Fish Sampling 139 



pick up. Certain kinds of fishes attempt to escape the shocker by diving 

 into brush and into pockets at the base of rocks, stumps, and logs lying in 

 the water, making these ideal collecting locations. Most fishes revive within 

 a period of 30 seconds to 2 minutes. Occasionally a fish is killed by direct 

 contact with an electrode. The shocker is not only used for sampling but 

 also for collecting fish with "full" stomachs (food-habit studies) and for 

 taking live specimens for stocking other waters. For some reason, many 

 la)Tnen have an idea that the electric shocker can be used to clear lakes of 

 undesirable fishes. When they discover that the fish stunned by the shocker 

 represent only a sample, they are often disappointed. 



Both direct and alternating current are used on boat shockers. For 

 collecting most kinds of fishes in shallow ponds, alternating current ap- 

 pears to be more eflFective. However, some biologists prefer a pulsating 

 direct current to give a combination of electrotaxis and forced swimming.-^ 

 Tests made in a webbing enclosure in a shallow lake (Minnesota) in- 

 dicated that about 240 interruptions per minute was most effective for 

 catching fish.^^ 



Angling. Fishing with certain kinds of gear (fly rod, spinning rod, etc.) 

 and certain types of artificial or natural baits may be highly selective for 

 certain kinds and sizes of fish. For this reason, angling is sometimes very 

 important as a method of sampling. Largemouth bass are usually taken 

 more readily on hook-and-line than by any known type of net or trap. 

 Several years ago I attempted to catch largemouth bass in a lake, at a 

 time when it contained almost no fish other than bass of about 7.5 inches 

 total length, by using 1-inch mesh wing nets with 60-foot lead nets. Six 

 nets were set and raised daily on six consecutive days. The catch of all 

 nets for the six-day period (36 net-days) was 6 of these small bass; on 

 the last day that the nets were set I caught 47 bass on fly rod "poppers" 

 in less than three hours. 



The ability to avoid nets and seines is shared also by smallmouth bass, 

 although they are somewhat more vulnerable than are largemouths. For 

 sampling smallmouths, a fly rod and artificial "popper" may serve effi- 

 ciently. For example, biologists captured 192 smallmouth bass (6 to 11 

 inches ) in 22 hours of fishing at the rate of 8.7 per hour.^- The fish were 

 used to restock a renovated lake. They probably could not have been 

 taken from the source lake ( a deep quarry lake ) at this rate by any other 

 method. 



Hook-and-line fishing may be useful for sampling specific fishes such 

 as male bluegills guarding nests, or for taking fishes that inhabit a certain 

 weed bed or lie beneath a log. 



Many kinds of fishes become trap-wise as well as hook-wise, so that most 

 types of fishing gear become less efficient with intensive use. 



