The Use of Electricity in Conjunction With a 

 12.5-Meter (Headrope) Gulf-of-Mexico Shrimp Trawl 



in Lake Michigan 



By 



JAMES E. ELLIS, Fishery Biologist 



National Marine Fisheries Service 



Fish Farm Experiment Station 



Kelso, Arkansas 71666 



ABSTRACT 



The catching efficiency of a 12.5-meter standard shrimp trawl and the same trawl 

 fitted with three different electrode array systems with power on and power off was 

 investigated. 



The standard trawl caught 1.54 times or 54.2% more kilograms of fish than the 

 electrode-equipped trawl with power off. The electrode array hanging across the mouth 

 area of the trawl acted as a visual stimulant and thus reduced the trawl's catch rate. 



Overall the electrical trawl with power on caught 1.19 times or 19.0% more kilo- 

 grams of fish than the electrical trawl with power off. Array 2 with power on had the 

 best catch rate — 1.86 times or 86.9% more kilograms of fish than the power off catch 

 rate. The avoidance of fish to an electrode array was more than offset with the catch 

 rate of array 2 with power on. The dominance patterns of the catches with each sys- 

 tem tested did not change significantly with the exception of chub catches with array 

 2 with power on. 



Length selectivity was highly significant for chubs caught with arrays 2 and 3 

 with power on. No significant length selectivity occurred with the other species landed. 



INTRODUCTION 



The work reported in this study is part of the 

 National Marine Fisheries Service investigations 

 into the use of electrical apparatus to improve 

 the efficiency of trawl nets for commercial 

 fishing and fishery resource assessment 

 methods. It has been reported by many in- 

 vestigators that from 10 to 60% of the fish which 

 enter a bottom trawl will escape (Kreutzer, 

 1964). McRae and French (1965) and Shen- 

 taykov (1965) have reported that electricity 

 raises the overall catch of an ordinary trawl 

 from 2 to 2.5 times. 



From May 14 to June 14, 1968, an electrical 

 fishing study was conducted in Lake Michigan. 

 The purpose of this study was to investigate the 

 effects of an electrical field upon the catch rate 

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

 trawl. Accordingly, the specific objectives were: 

 (1) to investigate the visually induced reactions 

 of the fish to electrode array elements by com- 

 paring the catch rates of a standard trawl (no 

 electrodes) to the catch rates of an electrode 

 array-equipped trawl with electrical power off, 

 and (2) to investigate the effects of changing 

 electrical lines of force in the array system upon 

 catch rates with power on. 



