There were six recovery attempts 

 made from the towers with this arrange- 

 ment of the dynamite circuit. Of these 

 attempts, only four were actually made 

 on tag-bearing salmon, and each of these 

 fish was successfully recovered. 



The numbers of salmon killed during 

 each of these attempts ranged from 1 1 to 

 22. These were recovered either by the 

 tower watchman working alone from a 

 skiff or assisted by one or two other men 

 in a second skiff. 



The fish killed by the explosions in- 

 variably sank to the bottom and rolled 

 downriver with the current. They were 

 retrieved by skiff using long -handled dip 

 nets and spears. 



CONSTRUCTION OF THE CIRCUIT 



The preparation of the charges was 

 simple and safe when proper methods 

 were used and safety precautions followed. 

 The 40-percent ammonia gelatin dynamite 

 recommended for this use is relatively 

 insensitive and less dangerous than other 

 types. The electric blasting caps contain 

 a small amount of highly sensitive explo- 

 sives and were therefore handled with 

 extreme care. At all times manufacturer's 

 instructions for handling of caps and dyna- 

 mite were carefully followed. 



The recommended method for capping 

 a charge (Institute of Makers of Explosives 

 1955) is shown in figure 5. Of the several 

 methods commonly used for securing elec- 

 tric caps to dynamite, this method was 

 found to offer the least resistance to 

 water current. 



The following tools were required for 

 preparation of the charges: a sharp knife, 

 a stick sharpened for punching the cap 

 and wire holes in the dynamite, and water- 

 proof rubber or plastic material for 

 covering the charges. An unprotected 

 charge remained effective for at least 

 three days but would eventually become 

 water-soaked and impossible to detonate. 



In planning the circuit it was important 

 to have an adequate source of current. 

 As recommended in the "Handbook of 

 Electric Blasting" (McFarland and Rol- 

 land 1959) at least 3/10 amperes of 

 direct current or 6/10 amperes of al- 



ternating current should pass through 

 each electric blasting cap in parallel 

 circuit firing. To calculate the current 

 required in a circuit, the resistances of 

 the "EB" caps and leading wire were 

 determined. Tables giving these values 

 were obtained when purchasing the blasting 

 supplies. The circuit diagram used at the 

 counting tower sites and calculation of 

 required voltage are shown in figure 6. 



DISCUSSION OF PROBLEMS 

 ENCOUNTERED 



The use of dynamite at the counting 

 tower sites presented several important 

 difficulties. The first of these was in 

 limiting the destruction of non-tag-bearing 

 salmon. Since all salmon within the lethal 

 range of the pressure wave are killed by 

 the blast, it is desirable that the wave be 

 limited or directed as much as possible 

 to exclude these salmon. Even though the 

 value of the information gained from the 

 recovery of a tag may far surpass the 

 value of salmon thus destroyed, it is a 

 waste which should be limited if possible. 



A second difficulty encountered was 

 in retrieving the dead salmon after a blast. 

 During the Kvichak tests long -handled 

 dip nets and spears were used for this 

 purpose with spearing proving to be the 

 best method. In situations where deep 

 pools are present below the tower sites 

 there may be considerable difficulty in 

 retrieving the salmon. In such a case it 

 would not be advisable to attempt recovery 

 by dynamite unless some type of a catching 

 device was present. 



A third difficulty was in the interrup- 

 tion of the migration by recovery activity 

 during a recovery attempt. During the 

 Kvichak recovery attempts all dead salmon 

 were retrieved for examination purposes 

 and this usually required from 20 to 30 

 minutes. In actual practice, when recovery 

 activity may cease after the tagged salmon 

 is retrieved, this time would be con- 

 siderably shortened. 



It is recognized that the disturbance 

 caused by the blast, together with silt 

 and chemicals released into the water 

 and carried downriver, may alter the 

 normal migration pattern so as to affect 

 subsequent hourly migration counts. The 

 Kvichak migration, however, was observed 



