SHIPBOARD 

 POWER 

 SUPPLY 



DIS- 

 CONNECT 



SOLUTION 

 jTRflNS- 

 FORMER 



TO ELECTRODE 

 ARRAYS 



Figure 2. — Block diagram of fish shocker and allied 

 equipment. 



PHYSICAL QUALITY OF WATER 



Water conductivity and temperature were 

 measured at 12 noon each day. These variables 

 did not noticeably affect the electrical current 

 drawn by the electrode arrays. 



Conductivity 



Measurements of water conductivity at fishing 

 depth were made with a conductivity bridge 

 coupled to a temperature-compensated probe. 

 Conductivity ranged from 210 to 250 micromhos 

 per cm with a mean of 230 micromhos per cm. 



Temperature 



Measurements of water temperature at fishing 

 depth were taken with a bathythermograph. The 

 temperature ranged from 8.5°C to 9.5°C with a 

 mean of 9.0°C. 



METHOD OF TESTING THE 

 ELECTRICAL TRAWL 



To permit an evaluation of the electrical trawl, 

 we designed two experiments: 



1. To investigate the effects upon catch rates 

 of visually induced avoidance behavior to 

 hanging vertical electrode arrays. 



2. To investigate the effects upon catch rates 

 of electrical lines of flux with electrode ar- 

 rays 1, 2, and 3. 



During the first experiment to investigate vis- 

 ually induced avoidance, a 12.5-m trawl (no elec- 

 trode arrays) was tested against the same trawl 

 equipped with electrode array 1 without electri- 

 cal power. Forty-eight drags were made — 24 

 under each condition. The array was removed 

 on alternate drags. 



During the second experiment to investigate 

 the effects of electrical lines of flux with arrays 

 1, 2, and 3 upon catch rates, the electrode array- 

 equipped trawl was used. Forty-eight drags 

 were made with arrays 1 and 2 respectively, and 

 46 drags were made with array 3. During the 

 testing of each array, the procedure was to turn 

 the electrical power on during alternate drags. 



All drags were of 10-min duration in 9 fath- 

 oms of water at a vessel speed of approximately 

 2.6 knots. Scuba divers adjusted the electrode 

 arrays in the net prior to testing. 



The fish in each of the 190 drags were usually 

 counted and weighed. However, when large 

 catches were made, a subsample of the catch was 

 counted and weighed and then expanded to cover 

 the total catch. Fish length-frequency data was 

 taken from the electrical trawl drags, power on 

 versus power off. 



RESULTS OF TESTING THE 

 ELECTRICAL TRAWL 



The test results were evaluated on the basis 

 of total catch rates and gear selectiveness. 



Catch Rates 



For the first experiment, the average catch 

 rate in kilograms per drag for the trawl fished 

 with and without electrodes is shown in Table 1. 

 The standard trawl averaged 42.7 kg of fish per 

 drag and caught 1.54 times or 54.2% more kil- 

 ograms than the electrode-equipped trawl with 

 power off. The reduction in catch with the elec- 

 trode-equipped trawl was obviously due to vis- 

 ually induced reactions of fish to hanging vertical 

 electrode elements. Similar results were exper- 

 ienced by Russian biologists. Their investiga- 

 tions showed that fish avoid trawl nets when 

 vertical hanging stimulants are placed in the 



