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Line 43: ==Biology and ecology== [[File:Heterodontus francisci 2.jpg\|thumb\|upright=1.2\|left\|Horn sharks rest during the day and only become active at night.]] The horn shark is a ~~clumsy,~~ sporadic swimmer that prefers to use its flexible, muscular pectoral fins to push itself along the bottom. It is usually solitary, though small groups have been recorded.<ref name="compagno"/> During the day, horn sharks rest motionless, hidden inside caves or crevices, or within thick mats of algae, though they remain relatively alert and will swim away quickly if disturbed. After dusk, they roam actively above the reef in search of food.<ref name="nelson and johnson"/> Horn sharks maintain small home ranges of around {{convert\|1000\|m2\|ft2\|abbr=on}}, which they may remain faithful to for over a decade, returning to the same shelter every day. The shelter is usually located at the edge of the resident shark's foraging area.<ref name="ebert"/> The longest documented movement for an individual horn shark is {{convert\|16\|km\|mi\|abbr=on}}.<ref name="buch"/> Unlike most fishes, the daily activity pattern of the horn shark is under [[exogenous]] control, meaning that it is regulated by environmental factors rather than by an internal physiological cycle. Observations of captive horn sharks show that the relevant cue is light intensity: the sharks become active immediately after the lights are turned off, and stop as soon as they are turned back on. In one experiment where the sharks were kept in darkness, they remained continuously active for 11 days before slowing, possibly from fatigue. In nature, horn sharks exposed to a bright light at night may stop swimming and sink to the bottom.<ref name="nelson and johnson">{{cite journal \|title=Diel Activity Rhythms in the Nocturnal, Bottom-Dwelling Sharks, ''Heterodontus francisci'' and ''Cephaloscyllium ventriosum'' \|author1=Nelson, D.R. \|author2=Johnson, R.H. \|journal=Copeia \|volume=1970 \|issue=4 \|date=December 12, 1970 \|pages=732–739 \|doi=10.2307/1442315 \|jstor=1442315 \|publisher=American Society of Ichthyologists and Herpetologists}}</ref>

Horn shark: Difference between revisions