0 FEET: EPIPELAGIC ZONE
Ample sunlight penetrates down to 650 feet, making photosynthesis possible. With abundant plant life (read: food), this zone is the most densely populated with fish.
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656 FEET: MESOPELAGIC ZONE
Too deep to support photosynthesis: The fish that survive here are sit-and-wait predators that tend to have large mouths and specialized retinas to increase light reception.
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1,640 feet: Maximum diving depth of the blue whale.
1,969 feet: The Deep Sound Channel, a layer in which acoustic signals travel far and fast.
1,969 feet: Maximum diving depth of nuclear-powered attack subs.

3281 FEET: BATHYPELAGIC ZONE
The ocean is dark at this level; the only glow is from bioluminescent animals. There are no living plants, and creatures subsist by eating the debris that falls from the levels above, including dead or dying fish and plankton.

3,281 feet: Maximum diving depth of the sperm whale. To navigate in the darkness, these whales emit high pitched sounds and use echoes to determine the location of prey.
3,937 feet: Maximum diving depth of the leatherback sea turtle.
4,000 feet: The domain of the Pacific sleeper shark, the largest toothed shark ever photographed. It can reach lengths of 28 feet.
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5,187 feet: Maximum diving depth of the elephant seal.
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13,123 FEET: ABYSSOPELAGIC ZONE
In the pitch-dark of the abyss, there is no light at all, the water temperature is near freezing. Of the few creatures found at these crushing depths, most are blind and have long tentacles - tiny invertebrates such as shrimp, basket stars, and small squids.
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19,685 FEET: HADOLPELAGIC ZONE
Despite the intense pressure and frigid temperature in the deepwater trenches and canyons, life still exists here, especially near hydrothermal vents on the ocean floor. Invertebrates such as starfish actually thrive.