escapement. Spawning ground recovery 

 has proven to be difficult, ineffective, and 

 expensive. The ideal place to intercept a 

 tagged fish is at the counting site where 

 the entire escapement is funneled along 

 each river bank and where tagged salmon 

 are frequently seen to pass. 



Recovery of tagged salmon is a major 

 problem in a large river since the fish 

 have an easy avenue of escape in deeper 

 water. A salmon disturbed by an unsuc- 

 cessful recovery attempt will generally 

 continue its upstream migration in deep 

 water beyond the range of visibility. 



THE EFFECT OF DYNAMITE 

 ON SALMON 



During June of 1959, experiments 

 on the effects of underwater explosions 

 were conducted on the Kvichak River at 

 Igiugig, Alaska. Tests were made in a 

 backwater channel of the Kvichak River 

 in water depths ranging from 2 to 6 feet. 

 The bottom was a uniform mixture of 

 sand and medium-sized gravel. 



Blasting supplies consisted of 14- 

 gage leading wire, 20 -gage connecting 

 wire, electric blasting caps.l^ by 8-inch 

 sticks of 40-percent gelatin dynamite, 

 and plastic electrician's tape. 



Fish used in the experiments were 

 mature male and female red salmon 

 (OncoThynchvs nerka) which were obtained 

 by beach seining in the main Kvichak River. 

 During the experiments the salmon were 

 contained in a small chicken-wire cage 

 which could be suspended in the water at 

 varying distances from the bottom. 



Of the factors which control the ef- 

 fect of an underwater explosion, those 

 recognized as being most important in 

 tag recovery work are: water depth, dis- 

 tance of fish from charge, orientation 

 of the fish with respect to the charge, 

 elevation above the river bottom of either 

 the fish or the charge, multiple charges, 

 sympathetic detonation of multiple 

 charges, strength of charge, and use of 

 reflectors or deflectors. Variables tested 

 include: (1) depth of water, (2) distance 

 offish from charge, (3) strength of charge, 

 (4) use of reflectors and deflectors. 



Observations made during prelim- 

 inary experiments served to establish a 



criterion for determining the effects of a 

 lethal explosion. Damage caused by a lethal 

 explosion was remarkably similar in fish 

 which were held at varying distances from 

 the charge as long as they were within 

 the lethal range of the charge. The only 

 external damage noted in any of the fish 

 was the disappearance of a small patch 

 of scales from each side of the fish in 

 the vicinity of the air bladder (fig. 1). 



Figure 1. 



-External damage to salmon caused by underwater 

 dynamite explosion. 



The internal damage was concentrated 

 in the organs and tissues surrounding the 

 air bladder and consisted of ruptured air 

 bladder, ribs torn loose from abdominal 

 walls, kidney ruptured in most instances, 

 ovaries or gonads torn, blood vessels 

 ruptured in body wall, adipose tissue and 

 spleen both torn. 



Fish used in the lethal range experi- 

 ments usually had been placed at or near 

 the lethal limits of the pressure wave 

 when killed. These fish often lived for 

 five or ten minutes after the blast but 



