According to the figures for June 2017, 33,330 passengers and 5,745 vehicles traveled to Northern Sporades with the ro-ro/ferries operating and passenger ships from the port of Volos.
In July 2017 the numbers increased with the same ships to 67,500 passengers and 11,300 vehicles.
Good and bad. 11,300 vehicles to the islands? Crikey! A conjecturist might have fun with those figures especially the July vehicle numbers.
Take those July 11,300 vehicles and surmise that half (5600 +/-) end up clogging Skiathos. Then assume that of the remaining 5600 vehicles, 2/3 or 3700+/- end up on Skopelos and 1800 +/- get off in Alonissos. That’s a lot of fresh cars to park anywhere they want.
The municipal car park at Skopelos port appears to have space for 260 cars to park “normally” and can probably contain 300+ uncomfortably. The additional space at the passenger/ferry loading area provides for maybe (guessing) another 150 at night after the boats stop running.
But don’t forget that there are many cars belonging to local residents which are on-island year round, plus the astounding rental car/ATV/scooter numbers. And August is just beginning.