That’s quite some range re the 5000 nautical miles spec. How much fuel does it need to carry achieve that range?
My understanding is that things like fishing boats get real shitty mileage, like 9 MPG on diesel, and I can’t imagine that a privately built sub would get much better, so figure on 500 - 600 gallons of fuel.
A sub would not be fighting wave action or wind and could take advantage of any prevailing ocean currents. As an example, here is what it looks like off the coast of Brazil.
Note that the subs are “semi-subs,” which I take to mean they can’t go very far down, so wind and wave action could still be a factor, I’d imagine. I’d also imagine that fishing boats (as well as fish) would try to take advantage of any surface currents that they could.
Although Nazis weren’t know for Andean drug smuggling, I did dig up the fact that a 200ft long type IX U boat had a fuel capacity of around 200 tons and a range of ~10,000 miles.
200 tons is roughly 6500 gallons.
With 7 tons of coke on board, I’d say it would need a grand total of…no gallons. Hook the prop up to a set of bike pedals, stick a straw in the “captain’s” nose, and your biggest problem will be keeping the wake manageable. 
From the information and the photos I think those vessels are not really “submarine” at all, just that they have very low freeboard - profile above water - in order to avoid radar detection. It seems to me the “semi-sub” name is just marketing hype by the DEA and by unthinking reporters.
I challenge the accuracy of that Coast Guard information.
Just like I challenge the accuracy of “street value” reported on captured drugs.
Didn’t the US sink vast amounts of research into submarine detection, during the Cold War? Sure, these things wouldn’t show up at a casual glance, but you’d think they’d be a lot easier to find than Soviet missile subs.
Yep, and the Navy and the Air Force are the ones with this technology, and they won’t give it up to any little Coast Guard guys if they can help it.
Well, duh, if they did that, the CIA would have to work harder to get the drugs into the country. 
They have snorkle tubes so I would guess they are at or just below the surface and operate kinda like the whaleback boats did on the great lakes. The idea is to drive through or under a wave instead of riding above it. I would also guess that you have to be right on top of them with radar to detect them.
Those do not look like snorkels to me but rather like good old fashioned cowl vents. In any case, I do not think they are really submersible to any degree (except when they sink). I think they just have a very low profile.