240 Fish Behavior and Angling 



Most small ponds and lakes are diermally stratified during summer 

 months (see Chapter 2, p. 3). The warm upper layer of water is often 

 above the optimum for warm -water fish; but cooler water may be found 

 at greater depths. When a fish moves downward from the warm upper 

 epilimnion into the transition zone ( metalimnion ) , it gradually enters 

 cooler water and the amount of dissolved oxygen decreases until at some 

 level it may disappear entirely. The optimum temperature-oxygen rela- 

 tionship may be at a level where the water is as cool as possible but with 

 enough dissolved oxygen for the fish to carry on respiration without dis- 

 comfort. Here the fish may remain, except during periods of active feed- 

 ing. If a fisherman can locate this level and keep his bait ( whether artifi- 

 cial or natural ) within this stratum of water, he may often catch fish when 

 others fishing the surface or at other depths may catch little or nothing. 

 Even bluegills may be caught by trolling a worm in this stratum when the 

 shore shallows are devoid of them. 



Some improvement in feeding activity and rate of catch occurs during 

 fall months, but less fishing is done in fall than during any other season. 

 There are some exceptions— most active fishing for muskellunge takes place 

 after waters have cooled from summer temperatures. 



Thus, water temperatures are important in afiFecting the behavior of 

 fishes and the successful angler adjusts his fishing operations to conform 

 to these temperature effects. 



Water Transparency. Most game and pan fishes important for angling 

 find their food more through sight than through taste. This is why artificial 

 lures are very effective in taking these fish. Thus, within limits there is 

 a positive correlation between an increasing clearness of water and in- 

 creasing catch. This was demonstrated at Fork Lake (Illinois) using 

 surface fly rod lures for bass and bluegills. When the transparency of this 

 pond (Secchi disk) was 0.5 to 2.0 feet the catch rate was 2.4 fish per 

 man-hour; with transparencies of 2.1 to 2.5 feet the catch rate was 2.86 

 fish per man-hour, and at 3.5 to 4.5 feet the catch was 6.59 fish per man- 

 hour.^ 



In most waters, turbidity is caused by suspended particles of clay or 

 silt stirred up by the action of bottom-rooting fishes or wind or carried 

 into the lake with inflowing water. Turbidity may also result from a 

 "bloom" of plankton algae stimulated by fertilization of the water. This 

 nonsilt type of turbidity has less of an effect upon rate of catch than 

 turbidity caused by clay or silt particles. In lakes and ponds containing 

 carp, suckers, or bullheads, a more-or-less constant turbidity may result 

 from the rooting and stirring action of these fish on the bottom. Im- 

 poundments that are "muddy" during periods of dry weather are often 

 kept so by these fish, and this type of turbidity is usually as bad for 

 angling as is silt brought in on floods. 



