AnimalTracks.wiki

What the sources say

Scalloped HammerheadSphyrna lewini

Every figure, record and mechanism on the Scalloped Hammerhead profile was written from a source, and this is the working table behind it: 48 claims checked word for word against these sources. The left column is what the page says. The right column is the source's own words, copied, not paraphrased; a ... marks a cut and[brackets] an insertion. Open any source and check it yourself.

Profile updated

Source
01

NOAA Fisheries

Scalloped Hammerhead Shark. NOAA Fisheries.

The page saysWarm temperate and tropical coastal seas worldwide
The source saysfound in coastal warm temperate and tropical seas worldwide
The page saysA scalloped hammerhead can weigh up to 335 pounds, grow up to 11 feet long and live up to 30 years, according to NOAA Fisheries
The source saysWeight Up to 335 pounds Length Up to 11 feet Lifespan Up to 30 yearsNote: NOAA Fisheries is the current institution page; ADW's older account gives a 31.5-year-old individual and 4.3 m, Florida Museum 'thought to be over 30 years'
The page saysIt lives in warm temperate and tropical coastal seas worldwide: the western Atlantic from New Jersey to Brazil, the eastern Atlantic from the Mediterranean to Namibia, the Indian Ocean from South Africa and the Red Sea to Myanmar, and the Pacific from Japan to New Caledonia and from southern California to Ecuador
The source saysfound in coastal warm temperate and tropical seas worldwide. In the western Atlantic Ocean, the scalloped hammerhead range extends from the northeast coast of the United States (from New Jersey to Florida) to Brazil ... In the eastern Atlantic, it can be found from the Mediterranean to Namibia. Populations in the Indian Ocean are found in the following locations: South Africa and the Red Sea to Pakistan, India, and Myanmar, and in the western Pacific, the scalloped hammerhead can be found from Japan and China to New Caledonia ... Distribution in the eastern Pacific Ocean extends from the coast of southern California (U.S.), including the Gulf of California, to EcuadorNote: quote trimmed before the source's trailing 'and possibly Peru,' which this claim does not assert
The page saysNOAA Fisheries says the species is threatened by commercial fishing, mainly for the fin trade
The source saysThey are threatened by commercial fishing, mainly for the shark fin trade
The page saysFishing, mostly for fins. NOAA Fisheries says scalloped hammerheads are threatened by commercial fishing, mainly for the shark fin trade.
The source saysThey are threatened by commercial fishing, mainly for the shark fin trade

Source
02

Florida Museum of Natural History, Discover Fishes

Sphyrna lewini. Florida Museum of Natural History, Discover Fishes.

The page saysSardines, reef fish, squid, octopus, crustaceans, smaller sharks and stingrays
The source saysCommon prey: small schooling fish such as sardines, conger eels, many reef fish species, squid, octopus, crustaceans as well as smaller elasmobranchs such as blacktip reef sharks, angelsharks and stingraysNote: 'reef fish' is the source's 'many reef fish species'
The page sayshunted at night
The source saysScalloped hammerheads spend most of the day closer inshore, moving offshore to hunt at night
The page saysSardines, many kinds of reef fish, squid, octopus and crustaceans are on the menu, along with smaller sharks and rays
The source saysCommon prey: small schooling fish such as sardines, conger eels, many reef fish species, squid, octopus, crustaceans as well as smaller elasmobranchs such as blacktip reef sharks, angelsharks and stingrays
The page saysStingrays seem to be a favorite, at a price: hammerhead sharks are often found with up to 50 or more stingray spines in their mouths and guts
The source saysUp to 50 or more stingray spines are often found in the mouth and digestive systems of hammerhead sharks, a price to pay for a favorite meal
The page saysGathering in large groups also makes them easier to catch in large numbers on longlines, bottom nets and trawls, which has wiped out populations in some areas
The source saysThis species tendency to aggregate in large groups making capture in large numbers on longlines, bottom nets and trawls even easier. This has led to complete die off of populations in certain areas
The page saysBecause the species gathers in large groups, it is easier to catch in large numbers on longlines, bottom nets and trawls, which has wiped out populations in some areas.
The source saysThis species tendency to aggregate in large groups making capture in large numbers on longlines, bottom nets and trawls even easier. This has led to complete die off of populations in certain areasNote: 'Because' carries the source's own 'tendency to aggregate in large groups making capture ... even easier'
The page saysdangerLevel: Medium
The source saysHammerheads are considered potentially dangerous sharks. According to the International Shark Attack File, there have been 17 unprovoked attacks for the genus Sphyrna , though none were fatal.Note: stats.dangerLevel, 'Can injure, but rarely seriously': genus-wide attacks, none fatal; ADW: 'no confirmed attacks on humans by this species'

Source
03

Animal Diversity Web, University of Michigan

Sphyrna lewini (scalloped hammerhead shark). Animal Diversity Web, University of Michigan.

