We've extensively documented that radioactivity from Fukushima is spreading to North America .
More than a year ago, 15 out of 15 bluefin tuna  tested in California waters were contaminated with radioactive cesium from Fukushima.
Bluefin tuna are a wide-ranging fish , which can swim back and forth between Japan and North America in a year:
But what about other types of fish?
Sockeye salmon also have a range spanning all of the way from Japan to Alaska, Canada, Washington and Oregon:
Associated Press reports  that both scientists and native elders in British Columbia say that sockeye numbers have plummeted:
Sockeye salmon returns plunge to historic lows.
Last month, [the Department of Fisheries and Oceans] noted returns for the Skeena River sockeye run were dire.
[Mel Kotyk, North Coast area director for the Department] said department scientists don’t know why the return numbers are so low.... “When they went out to sea they seemed to be very strong and healthy and in good numbers, so we think something happened in the ocean.”
“We’ve never seen anything like this in all these years I’ve done this. I’ve asked the elders and they have never seen anything like this at all.” [said Chief Wilf Adam]
Vancouver News 1130 notes that Alaskan and Russian salmon stocks have crashed as well:
“The sockeye runs way up north in the Skeena are low. The [fish] out of Bristol Bay, Alaska is down 30 to 35 per cent over last year. Russia has got a limited number of fish in the market. They are down about 40 per cent over all their salmon fisheries.”
(Russia's East Coast sits on the Sea of Japan . Indeed, Japan is closer to Russia than to Korea.)
Alaska's Juneau Empire newspaper writes :
We are concerned this hazardous material is hitching a ride on marine life and making its way to Alaska.
Currents of the world’s oceans are complex. But, generally speaking, two surface currents — one from the south, called the Kuroshio, and one from the north, called the Oyashio — meet just off the coast of Japan at about 40 degrees north latitude. The currents merge to form the North Pacific current and surge eastward. Fukushima lies at 37 degrees north latitude. Thousands of miles later, the currents hit an upwelling just off the western coast of the United States and split. One, the Alaska current, turns north up the coast toward British Columbia and Southeast Alaska. The other, the California current, turns south and heads down the western seaboard of the U.S.
The migration patterns of Pacific salmon should also be taken into consideration. In a nutshell, our salmon ride the Alaska current and follow its curve past Sitka, Yakutat, Kodiak and the Aleutian Islands. Most often, it’s the chinook, coho and sockeye salmon migration patterns that range farthest. Chum and pink salmon seem to stay closer to home. Regardless of how far out each salmon species ventures into the Pacific, each fish hitches a ride back to its home rivers and spawning grounds on the North Pacific current, the same one pulling the nuclear waste eastward.
We all know too much exposure to nuclear waste can cause cancer. And many understand that certain chemicals, such as cesium-137 and strontium-9, contained in said waste products can accumulate in fish by being deposited in bones and muscle permanently.
We are concerned our Alaska salmon are being slowly tainted with nuclear waste. We are worried about the impact this waste could have on our resources, and especially the people who consume them.
We urge scientists in Alaska to be proactive about conducting research and monitoring our salmon species.
Similarly, the Canadian Broadcasting Corporation reports  that salmon are migrating through the radioactive plume, but Canadian authorities aren't testing the fish:
[Award-winning  physician and preventative health expert Dr. Erica Frank, MD, MPH]: There are Pacific wild salmon that migrate through the radioactive plumes that have been coming off of Fukushima. Then those fish come back to our shores and we catch them.
CBC Reporter: The Canada Food Inspection Agency says it now relies on Japan for test results concerning radiation.
(American authorities aren't testing fish for radioactivity either .)
Another example - pacific herring - is even more dramatic. Pacific herring is wide-ranging fish, spanning all the way from Japan to Southern California:
Every single pacific herring examined by a biologist in Canada was found to be hemorrhaging blood. As Ene News reports :
SOURCE: Alexandra Morton via Vancouver 24 hrs 
Cover of Vancouver 24 hrs (SOURCE: Alexandra Morton )
The Globe and Mail , Aug 13, 2013 (Emphasis Added): Independent fisheries scientist Alexandra Morton  is raising concerns about a disease she says is spreading through Pacific herring causing fish to hemorrhage. [...] “Two days ago I did a beach seine on Malcolm Island [near Port McNeill on northern Vancouver Island] and I got approximately 100 of these little herring and they were not only bleeding from their fins, but their bellies, their chins, their eyeballs. [...] “It was 100 per cent … I couldn’t find any that weren’t bleeding to some degree. And they were schooling with young sockeye [salmon] ”
Sun News, Aug 12, 2013: [Morton] dragged up several hundred of the fish this past weekend and found the apparent infection had spread – instead of their usual silver colour the fish had eyes, tails, underbellies, gills and faces plastered with the sickly red colour. “I have never seen fish that looked this bad,” [...] In June, the affected fish were only found in eastern Johnstone Strait, but have since spread to Alert Bay and Sointula, she said.
Canada.com , Aug 16, 2013: Morton [...] pulled up a net of about 100 herring near Sointula and found they were all bleeding. “It was pretty shocking to see,” said Morton [...] Herring school with small sockeye salmon  and are also eaten by chinook and coho.
‘Response’ from Canadian Government
Vancouver 24 hrs , Aug 11, 2013: [Morton] says Fisheries and Oceans Canada [FOC] is ignoring the problem. [...] According to emails from FOC, the federal authority had asked the marine biologist to send in 20 to 30 herring in September 2011, saying that would be “more than sufficient for the lab to look for clinical signs of disease and provide sufficient diagnostics.” She did, and hasn’t heard back since. [...] FOC officials did not respond to a request for comment by the 24 hours presstime.
Canada.com , Aug 16, 2013: Fisheries and Oceans Canada is trying to confirm reports from an independent biologist that herring around northern Vancouver Island have a disease that is causing bleeding from their gills, bellies and eyeballs. [...] Arlene Tompkins of DFO’s [Department of Fisheries and Oceans'] salmon assessment section said staff in the Port Hardy area have not found bleeding herring. “We are trying to retrieve samples, but [Monday] we were not successful because of heavy fog,” she said. “We haven’t had any other reports of fish kills or die-offs [see salmon report below].” Tompkins has seen photographs provided by Morton [...]
Sea lions will eat a lot of different prey items: octopus, squid, small sharks. But their bread and butter is herring ....
Given that pacific herring are suffering severe disease, it is worth asking whether the "unusual mortality event"  of Southern California sea lions is connected.
The bottom line - as nuclear experts said 4 days  after the Japanese earthquake and tsunami - is that we all need to demand that fish be tested for radiation.
Notes: Apologists for reckless nuclear policy claim that low-level radiation is safe. Scientists have thoroughly debunked those claims .
We are not implying that all of the drop off in salmon populations is due to radiation. There may be many other factors, as well. Also, while tuna may in fact swim all of the way from Japan to North America, and salmon may swim hundreds or thousands of miles, no single salmon or herring swims all the way between Asia and the Americas.