If you can replace it should it fail, it may be simpler to try the experiment than to pre-emptively source something more specialized.
Unless there is a manufacturing flaw, the problem may be more sealing to the cable jacket than the cable itself leaking. You may have similar problems if you have anywhere that cables exit the hull, (especially if the bare wires are ultimately wetted by design, though things like wetted motors are probably reserved for fresh water)
You could consider pressurizing the housing on the surface end of the cable as well as the hull to greater than the pressure at depth (though beware the explosion hazard if you use materials not rated for this)
It's not entirely clear what you are doing though - I don't think USB is rated for 30 meters (ie, to the surface), so presumably both ends of the cable are on the submerged device. In that case, can you cut the connector off one end, cover the cable with some hose, and solder the wires back onto a compatible connector or directly to the PCB?
Not quite sure what you mean by the bio issue, but if you are concerned about contaminating the non-exchanged volume of water in something like a giant aquarium tank, covering the cable in hose made of a known-suitable material would seem wise. Or perhaps you just mean that there aren't any barnacles to grow on it?