Because that’s not a realistic threat. People send that shit through the mail (where, surprise, it does get scanned for.) No-one’s been affected by massive outbreaks of human-carried anthrax moved across borders.
Whereas they already have been affected by water-borne invasives.
No-one’s suggesting setting up a Bureau of Seawater Tanker Inspections. Boats are already being checked on the Interstates, the tankers just join the queue.
And all that’s got jack to do with the Precautionary Principle, by the way - the Principle says that in absence of scientific certainty either way (since no-one’s researched invasives in tankers yet AFAIK), the burden of proof is on you to show that shipping seawater sea-to-sea is not harmful. Expense arguments are irrelevant. Potential environmental harm is the only criterion. Which is why I said you need to show that tankers differ somehow from provably harmful bilges. That’s how you show there’ll be no harm. C’mon, the Precautionary Principle is Environmental Science 101 stuff. You might want to get more familiar with it if you’re going to advocate ignoring sensible environmental protections just because it might cost a few bucks.
The ocean is a desert, with its life underground,
And the perfect disguise above.
(I don’t know how everyone missed that… )
The invasive species problem happens because freighters would take on bilge water as ballast, and then pump it out at inopportune times, dumping hitchhikers in novel locations. This is supposedly how zebra mussels got started in the Great Lakes. They spread around the smaller lakes hitching rides now on or in the bilge of small boats that arrive by trailer from infected lakes.
A lot of freighters, too, were in the habit of relieving themselves of oil-contaminated bilge water, thus leaving oil slicks where they ended up. As regulations were tightened, Canada started to find these slicks offshore as the freighters waiting until they thought they were beyond detection before doing a cleansing cycle.
So journeying up and down a coastline into open ports probably does not matter. What’s on the hull and not killed by the journey probably is already there at the destination and does not matter. Coming from a distant and different ecosystem and potentially carrying quantities of unfiltered water from there is grounds for concern.
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