24 



MARINE AND FISHERIES 



6-7 EDWARD VII., A. 1907 



tougli membrane. Pollock were very easily killed for this reason; cunner, very diffi- 

 cult. 



Stated mathematically, the energy of the exploding dynamite varies directly with 

 the amount exploded, and diminishes with the distance away, according to an undeter- 

 mined law, which probably depends upon the relative position of the exploding charge 

 to the bounding water surfaces, upon the nature of the bottom, and possibly also upon 

 conformation. So far as fish are concerned its effects upon them were found to vary 

 (a) with the numbers near the site of explosion, X^) apparently with their depth be- 

 neath the surface, and (c) with the strength of their tissues, .especially the walls of the 

 swim bladder, and the sensitiveness of the nervous system, though this last was diffi- 

 cult to demonstrate. 



CAUSE OF DEATH. 



As already indicated, the immediate cause of death is rupture of the swim bladder, 

 and internal haemorrhage. The rupture is evidently due to pressure. When an ex- 

 plosion occurs, there is a sudden liberation of gas tending to produce compression of 

 the water at the site of the explosion The wave of compression travels outwards in all 

 directions — upwards, downwards and sideways. The direction of least resistance is, 

 of course, always towards the surface of the water — hence the upheaval which follows 

 an explosion. Quite frequently we found three other marked injuries, especially in 

 large fish like pollock. Often in these the liver was compressed into fragments, the 

 ribs were detached from the vertebrae along the whole length, and the flesh (temporal 

 muscle) over the skull, after the skin had been cut, could be raised from the surface of 

 the bone, leaving it as smooth and clean as a piece of polished ivory. Here again, the 

 cause of the dislocation of these structures was pressure. The fish is veritably flattened 

 between the compression wave of the explosion on the one side, and the unyielding 

 water on the other; the ribs are torn from their attachments, the liver crushed to 

 pieces and forced backwards into the extra-peritoneal cavity, and the flesh raised clean 

 off the flat bones of the head. The surgeon sometimes meets with a similar experience 

 in accidents due to crushing. 



No external marks or injuries were visible on any of the fish), in either fresh or 

 salt water. 



SINKING FISH. 



Very early in the investigation it became evident that besides those fish which came 

 to the surface and floated, a number were merely stunned, and subsequently escaped, 

 or were killed outright and sank to the bottom. This was important. The destructive- 

 ness of dynamite took on a wider aspect than that of merely counting the slain. The 

 wounded and missing had, if possible, to be accounted for. If one could put off a blast 

 in a large pond, count those killed at the surface, drain the pond dry, and then count 

 the living and dead lying on the bottom, the investigation could soon be closed; but 

 this was not the way in which the problem was presented. Accordingly other methods 

 of investigation had to be planned. A simple method, and one likely to throw some 

 light upon these points, was to use the water telescope. This was done in some of the 

 narrow channels off Canso. Cunner abound in the shallow waters along these shores 

 and between the islands, and after some expert knowledge had been gained by using, 

 first a stove pipe and then an old eaves pipe for an aquatic telescope, we put off a blast, 

 and counted our ' spoil.' Twenty-five dead floated belly up : that was one fact, or col- 

 lection of facts, if you please. Then by the persevering use of our improvised telescope, 

 one observer counted seven, and another of our party counted eleven dead cunner lying 

 on the bottom. We recovered two of these. Port-mortem examination failed to show 

 particularly why they had sunk. There was great visceral congestion, and profuse 

 haemorrhage. In one, the swim bladder was much torn, while in the other, the rupture 

 was so small that no air could be found escaping, except when the whole animal was 



