Editing Porbeagle (section)

==Distribution and habitat==
The porbeagle has an almost global amphitemperate distribution, i.e., it is absent from the tropics; in the North Pacific, its [[ecological niche|niche]] is assumed by the salmon shark. It is found mostly within 30–70°N and 30–50°S [[latitude]]s.<ref name="francis et al"/> In the North Atlantic, the northern limit of its range extends from the [[Grand Banks of Newfoundland|Newfoundland Grand Banks]] off [[Canada]], through southern [[Greenland]], to [[Scandinavia]] and [[Russia]]; the southern limit of its range extends from [[New Jersey]] and [[Bermuda]], through the [[Azores]] and [[Madeira]], to [[Morocco]]. It is found in the [[Mediterranean Sea]], but not the [[Black Sea]]. Normally, North Atlantic sharks only stray as far south as [[South Carolina]] and the [[Gulf of Guinea]],<ref name="compagno"/> but pregnant females from the western North Atlantic population are known to range into the [[Sargasso Sea]], almost as far as [[Hispaniola]], to give birth.<ref name="campana et al"/> In the Southern Hemisphere, the porbeagle apparently occupies a continuous band bound in the south by the [[Antarctic Convergence]], and extending as far north as [[Chile]] and [[Brazil]], the [[Western Cape]] [[Provinces of South Africa|province]] of [[South Africa]], [[Australia]] to southern [[Western Australia]] and southern [[Queensland]], and [[New Zealand]].<ref name="compagno"/> In New Zealand it is most common south of the Cook Strait.<ref name=":2">{{Cite book|title=The fishes of New Zealand|last1=Roberts|first1=Clive|last2=Stewart|first2=A. L.|last3=Struthers|first3=Carl D.|last4=Barker|first4=Jeremy|last5=Kortet|first5=Salme|last6=Freeborn|first6=Michelle|publisher=Te Papa Press|year=2015|isbn=9780994104168|volume=2|location=Wellington, New Zealand|pages=73|oclc=908128805}}</ref> The porbeagle is thought to have colonized the Southern Hemisphere during the [[Quaternary glaciation]] (beginning around 2.6 Mya), when the tropical climate zone was much narrower than it is today.<ref name="musick et al"/>

Offshore [[fishing bank]]s are the favored habitat of the porbeagle, though it can be found from a depth of {{convert|1360|m|ft|abbr=on}} in [[oceanic basin]]s to [[littoral]] (close to shore) waters less than {{convert|1|m|ft|abbr=on}} deep, over the entire [[water column]].<ref name="compagno"/><ref name="fishbase"/><ref name="campana et al 2010"/> A single, anomalous record was made of a juvenile in [[brackish water]] in [[Mar Chiquita]] in [[Argentina]].<ref name="martin"/> A tracking study off the [[British Isles]] has found substantial variation in the short-term movements of this species, both between and within individuals. Vertical movements tended to increase with water depth and corresponding temperature [[Ocean stratification|stratification]]; in shallow, unstratified waters, sharks either showed no pattern in changing depth or made reverse [[diel vertical migration|diel movements]], spending the day in shallow water and descending at night. In deeper, stratified waters, the sharks performed a regular diel migration, spending the day below the [[thermocline]] and rising towards the surface at night.<ref name="padea et al"/> The porbeagle has been reported across a temperature range of {{convert|1|to|23|C|F|abbr=on}}, with most records between {{convert|8|and|20|C|F|abbr=on}}.<ref name="compagno"/><ref name="campana and joyce"/> In a study that included 420 porbeagles caught in the northwest Atlantic off Canada, all were in water below {{convert|13|C|F|abbr=on}} and the majority between {{convert|5|and|10|C|F|abbr=on}}.<ref name="campana and joyce"/>

Porbeagle populations in the Northern and Southern Hemispheres appear to be completely separate. Two stocks are in the North Atlantic, east and west, that seldom mix; only one individual is known to have crossed the Atlantic, covering {{convert|4260|km|mi|abbr=on}} from [[Ireland]] to [[Canada]]. Several discrete stocks are likely present in the Southern Hemisphere, as well. This species segregates by size and sex in the North Atlantic, and at least by size in the South Pacific. For example, males outnumber females 2:1 off [[Spain]], females are 30% more numerous than males off [[Scotland]], and immature males are predominant in the [[Bristol Channel]]. Older, larger sharks may frequent higher latitudes than younger individuals.<ref name="francis et al"/>

Seasonal [[fish migration|migrations]] have been observed in porbeagles from both hemispheres. In the western North Atlantic, much of the population spends the spring in the deep waters of the [[Nova Scotia]] [[continental shelf]], and migrates north a distance of {{convert|500|-|1000|km|mi|abbr=on}} to spend late summer and fall in the shallow waters of the Newfoundland Grand Banks and the [[Gulf of St. Lawrence]].<ref name="francis et al"/><ref name="campana et al"/><ref name="joyce et al"/> In December, large, mature females migrate south over {{convert|2000|km|mi|abbr=on}} into the Sargasso Sea for pupping, keeping deeper than {{convert|600|m|ft|abbr=on}} during the day and {{convert|200|m|ft|abbr=on}} at night so as to stay in the cooler waters beneath the [[Gulf Stream]].<ref name="campana et al 2010"/> In the eastern North Atlantic, porbeagles are believed to spend spring and summer in shallow continental shelf waters, and disperse northwards to overwinter in deeper waters offshore.<ref name="padea et al"/> Migrating sharks may travel upwards of {{convert|2300|km|mi|abbr=on}}, though once they reach their destination they tend to remain within a relatively localized area.<ref name="francis et al"/><ref name="campana et al 2010"/><ref name="padea et al"/> In the South Pacific, the population shifts north past 30°S latitude into [[subtropical]] waters in winter and spring, and retreats south past 35°S latitude in summer, when sharks are frequently sighted off [[subantarctic]] islands.<ref name="francis et al"/>