The page saysnear continental and island shelves, seamounts, reefs and drop-offs
The source saysscalloped hammerheads can also be found near continental and island shelves ... At dawn, they move from their offshore hunting grounds to island shelves, seamounts, and enclosed bays and estuaries. During the day they migrate to drop-off zones and reefs
The page saysA wide, notched head
The source saysScalloped hammerheads have a small but prominent notch in the center of their characteristically-shaped head
The page sayswith electroreceptors on its underside
The source saysthese special electroreceptors are located on the underside of the snout
The page saysHunting at night, a scalloped hammerhead uses a "smash and grab" technique: it accelerates toward prey and either swallows it whole or disables it with a bite
The source saysScalloped hammerheads actively forage for food during the night, using a “smash and grab” feeding technique. They accelerate towards prey and either swallow it whole, or disable prey by biting it
The page saysBy day, scalloped hammerheads move to drop-off zones and reefs
The source saysAt dawn, they move from their offshore hunting grounds to island shelves, seamounts, and enclosed bays and estuaries. During the day they migrate to drop-off zones and reefs
The page sayswhere most females gather in all-female schools with the larger, more mature females in the center
The source saysmost females are found in sexually segregated schools with larger, more mature females in the centerNote: 'all-female' glosses 'sexually segregated'
The page saysAdult males join schools almost exclusively to find a mate
The source saysAdult males almost exclusively enter schools when in search of a mate
The page saysAt dusk the sharks head back offshore to hunt
The source saysAt dusk the sharks return to offshore pelagic areas and actively search for food
The page saysMost females travel in all-female schools, with the larger, more mature females in the center, while adult males join schools almost exclusively to find a mate.
The source saysmost females are found in sexually segregated schools with larger, more mature females in the center ... Adult males almost exclusively enter schools when in search of a mateNote: 'all-female' glosses 'sexually segregated'
The page saystags: electroreception
The source saysthey have special sensory organs called Ampullae of Lorenzini; these special electroreceptors are located on the underside of the snout and "hammer", and aid in the detection of buried prey

Source
04

Kajiura & Holland 2002

Kajiura & Holland (2002). Electroreception in juvenile scalloped hammerhead and sandbar sharks. Journal of Experimental Biology.

