Trabitha, being pregnant is one of the times you may want to limit your intake of species that store mercury.
http://www.epa.gov/fishadvisories/advice/
The fact is we can't measure the amount of mercury or other pollutants in the fish we eat daily. So, when we are
CAUTIONED on eating certain fish more than a couple of times a week. They err on the side of caution.
Having read what I have read from both sides of the argument. I no longer factor mercury threat in my diet.
In a survival situation, I don't believe anyone should avoid a nutrient rich food like Tuna.
Besides, a much bigger threat from Mercury comes from the dental industry. At least from what I have read...