Mackerel enter Lillebælt in the period from July to September. It's best to fish from a boat or at a deep water harbour, e.g. Middelfart or Fredericia. You can catch mackerel from land if you concentrate on finding coasts where there is deep water very close to the shore. The mackerel is a very strong fighter. Pound for pound, it is probably the strongest salt water fish in Northern waters. Most mackerel weigh 0.3-0.8 kg, although there are some larger fish. Fishing using a sea trout spinner rod is great sport.
You can catch mackerel at any time of day, especially from a boat. However, by tradition, mackerel fishing is best in the morning where the fish are sometimes seen to hunt at the surface. Cast your line into the perimeter of the shoal. You could try using a spinning rod and a sliding float with a bunch of herring on a single hook as bait. Experiment a little to find the correct distance between float and hook. You will often find mackerel swimming at some depth.