The page saysA wide head that seems to sense prey no better than a sandbar shark's, but searches a wider area and can pivot into sharp turns at high speed
The source saysoriented to dipole electric fields from the same maximum distance ... Scalloped hammerheads typically demonstrated a pivot orientation ... which enables the hammerheads to execute sharp turns at high speed ... the sphyrnid head morphology does not appear to confer a greater sensitivity to prey-simulating dipole electric fields, it does provide (1). a greater lateral search areaNote: 'an ordinary shark' is the sandbar shark, the carcharhinid the study compared against
The page saysIt appears to sense a weak electric field no better than a sandbar shark does, but seems to give a wider search area and sharp turns at high speed
The source saysoriented to dipole electric fields from the same maximum distance (approximately 30 cm) ... which enables the hammerheads to execute sharp turns at high speed ... the sphyrnid head morphology does not appear to confer a greater sensitivity to prey-simulating dipole electric fields, it does provide (1). a greater lateral search area
The page saysA hammerhead's wide head is called a cephalofoil, and one idea was that it evolved to sharpen the shark's electric sense
The source saysThe unique head morphology of sphyrnid sharks might have evolved to enhance electrosensory capabilities ... the edge of the cephalofoil closest to the dipoleNote: the abstract uses 'sphyrnid head morphology' and 'cephalofoil' for the same structure; 'one idea was' keeps the source's 'might have evolved' hedge
The page saysA 2002 study tested that by comparing juvenile scalloped hammerheads with sandbar sharks, which have no hammer, using a weak electric field like the one prey gives off
The source saysThe 'enhanced electroreception' hypothesis was tested by comparing the behavioral responses of similarly sized carcharhinid and sphyrnid sharks to prey-simulating electric stimuli. Juvenile scalloped hammerhead sharks Sphyrna lewini and sandbar sharks Carcharhinus plumbeus oriented to dipole electric fieldsNote: published 2002 (J Exp Biol 205(23)); sandbar sharks are the carcharhinids, which lack the sphyrnid head
The page saysBoth species picked it up from the same maximum distance, about 30 centimeters: the wide head does not appear to make the shark's electric sense sharper
The source saysoriented to dipole electric fields from the same maximum distance (approximately 30 cm) ... the sphyrnid head morphology does not appear to confer a greater sensitivity to prey-simulating dipole electric fields
The page saysWhat it does seem to give is a wider search area, which may help the shark find prey, and better maneuverability
The source saysit does provide (1). a greater lateral search area, which may increase the probability of prey encounter, and (2). enhanced maneuverability, which may aid in prey capture
The page saysThe hammerheads typically turned by holding the edge of the head nearest the target still and bending the body toward it, a sharp turn made at high speed
The source saysScalloped hammerheads typically demonstrated a pivot orientation in which the edge of the cephalofoil closest to the dipole remained stationary while the shark bent its trunk to orient to the center of the dipole ... which enables the hammerheads to execute sharp turns at high speedNote: 'nearest the target' glosses 'closest to the dipole'
The page saysThe wider-bodied sandbar sharks swam in a broader arc
The source saysBy contrast, sandbars swam in a broader arc towards the center of the dipole ... The greater trunk width of the sandbar sharks
The page saysIt doesn't appear to sharpen its electric sense.
The source saysthe sphyrnid head morphology does not appear to confer a greater sensitivity to prey-simulating dipole electric fields
The page saysA 2002 study compared juvenile scalloped hammerheads with sandbar sharks, which have no hammer, and both species picked up a weak electric field from the same maximum distance, about 30 centimeters.
The source saysJuvenile scalloped hammerhead sharks Sphyrna lewini and sandbar sharks Carcharhinus plumbeus oriented to dipole electric fields from the same maximum distance (approximately 30 cm)Note: published 2002 (J Exp Biol 205(23))
The page saysWhat the wide head does seem to give is a wider search area, which may help the shark find prey, and better maneuverability.
The source saysit does provide (1). a greater lateral search area, which may increase the probability of prey encounter, and (2). enhanced maneuverability, which may aid in prey capture
The page saysThe hammerhead typically holds the edge of its head nearest the target still and bends its body toward it, turning sharply at high speed.
The source saysScalloped hammerheads typically demonstrated a pivot orientation in which the edge of the cephalofoil closest to the dipole remained stationary while the shark bent its trunk to orient to the center of the dipole ... which enables the hammerheads to execute sharp turns at high speedNote: replaces the earlier 'pivoting onto prey faster than a narrow-headed shark': the abstract says sharp turns at high speed, and compares flexibility with sandbar sharks, not speed; 'nearest' glosses 'closest to the dipole'
The page saysThe wider-bodied sandbar sharks swam in a broader arc.
The source saysBy contrast, sandbars swam in a broader arc towards the center of the dipole ... The greater trunk width of the sandbar sharks
The page saysfor a shark that searches a wider area with its broad head and can pivot into sharp turns at high speed
The source saysScalloped hammerheads typically demonstrated a pivot orientation ... which enables the hammerheads to execute sharp turns at high speed ... it does provide (1). a greater lateral search areaNote: vibe.reason

Source
05

Wells et al. 2018

Wells et al. (2018). Movement, Behavior, and Habitat Use of a Marine Apex Predator, the Scalloped Hammerhead. Frontiers in Marine Science.

The page saysStudies have found them clustering around seafloor features such as seamounts, and a 2018 study listed possible reasons: better hunting, magnetic patterns in the seafloor, or simply that tagged sharks were tracked for only a short time
The source saysseveral studies have found that scalloped hammerheads have relatively small home ranges and display aggregative behaviors around bathymetric features, such as seamounts, potentially due to enhanced prey availability, geomagnetic associations from gradients in the seafloor, or simply short durations of tagged individualsNote: 'better hunting' paraphrases 'enhanced prey availability'; 'tracked for only a short time' paraphrases 'short durations of tagged individuals'; 'only a short time' is the source's 'short durations'
The page saysTheir fins are highly valued too: estimates published in the 2000s put 1.3 to 2.7 million scalloped and smooth hammerheads through the Hong Kong fin trade each year
The source saysScalloped hammerhead fins are highly valued in the shark fin trade (Abercrombie et al., 2005) with estimates ranging between 1.3 and 2.7 million scalloped and smooth hammerheads (S. zygaena) used in the Hong Kong fin trade annually (Clark et al., 2006 ; Camhi et al., 2009)Note: the estimates are cited to Clark et al. 2006 and Camhi et al. 2009, hence 'published in the 2000s'
The page saysAs of 2018, scientists weren't sure. Several studies have found scalloped hammerheads clustering around seamounts and other seafloor features, and a 2018 study listed possible reasons: better hunting, magnetic patterns in the seafloor, or simply that tagged sharks were tracked for only a short time.
The source saysseveral studies have found that scalloped hammerheads have relatively small home ranges and display aggregative behaviors around bathymetric features, such as seamounts, potentially due to enhanced prey availability, geomagnetic associations from gradients in the seafloor, or simply short durations of tagged individualsNote: 'weren't sure' reflects 'potentially due to'; 'better hunting' paraphrases 'enhanced prey availability'
The page saysTheir fins are highly valued, and estimates published in the 2000s put 1.3 to 2.7 million scalloped and smooth hammerheads through the Hong Kong fin trade each year.
The source saysScalloped hammerhead fins are highly valued in the shark fin trade (Abercrombie et al., 2005) with estimates ranging between 1.3 and 2.7 million scalloped and smooth hammerheads (S. zygaena) used in the Hong Kong fin trade annually (Clark et al., 2006 ; Camhi et al., 2009)Note: the estimates are cited to Clark et al. 2006 and Camhi et al. 2009, hence 'published in the 2000s'

