

With one eye on declining traffic volumes, Los Angeles and Long Beach are maintaining that the situation is not as bad as it seems. Long Beach is suffering more, with October down by 20% over the previous year.
Port officials blame much of the decline on the switch by California United Terminals, which accounted for about 10% of traffic, to Los Angeles next door. However, the move happened 10 months ago and industry insiders see the explanation as more of an excuse. They say that the real reason is the rickety US economy and that more depressing news is on the way.

Read the rest of the analysis at this Port Strategy link