Port Hedland shipped 30.1 million tonnes of iron ore to China last month, down from 31.2Mt in March.
The figure is the lowest level since November last year, with exports to most other key markets also dropping off.
All up the key export terminal shipped 35.3Mt of iron ore for the month, this was still up 500,000t or 2% on the same time last year.
The mixed result came as the iron ore price continued to stabilise, rising 2.4% to $US57.55 ($A73.40) a tonne.
In other key metrics total throughput at the port came in at 36Mt, an increase of 500,000t or 1% on the same time last year while imports were down 19% to 151,000t.
Port Hedland is the main export terminal for BHP Billiton, Fortescue Metals Group and a host of smaller miners, including Atlas Iron.
Elsewhere in the Pilbara the Port of Dampier delivered total throughput of 13.1Mt for April, a decrease of 1.4Mt or 10% from last year.
Imports rose 24,000t or 44% to 78,000t.