Source
06

Jorgensen, Klimley & Muhlia-Melo 2009

Jorgensen, Klimley & Muhlia-Melo (2009). Scalloped hammerhead shark Sphyrna lewini utilizes deep-water, hypoxic zone in the Gulf of California. Journal of Fish Biology.

The page saysOne shark tracked for 74 days was recorded diving into the Gulf of California's oxygen minimum layer, a deep band of water with extremely little oxygen, which expanded the range of depths the species was known to use
The source saysA hammerhead shark Sphyrna lewini tracked for 74 days revealed an expansion of the range of vertical distribution for the species to include the extreme hypoxic environment of the oxygen minimum layer in the Gulf of CaliforniaNote: 'a deep band of water with extremely little oxygen' defines 'extreme hypoxic environment' for young readers; 'deep' is from the title's 'deep-water, hypoxic zone'
The page saysDeeper than scientists once knew. One scalloped hammerhead tracked for 74 days was recorded diving into the Gulf of California's oxygen minimum layer, a deep band of water with extremely little oxygen.
The source saysA hammerhead shark Sphyrna lewini tracked for 74 days revealed an expansion of the range of vertical distribution for the species to include the extreme hypoxic environment of the oxygen minimum layer in the Gulf of CaliforniaNote: 'Deeper than scientists once knew' paraphrases 'revealed an expansion of the range of vertical distribution'
The page saysThat track, published in 2009, expanded the range of depths the species was known to use.
The source saysrevealed an expansion of the range of vertical distribution for the speciesNote: published 2009 (J Fish Biol 75)

Source
07

Quattro et al. 2013

Quattro et al. (2013). Sphyrna gilberti sp. nov., a new hammerhead shark (Carcharhiniformes, Sphyrnidae) from the western Atlantic Ocean. Zootaxa.

The page saysIn 2013, scientists named a new hammerhead species, Sphyrna gilberti, from young sharks caught off South Carolina that had passed as scalloped hammerheads
The source saysEighty juvenile hammerheads diagnosable as S. lewini were collected in the coastal waters of South Carolina from 2001–2003 using longline and gillnet gearNote: published 2013-08-26 (Zootaxa 3702(2)); the abstract: 'Sphyrna gilberti sp. nov. is described based on 54 specimens collected in the coastal waters of South Carolina'
The page saysIn body shape and anatomy, the only difference the paper found was the number of vertebrae in front of the tail
The source saysMorphologically, S. gilberti sp. nov. is separable from S. lewini (Griffith & Smith 1834) only in the number of precaudal vertebraeNote: 'in front of the tail' glosses 'precaudal'
The page saysNobody knew yet how far the new species ranged
The source saysDue to rarity of specimens and the highly migratory behavior of most sphyrnids, the range of S. gilberti sp. nov. is unknown

Source
08

Rigby et al. 2019

Rigby et al. (2019). Sphyrna lewini. The IUCN Red List of Threatened Species.

The page saysthe IUCN's 2019 assessment rates it Critically Endangered
The source saysCritically Endangered A2bdNote: read in Chrome 2026-09-17 on the assessment page (iucnredlist.org refuses scripts): 'Critically Endangered A2bd', DATE ASSESSED 08 November 2018, YEAR PUBLISHED 2019, no DOI; matches GBIF's copy of the category (CR), cached at node_modules/.cache/animaltracks/source-text/9980e4ff6d93e22e.txt. Expected hand check.
The page saysThe IUCN's 2019 assessment rates the species Critically Endangered.
The source saysCritically Endangered A2bdNote: read in Chrome 2026-09-17 on the assessment page (iucnredlist.org refuses scripts): 'Critically Endangered A2bd', DATE ASSESSED 08 November 2018, YEAR PUBLISHED 2019, no DOI; matches GBIF's copy of the category (CR), cached at node_modules/.cache/animaltracks/source-text/9980e4ff6d93e22e.txt. Expected hand check.

How the table was made: a writer drafted the profile from these sources and logged each claim with its quote, a reviewer with nothing but this table checked every sentence said no more than its quote, and a script confirmed each quote appears word for word in the source. The method is in the site'sAbout page.