I am by far not an expert on the matter, but what I have been told is they like the water at 50 degrees. Merwin is a reservoir with a lot of water entering and leaving the lake every day (10000 CFPS) so I am not sure how that affects the water temperature at different depths I know some lakes (turn over) in the winter and summer, cold on top warmer down low in the winter and warm on top cooler down low in the summer but they don't have that kind of flow. To say they are all down deep? I don't know but I doubt it. The one we caught was only 10-15 feet deep. The surface temp was 43 degrees. And in areas that we couldn't fish due to wind we were marking fish all over with the bulk of them 15-40 and then a bunch on the bottom. March and April last year (my first attempts at fishing Merwin) I watched a lot of fish caught flat lining gear less than 10 feet deep. Later in the summer I still saw gear on top early in the morning but later in the day dropping down. Everyone seems to have different theory's and methods. I wouldn't expect things to pick up for a few months yet.