EFFECTS OF DYNAMITE EXPLOSIONS ON FISH LIFE 23 

 SESSIONAL PAPER No. 22a 



VARIATIONS IN DESTRUOTIVENESS. 



The first explosion and its results were typical of all the work done last sum- 

 mer. Of course the results were not constant, for obvious reasons. The destructive- 

 ness of the explosive varied according to easily recognizable conditions. It varied 

 with (a) the charge of dynamite used, (h) with the depth of the water, (c) with the 

 number of fish present in the neighbourhood of the explosion, (d) with their distance 

 away, and (e) with the kind of fish. 



That the destructiveness varies with the weight of dynamite exploded, needs no 

 demonstration. This is probably true of all explosives. Many different charges 

 were used, usually varying from one cartridge up to eight. The larger charges did 

 not always result in bringing up the larger number of fish. The number killed 

 depended more upon the number of fish in the neighbourhood than upon any other 

 condition. For example, a charge of li- lbs. exploded in the Kingston harbour, west 

 of Garden Island, did not bring up a solitary fish, while one cartridge of -| lb. weight 

 in St. John harbour, JSTew Brunswick, killed over 800 fish. 



The depth of the water was another important condition affecting the destructive- 

 ness of dynamite. Explosions were effected at depths varying from li to 300 feet. 

 It produced little, if any, destruction of fish life at shallow depths, say, less than 10 

 to 12 feet. The reason of this probably is, that at slight depths, the pressure result- 

 ing from the explosion is not sufiiciently great to rupture the swim bladder. One 

 blast at 18 inches under the surface, sent up a column of water about 100 feet high; 

 another blast about 3 feet below the surface sent up a narrow column about 60 or 70 

 feet high. In neither case were fish killed, though some must have been present. 

 At 10 or 12 feet below the surface, the explosion lifted a broad cone or mound of water 

 6 or 8 feet high. At increasing depths, the 'surface disturbance became less and less 

 marked, until at 45 fathoms or thereabouts, the only evidence of the explosion, after 

 the noise and the tremendous blow on the bottom of the boat, was the appearance of a 

 vast number of small bubbles of gas covering a diameter of from 40 to 60 feet. There 

 was no upheaval of water. Evidently the large volume of gas generated at these 

 depths is, on its way towards the surface, broken up into a large number of distinct 

 bubbles, which separate as they ascend. 



As regards explosions at increasing depths, a few of our results may be tabulated 

 as follows: — 



No. Expt. Wt. of Dynamite. Depth of Water, Depth of Cartridge, No. of Fish 



Lb. in feet. in feet. Killed. 



1 -I 12 12 0* 



2 IJ 14 12 0 



3 J 10 10 0 



4 i 26 18 300 



5 i 25 18 160 



6 I 24 18 35 



It is difficult to say whether in ISTos. 1, 2, and 3 there were no fish present, or the 

 pressure was insufficient to kill them. The probable explanation of the difference be- 

 tween the number killed in No. 4, as compared with those in No. 5, is that many more 

 fish were present in the vicinity in the former case than in the latter. 



No. 6 illustrates another variation in the effects of a dynamite explosion. In this 

 instance not a single fish came up where the explosion occurred. About 30 yards away, 

 seven or eight sunfish were killed outright — not a movement in one of them when 

 picked up. A few moments later, a batch of perch and a few rock bass were seen com- 

 ing to the surface about 60 yards away. Clearly, therefore, the number of fish killed 

 varies directly with the number present, and varies also with their distance away from 

 the site of the explosion. 



Lastly the number killed depends upon the kinds of fish. Those with a thin, 

 delicate texture of the swim bladder are more easily killed than fish possessing a thick, 



22a— 44 



