Editing Swim bladder (section)

==Deep scattering layer==
{{main|Deep scattering layer}}

[[File:california headlightfish.png|thumb|260px|right|Most mesopelagic fishes are small [[filter feeder]]s which ascend at night using their swimbladders to feed in the nutrient rich waters of the [[epipelagic zone]]. During the day, they return to the dark, cold, oxygen deficient waters of the mesopelagic where they are relatively safe from predators. [[Lanternfish]] account for as much as 65 percent of all deep sea fish [[biomass]] and are largely responsible for the [[deep scattering layer]] of the world's oceans.]]

Sonar operators, using the newly developed sonar technology during World War II, were puzzled by what appeared to be a false sea floor 300–500 metres deep at day, and less deep at night. This turned out to be due to millions of marine organisms, most particularly small mesopelagic fish, with swimbladders that reflected the sonar. These organisms migrate up into shallower water at dusk to feed on plankton. The layer is deeper when the moon is out, and can become shallower when clouds obscure the moon.<ref name="TeAraMZ">{{cite web |author=Ryan P |url=http://www.teara.govt.nz/EarthSeaAndSky/SeaLife/DeepSeaCreatures/2/en |title=Deep-sea creatures: The mesopelagic zone|website=Te Ara - the Encyclopedia of New Zealand|date= 21 September 2007}}</ref>

Most mesopelagic fish make daily [[Diel vertical migration|vertical migration]]s, moving at night into the epipelagic zone, often following similar migrations of zooplankton, and returning to the depths for safety during the day.<ref name="Moyle585">{{cite book|last1=Moyle|first1=Peter B.|last2=Cech|first2=Joseph J.|title=Fishes : an introduction to ichthyology|date=2004|publisher=Pearson/Prentice Hall|location=Upper Saddle River, N.J.|isbn=9780131008472|page=585|edition=5th}}</ref><ref>{{cite book|last1=Bone|first1=Quentin|last2=Moore|first2=Richard H.|title=Biology of fishes|date=2008|publisher=Taylor & Francis|location=New York|isbn=9780203885222|page=38|edition=3rd|chapter=Chapter 2.3. Marine habitats. Mesopelagic fishes}}</ref> These vertical migrations often occur over large vertical distances, and are undertaken with the assistance of a swim bladder. The swim bladder is inflated when the fish wants to move up, and, given the high pressures in the mesopelagic zone, this requires significant energy. As the fish ascends, the pressure in the swimbladder must adjust to prevent it from bursting. When the fish wants to return to the depths, the swimbladder is deflated.<ref>{{cite journal | last1 = Douglas | first1 = EL | last2 = Friedl | first2 = WA | last3 = Pickwell | first3 = GV | year = 1976 | title = Fishes in oxygen-minimum zones: blood oxygenation characteristics | url = http://www.sciencemag.org/cgi/content/abstract/191/4230/957 | journal = Science | volume = 191 | issue = 4230| pages = 957–959 | doi = 10.1126/science.1251208 | pmid = 1251208 | bibcode = 1976Sci...191..957D | url-access = subscription }}</ref> Some mesopelagic fishes make daily migrations through the [[thermocline]], where the temperature changes between {{cvt|10|and|20|°C}}, thus displaying considerable tolerance for temperature change.

Sampling via deep [[trawling]] indicates that [[lanternfish]] account for as much as 65% of all deep sea fish [[biomass]].<ref name=EoF>{{cite book |editor=Paxton, J.R. |editor2=Eschmeyer, W.N.|author= Hulley, P. Alexander|year=1998|title=Encyclopedia of Fishes|publisher= Academic Press|location=San Diego|pages= 127–128|isbn= 978-0-12-547665-2}}</ref> Indeed, lanternfish are among the most widely distributed, populous, and diverse of all [[vertebrate]]s, playing an important [[ecology|ecological]] role as prey for larger organisms. The estimated global biomass of lanternfish is 550–660 million [[tonne]]s, several times the annual world fisheries catch. Lanternfish also account for much of the biomass responsible for the [[deep scattering layer]] of the world's oceans. [[Sonar]] reflects off the millions of lanternfish swim bladders, giving the appearance of a false bottom.<ref>{{cite web |title=Deep-sea fish diversity and ecology in the benthic boundary layer |author1=R. Cornejo |author2=R. Koppelmann |author3=T. Sutton |name-list-style=amp |url=http://www.agu.org/meetings/os06/os06-sessions/os06_OS45Q.html |access-date=2015-03-26 |archive-date=2013-06-01 |archive-url=https://web.archive.org/web/20130601024839/http://www.agu.org/meetings/os06/os06-sessions/os06_OS45Q.html |url-status=dead }}</ref>

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