SEASONAL CHANGES

Fish movements take place in daily and seasonal patterns. Daily movements are primarily triggered by changes in light intensity, weather, and feeding habits. For example, a fish may occupy one location when it is inactive and resting, and make daily migrations to another location to feed.

Permanent changes in location usually happen over a number of years and most often are a result of fish populations adapting to a slowly changing environment. The seasonal change in location is usually the most profound, easiest to recognize, and has the most effect on how and where we catch fish.

Spawning runs are the most obvious example of the effects of seasonal change on fish biology. Triggered by seasonal changes in the length of days and water temperature, the changes in fish behavior are obvious even to the non-angler at spawning time.

However, in any fishing situation we must consider the seasonal influence on the predator/prey relationship, water temperature, water clarity, oxygen levels, and fish biology of the particular fish in the particular body of water.

Water temperature is the most obvious manifestation of seasonal change, and to a large degree controls the processes of all aquatic environments. All bodies of water generally warm up in spring and stabilize for the midsummer period. Fall brings a general cooling trend ending in a period of turmoil when waters of different temperatures mix and homogenize before stabilizing for a period of cold and possibly frozen water.

Within this general trend, the variables are endless: latitude, lake or river type, local weather, water clarity, and a number of other factors influence the annual cycle. Each species of fish responds to seasonal changes differently.

For example, in Canadian oligotrophic lakes the lake trout may spawn during the full moon in October while the smallmouth bass are eight months away from spawning in completely different areas of the lake. Largemouth bass in two similar lakes may spawn four months apart if one lake is in Georgia and the other in Quebec.

In the spring, lake trout may feed mainly on seasonal shallow-water insect hatches or perch holding on shallow-water structure. As the lake is only beginning to warm, this cold-water predator has unrestricted access to shallow water. As summer progresses, thermal stratification forces lake trout into deep water. The diet of these fish changes to deep cold-water baitfish such as smelt. Access to the perch inhabiting the shallows is obstructed by the barrier of water temperature.

In the summer, warm water and stable weather combine to attract walleyes and smallmouth bass to shoals with shallow slopes in natural lakes. These slow tapers provide maximum habitat for forage items. A high degree of fish activity and stable conditions make immediate access to the security of deep water less of a concern.

In summer, these fish are willing to make the occasional relatively long trip to deep-water retreats. In the fall, this situation changes; a slow metabolism due to cold water and an unstable cold front dictate the autumn location of walleyes and bass on steep drop-offs. Quick access to deep water becomes an important factor for these sluggish fish coping with unstable weather conditions.

Fish do not always change location with every seasonal change. Recent radio telemetry studies show some meso lake walleyes inhabit the same weedbed all year round except for one annual migration directly to and from the spawning beds. The In-Fisherman Handbook is a must for anyone wishing to undertake in-depth study of fish movements (see Suggested Reading).

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