From what I can find, you're in no danger.
As you noted, King mackerel is the dangerous variety, as noted
in this Texas Department of Health news release in 1997:
"The advisory recommends not eating king mackerel longer than 43
inches. It limits consumption of king mackerel measuring from 37
to 43 inches in length to one eight-ounce serving per week for
adults and one per month for children and females of childbearing
age. The advisory does not restrict consumption of king mackerel
under 37 inches."
"The advisory does not apply to canned mackerel, a different
species of mackerel."
Likewise, this page from BabyCenter.com notes the following, in
addressing the diets of pregnant women:
"According to the FDA/ EPA guidelines, you should also limit
yourself to 12 ounces a week (about two servings) of canned
"light" tuna and other cooked fish. Once again, our
recommendations are more protective ? eat fewer than 8 ounces
a week of canned "light" tuna. And you should completely
avoid shark, swordfish, king mackerel, and tilefish (also
called golden or white snapper), tuna steak (fresh or frozen),
orange roughy, Spanish mackerel, marlin, and grouper because
these fish are at the top of the food chain and contain the
highest levels of mercury."
"There are plenty of other tasty varieties ? salmon, rainbow
trout, and canned mackerel, for instance ? that contain low
levels of mercury and are high in healthy fats. The FDA
considers these fish safe for pregnant women to eat twice a
This page on NutraJoint notes that the variety of mackerel
which is canned is Pacific jack mackerel (also called horse
This summary of a 2004 study by the Institute of Food
Technologists notes that, when canned tuna, salmon and
mackerel were tested, mackerel had a relatively low
concentration of mercury:
"Mean mercury concentration in tuna, salmon, and mackerel
were 188, 45, and 55 ppb, respectively."
The full study is available in this document file:
Additional information may be found from further exploration
of the links provided above, as well as those resulting from
the Google searches outlined below.
Searches done, via Google:
mercury "king mackerel" "canned mackerel"
mercury ppb fda "canned mackerel"