Injuries to Pacific mackerel (<i>Scomber japonicus</i>) from underwater explosions

Abstract This study expands previous work examining the effects on fishes from exposure to a single 4.5 kg underwater explosive detonation. Experiments were done in the field, with fish in cages at different distances from the source. Although our earlier work reported high acoustic dosage levels (e.g. based on peak pressure) correlating with severe injuries, dosage levels that result in moderate, or mild injuries were not clearly established. Thus, in this study, caged Pacific mackerel (Scomber japonicus) were placed at targeted ranges of 150–800 m from the source. All procedures were the same as in the earlier study except that animals were left at depth for ∼3 hours post-exposure to determine immediate effects on survival. Fish were then retrieved and assessed for physical damage. The only statistically significant tissue injuries were swim bladder bruising and in a reduction in inner ear sensory hair cell density that lessened with distance from the source. Still, results must be taken with caution since they may vary with different source levels, water depths, location of the fish in the water column, and by species.