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COMPTUEX/JTFEX EA/OEA Final Chapter 4susceptibility between fish with these two types of bladders (Yelverton et al., 1975; Yelverton, 1981).After a nearby underwater blast, most fish that die do so within 1–4 hours, and almost all do so within 24hours (Yelverton et al., 1975; Yelverton, 1981).The rapid rise time of the shock wave resulting from detonation of high explosives causes most of theorgan and tissue damage. Mortality of fish correlates better with impulse, measured in units of pressuretime, than with other blast parameters (Yelverton, 1981). The received impulse depends on the depth atwhich the fish is swimming, the depth of the charge, the mass of the charge, and the distance from chargeto fish. Fish near the bottom or near a bank will receive a larger impulse. A fish on the bottom over ahard surface would receive a greater impulse than it would in open water (Yelverton et al., 1975;Yelverton, 1981). Bottom reflection can also be enhanced if it is focused by bottom terrain.Data from explosive blast studies indicate that very fast, high-level acoustic exposures can cause physicaldamage and/or mortally wound fishes (Hastings and Popper, 2005). There is also reason to believe thatlesser effects might also occur, but these have not been well documented. Just as in investigations testingthe effects of sound, however, the number of species studied in tests of the effects of explosives is verylimited, and there have been no investigations to determine whether blasts that do not kill fish have hadany impact on short- or long-term hearing loss, or on other aspects of physiology (e.g., cell membranepermeability, metabolic rate, stress), and/or behavior (e.g., feeding or reproductive behavior, movementfrom preferred home sites).In addition to impacts occurring near the ocean surface, there is also the possibility that falling fragmentsmay injure or kill individual fish. However, most missiles hit their target or are disabled before hitting thewater. Therefore, most of these missiles and targets hit the water as fragments, which quickly dissipatetheir kinetic energy within a short distance from the surface. Similarly, expended small-arms rounds mayalso strike the water surface with sufficient force to cause injury, but most fish swim some distance belowthe surface of the water. Therefore, fewer fish are exposed to mortality from falling fragments whoseeffects are limited to the near surface.Given the random distribution of juvenile and adult pelagic fish species, planktonic eggs and larvae, andprey items, the relatively large area of the range, and the relatively infrequent number of operations,recovery is expected to occur quickly. The abundance and diversity of fish within the OPAREAs areunlikely to measurably decrease as a result of implementation of the No Action Alternative or ProposedAction. Significant impacts on fish populations are not anticipated with implementation of the No ActionAlternative or Proposed Action.4.3.1.3.3 SoundThere are insufficient data on the effects of exposure to sound, in particular mid-frequency sound, on thevast majority of fishes, and there is a great diversity of ear structures, hearing capabilities, and/or acousticbehaviors among fish. The literature on the detection of, and response to, sound are limited and the dataon vulnerability to injury are almost totally non-existent, only relevant to particular species, and becauseof the great diversity of fishes are not easily extrapolated.If the sound is loud enough and within the range of frequencies that a fish can hear, a sound will bedetected by a fish at some distance from the source. Because of the variable hearing thresholds, thisdistance will vary among species. Theoretically, a yellowfin tuna would have to be much closer than anAtlantic cod to hear a low-frequency sound at a given energy level. Underwater sounds have been usedby fishermen to guide herring and other schooling fish to their nets (Yelverton, 1981), or to exclude fishfrom water intakes (Haymes and Patrick, 1986). The noises made by fishing boats can scare some targetFebruary 2007 4-14