Bf 109 with ski undercarriage

[Seaplanes]

Being no Bf 109 specialist at all, I turn to you for further info. In the little litterature I have on this aircraft, I have only found that skis were only experimentally fitted to the Bf 109E model. However, during examination of some intelligence material, I found the following related to II./J.G.5 in Alakurtti in Northern Finland on 06.01.1943:
The unit reported a strength of 23 Bf 109F-4 of which 17 were serviceable. The 6 unserviceable aircraft were W.Nr. 8103, 8122 and 10252 being fitted with skiis, W.Nr. 10128 engine change, 13074 changing wings and 13138 for special tests.
In addition the unit had 2 Bf 109G-2 of which 1 was serviceable.
W.Nr. 13904 was unserviceable due to special tests.
This is the first time I have seen evidence that Bf 109 was used operationally with ski undercarriage.
Can anyone elaborate.