When we want species data from deeper than 1 meter we do a 100 m transect line or dive points (which are basically the same as wading points, only done with the help of dive gear). Wading cannot be done in deeper than 1 meter because at that depth we cannot see the bottom substrate or the species that well anymore and there is a big chance for losing valuable information. With drop-videos we can do mapping in deeper areas but we cannot get accurate species information with species coverage.
Diving is time consuming but it is also our most valuable method. Usually we choose the dive site carefully in advance at the office and on the field we just drive the boat to the right spot and start putting the 100 m transect line down. Often the other end of the transect is put on a shore of an island and the other end goes straight out from the shore. We mark both ends of the transect with a buoy so that the divers can find it easily and so that it is easy to see that there is something going on in the water and that people driving boats should be aware. We of course also have a dive flag on the boat when divers are down.
We have to have a team of three when diving. We can choose if two divers go down and one dive supervisor stays on the boat or if one diver goes down with a rope and two supervisors stay on the boat and communicate with the diver by giving signals with the rope. The team of three is very important for safety because usually two persons are needed for pulling one person up to the boat from the sea and for transporting the victim to the shore.
Written by Suvi Saarnio, Metsähallitus