Arcticfox,
I would echo Dougie's sentiments. I have also found that when they are spawning they have their minds on other things than food.
If it is cold weather that worries you - fear not. They will seek out comfort and food. So in the winter they will be in shallower water that the sun can penetrate and warm them and the water up a bit. In summer/autumn when the water IS warm, they go out deeper seeking to keep a bit cool. Much like we seek shade on a hot day. They will try and stay at a similar temperature, so lay in the thermoclime.
Wind can also affect the water temperature - the warmer water is in the upper layers and the wind can blow this warmer water across a lake, making the leeward shore warmer than the windward one - back to the old thing about casting into the teeth of a gale (from shore) - you go to the downwind side of the lake, for trout, insects and food get blown there, for pike the warmer water and the smaller fish eating the insects.......so both
In rivers, pike are not trout, they will not readily lie in fast water by my experience, so seek out the slacker spots. Even a bridge piling might provide enough respite for the current to create a slack "hole" that a pike can lay in without burning loads of energy just trying to stay put.
Think: warm water, easy food, easy swimming and a bit of cover. You won't go far wrong.
Don't go trying for them without good strong takle though - I am one of those who thinks anything less than a #9 is not good for the pike. I use nothing less than my #10 Zero Gravity - with the backbone to tame a 100lb+ tarpon it deals with pike very easily, yet a 3lber will still put a good bend in her. I am more concerned with the welfare of the fish than getting a bit more arc in my rod for MY pleasure. I get enjoyment enough out of playing the fish in and then even more from seeing it go away quickly, strongly and without having had to spend many minutes trying to get it able to stay on an even keel - too many people play fish to exhaustion. I think many of these very tired fish that are seen to go back and look OK, actually die later of a heart attack or similar kind of problem later on, maybe the same day, maybe the next day when they try to chase again. The lactic acid build up in their muscles can be toxic to them, hence why they don't waste energy.
There is loads of good information, friendly advice and more on the PFFA website (Pike Fly Fishing Association). Worth taking a look.
Please folks - think of the fish, not just your catching of them. Pike are actually fairly easy to catch on fly once you get into "pike fishing mode" and can read the water like a pike - just like you do for trout or whatever. Same system, different signs.