Editing Herring (section)

===Prey===
{{See also|Hunting copepods}}

Herrings consume [[copepod]]s, [[arrow worm]]s, [[Hyperiidae|pelagic amphipod]]s, [[mysid]]s, and [[krill]] in the [[pelagic zone]]. Conversely, they are a central prey item or [[forage fish]] for higher [[trophic level]]s. The reasons for this success are still enigmatic; one speculation attributes their dominance to the huge, extremely fast cruising [[Shoaling and schooling|schools]] they inhabit.

Herring feed on [[phytoplankton]], and as they mature, they start to consume larger organisms. They also feed on zooplankton, tiny animals found in [[ocean]]ic [[photic zone|surface waters]], and small fish and fish larvae. Copepods and other tiny crustaceans are the most common zooplankton eaten by herring. During daylight, herring stay in the safety of deep water, feeding at the surface only at night when the chance of being seen by predators is less. They swim along with their mouths open, filtering the plankton from the water as it passes through their gills.
Young herring mostly hunt copepods individually, by means of "particulate feeding" or "raptorial feeding",<ref name=Kils1992>Kils U (1992) ''[https://archive.today/20001015111747/http://cbl.umces.edu/fogarty/usglobec/news/news8/news8.atoll.html The ATOLL Laboratory and other Instruments Developed at Kiel]'' U.S. GLOBEC News, Technology Forum Number 8: 6–9.</ref> a feeding method also used by adult herring on larger prey items like krill. If prey concentrations reach very high levels, as in microlayers, at fronts, or directly below the surface, herring become [[filter feeder]]s, driving several meters forward with wide open mouth and far expanded [[operculum (fish)|opercula]], then closing and cleaning the [[gill raker]]s for a few milliseconds.

Copepods, the primary zooplankton, are a major item on the forage fish menu. Copepods are typically {{convert|1-2|mm|in|frac=32|abbr=on}} long, with a teardrop-shaped body. Some scientists say they form the largest animal [[biomass]] on the planet.<ref>[http://www.uni-oldenburg.de/zoomorphology/Biology.html Biology of Copepods] {{webarchive|url=https://web.archive.org/web/20090101205840/http://www.uni-oldenburg.de/zoomorphology/Biology.html |date=2009-01-01 }} at [[Carl von Ossietzky University of Oldenburg]]</ref> Copepods are very alert and evasive. They have large [[Antenna (biology)|antennae]] (see photo below left). When they spread their antennae, they can sense the pressure wave from an approaching fish and jump with great speed over a few centimetres. If copepod concentrations reach high levels, schooling herrings adopt a method called [[ram feeding]]. In the photo below, herring ram feed on a school of copepods. They swim with their mouths wide open and their operculae fully expanded.

{{multiple image
 | align = center
 | direction = horizontal
 | header            = Hunting copepods
 | header_align      = center
 | caption_align = center
 | image1    = Copepodkils.jpg
 | width1    = 215
 | alt1      = 
 | caption1  = This copepod has its antennae spread. The antennae detect the pressure wave of an approaching fish.
 | image2    = Herringramkils.jpg
 | width2    = 253
 | alt2      = 
 | caption2  = School of herrings [[ram feed]]ing on a school of [[copepod]]s with [[Operculum (fish)|opercula]] and mouth expanded: The fish swim in a grid with a distance of the jump length of their prey, as indicated by the animation at the right.
 | image3    = Synchropredation.gif
 | width3    = 255
 | alt3      = 
 | caption3  = Animation showing how herrings hunt in a synchronised way to capture an alert and evasive copepod
}}

{{clear}}

The fish swim in a grid where the distance between them is the same as the jump length of their prey, as indicated in the animation above right. In the animation, juvenile herring hunt the copepods in this synchronised way. The copepods sense with their antennae the pressure wave of an approaching herring and react with a fast escape jump. The length of the jump is fairly constant. The fish align themselves in a grid with this characteristic jump length. A copepod can dart about 80 times before it tires. After a jump, it takes it 60 milliseconds to spread its antennae again, and this time delay becomes its undoing, as the almost endless stream of herring allows a herring to eventually snap up the copepod. A single juvenile herring could never catch a large copepod.<ref name=Kils1992 />

Other pelagic prey eaten by herring includes fish eggs, larval [[snail]]s, [[diatom]]s by herring larvae below {{convert|20|mm|in|frac=16|abbr=on}}, [[tintinnid]]s by larvae below {{convert|45|mm|in|frac=16|abbr=on}}, [[mollusc]]an larvae, [[menhaden]] larvae, [[krill]], [[mysid]]s, smaller fishes, [[pteropod]]s, [[annelid]]s, ''[[Calanus]]'' spp., [[Centropagidae]], and ''[[Meganyctiphanes norvegica]]''.

Herrings, along with [[Atlantic cod]] and [[Sprattus sprattus|sprat]], are the most important commercial species to humans in the Baltic Sea.<ref name="Koster2001">Friedrich W. Köster, et al. "Developing Baltic Cod Recruitment Models. I. Resolving Spatial And Temporal Dynamics Of Spawning Stock And Recruitment For Cod, Herring, And Sprat." ''Canadian Journal of Fisheries & Aquatic Sciences'' 58.8 (2001): 1516. Academic Search Premier. Web. 21 Nov. 2011. p. 1516. [http://bioweb.coas.oregonstate.edu/~ciannellilab/cameo/articles/neuenfeldt/2001k%F6steretal.pdf]{{dead link|date=November 2017|bot=InternetArchiveBot|fix-attempted=yes}}</ref> The analysis of the stomach contents of these fish indicate Atlantic cod is the top predator, preying on the herring and sprat.<ref name=Koster2001 /><ref>Maris Plikshs, et al. "Developing Baltic Cod Recruitment Models. I. Resolving Spatial And Temporal Dynamics Of Spawning Stock And Recruitment For Cod, Herring, And Sprat." ''Canadian Journal of Fisheries & Aquatic Sciences'' 58.8 (2001): 1516. Academic Search Premier. Web. 23 Nov. 2011, p.1517 [http://0-web.ebscohost.com.patris.apu.edu/ehost/pdfviewer/pdfviewer?sid=c279867d-bd9d-41d5-a8b4-3b60f2c686b4@sessionmgr13&vid=2&hid=24]{{dead link|date=December 2017|bot=KAP03|fix-attempted=yes}}</ref> Sprat are competitive with herring for the same food resources. This is evident in the two species' [[vertical migration]] in the Baltic Sea, where they compete for the limited zooplankton available and necessary for their survival.<ref name="Casini2004">Casini, Michele, Cardinale, Massimiliano, and Arrheni, Fredrik. "Feeding preferences of herring (Clupea harengus) and sprat (Sprattus sprattus) in the southern Baltic Sea." ''ICES Journal of Marine Science'', 61 (2004): 1267–1277. Science Direct. Web. 22 November 2011. p. 1268. [https://archive.today/20130113024805/http://icesjms.oxfordjournals.org/content/61/8/1267.full.pdf+html]</ref> Sprat are highly selective in their diet and eat only zooplankton, while herring are more eclectic, adjusting their diet as they grow in size.<ref name=Casini2004 /> In the Baltic, copepods of the genus ''[[Acartia]]'' can be present in large numbers. However, they are small in size with a high escape response, so herring and sprat avoid trying to catch them. These copepods also tend to dwell more in surface waters, whereas herring and sprat, especially during the day, tend to dwell in deeper waters.<ref name=Casini2004 />