Ship losses in the Baltic Sea

[MechFO]

After taking Leningrad the Baltic Sea has been a German lake for over a year but I'm still constantly losing cargo ships. This is due to Neutral Sea hexes causing attrition.

I realise that Hanko is still Soviet but even they must be mainly concerned with growing potatoes by now.

I suggest that capturing Leningard creates some naval interdiction accross much of the baltic to reduce the attrition or, if this is not possible, that ship production is increased once Leningrad falls.