Believe what you want, but there is zero (0) data to support the doomsday predictions so far. All, yes ALL, of the graphics I've seen regarding the "plume" are actually NOAA images that either modeled the tsunami wave action through the Pacific or modeled the potential path of the tsunami debris. Not a single one is based on samples, data or anything having to do with radiation.
The Fukushima site itself is a horrible problem to be sure and we're far from being out of the woods there. But there is no radioactive plume that we know of - except in our imaginations and on the pages of oodles of "look at me! I get $$ from page hits!" alarmist "news" sites and the infoblogs that use them as "sources."
Bluefin Tuna is showing higher levels of radiation. I also heard that plankton is some places is, too. This IS a problem. Its not the end of the world, oh-my-god-the-fisheries-collapse-is-happening situation its being made out to be in the social media idiot storm.
I work with the scientists who keep track of this stuff and the biggest problem right now is that there is very little hard data being collected. The Pacific is HUGE and its very expensive to get any kind of indicative samples much less track that number of remote sampling sites over time. All we have are a few fish samples, models of ocean currents - which aren't particularly reliable - and the overactive imaginations of a public that still remembers the nuclear scare of the cold war.
Panic if you want. Its as good an imaginary reason to panic as the many others available to us. Just understand that the panic is based on nothing except hype generated in a vacuum of real information.