STUDY AREA 



The electrofishing study was conducted be- 

 tween Saugatuck and Holland, Mich., on the east- 

 ern side of Lake Michigan in 9 fathoms of water. 

 The bottom in the study area was typically fine 

 sand with some scattered boulders. The area 

 afforded excellent trawling grounds owing to the 

 gradual slope and regular contours of the bottom. 



The fish population at the time of the study 

 was predominantly alewife (Alosa pseudoha- 

 rengus), chub (Leucichthys hoyi), and smelt 

 (Osmerus mordax), with good populations of 

 yellow perch (Perca flavescens) and lake trout 

 (Salvelinus namaycush) . 



EQUIPMENT 



Trawl 



A 12.5-m (headrope) Gulf-of-Mexico shrimp 

 trawl fitted with an electrode array system de- 

 signed to retain fish once they enter the net was 

 used. This nylon net had 3.2-cm mesh (stretched 

 measure) wings and body and a 2.7-cm mesh 

 cod end with a 1.3-cm mesh liner. The trawl 

 was rigged with twelve 29.1-cm diameter plastic 

 floats evenly spaced on a 12.5-m headrope and 

 had 13.1 m of 0.9-cm diameter ground chain in- 

 serted in the 10.2-m diameter canvas hose along 

 the 13.1-m footrope. 



One electrode array with three variations in 

 electrode element spacing was used, hereafter 

 referred to as arrays 1, 2, and 3. The cathode 

 was a vertical panel approximately 12.5 m long 

 by 3.7 m high, composed of lengths of 2.5-cm 

 hollow braided tinned-copper battery strapping. 

 This strapping was fitted with an inner core of 

 0.9-cm diameter nylon and had a covering of 

 1.6-cm diameter nylon hollow braided rope. The 

 anode consisted of two horizontal panels, 1.8 m 

 long by 0.9 m wide, composed of copper screening 

 (260 meshes per 2.5 cm). 



Electrode Arrays 



The array was positioned in the net as shown 

 in Figure 1. 



Array 1 — The cathode was comprised of 42 

 vertical hanging electrode elements spaced 0.3 m 

 apart and tied to the headrope and the footrope 

 of the mouth area of the trawl. One of the anode 



panels was attached to the top of the net body, 

 and the other was fastened to the bottom of the 

 net body, 1.5 m behind the cathode. 



Array 2 — The cathode was the same as de- 

 scribed under array 1 with the exception that 

 every other electrode element was disconnected 

 electrically. The anode was as described under 

 array 1. 



Array 3 — The cathode was similar to that de- 

 scribed for array 1. The anode was one section 

 of copper screening attached to the bottom of 

 the net body. 



Electrical Shocker 



Primary power was supplied by a portable 

 10 kw AC generator coupled to a commercial 

 electrical shocker (Superior Electric Shocker). 

 Pulsed directed current was supplied from the 

 shocker to the electrode arrays through 152.4 m 

 of two-conductor number 10 Type SO cable. We 

 used 150 v DC at 12 amp at 10 pulses per sec 

 with a pulse duration of 20 milliseconds and a 

 duty cycle of 26%. Pulse shape was essentially 

 rectangular. This set of electrical conditions 

 was selected as the most effective from prior 

 investigations in the field and laboratory by the 

 author. The electrical cable was set and re- 

 trieved by a hydraulically powered storage reel. 

 A diagram of the electrical system is shown in 

 Figure 2. 



Figure 1. — Diagram of electrical trawl showing basic 

 electrode arrays. 



