Quote:
Originally Posted by Icelander
These things can survive at significant depths and also out of the water for a period of at least an hour, perhaps longer.
It is entirely possible that magic is involved when it comes to extremes of environmental tolerence they are believed to have exhibited, but at the very least, they seem to be as versatile as dolphins when it comes to the depths they can occupy. I imagine that they have something analogous to swim bladders, if not to lungs.
Of course, the PCs suspect that there are more than one species of marine ultraterrestials, at least one apparently similar to humanoid marine mammals, one or more type of human hybrids and another species (or more) adapted entirely to underwater life, incapable of surviving on land without supernatural means.
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As far as the technical details of buoyancy control go (excluding magic), sharks can be nearly neutrally buoyant by having large oil-filled livers and not having mineralized bones, as well as using hydrodynamic lift while swimming. Squid likewise have no mineralized structures in their bodies. Although muscle is more dense than water (making them somewhat negatively buoyant), they can compensate for thus by using lift from their fins and active swimming. Things that live in the deep sea often significantly reduce their muscle mass, becoming largely gelatinous. While this reduces their athletic ability, it does allow them to float suspended in the water column. The giant squid is a deep sea animal but is also muscular and athletic, it keeps neutral buoyancy by replacing sodium with ammonium for its electrolytes. But for athletic things with hard, mineralized body parts (bones, shells), gas filled structures seem to be about the only way to go.
Also, as far as weaponizing sonar goes - if you can focus the sonar beam to the point of producing cavitation at the target, gas-tissue interfaces become moot and the cavitation bubbles will just tear the target apart. But getting sonar to this point will probably require some R&D (not necessarily getting sonar to produce cavitation - it does this all too easily, and is bad for detection so the engineers want to avoid it. But rather the ability to produce cavitation at a desired point far from the emitter, and also the focusing and targeting of the beams).
Luke