Effects of underwater explosions on larval fish: Implications for a coastal engineering project

Determination of the impacts of underwater explosions on animals has focused upon the mortality of adult fish, turtles, and marine mammals. For these animals, mortality can be predicted and abundance and distribution in the impact area can be determined with acceptable accuracy. The sensitivity of larvae and small juveniles, however, has not been adequately examined, and the abundance and distribution of young fishes is difficult to estimate. We determined sensitivities of the larvae and small juveniles of two species of fishes to shock wave exposure under experimental conditions. This determination was used to develop models that relate larval and small juvenile fish mortality to shock wave exposure. Resulting shock waves were monitored at three distances from the blast. Injuries were assessed by gross examination and by histopathology. Specific impulse was determined the critical parameter for injury assessment because it was of high magnitude over a longer distance when compared with pressure maxima or energy flux density. Impulse ranged from 1.855 to 12.080 Pa s. The proportion of fish lethally injured by these impulses ranged from 0.14 to 1.00. Total injury doses of 50% ranged from 5.286 to 8.910. Total injury doses of 50% were applied to an engineering blasting project in Wilmington Harbor, North Carolina. This application indicated that nearly 8.2 X 10(8) larvae could be killed over the duration of the project. This represents 2-3% of the larvae in the system and is unlikely to seriously affect fishes at the population level.