My little Hummingbird depth sounder is fitted with a water temperature sensor.
I fill a log each time I go out and note the water temperature as well as other details , like broken gear that needs attention..
The warm current that flows northward up the east coast of Japan bumps into the southward flowing just off where I live.
Rich fishing grounds.
They say that it's not worth fishing after the end of August because the southward current takes over and the water cools.
Does it what!
I saw water temps drop from 26 degrees to 15 degrees in two days. Will get down to 12 or 11 which is good for the scallops, oysters and kelp.
But makes for cold winter sailing.

gary